SUPRASPINATUS MUSCULOTENDINOUS ARCHITECTURE: A CADAVERIC AND IN VIVO ULTRASOUND INVESTIGATION OF THE NORMAL AND

PATHOLOGICAL MUSCLE

by

Soo Young Kim

A thesis submitted in conformity with the requirements

for the degree of Doctor of Philosophy

Graduate Department of Rehabilitation Science

University of Toronto

© Copyright by Soo Young Kim 2009

ii

Supraspinatus musculotendinous architecture: a cadaveric and in vivo ultrasound investigation of the normal and pathological muscle

Soo Young Kim

Doctor of Philosophy, Graduate Department of Rehabilitation Science

Faculty of Medicine, University of Toronto, 2009

Abstract The purpose of the study was to investigate the static and dynamic architecture of supraspinatus throughout its

volume in the normal and pathological state. The architecture was first investigated in cadaveric specimens free

of any tendon pathology. Using a serial dissection and digitization method tailored for supraspinatus, the

musculotendinous architecture was modeled in situ. The 3D model reconstructed in Autodesk MayaTM allowed

for visualization and quantification of the fiber bundle architecture i.e. fiber bundle length (FBL), pennation

angle (PA), muscle volume (MV) and tendon dimensions. Based on attachment sites and architectural

parameters, the supraspinatus was found to have two architecturally distinct regions, anterior and posterior,

each with three subdivisions. The findings from the cadaveric investigation served as a map and platform for

the development of an ultrasound (US) protocol that allowed for the dynamic fiber bundle architecture to be

quantified in vivo in normal subjects and subjects with a full-thickness supraspinatus tendon tear. The

architecture was studied in the relaxed state and in three contracted states (60º abduction with either neutral

rotation, 80º external rotation, or 80º internal rotation). The dynamic changes in the architecture within the

distinct regions of the muscle were not uniform and varied as a function of joint position. Mean FBL in the

anterior region shortened significantly with contraction (p<0.05) but not in the posterior. In the anterior region,

mean PA was significantly smaller in the middle part compared to the deep (p<0.05). Comparison of the

normal and pathological muscle found large differences in the percentage change of FBL and PA with

contraction. The architectural parameter that showed the largest changes with tendon pathology was PA. In

sum, the results showed that the static and dynamic fiber bundle architecture of supraspinatus is heterogeneous

throughout the muscle volume and may influence tendon stresses. The architectural data collected in this study

and the 3D muscle model can be used to develop future contractile models. The US protocol may serve as an

assessment tool to predict the functional outcome of rehabilitative exercises and surgery.

iii

Acknowledgements

I would first like to give great thanks to my supervisor, mentor, and friend, Dr.

Anne Agur, for providing a wonderful opportunity to learn and grow. I am so grateful

for the positive and rich learning environment that Dr. Agur has provided.

I’d also like to extend a sincere thanks to my committee members Drs Erin

Boynton, Robert Bleakney, Tim Rindlisbacher, and Denyse Richardson for their

expertise and advice. In particular, thank you Dr. Boynton for your enthusiasm and

passion, Dr. Bleakney for your dedication and all the hours of scanning, Dr.

Rindlishbacher and Richardson for your encouragement and referrals for the study.

To my mother and father, I thank you for all your years of hard work to provide

your two daughters with the best. Your love and support have allowed me to be who I

am and be where I am today. To my sister Hyon and brother-in-law Peter, I truly could

not have done it without your help, encouragement, humor, and prayers. Thank you so

very much for bearing some of my burdens with me in the past four years.

Most importantly, I give my loving husband, Jae Young, my deepest thanks.

Without you, I would have never discovered my passion for teaching, and without your

immense sacrifice this dream of becoming a professor could not have come true. Thank

you for your love, patience, gentleness, and support. Also, to my precious Noah—you

are a true gift from God. To my father-in-law and mother-in-law in Korea, thank you for

your constant support from afar.

Acknowledgement is made to the Canadian Orthopaedic Foundation, the Division

of Anatomy, Faculty of Medicine, University of Toronto for financial support.

iv

Table of Contents Page Abstract ii Acknowledgements iii Table of Contents iv List of Figures x List of Tables xii List of Abbreviations xvi Chapter 1: Introduction 1

1.1 Contents of thesis 2 Chapter 2: Literature Survey 4

2.1 Structure of human skeletal muscle 5 2.1.1 Organization of contractile and connective tissue elements 5 2.1.2 Contractile mechanism 7 2.2 Muscle architecture 9 2.2.1 Overview 9

2.2.2 Architectural parameters and importance to function 11 2.2.2.1 Muscle 11 2.2.2.2 Tendon 15

2.2.3 Methods used to study muscle architecture 16 2.2.3.1 Cadaveric dissection 16 2.2.3.2 Ultrasound 17 2.2.3.3 Magnetic resonance imaging 18

v

2.3 Muscle architecture of normal supraspinatus 19 2.3.1 Morphology of supraspinatus 19

2.3.2 Cadaveric investigation of normal supraspinatus 21 2.3.2.1 Overview 21 2.3.2.2 Comparison of methodologies 24 2.3.2.2.1 Fiber bundle length 24 2.3.2.2.2 Pennation angle 25 2.3.2.2.3 Muscle volume 25 2.3.2.2.4. Muscle length 26 2.3.2.2.5 Physiological cross sectional area 26 2.3.2.2.6 Tendon dimensions 26 2.3.2.3 Comparison of results 31 2.3.2.3.1 Fiber bundle length 31 2.3.2.3.2 Pennation angle 31 2.3.2.3.3 Muscle volume 32 2.3.2.3.4 Muscle length 32 2.3.2.3.5 Physiological cross sectional area 32 2.3.2.3.6 Tendon dimensions 32 2.3.3 Ultrasound investigation of normal supraspinatus 35

2.3.3.1 Overview 35 2.3.3.2 Comparison of methodologies 36 2.3.3.3 Comparison of results 37 2.3.4 Magnetic resonance imaging of normal supraspinatus 38 2.4 Muscle architecture of pathological supraspinatus 39 2.4.1 Overview 39

2.4.2 Cadaveric investigation of pathological supraspinatus 40 2.4.3 Imaging investigation of pathological supraspinatus 42

2.5 Modeling of skeletal muscles 43 2.5.1 Overview 43

2.5.2 Type of models 44 2.5.2.1 Phenomenological models 44

2.5.2.2 Structural models 45

vi

2.5.2.3 Use of architectural parameters in muscle 45 models

2.5.3 Models of shoulder region: sources of architectural data 46 2.5.4 Use of digitized data for muscle modeling 47

2.6 Role of supraspinatus in abduction and glenohumeral stabilization 47 2.7 Summary 51

Chapter 3: Hypotheses and Objectives 52 3.1 Hypotheses 52 3.2 Objectives 53 3.3 Significance 54 Chapter 4: Methods 55 4.1 Cadaveric investigation of normal supraspinatus 55

4.1.1 Specimens 55 4.1.2 Dissection and digitization 55

4.1.3 MicroscribeTM G2 Digitizer 56 4.1.4 Modeling 57 4.1.5 Data analysis 58 4.2 Ultrasound investigation of normal supraspinatus 59

4.2.1 Subjects 59 4.2.2 Equipment 60 4.2.3 Positioning and screening of subjects 60 4.2.4 Protocol 60 4.2.4.1 Protocol development 62 4.2.4.2 Development of acromion correction factor 63 4.2.4.2.1 Dissection and digitization 63 4.2.4.3 Ultrasound investigation 64 4.2.5 Measurement of architectural parameters from US scans 65 4.2.6 Data analysis 68

vii

4.3 Ultrasound investigation of pathological supraspinatus 69 4.3.1 Subjects 69 4.3.2 Protocol 69 4.3.3 Measurement of architectural parameters from 70

US scans 4.3.4. Data analysis 70

4.4 Reliability and validity of measurements 71 4.4.1 Intra-rater reliability 71 4.4.2 Inter-rater reliability 71 4.4.3 Validity 72 Chapter 5: Results 73 5.1 Introduction 73 5.2 Cadaveric investigation of normal supraspinatus 73 5.2.1 Tendon architecture 73 5.2.2 Muscle architecture 74 5.2.2.1 Anterior region 75 5.2.2.2 Posterior region 76 5.2.2.3 Fiber bundle length 79 5.2.2.4 Pennation angle 79

5.3 Ultrasound investigation of normal supraspinatus 81 5.3.1 Pre-scanning 81 5.3.2 Intramuscular tendon 82 5.3.3 Muscle architecture 83 5.3.3.1 Muscle thickness 83 5.3.3.2 Anterior region 84 5.3.3.3 Posterior region 85 5.4 Ultrasound investigation of pathological supraspinatus 89 5.4.1 Pre-scanning 89 5.4.2 Intramuscular tendon 90 5.4.3 Muscle architecture 91

viii

5.4.3.1 Muscle thickness 92 5.4.3.2 Anterior region 93

5.4.3.3 Posterior region 96

5.5 Comparison of pathological and normal data 98 5.5.1 Pre-scanning 98 5.5.2 Intramuscular tendon 99 5.5.3 Muscle architecture 100 5.5.3.1 Muscle thickness 100 5.5.3.2 Anterior region 101 5.5.3.3 Posterior region 104 5.6 Reliability and validity of measurements 104 5.6.1 Intra-rater reliability 104 5.6.2 Inter-rater reliability 105 5.6.3 Validity 105 5.7 Summary of main results 106

Chapter 6: Discussion 109 6.1 Cadaveric investigation of normal supraspinatus 109

6.1.1 Three-dimensional modeling 109 6.1.2 Measurement of architectural parameters 110 6.1.3 Comparison of architectural parameters 111 6.1.3.1 Fiber bundle length 111 6.1.3.2 Pennation angle 112 6.1.3.3 Muscle volume 113 6.1.3.4 Tendon architecture 113

6.2 Ultrasound investigation of normal supraspinatus 114 6.2.1 Measurement of architectural parameters 116

6.2.2 Muscle architecture 117

ix

6.3 Functional implications of cadaveric and in vivo findings 118 of normal subjects 6.4 Ultrasound investigation of pathological supraspinatus 123 6.5 Functional implications of in vivo findings of pathological 125 subjects 6.6 Clinical implications 126 6.7 Summary 128

Chapter 7: Conclusions 130 Chapter 8: Future Directions 133 References 135 Appendix A: Sample size calculation 145 Appendix B: Ethics approval 146

x

List of Figures

Chapter 2: Page Figure 2.1 Organization of skeletal muscle. 6 Figure 2.2 Muscle architecture: Various arrangements of muscle 10 fibers. Figure 2.3 Effect of pennation angle. 14 Figure 2.4 Rotator cuff muscles. 20 Chapter 4: Figure 4.1 Cadaveric investigation: Digitization and dissection of 56

supraspinatus. Figure 4.2 Cadaveric investigation: MicroscribeTM G2 Digitizer. 57 Figure 4.3 Cadaveric investigation: 3D computer model of 58

supraspinatus. Figure 4.4 Cadaveric investigation: FBL and PA measurement. 59 Figure 4.5 Ultrasound investigation of normal supraspinatus: 61

Architecturally distinct regions of supraspinatus used to develop US protocol.

Figure 4.6 Ultrasound investigation of normal supraspinatus: 65

Subject arm position for US scanning.

xi

Figure 4.7 Ultrasound investigation of normal supraspinatus: 67 Measurement of FBL and PA on US scans. Figure 4.8 Ultrasound investigation of normal supraspinatus: 68

Measurement of MT and distance of intramuscular tendon to superficial surface of muscle belly (TD).

Figure 4.9 Ultrasound investigation of pathological supraspinatus: 69

US scan of pathological left rotator cuff. Chapter 5: Figure 5.1 Cadaveric investigation of normal supraspinatus: 78

Dissection and 3D modeling of the architecturally distinct regions of left shoulder supraspinatus, superior views.

Figure 5.2 Cadaveric investigation of normal supraspinatus: 79

Superior view of left scapula. Figure 5.3 Ultrasound investigation: US scans of anterior region 87

of right supraspinatus in relaxed and contracted states. Figure 5.4 Ultrasound investigation: Comparison of US scans of 92

pathological and contra-lateral supraspinatus of same subject.

Figure 5.5 Ultrasound investigation: Comparison of US scans of 99

normal and pathological supraspinatus.

xii

List of Tables

Chapter 2: Page Table 2.1 Summary of fiber types found in skeletal muscles. 8 Table 2.2 Summary of the types of architectural data obtained from 23

cadaveric studies of supraspinatus muscle. Table 2.3 Comparison of the methodologies used by Jensen et al. (1995), 28-30

Juul-Kristensen et al. (2000), Roh et al. (2000), and Ward et al. (2007).

Table 2.4 Summary of architectural data obtained from cadaveric 34

studies of supraspinatus muscle. Table 2.5 Summary of architectural data obtained from cadaveric 35

studies of supraspinatus tendon. Table 2.6 Summary of architectural data obtained from in vivo US 38

studies of normal supraspinatus muscle. Table 2.7 Summary of findings by Itoi et al. (1995): Architectural 42

data collected through cadaveric investigation of pathological supraspinatus.

Chapter 5: Table 5.1 Cadaveric investigation of normal supraspinatus: Summary 74

of mean tendon dimensions. Table 5.2 Cadaveric investigation of normal supraspinatus: Summary 80

of mean architectural parameters for anterior and posterior regions

xiii

Table 5.3 Cadaveric investigation of normal supraspinatus: Summary 81 of mean architectural parameters for superficial, middle, and deep parts of the anterior and posterior regions of supraspinatus muscle.

Table 5.4 Ultrasound investigation of normal supraspinatus: Mean TD 83

Table 5.5 Ultrasound investigation of normal supraspinatus: Mean MT 84 Table 5.6 Ultrasound investigation of normal supraspinatus: 88

Architectural parameters of the anterior and posterior regions.

Table 5.7 Ultrasound investigation of normal supraspinatus: 89

Architectural parameters of the middle and deep parts of the anterior region.

Table 5.8 Ultrasound investigation of pathological supraspinatus: 90 Summary of tendon pathology on the contra-lateral shoulder. Table 5.9 Ultrasound investigation of pathological supraspinatus: 91

Comparison of mean TD between pathological and contra-lateral supraspinatus.

Table 5.10 Ultrasound investigation of pathological supraspinatus: 93

Comparison of mean MT between the pathological and contra-lateral supraspinatus

Table 5.11 Ultrasound investigation of pathological supraspinatus: 95

Comparison of mean FLB and percentage change of anterior region between pathological supraspinatus and contra-lateral supraspinatus.

xiv

Table 5.12 Ultrasound investigation of pathological supraspinatus: 95 Comparison of mean PA and percentage change between pathological and contra-lateral supraspinatus.

Table 5.13 Ultrasound investigation of pathological supraspinatus: 96

FBL and PA of anterior region for relaxed and contracted states and percentage change for each individual subject.

Table 5.14 Ultrasound investigation of pathological supraspinatus: 97

Comparison of mean FBL of posterior region between pathological and contra-lateral supraspinatus.

Table 5.15 Ultrasound investigation of pathological supraspinatus: 98

Mean FBL for each individual subject.

Table 5.16 Ultrasound investigation: Comparison of mean TD 100 between normal controls and pathological supraspinatus.

Table 5.17 Ultrasound investigation: Comparison of mean MT 101 between normal controls and pathological supraspinatus.

Table 5.18 Ultrasound investigation: Comparison of mean FBL 103

and percentage change of anterior region between normal controls and pathological supraspinatus.

Table 5.19 Ultrasound investigation: Comparison of mean PA 103

and percentage change of anterior region between normal controls and pathological supraspinatus.

Table 5.20 Ultrasound investigation: Comparison of mean 104

FBL of posterior region between normal controls and pathological supraspinatus.

xv

Table 5.21 Summary of mean FBL measurements made on 106 one male fresh cadaveric specimen: US scans and digitized data.

xvi

List of abbreviations

A actin

Acf acromial correction factor

Acr acromion

AD anterior region deep part

ADP adenosine diphosphate

AM anterior region middle part

AP anterior posterior

AS anterior region superficial part

ATP adenosine triphosphate

CSA cross-sectional area

ER external rotation

F force

F female

FBL fiber bundle length

IR internal rotation

Lat lateral

Lf normalized fiber bundle length

xvii

M male

M myosin

Med medial

ML medial lateral

ML muscle length

MRI magnetic resonance imaging

MT muscle thickness

MV muscle volume

PA pennation angle

PD posterior region deep part

Pi inorganic phosphate

PM posterior region middle part

PS posterior region superficial part

PSCA physiological cross-sectional area

SC subcutaneous tissue

SF supraspinous fossa

SK skin

Sup superficial

TD distance of intramuscular tendon to the superficial surface of the muscle

xviii

TP trapezius

US ultrasound

V volume

Þ muscle density

ΔL change in length of the myofibril

бl change in length of sarcomere

2D two-dimensional

3D three-dimensional

Units cm centimeters deg degrees MHz megahertz mm millimeters

xix

Glossary of Terms *Definition from Stedman’s Medical Dictionary (2000) aponeurosis, pl. aponeuroses*: A flat fibrous sheet of connective tissue that serves to attach muscle to bone or other tissues. endomysium*: A thin sheet of connective tissue consisting principally of reticular fibers that invests each striated muscle fiber and binds the fibers together within a fasciculus. epimysium*: Outermost sheath of connective tissue that surrounds a skeletal muscle. fascia, pl. fasciae*: A fibrous membrane covering, supporting and separating muscles. fascicle (fiber bundle)*: A small bundle of muscle fibers muscle fiber (myofiber)*: A single skeletal muscle cell myofibril*: Component of a skeletal muscle fiber; comprising of many regularly overlapped thick and thin filaments. myofiliament*: The ultramicroscopic threads of filamentous proteins (actin and myosin) making up the myofibrils in striated muscle. perimysium*: The fibrous sheath enveloping each of the fascicles of skeletal muscle fibers. sarcomere*: The segment of the myofibril between two adjacent Z lines, representing the functional unit of striated muscle. skeletal muscle*: A muscle consisting of elongated, multinucleated, transversely striated skeletal muscle fibers together with connective tissues, blood vessels, and nerves.

xx

tendon*: A fibrous cord or band of variable length that is the part of the muscle that connects the fleshy (contractile) part of muscle with its bony attachment or other structure; it consists of fascicles of very densely arranged, almost parallel collagenous fibers, rows of elongated fibrocytes, and a minimum of ground substance.

1

Chapter 1: Introduction

Skeletal muscles are responsible for force generation and movement of the body

(Ross, 2006). Muscle architecture is the primary determinant of muscle function and is

defined as the arrangement of fiber bundles relative to the line of force (Lieber and Friden,

2001). A detailed understanding of muscle architecture provides insight into the

functional role(s) of a muscle (Lieber, 1993). Studying the fiber architecture i.e. fiber

bundle length, pennation angle, and muscle thickness, of both normal and pathological

muscles can aid in optimizing the outcome of rehabilitative exercises and surgery.

The supraspinatus was chosen for this architectural study because among the shoulder

muscles it is most often involved in shoulder pathology (Howell, 1986; Codman 1990,

Harryman, 1991). Rotator cuff tendon impingement, tendinosis, and tears often start in

the supraspinatus, and as the pathology worsens it involves the other rotator cuff muscles

(Matsen, 2004).

Understanding the fiber architecture of supraspinatus in normal and pathological

states is also needed to better understand the association of the musculotendinous

architecture and tendon pathology. Traditionally, the etiology of tendon pathology has

been explained by changes in the tendon properties and compression and abrasion by the

undersurface of the acromion (Lindblom, 1939; Rothman & Parke, 1976, Matsen et al.,

2004; Bigliani et al., 1990). However, the muscle architecture and changes associated

2

with activity, inactivity, injury, or pain episode may be important factors in the

development of tendon tears. Changes in the muscle belly, which have commonly been

thought to be compensatory in nature to tendon pathology, may in fact play an important

role in the development of tendon tears.

In this thesis, the static and dynamic architecture of supraspinatus throughout its

volume has been investigated and quantified using advanced computer modeling

techniques and real-time ultrasound. The architectural data was collected from both the

normal and pathological supraspinatus in vivo which allowed for novel analysis and

comparison.

1.1 Contents of thesis

The present thesis is comprised of eight chapters that are presented in the following

order:

• Chapter 1 introduces the study of skeletal muscle architecture and discusses

the relevance and rationale for this study.

• Chapter 2 is the literature survey that provides background information on the

structure of skeletal muscle, the importance of studying muscle architecture,

methods used to study muscle architecture including cadaveric and in vivo

imaging studies, and muscle modeling. This chapter also discusses previous

3

studies that investigated the musculotendinous architecture of supraspinatus

and outlines their limitations.

• Chapter 3 outlines the hypotheses, objectives, and significance of the thesis.

• Chapter 4 presents the methods used to address the hypotheses and objectives

of this thesis. The first section outlines the methods used in the cadaveric

study. The following sections summarize the methods used to develop and

carry out an ultrasound protocol on subjects with a normal or pathological

supraspinatus muscle.

• Chapter 5 summarizes the results of this thesis. The first section summarizes

the findings from the cadaveric investigation and muscle modeling. In the

following section, the findings from in vivo US investigation are summarized.

In the last section, the architectural data of normal controls and pathological

subjects are compared and contrasted.

• Chapter 6 is a discussion of the results with the functional and clinical

implications.

• Chapters 7 and 8 include the conclusions of this thesis and outline the future

directions for this study.

4

Chapter 2: Literature Survey

The aim of the literature survey is to provide the necessary background information for

this architectural study of the human supraspinatus muscle. The chapter is divided into

the following sections:

• Section 2.1 discusses the structure of skeletal muscle.

• Section 2.2 provides an overview of muscle architecture and the importance to

function.

• Section 2.3 discusses previous cadaveric, ultrasound, and magnetic imaging

studies of the normal supraspinatus and compares methods and results where

possible.

• Section 2.4 provides a summary of the pathological supraspinatus and previous

cadaveric and imaging investigations.

• Sections 2.5 discusses modeling of skeletal muscles.

• Section 2.6 discusses the role of supraspinatus in abduction and glenohumeral

stabilization as documented in the literature.

• Section 2.7 summarizes the literature survey.

5

2.1 Structure of human skeletal muscle

Skeletal muscles are the “building blocks” of the muscular system (Ganong, 2005). As

a muscle contracts, it “delivers work to its outside world by exerting force while changing

length” (Huijing, 1998). Skeletal muscles are specifically tailored for force generation

at both the mirco- and macroscopic levels (Gans & Gaunt, 1991).

2.1.1 Organization of contractile and connective tissue elements

Architecturally, skeletal muscle is comprised of bundles of muscle fibers called

fascicles. Each fascicle is in turn composed of hundreds or even thousands of individual

muscle fibers or muscle “cells”. The muscle fiber consists of longitudinally arranged

strands called myofibrils which are the fundamental contractile elements within skeletal

muscle. Myofibrils are composed of two types of myofilaments: (1) thick filaments

composed of the protein myosin and (2) thin filaments composed of the protein actin

(Ross, 2006). The interdigitation of the two types of myofilaments creates a transverse

banding pattern of alternating light and dark striations which are visible by light

microscopy (Ganong, 2005). Each reiteration of the light-dark-light transverse banding

pattern is termed a sarcomere. The sarcomere is the functional contractile unit within a

skeletal muscle (Nordin, 2001).

The thick myofilaments are found in the central region of the sarcomere where their

volume and density give rise to the dark bands, also known as A bands for their

6

anisotropic appearance on microscopy. The thin myofilaments are found on either side of

the central dark band of thick myofilaments. The reduced volume and density of the

thin myofilaments manifests as the light bands or I bands for their isotropic appearance.

The thin myofilaments of adjacent sarcomeres are attached to each other and form a

boundary structure termed the Z line. Thus, the sarcomere extends from one Z line to the

next and contains one iteration of the light-dark-light banding pattern. The thin actin

myofilaments of each sarcomere extend from the Z line where they are bound to the thin

myofilaments of the adjacent sarcomere, to the central dark band region of the sarcomere

where they are unattached and interdigitate with the thick myosin myofilaments. Figure

2.1 illustrates the organization of skeletal muscles.

Figure 2.1 Organization of skeletal muscle.

Skeletal muscles have three connective tissue coverings: the epimysium, the

perimysium, and the endomysium (Figure 2.1). The epimysium is the dense connective

7

tissue the surrounds the muscle. The major blood vessels and nerves that supply the

muscle will penetrate the epimysium. The perimysium is the connective tissue that

surrounds bundles of fibers or fascicles within the muscle. Finally, the endomysium

is the delicate connective tissue that covers individual fiber bundles (Ross, 2006).

2.1.2 Contractile mechanism

The contractile mechanism in skeletal muscles depends on the interaction of the

myofilaments during a process known as the cross-bridge cycle (Webb and Trentham,

1981). In its simplest form, during the cross-bridge cycle, actin (A) combines with

myosin (M) and adenosine triphosphate (ATP) to produce force, adenosine diphosphate

(ADP) and inorganic phosphate (Pi). This can be represented as a chemical reaction:

A + M + ATP A + M + ADP + Pi + Force

Since the muscle fiber is the smallest complete contractile unit, it requires a subsystem

for metabolism. During metabolism, nutrients are brought into the cell and oxidized to

release energy. The most common examples of this are glycolysis and fatty acid

breakdown (Ross, 2006).

There are variations in the metabolism, myosin ATPase activity, and contractile

properties of the different fibers that make up muscles (Ganong, 2005). Based on these

8

variations, skeletal muscle can be characterized into three main fiber types: Type I, Type

IIB, and Type IIA (rare in humans). For the most part, human muscles have a mixture

of all three fiber types, but the proportions of these fiber types will vary with the

functional role of the muscle (Ross, 2006). Muscles that contain a majority of type I

fibers respond slowly, have a long latency, and are suited for long, slow, posture-

maintaining contractions. Muscles that contain many Type IIB fibers have a short

twitch duration and are adapted for fine, skilled movement. The properties of the three

main types of fibers found in skeletal muscles are summarized in Table 2.1.

Type I Type IIB Type IIA

Other names Slow oxidative; red

Fast glycolytic; white

Fast oxidative; red

Myosin isoenyzme ATPase activity

Slow Fast Fast

Diameter Moderate Large Large

Glycolytic capacity Moderate High High

Oxidative capacity* High Low High

Table 2.1 Summary of fiber types found in skeletal muscles. *correlates with content of mitochondria, capillary density, myoglobin content. Adapted from Ganong,

2005.

9

2.2 Muscle architecture

2.2.1 Overview

While much research has been focused on elucidating the cellular and metabolic

properties of muscle (Eisenberg 1983; Goldman 1987; McCray et al., 1980), less attention

has been given to the study of the macroscopic properties of human muscle (Lieber &

Frieden, 2001).

The function of skeletal muscles is dependant on its musculotendinous architecture,

“the arrangement of contractile and connective tissue elements within a muscle” (Lieber

and Fridén, 2001). Although muscles of different sizes may have a relatively consistent

fiber diameter, the arrangements of these fibers and the dimensions of the corresponding

tendon can differ significantly (Lieber, 1993).

The contractile elements, the muscle fibers, can be oriented in many ways, but most

skeletal muscles associated with the limbs are either parallel or pennate in arrangement

(Kawakami et al., 1993; Narici, 1999). Pennate muscles can be unipennate, bipennate,

and multipennate (Hamill, 2009). In muscles with parallel arrangement, the fibers run

parallel to the line of force. The line of force is defined as the line to which forces of

contracting fiber bundles will be projected (Lieber, 1993). In pennate muscles, the

fibers run obliquely to the line of force (Kawakami et al., 1998). The obliquity of the

muscle fibers to the line of action is the pennation angle. Figure 2.2 illustrates various

10

arrangements of muscle fibers found in skeletal muscles.

Figure 2.2 Muscle architecture: Various arrangements of muscle fibers

The connective tissue elements in skeletal muscles not only include the epimysium, the

perimysium, and the endomysium, but also include tendons and aponeuroses. The

primary function of the tendon and aponeurosis are to transmit force from the muscle to

the skeleton and to store elastic energy (Enoka, 2002). Tendons are flexible cordlike

structures that attach muscle to bone and consist of parallel bundles of collagen fibers

11

interposed with tendinocytes (fibroblasts). The tendon often becomes flattened when it

extends into the muscle as an aponeurosis. Aponeuroses are multilayered where the

collagen fibers in each layer are arranged at a 90º angle to those in apposing layers (Ross,

2006).

The shape, number, and dimensions of tendons and aponeuroses can also vary

significantly (Hamill, 2009). For example, in pennate muscles, tendons are often long

and aponeuroses can extend intramuscularly, whereas in parallel fiber muscles, these

connective tissue elements tend to be extra-muscular (Griffiths et al., 1991).

2.2.2 Architectural parameters and importance to function

2.2.2.1 Muscle

Specific architectural parameters of the muscle include fiber bundle length (FBL),

pennation angle (PA), and muscle volume (MV). Fiber bundle length is defined as the

distance between the attachment sites of a fiber bundle, and if often measured with

linearly with a ruler or caliper (Keating et al.,1993; Juul-Kristensen et al., 2000a).

However, since fiber bundles are often curved, FBL measurement may not be accurate.

Thus, using a method that can account for FBL curvature is important. Pennation angle

is defined as the acute angle that a muscle fiber bundle creates with the line of force

(Murray et al., 2000). Specifically, the line of force is the line that intersects the centroids

12

of cross-sections through the muscle volume (Jensen & Davy, 1975). Since this line of

force cannot be visualized on a specimen, previous studies have resorted to measuring the

surface PA (Lieber et al., 1990; Roh et al., 2000). Surface PA is the angle between the

fiber bundle and its attachment sites to bone, tendon, or aponeurosis, which is often not to

the line of force. Finally, MV is generally measured by liquid displacement techniques

(Roh et al., 2000) or 3D reconstructions of MRI images (Holzbaur et al., 2007). Muscle

volume has also been calculating by dividing muscle mass with a previously published

muscle density data (Mendez and Keys, 1960; Ward and Lieber, 2005). However,

muscle density has been found to vary with the method and duration of fixation (Ward

and Lieber, 2005).

Variations in skeletal muscle architectural properties indicate that muscles are

constructed for different functions. That is, the architectural properties allow for

muscles to be specialized in force production or excursion.

Functionally, muscle velocity and excursion are proportional to the number of

sacromeres in series i.e. FBL (Powell et al., 1984; Bodine et al, 1982; Gans & Gaunt,

1991, Fukunaga et al., 1997). Since FBL reflects the number of sarcomeres in series in the

fibers, muscle fiber length can be used to determine the shortening velocity of muscle fibers

and the range of lengths over which a muscle can produce active force (Lieber, 1993).

When a muscle contracts, each sacromere shortens proportionately (Enoka, 2002), which

13

in turn results in shortening of the myofibril. This change in length can be described as

ΔL=n(δl)

(ΔL is the change in length of the myofibril, n is the number of sacromeres in series, and

δl is the change in length of a sarcomere). To further illustrate this relationship of

muscle fiber length and excursion, consider two hypothetical muscles that only differ in

fiber lengths. The muscle with longer muscle fibers has a greater number of sarcomeres

in series, thus on contraction it has a greater absolute change in active length and will

undergo greater excursion and have a greater shortening velocity.

Muscle force is proportional to the total CSA of sarcomeres. In muscles with parallel

fiber arrangement, the force generated is related to the number of myofibrils arranged in

parallel. This relationship can be defined as

Fmyofibril= nf

(F is force, n is the number of myofibrils arranged in parallel, and f is the average force

exerted by one myofibril). Thus, increasing the number of myofibrils arranged in

parallel would increase the muscle force. However, most skeletal muscles in human are

pennated which means that each fiber is oriented at an angle to the line of force (Gans and

Bock, 1965). The force transmitted from the muscle fiber to the tendon has been shown to

be influenced by the PA of the myofibrils (Roy and Edgerton 1992; Lieber 1993). This

relationship can be defined as (Narici, 1999):

14

Ftendon= Fmyofibril cos θ

(Ftendon is the force acting on the tendon, Fmyofibril is the force acting along the fibers, and

θ is PA). Therefore, when muscle fibers are oriented at an angle relative to the line of

force, only a portion of their force is transmitted to the tendon. See the schematic

illustration of the effect pennation in Figure 2.3.

Figure 2.3 Effect of pennation angle. Muscle fibers oriented parallel to the axis of force generation transmit all of their force to the tendon.

However, muscle fibers oriented at a 30º angle relative to the line of force transmit only a portion of their

force (cos θ) to the tendon. Adapted from Lieber and Fridén, 2001.

Using architectural parameters such as FBL, PA, and MV, physiological cross-sectional

area (PCSA) can be calculated. Physiological cross-sectional area “represents the sum

of the cross-sectional areas of all the muscle fibers within a muscle” and is linearly

proportional to the contractile force of a muscle (Lieber et al., 1990). A muscle’s peak

isometric force can be calculated by multiplying the PCSA and the maximum stress

constant (Lemay & Crago, 1996). Thus, when maximum stress is assumed to be

(θ=0º)

Force=x

(θ=30º)

θcos'=

xForce

θ

Force’=xcosθ

=0.87x

Force= x

15

constant between two muscles, PCSA can be used to compare the relative force

generating capabilities between different muscles. The formula for physiological cross-

sectional area is as follows:

(V is the muscle volume).

Physiological cross-sectional area is problematic since the equation assumes that

muscle fiber PA is constant during muscle contraction. However, experiments using

different techniques have shown that this is not the case. For example, using a

photographic technique, Zuurbier and Huijing (1993) examined the PA of the unipennate

muscle in rats during isometric contractions at different muscle lengths. They found

that when the muscle was relaxed, PA was approximately 30º but when the muscle was

contracted the PA increased to about 60º. Through in vivo US investigation of human

skeletal muscles, PA has also been found to vary considerably with muscle contraction

and when muscle length changed (Chow et al., 2000; Fukunaga et al., 1997; Kawakami et

al., 1998).

2.2.2.2 Tendon

In addition to architectural parameters of the muscle, the properties of the tendon are

also important to quantify. The width, length, thickness and cross-sectional area (CSA)

FBLcos(PA) V PCSA ∗

=

16

of tendons provide insight into how the force-generating capabilities of a muscle may be

modulated. For example, longer tendons have a greater capacity to store elastic energy

(Hamill, 2009). The properties of the tendon and aponeuroses can also provide insight

into the presence of muscular partitions. That is, the distinct regions of skeletal muscles

have been defined based on the attachment to distinctive parts of the tendons and

aponeuroses (Wickham and Brown, 1998; Segal et al., 1991).

2.2.3 Methods used to study musculotendinous architecture

Musculotendinous architecture has been investigated using cadaveric dissection and

various imaging techniques including ultrasound (US) and magnetic resonance imaging

(MRI).

2.2.3.1 Cadaveric dissection

Using cadaveric tissue to study muscle and tendon architecture is advantageous

because structural features of the entire muscle and tendon can be observed directly

(Oxorn et al., 1998). However, the majority of previous studies have focused on the

gross morphology of the muscle (i.e. volume and muscle lengths). Although MV and

muscle length (ML) influence the contractile properties of muscles, accurate predictions

of muscle function cannot be obtained from these parameters alone (Lieber et al., 1990).

Previous cadaveric studies that measured FBL and PA are limited because one average

value for FBL is usually assigned to the entire muscle despite distinctive divisions within

17

the muscle (Aluisio et al., 2003; Juul-Kristensen et al., 2000b; Jensen et al., 1995; Keating

et al., 1993; Bassett et al., 1990). In addition, the number of fiber bundles and location

of fiber bundle sampling were not specified. Fiber bundle length was usually measured

directly from specimens using a ruler or calipers and PA using a protractor or goniometer.

However, in recent studies, architectural parameters have been quantified algebraically

from 3D computer models created from digitized cadaveric data obtain with the muscle in

situ (Agur et al., 2003). By digitizing hundreds of fiber bundles throughout the entire

volume of the muscle, a comprehensive model can be created through 3D reconstruction

and architectural parameters quantified. Using digitized data, FBL curvature is

accounted since FBL is quantified by summating the distances between digitized points.

2.2.3.2 Ultrasound

Real-time US enables direct visualization of skeletal muscle architecture in vivo in

relaxed and contracted states. Architectural parameters such as FBL and PA associated

with muscle contraction and various joint positions can be directly observed and

quantified (Fukunaga et al., 1997; Chow et al., 2000). This is an invaluable feature to

US especially since “the architecture of actively contracting muscle fibers differs

considerably than that which occurs when movement is passively induced” (Fukunaga et

al.,1997). The hypoechoic muscle fiber bundles are dark on US scans and can be well

delineated by the pale hyperechoic connective tissue between them.

18

The reliability of US measurements has been tested in numerous studies. For example,

Morse et al. (2008) measured FBL , PA, and MV from US scan of lateral gastrocnemuis

on separate days and found the high intra-rater correlation for all the parameters

(FBL=0.90, MV= 0.94; PA=0.80). Kawakami et al. (1998 & 1993) found that the

coefficients of variation between two to three different measurements of muscle thickness

(MT), FBL, and PA ranged between 0-2%.

Kawakami et al. (1993) validated the use of US to measure architectural parameters by

carrying out the measurements on the triceps brachii of three human cadavers. The

results demonstrated that architectural parameters measured from US scans differed from

manual measurements from cadavers by 0-1mm for MT and by 0-1º for PA.

2.2.3.3 Magnetic resonance imaging

Magnetic resonance imaging is a validated tool for measuring MV accurately (Narici

1999; Holzbaur et al., 2007). This is achieved through the following steps: (1)

contiguous axial images are performed along the muscle belly; (2) each axial image is

digitized and its anatomical CSA is calculated; and (3) MV is obtained by summating the

individual CSA of each image and multiplying by the sum of slice thickness.

Although MRI can been used to measure PA and MT, the technique has numerous

limitations summarized by Narici (1999) who found that “the measurement of pennation

angle and muscle thickness by MRI proved to be particularly time-consuming and

19

expensive since repeated scans were required to locate the optimal plane for pennation

angle determination”.

2.3 Muscle architecture of normal supraspinatus

2.3.1 Morphology of supraspinatus

Supraspinatus is one of four rotator cuff muscles. The other rotator cuff muscles

include the infraspinatus, teres minor, and subscapularis (Figure 2.4). These muscles

form a musculotendinous cuff around the glenohumeral joint and blend with the fibrous

layer of the joint capsule prior to attaching to the humerus (Moore, 2006). The belly of

supraspinatus lies in supraspinous fossa of the scapula and its tendon extends laterally,

deep to the acromion, to attach to the superior facet of the greater tubercle of the humerus

(Agur, 2009; Clemente, 2007).

The supraspinatus is reported to act as an abductor of the shoulder that works “in

concert” with the deltoid (Moore, 2002). The muscle also works with the other rotator

cuff muscles –infraspinatus, teres minor, and subscapularis– to stabilize the glenohumeral

joint by forming a musculotendinous cuff. During shoulder movement, the tonic

contraction of the rotator cuff muscles holds the humeral head in the shallow glenoid

cavity of the scapula (Moore, 2006).

20

Figure 2.4 Rotator cuff muscles. A. Posterior view B. Anterior view.

21

2.3.2 Cadaveric investigation of normal supraspinatus

2.3.2.1 Overview

Based on descriptions found in the literature, the normal supraspinatus muscle and

tendon each have anterior and posterior parts. The anterior part of the supraspinatus

tendon is “tubular” in shape and lays both intra- and extramuscularly (Roh et al., 2000;

Vahlensieck et al., 1994). In contrast, the posterior part of the supraspinatus tendon is

“flat and broad” in shape and entirely extramuscular (Ward et al., 2006). The muscle

belly of supraspinatus has an anterior and posterior region (Roh et al., 2000; Vahlensieck

et al., 1994). The fiber bundles of the anterior region of the muscle belly originate from

the anterior part of the supraspinous fossa and laterally attach to the anterior part of the

supraspinatus tendon. The posterior part of the supraspinous fossa and the spine of the

scapula is the origin of the posterior region of the supraspinatus muscle belly. The fiber

bundles of the posterior region extend laterally to attach to the posterior part of the

supraspinatus tendon.

To date, few studies have quantified the architectural parameters of normal cadaveric

supraspinatus. Table 2.2 lists the previous cadaveric studies and the architectural

parameters that were examined. Limitations are as follows:

• architectural parameters have mostly been quantified for the muscle as a whole

rather than for anterior and posterior regions

22

• the site of fiber bundle sampling was not stated in some studies and in others fiber

bundles were sampled only from the superficial surface of the muscle

• a variable number of parameters (1-4) are quantified in each study

• often the gender and age of the specimens were not reported making comparison

between studies difficult

23

Author (year) n (sex) Age Part of muscle FBL PA MV ML PCSA Wood et al. (1989)

1

(1M)

—

X

—

—

*

*

—

Keating et al. (1993)

5

—

X

*

—

*

—

*

Vahlensieck et al. (1994) 49 (52-97) X — — — * — Jensen et al. (1995)

1

—

Superficial

Deep

*

*

*

*

—

Itoi et al. (1995)

11 — X * — — — —

Juul-Kristensen et al. (2000b)

9 (F)

78.9 (55-87)

X * * * — *

Roh et al. (2000) 25 (10M/15F)

82 Anterior Posterior

* * * — *

Volk and Vangsness (2001)

20 (10M/10F)

(48-76) X — — — * —

Ward et al. (2006) 10 Anterior Posterior

* * — * *

TABLE 2.2 Summary of the types of architectural data obtained from cadaveric studies of supraspinatus muscle. Mean fiber bundle length (FBL), pennation angle (PA), muscle volume (MV), muscle length (ML), physiological cross-sectional area (PCSA). Male (M), female (F), data not collected —, data reported *, not specified X

24

2.3.2.2 Comparison of methodologies

In the following section, architectural parameters investigated in previous cadaveric studies

will be discussed and where possible methodologies will be compared. A comparison of the

methodologies used in four studies that investigated the most number of parameters is

provided in Table 2.3.

2.3.2.2.1 Fiber bundle length

In previous studies, the number of fiber bundles sampled was small relative to the total

volume of the muscle. For example, Juul-Kristensen et al. (2000b) sampled three fiber

bundles for the entire muscle and Ward et al. (2006) fifteen fiber bundles. In the other

studies, the number of fiber bundles sampled was not stated (Jensen et al., 1995; Keating et

al., 1993; Itoi et al., 1995; Roh et al., 2000). Keating et al. (1993) and Juul-Kristensen et al.

(2000b) measured FBL in situ, whereas Roh et al., (2000) and Ward et al. (2006) measured

FBL on excised fiber bundles. Furthermore, detail on the location of sampled fiber bundles

is often lacking in the literature. For example, Keating et al. (1993) and Jensen at al. (1995)

state that FBL were measured at “various locations within the muscle”. Roh et al. (2000)

and Ward et al. (2006) stated the general region from which fiber bundles were sampled, but

did not provide details on the depth of fiber bundle sampling (Table 2.3). In some studies,

FBL was measured between medial and lateral attachment sites using calipers whereas in

25

other studies FBL was not defined and the measurement tool not specified.

2.3.2.2.2 Pennation angle

Definitions of PA varied among the previous studies. For example, Juul-Kristensen et al.

(2000b) defined PA as the angle between the muscle fibers and the most centrally located

tendon of insertion. Ward et al. (2006) defined “surface pennation angle” as the angle

between the fibers and the distal tendon. Similarly, Roh et al. (2000) defined the PA as the

angle between the axis of the tendinous portion and its inserting muscle fibers. In contrast,

Jensen et al. (1995) defined PA as the angle between the fiber orientation and the line

connecting the greater tubercle of the humerus and the medial margin of the scapula in the

supraspinatus fossa. Similar to FBL measurements, the number of PA measurements made

was small relative to the total volume of the muscle. A goniometer was used by Roh et al.

(2000) and Ward et al. (2006) whereas Juul-Kristensen et al. (2000b) and Jensen et al. (1995)

did not state the instrument used to measure PA.

2.3.2.2.3 Muscle volume

Volume of the entire muscle was measured by Wood et al. (1989), Keating et al. (1993),

Jensen et al. (1995), and Juul-Kristensen et al. (2000). In addition to measuring the volume

for the entire muscle, Roh et al. (2000) also separated the anterior and posterior regions to

measure MV for each region. Fluid displacement was used in most of these studies;

26

Jensen et al. (1995) did not report the method.

2.3.2.2.4 Muscle length

Ward et al. (2006) was the only study that provided a definition for ML. It was defined as

“the distance from the origin of the most proximal fiber to the insertion of the most distal

fiber”. In the other studies, it was not possible to determine whether ML was the length of

the muscle belly or a combination of belly and tendon length.

2.3.2.2.5 Physiological cross-sectional area (PCSA)

Physiological cross-sectional area has been calculated in various ways. For example, Juul-

Kristensen et al. (2000b) used FBL and MV to calculate PCSA. Roh et al. (2000) and

Ward et al. (2006) also included PA whereas Ward et al. (2006) was the only study that

normalized FBL with sarcomere length. Keating et al. (1993) did not report the formula

used to calculate PCSA.

2.3.2.2.6 Tendon dimensions

Roh et al. (2000), Volk and Vangsness (2001), and Itoi et al. (1995) measured tendon

dimensions after removing the muscle and tendon from the specimen. Roh et al. (2000)

measured the width and thickness of the anterior and posterior parts of the tendon, Volk and

Vangsness (2001) the lengths, and Itoi et al. (1995) the length of the intramuscular tendon

and the width of the extramuscular tendon. Tendon thickness was also measured by Itoi et

27

al. (1995), but the location of measurement was not clearly stated. Dugas et al. (2002),

however, measured the tendon dimensions by outlining the attachment of the periphery of the

tendon on the humeral head in situ, then measured the dimensions on the marked outline on

the humerus after removal of the muscle and tendon.

28

Jensen et al. (1995)

Juul-Kristensen et al. (2000b)

Roh et al. (2000)

Ward et al. (2006)

FBL

·Number of FB measurements: not specified ·Location of measurements: “various locations” ·Instrumentation: not reported

·Number of FB measurements: three · Location of measurements: in situ and “measured on both sides of the most centrally located muscle tendon and from the superficial fascia of the muscle to the deep fascia” ·Instrumentation: not reported

·Number of FB measurements: “Multiple representative FBs” ·Location of measurements: on excised fibers from anterior and posterior region of the muscle · Instrumentation: calipers

·Number of FB measurements: fifteen ·Location of measurements: on excised fibers from anterior and posterior region of muscle ·Instrumentation: digital calipers

ML

·Not defined

·Not measured

·Not measured

·Defined as: “the distance from the origin of the most proximal fiber to the insertion of the most distal fiber”

Table 2.3 Continued on next page

29

Jensen et al. (1995)

Juul-Kristensen et al. (2000b)

Roh et al. (2000)

Ward et al. (2006)

MV ·Method not reported ·Fluid displacement (cm³) ·Fluid displacement (mL) ·Not measured PA · Number of measurements:

not specified · Location of measurements: superficial and deep part of muscle · Defined as: “the angle between the fiber orientation and the line connecting the greater tubercle of the humerus and the medial margin of the suprascapular fossa” ·Instrumentation: not reported

·Number of measurements: not specified · Location of measurements: “on both sides of the most centrally located muscle tendon and from the superficial fascia of the muscle to the deep fascia” ·Not defined · Instrumentation: not reported

·Number of measurements: “Multiple measurements” ·Location of measurements: anterior and posterior regions of the muscle ·Defined as: “the angle between the axis of each tendinous portion and its inserting muscle fibers” ·Instrumentation: goniometer

·Number of measurements: fifteen · Location of measurements: anterior and posterior regions of the muscle ·Defined as: “the angle between the fibers the distal tendon” · Instrumentation: goniometer

Table 2.3 Continued on next page

30

Jensen et al. (1995)

Juul-Kristensen et al. (2000b)

Roh et al. (2000)

Ward et al. (2006)

PCSA

·Not measured

·Calculated for the entire muscle ·Equation used was not stated.

·Calculated for the anterior and posterior muscle belly separately

θcos)( 2

LVmmPCSA =

where θ is the muscle PA (in degrees), V is muscle volume (in mL) and L is average muscle fiber length (in mm)

·Calculated for the entire muscle

)()/(cos)()(

3 mmgLfmgggMmmPCSA

ρθ

=

where Þ =muscle density (1.112cm²), θ is the muscle pennation angle (in degrees), Lf is normalized fiber bundle length

Table 2.3 Comparison of the methodologies used by Jensen et al. (1995), Juul-Kristensen et al. (2000b), Roh et al. (2000), and Ward et al. (2006). Fiber bundle= FB, Fiber bundle length=FBL, muscle volume=MV, muscle length=ML, pennation angle= PA, physiological cross-sectional area= PCSA.

31

2.3.2.3 Comparison of results

The architectural parameters that have been quantified in previous studies are summarized

in Table 2.4. The parameters include FBL, PA, MV, ML, and PCSA. It should be noted

that there was variability in the parameters quantified in each study. Tendon dimension data,

width, length and thickness, are summarized in Table 2.5. Comparison of parameters

between studies was difficult because of differences in methodology and treatment of data.

2.3.2.3.1 Fiber bundle length

Mean FBL for the entire muscle was found to be 5.6 cm by Keating et al. (1993) and 6.5

cm by Jensen et al. (1995). When Itoi et al. (1995) normalized their data to scapular length

and Ward et al. (2006) to sarcomere the mean FBL was less than the mean reported by

Keating et al. (1993) and Jensen et al. (1995). Mean FBL for the anterior and posterior

regions of the muscle belly, which was reported only by Roh et al. (2000), was found to be

8.3±0.09 cm and 6.5±1.2 cm respectively.

2.3.2.3.2 Pennation angle

Mean PA for reported for the entire muscle was found to be 11.4º±7.8 º by Juul-Kristensen

et al. (2000b) but 5.1º±0.8º by Ward et al. (2006). Roh et al. (2000) found mean PA for the

anterior region of the muscle belly to be 14º±3º and 10º±3º for the posterior region. Jensen

et al. (1995) reported the range of PA for the superficial and deep part of the muscle belly.

32

For the superficial part, PA ranged from 20º-25º degrees and 10º-12º for the deep part.

2.3.2.3.3 Muscle volume

Mean MV for the entire muscle belly ranged from 23 cm³ to 39.3 cm³ (Wood et al., 1989;

Keating et al., 1993; Jensen et al., 1995; Itoi et al., 1995; Juul-Kristensen et al., 2000b; Ward

et al., 2006). Roh et al. (2000) found the anterior region of the muscle belly to have a

volume of 12 cm³ and the posterior region to have a volume of 4 cm³.

2.3.2.3.4 Muscle length

Mean ML for the entire muscle ranged from 8.6 cm to 14.5 cm. It is difficult to comment

on the findings since most studies did not define ML.

2.3.2.3.5 Physiological cross-sectional area

Physiological cross-sectional area for the entire muscle was found to be 66±2.6 mm2 by

Juul-Kristensen et al. (2000b) and 66.5 ±5.6 mm2 by Ward et al. (2006). Roh et al. (2000)

found the PCSA for the anterior and posterior regions to be 140±44 mm2 and 62 ±25 mm2

respectively.

2.3.2.3.6 Tendon dimensions

The mean length of the anterior part of the supraspinatus tendon was greater than the

posterior part. Itoi et al. (1995) and Volk and Vangsness (2001) found the mean length of

the anterior tendon to be 4.08±1.03 cm and 5.4 cm respectively, whereas the mean length of

33

the posterior part was found to be 2.8 cm by Volk and Vangsness (2001). Roh et al. (2000)

found the thickness of the anterior tendon (0.31±0.07 cm) to be slightly greater than the

posterior (0.25±0.07 cm). The tendon thickness reported by Itoi et al. (1995) was 0.22±0.04

cm, but it is not clear what part of the tendon was measured.

The mean width of the entire supraspinatus tendon (both the anterior and posterior parts)

was reported to be 1.53±0.03 cm by Itoi et al. (1995). Roh et al. (2000) found the mean

width of the anterior tendon (0.84±0.21 cm) was smaller than the posterior tendon (1.28±0.28

cm). The width and length of the tendon insertion on the humerus was found to be

1.63±0.55 cm and 1.27±0.63 cm respectively by Dugas et al. (2002).

34

Author (year) n

Part of muscle

FBL (cm)

PA(deg) MV (cm³) ML (cm) PCSA (mm2)

Wood et al. (1989) 1 X — — 39.3 8.6 — Keating et al. (1993) 5 X 5.6 (4.7-6.5) — 23 (15-31) — Vahlensieck et al. (1994)

49 anterior posterior

— — — 10.6 8.9

—

Jensen et al. (1995) 1 superficial deep

6.5 (6.0-7.5) (20-25) (10-12)

36 11 —

Itoi et al. (1995)

11 X 2.8 ± 0.5 (normalized data)

— — —

Juul-Kristensen et al. (2000b)

9

X 4.7 ± 1.1 11.4 ± 7.8 29.7 ± 11.6 — 66±2.6

Roh et al. (2000) 25

anterior

posterior

8.3 ± 0.9 (4.5-11.7) 6.5 ± 1.2 (3.5-10.1)

14 ± 3 (8-20) 10 ± 3 (2-20)

12 ± 4 (7-25) 4 ± 2 (1-8)

— 140±44

62 ±25

Volk and Vangsness (2001)

20

X — — — 14.5 (12.2-16.8)

—

Ward et al. (2006) 10

X 4.50 ± 0.32 (normalized data )

5.1 ± 0.8 — 8.5 ± 0.4 66.5 ±5.6

TABLE 2.4 Summary of architectural data obtained from cadaveric studies of supraspinatus muscle. Mean fiber bundle length (FBL), pennation angle (PA), muscle volume (MV), muscle length (ML), physiological cross-sectional area (PCSA), ± standard deviation (range), —data not collected, not specified X

35

Author (year) n Part of tendon Length (cm)

Width (cm)

Thickness (cm)

Itoi et al. (1995) 11 intramuscular extramuscular

4.08±1.03

—

—

1.53±0.03

—

0.22±0.0.4*

Roh et al. (2000) 25 anterior

posterior

—

—

0.84 ± 0.21 (0.49-1.34) 1.28 ± 0.28 (0.66-1.57)

0.31 ± 0.07 (0.2-0.42)

0.25 ± 0.07 (0.2-0.43)

Volk and Vangsness (2001)

20 anterior

posterior

5.4 (4.1-7.7)

2.8 (2-3.7)

—

—

—

—

Dugas et al. (2002)

20 area of insertion

1.3 ±0.6 (0.7-1.5)

1.6 ± 0.6 (1.0-2.1)

—

TABLE 2.5 Summary of architectural data obtained from cadaveric studies of supraspinatus tendon. Mean tendon length, width, thickness, ± standard deviation (range) when reported. —data not collected. *location of tendon thickness measurement was not clearly stated. 2.3.3 Ultrasound investigation of normal supraspinatus

2.3.3.1 Overview

To date, in vivo US has only been used to investigate gross morphological features of

supraspinatus such as CSA and MT (Juul-Kristensen et al., 2000a; Dupont et al., 2001;

36

Katayose & Magee, 2001). Furthermore, these parameters have only been measured with

the muscle in the relaxed state. Quantitative measurements of architectural parameters such

as FBL and PA of supraspinatus have not been previously investigated with US.

2.3.3.2 Comparison of methodologies

Juul-Kristensen et al. (2000a) and Dupont et al. (2001) investigated the thickness of

supraspinatus using US. The aim of both studies was to determine how measurements taken

by US compared with measurements taken by MRI. It is important to note that the

positioning of patients was different between the two studies. Juul-Kristensen et al. (2000a)

measured MT with subjects seated with their arm hanging along the side of the body. In

contrast, Dupont et al. (2001) had the subjects positioned in prone with the arms held straight

alongside the torso resting on the table.

The location along the muscle belly and position of the US probe differed between the two

studies. Juul-Kristensen et al. (2000a) measured MT at the midpoint of the muscle length

with the US probe parallel to the muscle line of force. Dupont et al. (2001), however,

measured MT at various locations along the muscle length with the US probe held

perpendicular to the skin surface with the imaging plane transverse to the muscle line of force.

Both studies used a 5 MHz US transducer.

Juul-Kristensen et al. (2000a) measured the CSA of supraspinatus at the middle and medial

37

fourth of the muscle length with subjects seated in the same position that was used to

investigate MT. The 5 MHz US probe was held transverse to the muscle line of force. In

the study by Katayose & Magee (2001), subjects were also seated with the shoulder in the

neutral position. The CSA was measured at the midpoint of spine of the scapula with the

imaging plane transverse to the line of force. A 7.5 MHz transducer was used and the probe

was angled between 30º and 40 º.

2.3.3.3 Comparison of results

Only three quantitative US studies of supraspinatus were found in the literature. Muscle

thickness was reported in one study and CSA in two (Table 2.6). Juul-Kristensen et al.

(2000a) found the mean MT to be 2.0 cm and the mean CSA of supraspinatus, measured at

the middle of the muscle length to be 5.6 cm². The mean CSA for subjects within a similar

age range (between 30-39 years of age) was found to be 7.3 cm² by Katayose & Magee

(2001).

38

Author (year)

n (sex)

Age (range)

MT (cm)

CSA (cm2)

Juul-Kristensen et al. (2000a)

8 (F)

39.8

(27-54)

2.0

5.6

Dupont et al. (2001)

6

(3M/3F)

(24-51)

NR

—

Katayose & Magee (2001)

72 (M)

(30-39)

—

7.3

TABLE 2.6 Summary of architectural data obtained from in vivo US studies of normal supraspinatus muscle. Mean muscle thickness (MT), cross-sectional area (CSA), male (M), female (F), data not collected —, date not reported (NR)

2.3.4 Magnetic resonance imaging of normal supraspinatus

Juul-Kristensen et al. (2000) and Dupont et al. (2001) measured MT using both US and

MRI and then compared and correlated the results of the two methodologies. The

correlation coefficients in the Juul-Kristensen et al. (2000) study was 0.808 and in the Dupont

et al. (2001) study, 0.96. Both Juul-Kristensen et al. (2000) and Dupont et al. (2001)

concluded that US, a less expensive imaging technique, could accurately measure

supraspinatus MT.

39

2.4 Muscle architecture of pathological supraspinatus

2.4.1 Overview

In individuals over 40 years of age, rotator cuff tears, most commonly involving the

supraspinatus, is one of the major causes of shoulder pain and functional deficit (Winter et al.,

1997). The prevalence of tears markedly increases after 60 years of age – the incidence

reaching nearly 30% (Lehman et al., 1995). In dissection studies, the incidence of full-

thickness tears has been found to range between 19-48% (Itoi et al., 1995; Keyes et al., 1933).

Rotator cuff tears also account for a large percentage of work-related disorders, with a

reported incidence rate of 19.9 per 10,000 full-time employees per year (Silverstein et al.

1998). Significant pain, weakness in shoulder elevation, and limited function are typical

manifestations of supraspinatus tendon pathology (Bey et al. 2002).

Traditionally, structural deficits of the supraspinatus tendon have been focused on to

understand the etiology of supraspinatus tendon tears. Two theories have been popular: (1)

impaired perfusion to the critical zone of the supraspinatus tendon, and (2) compression and

abrasion of the supraspinatus tendon from the inferior surface of the acromion. The first

theory is predicated on anatomical studies that have found limited vascularity of the

supraspinatus tendon at and near its bony insertion (Lindblom, 1939; Rothman & Parke,

1976). The second theory, on the other hand, attributes degeneration of the supraspinatus

40

tendon to mechanical compression. According to Neer (1972) and others (Matsen et al.,

1998; Bigliani et al., 1991), the close proximity of the humeral head to the acromion as well

as the shape of the acromion are both associated with tendon tears.

More recently, however, deficits of the neuromuscular system have been highlighted in

the etiology of supraspinatus tendon tears. Muscular imbalance, instability impingement,

muscle overuse, and fatigue are now viewed as important factors in the pathogenesis of

tendon tears (Irlenbusch & Gansen, 2003, McCully et al., 2006).

Complete tears of the rotator cuff tendons are associated with fatty degeneration (Khoury et

al., 2008). Fatty degeneration is characterized by infiltration of fat within the muscle

volume (Goutallier et al. 2003). As the muscle atrophies, spaces are left between the muscle

fibers that become filled with fat. This process is progressive and often irreversible

(Thomazeau et al., 1997). Theses changes in the muscle belly are “negative prognostic

factors for the anatomic and functional results after tendon repair” (Khoury et al., 2008).

2.4.2 Cadaveric investigation of pathological supraspinatus

Previous cadaveric studies of the pathological supraspinatus have mostly been descriptive

(Keyes et al., 1933; Petersson et al 1984) with the exception of one quantitative study by Itoi

et al. (1995). In this study of forty-one embalmed cadaveric specimens, mean age of 84

years, thirty had varying degrees of tendon tears and eleven had an intact tendon. The

41

results of the normal specimens have been reported in section 2.3 of this thesis. Once a

tendon tear was identified, the maximal width and length of the tear was measured using

digital calipers. The supraspinatus was then excised from the specimen and the

extramuscular tendon length was measured at the center of the tendon on its articular side

from its lateral end to the musculotendinous junction. “Total tendon length”, was measured

from the lateral margin of the extramuscular tendon to the most medial edge of the

intramuscular tendon. “Functional tendon length” was defined as the sum of the

extramuscular tendon length and the tear length. Fiber bundle length was measured at four

unspecified locations on the superficial surface of the muscle. Tendon and muscle volumes

were measured by water displacement. Cross-sectional area of the muscle was calculated by

dividing the MV by FBL.

The mean tendon dimensions, muscle fiber lengths, and cross-sectional areas were

organized into four groups: (1) intact cuff- 27%; (2) partial tears comprising partial thickness

tears of the supraspinatus-29% (3) small tears comprising full-thickness tears of the

supraspinatus-27%, and (4) large tears with tears of more than 2 tendons-17%. All data was

normalized by dividing the raw data by the scapular length and multiplying by 100. Table

2.7 provides a summary of the findings by Itoi et al. (1995).

The mean total tendon length and width decreased as the size of the tendon tear increased.

42

Similarly, mean FBL, MV, and CSA decreased as the tendon pathology worsened. Mean

tendon thickness varied little with tendon pathology.

Partial tear (n=12) Small tear (n=11) Large tear (n=7) Tendon length (cm)

Extramuscular

Total

Functional

1.97 ± 0.45

4.50 ± 0.90

2.46 ± 0.96

1.58 ± 0.55

3.51 ±0.78

3.11 ±0. 88

1.53 ±0.38

3.26 ±1.07

4.18 ± 0.91

Tendon width (cm)

1.60 ± 0.38 1.58 ± 0.51 1.41 ± 0.24

Tendon thickness (cm)

0.24 ± 0.07 0.25 ± 0.07 0.26 ± 0.06

FBL (cm)

3.10 ± 0.63 2.55 ± 0.60 2.35 ± 0.54

MV (cm3)

26.1 ± 10.4 23.7 ± 9.0 18.5 ± 19.5

Muscle CSA (cm2)

0.7 ± 0.2 0.8 ±0.2 0.9 ±0.3

Table 2.7 Summary of findings by Itoi et al. (1995): Architectural data collected through cadaveric investigation of pathological supraspinatus. Fiber bundle length (FBL), muscle volume (MV), cross-sectional area (CSA).

2.4.3 Imaging investigations of pathological supraspinatus

Imaging studies of the pathological supraspinatus tend to focus on two muscle qualities:

(1) muscle atrophy which is reflected by the muscle CSA, and (2) fatty infiltration which is

the replacement of muscle fibers by fat. To study muscle atrophy and fatty infiltration, MRI

43

is considered the gold standard (Thomazeau et al., 1997; Strobel et al; 2005). However, recent

studies have found US to be as reliable and valid to investigate muscle atrophy (Juul-

Kristensen et al., 2000a; Dupont et al., 2001).

Computer tomography (CT) has been used to investigate fatty infiltration (Goutallier et

al.,1994). Goutallier et al. (1994) established a CT based classification system of fatty

infiltration for the supraspinatus that has also been used with T1 weighted MRI scans

(Gladstone et al., 2007).

To date, architectural parameters such as FBL and PA of supraspinatus have not been

quantified in vivo with US or MRI.

2.5 Modeling of skeletal muscles

2.5.1 Overview

Modeling of skeletal muscles started in the seventeenth century. Through the use of

mathematical formulas, muscle models can create simplified images of what is happening at

the muscle level (van den Bogert et al., 1998). By manipulating architectural parameters that

are used in the formula, insight into their effects on muscle properties can be gained (Huijing,

1998).

44

2.5.2 Types of models

Depending on the purpose of modeling, muscle models can be of two general types:

phenomenological or structural (Jacobs & Rikkert, 1991). If the purpose of modeling is to

“describe” functional properties, then a phenomological model is developed. However, if

the purpose of modeling is to “explain” functional properties, then a structural model is

developed.

2.5.2.1 Phenomological models

One of the earliest phenomenological skeletal models was developed by Hill (1938).

Although the model has been modified over the years to account for shortcomings, Hill’s

model is the most commonly used muscle model in simulation of human movement (Cole et

al., 1996; Winters., 1990). As a phenomenological type of model, Hill’s model provides

little insight into the mechanisms of muscular contraction (Cole et al., 1996). Instead, Hill

wanted to model the macroscopic contractile phenomenon of whole muscles.

The classic Hill’s model is the three component configuration. The three components,

are a contractile element in parallel with a passive elastic element that are both in turn

connected in series with another elastic element. The contractile element corresponds to

the active characteristics of the muscle fibers, and it includes the force-length and force-

velocity behavior of the muscle. The series elastic element represents all elastic components

45

of the muscle-tendon unit (i.e. the tendon and cross-bridge elasticity) in series with the

contractile element. The parallel elastic elements represent the connective tissue around the

muscle fibers and fiber bundles.

2.5.2.2 Structural models

Structural models account for the biochemical reactions during muscle contraction (Otten,

1991). The Distribution Moment model developed by Zahalak (1990) is an example of a

structural model that explains the force-velocity characteristics of skeletal muscle. This

model incorporates the basics of the cross-bridge model that was initially proposed by

Huxley (1957).

2.5.2.3 Use of architectural parameters in muscle models

Over the years, classic muscle models such as the Hill’s Model and the Distribution

Moment model have evolved to be able to account for different muscle properties (Stensen,

1667; Hill, 1938; Woittiez et al., 1984; Williams & Goldspink et al., 1978; van der Linden et

al., 1998). However, as stated by Otten (1991), “A simple rule of thumb is the following: If

the model is changed to something closer to the observed structures or characteristics, and

the model improves in performance, this may indicate increased insight.”

Despite the availability of new techniques like MRI, data of musculotendinous parameters

for muscle modeling is still highly dependent on cadaveric studies (Veeger et al., 1991;

46

Johnson et al., 1996). Since the predictive value of muscle models will heavily depend on

the parameters describing the characteristics of the system, the more accurate the

architectural data, the greater the predictive value of the muscle model.

2.5.3 Models of shoulder region: source of architectural data

Musculoskeletal models of the glenohumeral joint or shoulder mechanism often rely on

cadaveric specimens for architectural data. Veeger et al. (1991) states that due to the

complexity of the shoulder mechanism, “assumptions have to be made for muscle

characteristics in order to develop an adequate and manageable model.”

When modeling supraspinatus, the architectural data that is used is often based on a

limited number of measurements (Wood et al., 1989; Bassett et al., 1983, Poppen and Walker

et al., 1978). For example, Bassett et al. (1990) established fiber length of supraspinatus

from “one measurement of an individual fiber lying obliquely parallel between tendon plates

of origin and insertion using a micrometer.” Thus, fiber bundles throughout the muscle

volume were not measured. Johnson et al. (1996) stated that “It (supraspinatus) exhibited

no morphological features that justified defining more than a single fascicle.” Second, fiber

bundles are often characterized as being straight and linear. In order words, the curvature of

fiber bundles is not considered (van der Linden et al., 1998, van Leeuwen and Spoor, 1992).

2.5.4 Use of digitized data for muscle modeling

47

Modeling techniques developed by Agur (2003) and Ng-Thow-Hing (2001) allow for

capture and 3D modeling of tendons, aponeuroses, and hundreds of fiber bundles throughout

the volume of individual skeletal muscles.

Once the specimen and muscle of interest have been securely mounted and exposed, fiber

bundles on the superficial surface of the muscle are identified and digitized in situ from their

medial to lateral attachments. Following digitization, the fiber bundles are removed to

expose the subsequent layer of fiber bundles. This process is repeated throughout the

muscle volume. At each level of dissection, aponeuroses and tendon, if present, are

simultaneously digitized. The digitized data is imported into MayaTM (3D computer

modeling software) enhanced by plug-ins for three-dimensional visualization and

quantification of architectural parameters. Architectural parameters such as FBL and PA

can be easily computed, with fiber bundle curvature being accounted for and PA being

measured to the line of force.

2.6 Role of supraspinatus in abduction and glenohumeral abduction

Below, studies related to elucidating the role of supraspinatus in glenohumeral abduction

will be discussed first followed by an overview of studies that investigated the contribution of

supraspinatus relative to the other rotator cuff muscles to joint stabilization.

48

Numerous studies have been carried out to better understand the contribution of

supraspinatus in shoulder abduction. Howell et al. (1986) investigated the torque produced

by supraspinatus within two planes of motion, forward flexion and elevation in the plane of

the scapula, in ten healthy male volunteers between the ages of 24 and 29 years. With the

use of an isokinetic dynamometer, the reduction of torque as a result of isolated paralysis of

the suprascapular and axillary nerves was measured. The study found that with paralysis of

either the suprascapular nerve or the axillary nerve, torque decreased to approximately 50%

of the value for the non-paralyzed shoulder in both planes of motion. No significant

differences in the mean reduction in torque was found between paralysis of the suprascapular

and axillary nerves. Thus, the study concluded that the supraspinatus and deltoid muscles

were equally responsible for producing torque about the shoulder joint in the two planes of

motion. Sharkey et al. (1994) investigated the contribution of the deltoid, supraspinatus,

infraspinatus, teres minor and subscapularis to abduction in five fresh cadaveric specimens.

In this study, the amount of force required to abduct the shoulder was computed for: 1)

deltoid only, 2) deltoid and all four rotator cuff muscles, 3) deltoid and supraspinatus, and 4)

deltoid and infraspinatus, teres minor, and subscapularis. When the deltoid muscle was

concurrently stimulated with the supraspinatus, the average amount of force required by the

deltoid reduced significantly (28%), suggesting that the supraspinatus is actively involved in

49

shoulder abduction. The study also found that the contribution of supraspinatus to

abduction of the arm was greatest between 30º-60º and insignificant by 120º. McMahon et

al. (1995), using a dynamic shoulder testing apparatus, evaluated the muscle forces of

supraspinatus and middle deltoid during glenohumeral abduction in the scapular plane. The

muscle forces were evaluated with different force ratios applied to the two muscles (i.e. equal

force to each tendon; 2:3 ratio of force applied to deltoid/supraspinatus; 3:2 ratio; no force

applied to the supraspinatus tendon). The study found that full glenohumeral abduction was

achieved in all force ratios, suggesting that the supraspinatus and deltoid can compensate for

each other when one is not fully functioning. The study also found that near the beginning

of abduction (0-15º), a larger contribution of force from the supraspinatus was required,

whereas near the end of the abduction greater activity of the middle deltoid was needed.

There have also been many studies that have aimed at better understanding the contribution

of the supraspinatus, relative to the other rotator cuff muscles, to shoulder stabilization and

kinematics. In a cadaveric study, Keating et al. (1993) calculated the PCSA of each of the

four rotator cuff muscles and the percentage contribution of each muscle to the total PCSA of

all four muscles. The study found that the mean percentage contribution of supraspinatus to

the total PCSA to be 15%, whereas the infraspinatus contributed 23%, teres minor 10%, and

subscapularis 51%. In the studies by Howell et al. (1986) and McMahon et al. (1995)

50

simulated supraspinatus paralysis was not found to affect the normal ball-and-socket

kinematics of the glenohumeral joint during abduction. Howell et al. (1986) suggested that

“joint compression through the action of the remaining rotator cuff muscles was sufficient to

provide a fixed fulcrum for concentric rotation of the glenohumeral joint during abduction”.

Similarly, in a cadaveric study by Wuelker et al. (1994), the function of the supraspinatus was

examined using a dynamic shoulder model. The investigators found that loss of force of the

supraspinatus only produced minor changes in the glenohumeral joint mechanics and

concluded that the supraspinatus does not have a significant effect on the centering of the

humeral head on the glenoid during elevation. However, because of large differences

between specimens, the findings were not statistically significant. In an MRI study,

Werner el al. (2006) eliminated supraspinatus and infraspinatus action at the shoulder with

paralysis of the suprascapular nerve but found that during active shoulder abduction superior

migration of the humeral head could not be provoked.

Few studies have discussed the function of the anterior and posterior regions of the

supraspinatus. Vahlensiek et al. (1993) suggested that the anterior region may act as an

internal rotator, whereas the posterior region was hypothesized to act as an abductor based on

fiber bundle and tendon orientation following dissection of four cadaveric specimens and

MRI scans. Based on PCSA differences for the anterior and posterior regions of

51

supraspinatus, Roh et al. (2000) suggested that the majority of the contractile force was

produced in the anterior region of the muscle.

2.7 Summary:

The supraspinatus, one of the four rotator cuff muscles, is a relatively small muscle that sits

in the supraspinatus fossa and functions with many other muscles to move the shoulder.

Clinically, the supraspinatus is important as its muscle-tendon unit is “the most vulnerable

component of the rotator cuff mechanism” (Howell et al., 1986). Understanding its fiber

architecture has significant clinical implications in the evaluation and management of patients

with shoulder pathology.

A study investigating the static and dynamic fiber bundle architecture throughout the

muscle volume in the normal and pathological supraspinatus is lacking. Fiber bundle

measurements (i.e. FBL and PA) of supraspinatus reported previously in the literature are

limited to a small number of fiber bundle measurements with fibers from only the superficial

region of the muscle belly being investigated. Dynamic investigation of the fiber bundle

architecture of supraspinatus has been limited to qualitative assessment. In vivo

architectural data of FBL and PA of supraspinatus has not been collected to date.

52

Chapter 3: Hypotheses and Objectives

3.1 Hypotheses

The hypotheses for this thesis are as follows:

1. A 3D computer model of the musculotendinous architecture of the cadaveric

supraspinatus can be generated and used to quantify the musculotendinous

architecture throughout the muscle volume.

2. From the 3D model of supraspinatus, an US protocol can be developed to investigate

and quantify the in vivo musculotendinous architecture both statically and

dynamically.

3. Fiber bundle lengths, PA and MT throughout the volume of supraspinatus are variable

and can be used to identify architecturally distinct regions.

4. In vivo FBL and PA will change significantly with contraction and the percentage

change will not be uniform throughout the muscle volume.

5. In vivo changes in FBL, PA and MT in the relaxed and contracted state will differ

between the normal and pathological supraspinatus.

53

3.2 Objectives

The objectives for this thesis are as follows:

1. To model the 3D musculotendinous architecture of supraspinatus throughout its

volume in cadaveric specimens.

2. To establish an architectural database from the 3D model of supraspinatus.

3. To develop a comprehensive in vivo US protocol that takes into account the

musculotendinous architecture of the entire supraspinatus based on the findings of the

cadaveric model.

4. To investigate the static and dynamic musculotendinous architecture of supraspinatus,

in vivo, in normal subjects and in subjects with a full-thickness tear of the anterior

supraspinatus tendon.

5. To compare the architectural data collected from normal subjects with data from

subjects with a full-thickness tear of the supraspinatus tendon.

54

3.3 Significance

This study will provide detailed architectural data of the static and dynamic

supraspinatus throughout its entire volume. The findings will provide greater insight into

fiber bundle changes as a function of glenohumeral positioning, muscle contraction, and

rotator cuff pathology.

The 3D model will serve as an architectural map for future studies, and the data

collected from cadaveric specimens and in vivo may be used to create models that can

account for fiber bundle heterogeneity and dynamic changes. Clinically, in vivo US

investigation of the normal and pathological musculotendinous architecture of supraspinatus

may lead to the development of assessment tools capable of planning and predicting the

outcome of rehabilitation, surgery, and training regimens.

55

Chapter 4: Methods

4.1 Cadaveric Investigation

4.1.1 Specimens

Ten formalin embalmed human cadaveric specimens with a mean age of 61.9 ± 16

years were used for this study. Specimens with evidence of visible gross shoulder

abnormality, previous surgery, or tendon pathology were excluded. Only male

specimens were used in this study since all female specimens were excluded due to

tendon pathology. Ethics approval was received from the University of Toronto

(protocol # 20830). See Appendix B.

4.1.2 Dissection and digitization

The supraspinatus was exposed by removing all overlying structures and the acromion.

To prevent movement, the shoulder joint was fixated in 0˚ of abduction, flexion and

lateral rotation with a metal plate screwed to the humerus and scapula. Then the

specimen was clamped into a securely mounted vice and three reference points (scapular

spine, coracoid process, greater tubercle) were demarcated with a screw. These

reference points were later used to reconstruct the specimen in 3D. Next, the periphery

of the supraspinatus tendon was outlined with points using a paint pen. Each point was

digitized using a MicroscribeTM G2 Digitizer to obtain its x, y, and z coordinates. The

56

supraspinatus muscle belly was then serially dissected in situ with the aid of a dissection

microscope. At each layer (1.5 -2 mm in thickness), 10-60 fiber bundles were identified

and traced from their medial to their lateral attachment sites. The attachment sites and

10-20 intervening points were digitized for each fiber bundle. Following digitization,

fiber bundles were sequentially removed to expose the next layer. Digitization of the

tendon periphery was repeated at every 3-5 layers of the muscle (Figure4.1).

Figure 4.1 Cadaveric investigation: Digitization and dissection of supraspinatus. Superficial view of supraspinatus with acromion cut. White dots demonstrating the digitized locations

along a fiber bundle. Periphery and surface of tendon stippled in black dots.

4.1.3 MicroscribeTM

Mircroscribe

G2 Digitizer

TM G2 Digitizer (Figure 4.2), which was used to digitize the fiber bundles

and tendons of supraspinatus, has an accuracy of 0.24mm. For further details on this

apparatus see http://www.immersion.com/digitizer/.

57

Figure 4.2 Cadaveric investigation: MicroscribeTM G2 Digitizer. A: Digitizer. B: Digitizing arm digitizing object. C: Reconstruction of digitized data in 3D.

4.1.4 Modeling

Digitized data was imported into Autodesk Maya™, a 3D modeling and animation

software, using plug-ins developed in our laboratory. The plug-ins facilitated the

reconstruction of the digitized data of the supraspinatus muscle belly and tendon in 3D by

aligning the digitized layers in each specimen using the coordinates of the reference

points (screws). The reconstructed model enabled 3D visualization of the muscle belly

and tendon throughout its volume (Figure 4.3). From the model, the extent and location of

internal and external tendons was documented and the location and attachment sites of the

fiber bundles were investigated to determine if there were any architecturally distinct

regions.

A. B. C.

58

Figure 4.3 Cadaveric investigation: 3D computer model of supraspinatus. Superficial

view.

4.1.5 Data analysis

Algorithms were derived and implemented in Python to perform computer-automated

calculations of individual fiber bundle parameters. These parameters included FBL, PA,

MV and dimensions of intra- and extramuscular tendons. Fiber bundle length was

calculated as the sum of the distances between each of the digitized points along the fiber

bundle and the PA as the acute angle between the fiber bundle and line of force (Figure

4.4). Line of force is defined as the line that intersects the centroids of cross-sections

through the muscle volume (Jensen and Davy, 1975). To measure MV, the fiber bundles

were treated as 3D cylinders. The FBL was used as the height of the cylinder while the

radius was calculated as half the average distance to its closest neighboring fiber bundle.

Finally, the volume of each fiber bundle was computed and their sum yielded the MV.

Medial Lateral Anterior

Posterior

Tendon

Anterior region

Posterior region

59

Fiber bundle length, PA for the medial and lateral ends of the fiber bundles, and volume

of architecturally distinct parts of the muscle were characterized with descriptive statistics

(mean, standard deviation and range). Paired t-tests and ANOVA followed by Tukey’s

post-hoc test were carried out to compare means. Statistical significance was set at

p<0.05.

Figure 4.4 Cadaveric investigation: FBL and PA measurement

4.2 Ultrasound investigation of normal supraspinatus

4.2.1 Subjects

Seventeen subjects (8M/9F) were recruited for this study. The number of subjects was

based on a sample size calculation (Appendix A). The mean age of the subjects was

60

36.4±12.7, with a range of 21-60 years. Subjects with a history of rotator cuff pathology

or neuromuscular disease were excluded. Written informed consent was obtained from all

subjects. Ethics approval for this study was granted from the University of Toronto

(#15513) and Mount Sinai Hospital Research Ethics Board (05-0235-E). The same

musculoskeletal radiologist scanned all subjects. See Appendix B.

4.2.2 Equipment

An HDI 5000, Advanced Technology Laboratories (ATL) real-time US scanner with a

linear (38 mm) 12 MHz transducer was used for the study. Information was processed

with eFilm Merge PACS system.

4.2.3 Positioning and screening of subjects

Throughout the scanning process, subjects were seated in a chair with their back

supported. To ensure there was no pathology at the shoulder, the muscles and tendons

of the rotator cuff were scanned bilaterally on all subjects. Provided there was no

pathology, the radiologist continued with the in vivo protocol.

4.2.4 Protocol

The US protocol was developed on completion of the cadaveric study. The protocol

was based on the architecturally distinct regions of the supraspinatus muscle belly and

tendon morphology defined in the cadaveric portion of this thesis. In the cadaveric

study, the muscle belly was found to have two distinct regions, anterior and posterior,

61

each consisting of three parts: superficial, middle and deep (Figure 4.5). The tendon

consisted two parts: an extramuscular posterior part and an intra- and extramuscular

anterior part.

Figure 4.5 Ultrasound investigation of normal supraspinatus: Architecturally distinct regions of supraspinatus used to develop US protocol. Superior views. A: Superficial. B: Intermediate. C: Deep; Anterior part of supraspinatus tendon is

reflected. Superficial part of anterior region (AS); middle part of anterior region (AM); deep part of anterior

region (AD); posterior region (PR); anterior part of supraspinatus tendon (*); area of acromial shadowing

(Acr).

62

4.2.4.1 Protocol development

To develop a protocol, a preliminary study was carried out to determine whether the

musculotendinous architecture of each region of the muscle belly and the intramuscular

portion of the anterior tendon could be visualized using US. Using panoramic coronal

US images, it was found that fiber bundles of the middle and deep parts of the anterior

region could be imaged along with the intramuscular portion of the anterior tendon.

From the scans, FBL and PA of the fiber bundles were measured relative to their

attachment sites to the supraspinous fossa and intramuscular portion of the anterior

tendon. Fiber bundles of the smaller superficial part could not be consistently visualized,

but the distance between the intramuscular tendon and the superficial surface of the

muscle belly was measurable and documented as tendon depth (TD). The fiber bundles

of the deep part of the posterior region could be visualized until they passed deep to the

acromion. Thus, PA could not be measured. Another preliminary study was carried

out to determine how much of the FBL is shadowed by the acromion. The superficial

and middle parts of the posterior region could not be independently scanned as the fiber

bundle planes were difficult to locate consistently. Using sagittal US images, the

thickness of the entire muscle (MT) could be visualized and measured along the muscle

belly.

63

4.2.4.2 Development of acromial correction factor

To determine the mean length of the fiber bundles of the posterior region that is

shadowed by the acromion, ten formalin embalmed cadaveric specimens were used

(9M/1F). The mean age was 75.4±10.3 (53-87) years. Specimens with evidence of tendon

or joint pathology were excluded.

4.2.4.2.1 Dissection and Digitization

On each specimen, the supraspinatus muscle, spine of the scapula and the acromion

were exposed. Next, the shoulder was stabilized at 0˚ of abduction, flexion , and lateral

rotation with a metal plate screwed to the humerus and scapula as in the cadaveric portion

of the study. The muscle belly was incised along the medial border of the acromion to

demarcate the extent of the acromion. Next, the acromion was excised and the muscle

and tendon exposed. In order to determine the length of the fiber bundles that were

obstructed by the acromion, fiber bundles lateral to the incision were serially dissected

and digitized using the techniques described in section 4.1.2. Mean lengths of the

digitized fiber bundle segments were computed for the superficial, middle and deep parts

of the posterior region. The “acromial correction factor” will be used to refer to the

mean lengths of the fiber bundles shadowed by the acromion. The acromial correction

factor was added to in vivo FBL measurements of the posterior region to obtain an

64

estimate of actual FBL.

4.2.4.3 Ultrasound investigation

The US protocol developed in the preliminary study was then used to scan fiber bundles

of the middle and deep parts of the anterior region and the deep part of the posterior

region. All subjects were scanned bilaterally in relaxed and contracted states. For the

relaxed state, the muscle was scanned with the arm resting by the subjects’ side and the

palm of hand at the side of the chair. For the contracted state, the muscle was scanned

with the shoulder in three different positions: 60˚ abduction; 60˚ abduction wi th 80̊

external rotation; 60˚ abduction with 80˚ internal rotation (Figure 4.6). Panoramic coronal

US images were used to capture fiber bundles and the intramuscular tendon; sagittal US

images were used to assess the thickness of the muscle. All scans were saved as JPEG

images for further analysis.

65

Figure 4.6 Ultrasound investigation of normal supraspinatus: Subject arm positions for US scanning. Contracted states: A: 60º abduction; B: 60º abduction with 80º external rotation; C: 60º abduction with 80º

internal rotation

4.2.5 Measurement of architectural parameters from US scans

Architectural parameters were computed using software developed in our laboratory.

Fiber bundle length was computed as the distance along the fiber bundle between the

attachment sites. If fiber bundle curvature was observed, the fiber bundle was segmented

and the length of each segment was summated to give the total FBL. To compute FBL

of the deep part of the posterior region, the acromial correction factor was added to the in

66

vivo FBL measurements (Figure 4.7B). Pennation angle was measured as the angle

between the fiber bundle and its attachment to the intramuscular tendon (Figure 4.7A).

Muscle thickness was computed at the midpoint of the muscle belly between the medial

border of the acromion and the most medial point of attachment of the muscle belly in the

suprascapular fossa (Figure 4.8A). The position of the intramuscular tendon (TD) was

computed as the distance between the superficial surface of the muscle belly and the

intramuscular tendon at the medial border of the acromion (Figure 4.8B).

67

Figure 4.7 Ultrasound investigation of normal supraspinatus: Measurement of FBL and PA on US scans. Longitudinal US scans of left supraspinatus. Note: images are not uniform in scale. A: One fiber bundle

from middle part of the anterior region has been demarcated by a white line (↔), pennation angle

demarcated by (a). B: One fiber bundle from posterior region has been demarcated by a white line (↔ ).

Only a portion of the acromial correction factor (acf) is shown. Fiber bundle length (FBL); pennation

angle (*); skin (SK); subcutaneous tissue (SC); trapezius muscle (TP); supraspinous fossa (SF);

intramuscular tendon ( ○ ○ ); middle part of anterior region (AM); deep part of anterior region (AD);

acromial shadow (Acr).

68

Figure 4.8 Ultrasound investigation of normal supraspinatus: Measurement of MT and distance of intramuscular tendon to superficial surface of muscle belly (TD). A: Saggital US scan of right supraspinatus at the midpoint of muscle belly. Muscle thickness (MT). B:

Longitudinal US scan of right supraspinatus. Distance between the intramuscular tendon and the

superficial surface of the muscle belly (TD). Subcutaneous tissue (SC); trapezius muscle (TP);

supraspinous fossa (SF); superficial part of anterior region (AS); middle part of anterior region (AM);

intramuscular tendon (○ ○); acromial shadow (Acr).

4.2.6 Data analysis

Fiber bundle length, PA, MT and TD data was imported into SPSS. Each architectural

parameter was characterized with descriptive statistics (mean, standard deviation and

range) for the relaxed and each contracted states (60˚ abduction; 60˚ abduction with 80˚

external rotation; 60̊ abduct ion with 80̊ internal ro tation). Paired t-tests were used to

compare means between the anterior and posterior regions, and repeated measures

ANOVA was carried out to compare means between different shoulder positions.

Statistical significance was set at p<0.05.

69

4.3 Ultrasound investigation of pathological supraspinatus

4.3.1 Subjects

Five subjects (2M/3F) with a full-thickness tear of the anterior supraspinatus tendon, as

diagnosed by MRI and/or US, were investigated for this study (Figure 4.9). The mean

age of the subjects was 59± 7.7 years, with a range of 50-69 years. Subjects with a

history of shoulder surgery or neuromuscular disease were excluded. Written informed

consent was obtained from all subjects. Ethics approval for this study was granted from

the University of Toronto (#19084) and Mount Sinai Hospital Research Ethics Board (06-

0107-E).

Figure 4.9 Ultrasound investigation of pathological supraspinatus: US scan of pathological left rotator cuff. Full-thickness anterior tendon tear. Tendon (T). Dotted line showing extent of tear.

4.3.2 Protocol

The same musculoskeletal radiologist that scanned the normal subjects performed scans

on the subjects with rotator cuff tears using the same US equipment (12 MHz transducer).

70

As in the study of normal supraspinatus, subjects were seated in a chair with their back

supported.

First, the torn rotator cuff was scanned to document the location and dimensions of the

supraspinatus tendon tear. The supraspinatus of the contra-lateral shoulder was also

scanned and if any pathology was found, the location and dimensions were documented.

The US protocol as outlined in Section 4.2.4.3 was used to scan the middle and deep

parts of the anterior region, the deep part of the posterior region, the thickness of the

muscle and the position of the intramuscular tendon. However, the muscle was only

scanned in the relaxed state and in one contracted position (60˚ abduction with neutral

rotation against gravity). Panoramic coronal US images were used to capture fiber

bundles of the middle and deep parts of the anterior region, deep part of the posterior

region and tendon position; sagittal US images were used to assess the thickness of the

muscle. All data was saved as JPEG images and transferred to a computer in the

laboratory for analysis.

4.3.3 Measurement of architectural parameters from US scans

Fiber bundle length, PA, MT and TD, were computed using the same methods were

used in section 4.2.3.

4.3.4 Data analysis

The FBL, PA, MT and TD data was imported into SPSS. Each architectural

71

parameter was characterized with descriptive statistics (mean, standard deviation and

range) for the relaxed and contracted states. Paired t-tests were used to compare means

between relaxed and contracted states. A one-way between groups ANOVA with post-

hoc tests was conducted to explore the mean differences between the pathological

supraspinatus, contra-lateral supraspinatus, and normal supraspinatus. Statistical

significance was set at p<0.05.

4.4 Reliability and validity of measurements

4.4.1 Intra-rater reliability

To determine intra-rater reliability of measurements made on normal subject scans,

fiber bundles in all regions of two normal subjects were re-measured eight weeks later by

same investigator. To determine intra-rater reliability of measurements made on

pathological subject scans, fiber bundles in all regions of all subjects was also re-

measured eight weeks later by the same investigator.

4.4.2 Inter-rater reliability

To establish inter-rater reliability of measurements made on normal and pathological

subject scans, a second blinded investigator measured FBL and PA on all US scans of two

normal subjects and all five pathological subjects.

72

4.4.3 Validity

To validate the measurements of FBL, the US protocol was carried out on the

shoulder of a 65 year old male cadaveric specimen. Fiber bundles from the middle and

deep parts of anterior region and the visible portion from the deep part of the posterior

region were scanned. Three fiber bundles from each region were measured using the

methods outlined in section 4.2.3. Following this, three fiber bundles from the

corresponding part of the muscle were digitized using the methods outlined in section

4.1.2. The investigator was blinded to the measurements made on US scans when fiber

bundles were digitized. Mean FBL measurements computed from the US scans were

then compared with the digitized data.

4.4.4 Data analysis

Reproducibility and validity of measurements of FBL and PA were tested by paired t-

tests and Pearson product-moment correlations (r) were calculated.

73

Chapter 5: Results

5.1 Introduction

The results of this thesis will be presented in four sections. In the first section, the

results of the cadaveric investigation and 3D modeling study will be presented. The

second section will present the results from in vivo US investigation of supraspinatus in

normal subjects. The following section will present the results from in vivo US

investigation of supraspinatus in subjects with a full-thickness tear of the anterior

supraspinatus tendon. The final section will present the results of a comparative analysis

between five age matched normal subjects and the subjects with rotator cuff pathology.

5.2 Cadaveric investigation of normal supraspinatus architecture

5.2.1 Tendon architecture

The supraspinatus tendon of insertion consisted of an anterior and a posterior tendon

found in all ten specimens. See Figure 5.1 for an example.

The quadrangular shaped posterior tendon was found on the lateral aspect of

supraspinatus. The posterior tendon blended with the fibrous layer of the capsule of the

shoulder joint and terminated by inserting onto the posterosuperior aspect of the greater

tubercle of the humerus. The only muscular attachment to the posterior tendon was to its

medial aspect. In three of the ten specimens, a distinct short intramuscular tendinous slip

74

(1.0 ± 0.2 cm) extended medially from the posterior tendon into the muscle belly. The

average width of the posterior tendon was 1.6 ± 0.3 cm and the average length is 2.9 ± 0.6

cm. (Table 5.1)

The cord-like anterior tendon blended with the joint capsule but then attached to the

anterosuperior aspect of the greater tubercle of the humerus. Laterally, the anterior

tendon was extramuscular, but became intramuscular medially. The length and width of

the entire anterior tendon was found to be significantly longer and narrower than the

posterior tendon (p<0.05). The average width of the anterior tendon was 0.8 ± 0.2 cm; the

average length 6.1 ± 0.7 cm (Table 5.1).

Part of Tendon

n

Length (cm)

Width (cm)

Anterior

8*

6.1 ± 0.7 (5.0-6.9)

0.8 ± 0.2 (0.6-1.0)

Posterior

8*

2.9 ± 0.6 (2.3-4.0)

1.6 ± 0.3 (1.2-2.1)

TABLE 5.1 Cadaveric investigation of normal supraspinatus: Summary of mean tendon dimensions. Mean length, width, ± standard deviation (range) are reported for the anterior and posterior parts of

supraspinatus tendon. * Tendon data was not collected from the first two digitized specimens.

5.2.2 Muscle architecture

The muscle belly was partitioned into two large architecturally distinct regions, anterior

and posterior, each of which could be further subdivided into superficial, middle, and

75

deep parts based on attachment sites and architectural parameters (Figure 5.1). In some

cases, an additional small anterior part was identified in the posterior region.

Anterior and posterior regions were found in all ten specimens. The average MV of the

anterior region was 15.4 ± 5.7 cm3, while the average MV of the posterior region was 2.5

± 0.7 cm3. The large anterior region occupies approximately the anterior three quarters of

the supraspinous fossa while the posterior region, located dorsally in the supraspinous

fossa, is partially overlapped by the anterior region. These regions were defined by their

lateral attachments: fiber bundles of the anterior region attached to the periphery and deep

surface of the anterior tendon whereas fiber bundles of the posterior region attached to the

medial aspect posterior tendon. In three of the youngest specimens (<50 years of age),

the anterior part of the posterior region formed a distinct bipennate muscle segment which

attached to the intramuscular tendinous slip of the posterior tendon.

The architecture of the subdivisions of the anterior and posterior regions (superficial,

middle, and deep) is described in the next sections of this thesis.

5.2.2.1 Anterior region

The anterior region consisted of superficial (AS), middle (AM) and deep (AD) parts that

were superimposed on each other. Each part is described below.

• The fiber bundles of the superficial part of AS attached medially to two sites:

(1) the anteromedial border of the supraspinous fossa and (2) the medial third

76

of the superior border of the scapular spine. The fiber bundles converged to

attach to the periphery and superficial surface of the anterior tendon laterally

(Figure 5.1 A and B).

• The AM that lies deep to the AS extended from the medial two-thirds of the

supraspinous fossa in a bipennate fashion to the periphery and deep surface of

the medial half of the anterior tendon (Figure 5.1 C and D).

• The fiber bundles of AD were parallel in arrangement and spanned between

the lateral third of the supraspinous fossa and the deep surface of the lateral

half of the anterior tendon (Figure 5.1 E and F).

5.2.2.2 Posterior region

The posterior region also consisted of three parts: superficial (PS), middle (PM) and deep

(PD). Each part is described below.

• The fiber bundles of PS were directed anterolaterally from the superficial part

of posterior wall of the supraspinous fossa (Figure 5.2) to the medial border of

the posterior tendon. A cleavage plane separated the PS from the underlying

PM (Figure 5.1G and H).

77

• The fiber bundles of PM attached medially to the posterior wall of the

supraspinous fossa (Figure 5.2), deep to PS, and laterally to the medial border

of the posterior tendon (Figure 5.1 I and J).

• The PD was located deep and anterior to the PM. Fiber bundles attached

medially to the base of the supraspinous fossa (Figure 5.2) and laterally to the

medial border of the posterior tendon (Figure 5.1 I and J).

78

Figure 5.1 Cadaveric investigation of normal supraspinatus: Dissection and 3D modeling of the architecturally distinct regions of left shoulder supraspinatus, superior views. A. and B. Superficial part of anterior region (AS) and entire posterior region (PR). C. and D. Middle part of

anterior region (AM). E. and F. Deep part of anterior region (AD). The anterior part (*) of the

supraspinatus tendon is reflected. G. and H. Superficial (PS), middle (PM) and deep (PD) parts of the

posterior region. I. and J. Middle (PM) and deep (PD) parts of the posterior region. Anterior part of

supraspinatus tendon (*); posterior part of supraspinatus tendon (X); medial aponeurosis (+).

79

FIGURE 5.2 Cadaveric investigation of normal supraspinatus: Superior view of left scapula.

5.2.2.3 Fiber bundle length

The mean FBL for the entire anterior and posterior region were very similar: mean

FBL for the anterior and posterior regions were 6.7±0.7 and 6.7±0.5 cm respectively

(Table 5.2). Within the volume of the anterior region, mean FBL of the AS (6.7± 0.5 cm),

AM (6.6± 0.6 cm), and AD (6.6± 0.6 cm) were consistent. In contrast within the posterior

region, mean FBL of PM (7.0 ± 0.6 cm) was significantly longer (p<0.05) than PD (6.2 ±

0.5 cm).

5.2.2.4 Pennation angle

The mean lateral PA was greater than the mean medial PA for both the anterior and

posterior regions and all their respective parts (Table 5.2). The mean lateral PA of the

anterior region (60.0º±12.0º) was smaller than that of the posterior region (82.2º± 4.0º),

80

whereas the mean medial PA for the anterior (11.8º± 2.7º) and posterior (12.4º± 3.6º)

regions were similar.

Region of

muscle

n

FBL (cm)

Lateral PA

(deg)

Medial PA

(deg)

MV (cm³)

Entire muscle

10

6.7±0.6 (5.7-7.9)

73.2±14.7 (41.8-85.9)

13.2 ±5.7 (8.5-18.4)

17.9±6.4 (7.6-30.4)

Anterior region

10

6.7±0.7 (5.8-7.9)

60.0±12.0 (41.8-74.5)

11.8±2.7 (8.5-16.6)

15.4±5.7 (6.2-26.6)

Posterior

region

10

6.7±0.5 (5.7-7.6)

82.2±4.0

(74.7-85.9)

12.4±3.6 (7.1-18.4)

2.5±0.7 (1.4-3.8)

TABLE 5.2 Cadaveric investigation of normal supraspinatus: Summary of mean architectural parameters for the anterior and posterior regions. Mean fiber bundle lengths (FBL), lateral and lateral pennation angle (PA), muscle volume (MV), ± standard

deviation (range) are reported for the anterior and posterior region.

In the anterior region, the mean lateral PA for the middle part was significantly less

than the deep part (p<0.05); however, the superficial part was not different when

compared to the middle and deep parts. The mean medial PA of the deep part was

significantly greater when compared to both the superficial and middle parts (p< 0.05);

there was no statistical difference between the superficial and middle parts (Table 5.3).

In the posterior region, no significant difference was found in the lateral PA among the

superficial, middle, and deep parts. However, the mean medial PA of the superficial part

was significantly greater than the middle and deep parts (p<0.05); no significant

81

difference was found between the middle and deep parts (Table 5.3). Mean FBL was

found to be significantly longer in the middle part compared to the deep part (p<0.05)

Part of muscle

n

FBL (cm)

Lateral PA (deg)

Medial PA (deg)

Anterior region:

Superficial

10

6.7±0.5a (5.7-7.5)

64.6±12.7a (44.6-79.0)

11.4±2.8a (6.6-15.5)

Middle

10

6.6±0.6a (5.7-7.9)

51.4±13.1ab (34.3-70.0)

9.8±2.3a (7.58-14.5)

Deep

10

6.6±0.6a (5.4-7.4)

74.1±10.2ac (54.9-86.0)

16.8±6.1b (9.5-30.6)

Posterior region:

Superficial

10

6.9±0.9d (5.2-7.9)

84.4±3.1d (78.6-88.5)

18.6±7.6d (7.9-31.9)

Middle

10

7.0±0.6de (6.2-8.1)

82.0±4.3d (74.0-86.2)

11.3±4.6e (6.7-20.7)

Deep

10

6.2±0.5df (5.4-7.2)

82.5±4.9d (75.6-88.8)

11.2±3.6e (6.6-19.7)

TABLE 5.3 Cadaveric investigation of normal supraspinatus: Summary of mean architectural parameters for superficial, middle, and deep parts of the anterior and posterior regions. Mean fiber bundle lengths (FBL), lateral and medial pennation angle (PA), ± standard deviation (range) are

reported for all the architecturally distinct parts of supraspinatus. Superscript letters are used to indicate the

presence or absence of statistical significance between the anterior or posterior regions. If the superscript

letters in a column block differ, then the result is statistically significant. If the letter is repeated, there is no

statistical significance. Note: statistical comparison was only made within each region

5.3 US investigation of normal supraspinatus

5.3.1 Pre-scanning

All recruited subjects were included in the study as no rotator cuff pathology was found

82

in either their right or left shoulders.

5.3.2 Intramuscular tendon

In sixteen of the seventeen subjects investigated, a single intramuscular tendon, a

continuation of the extramuscular portion of the anterior tendon, was found extending

medially from the acromion. For most of its length, the intramuscular tendon was close

and parallel to the superficial surface of the muscle belly. In one subject, two coalescing

intramuscular tendons were found. Well-defined fiber bundles of the middle and deep

parts of the anterior region were seen in all subjects extending from the supraspinous

fossa to the deep surface of the intramuscular tendon. The fiber bundles of the superficial

part of the anterior region were seen as a layer superficial to the intramuscular tendon.

However, individual fiber bundles could not be seen and therefore TD (the distance

between the intramuscular tendon and the superficial surface of the muscle belly) was

measured. The site of measurement was at the medial aspect of the acromion. Mean TD

in the relaxed state (0.35±0.07 cm) was significantly smaller than in all contracted states

(p<0.05). In 60° abduction with neutral rotation mean TD increased to 0.40±0.09 cm; in

60° abduction with 80° external rotation it increased to 0.41±0.12 cm and in 60°

abduction with 80° internal rotation to 0.56±0.15 cm, see Table 5.4. Mean TD was

significantly larger in 60° abduction with 80° internal rotation than in the other contracted

positions (p<0.05).

83

State

TD (cm)

Relaxed

0.35 ±0.07a (0.21-0.49)

Contracted*:

0° rotation

80° ER

80° IR

0.40 ±0.09b (0.16-0.57)

0.41 ±0.12b (0.06-0.72)

0.56 ±0.15c (0.22-0.84) TABLE 5.4 Ultrasound investigation of normal supraspinatus: Mean TD. Mean TD, ± standard deviation (range); *, in 60° abduction; ER, external rotation; IR, internal rotation. If

the superscript letters in the column differ, then the result is statistically significant. If the letter is repeated,

there is no statistical significance.

5.3.3 Muscle architecture

5.3.3.1 Muscle thickness

The thickness of supraspinatus, measured at the midpoint between the medial border of

the acromion and the most medial point of attachment of the muscle belly in the

suprascapular fossa, increased significantly from the relaxed state and to all contracted

states (Table 5.5). Among the contracted states, mean MT in the externally rotated

position was significantly larger (2.15±0.35 cm) than in the neutral (2.03± 0.32 cm) and

internally rotated (2.01±0.35 cm) positions.

84

State

Muscle thickness (cm)

Relaxed

1.74±0.33a (0.91-2.36)

Contracted*: 0° rotation

80° ER

80° IR

2.03± 0.32b (1.50-2.77)

2.15±0.35c (1.60-2.96)

2.01±0.35bd (1.47-2.88)

TABLE 5.5 Ultrasound investigation of normal supraspinatus: Mean MT Mean MT, ± standard deviation (range);*, in 60° abduction; ER, external rotation; IR, internal rotation.

Superscript letters are used to indicate the presence or absence of statistical significance between the

relaxed and contracted states. If the superscript letters differ, then the result is statistically significant. If the

letter is repeated, there is no statistical significance.

5.3.3.2 Anterior region

Ultrasound scans of the relaxed and all contracted states are presented in Figure 5.3 and

the architectural parameters in Table 5.6. For all contracted states i.e. 60° abduction with

neutral rotation; 60° abduction with 80° external rotation; 60° abduction with 80° internal

rotation, the mean FBL was significantly shorter than the mean FBL in the relaxed state

(p<0.05). The percentage of shortening of FBL between the relaxed and contracted states

ranged between 9% and 21%, with the smallest percentage of difference found when the

arm was held in 60° abduction with internal rotation.

When the muscle was contracted in the 80° internally rotated position, the amount of

shortening was significantly less than in neutral and 80° externally rotated positions

(p<0.05). The amount of shortening between the neutral and 80° externally rotated

85

positions were similar, 4.64 ±0.64 cm and 4.87 ±0.90 cm.

Differences in mean PA were also found between the relaxed and contracted states

(Table 5.6). The mean PAs for all contracted states were significantly larger than the

mean PA in the relaxed state (p<0.05). The percentage change in mean PA between the

relaxed and contracted states ranged between 22% and 44%, with the smallest percentage

of change found when the arm was held in 60° abduction with 80° external rotation.

The amount of change when the muscle was contracted in the externally rotated

position was significantly less than in neutral and 80° internally rotated positions

(p<0.05). Furthermore, the amount of change in PA between the neutral and internally

rotated positions was similar.

When comparing the middle and deep parts of the anterior region, mean FBL was

similar in both relaxed and contracted states with no significant difference. In contrast,

the mean PA of the deep part was significantly greater than the mean PA of the middle

part (p<0.05), see Table 5.7.

5.3.3.3 Posterior region

Fiber bundles of the deep part of the posterior region could be defined in 13 of 17

subjects. The acromial correction factor, to account acromial shadowing of fiber bundles,

was determined to be 3.2 cm. Therefore, 3.2 cm was added to each in vivo FBL

measurement for the deep part. The lateral attachment of fiber bundles were obscured by

86

the acromion and thus PA could not be measured.

The mean FBLs of the deep part of the posterior region were similar for the relaxed and

contracted states (Table 5.6). In the internally rotated position, the mean FBL was

slightly longer than in the relaxed state suggesting that the muscle may be eccentrically

contracting. Compared to the anterior region, the mean FBL of the posterior region was

significantly longer in the relaxed state and in all contracted states (p<0.05).

87

FIGURE 5.3 Ultrasound investigation: US scans of anterior region of right supraspinatus in relaxed and contracted states. Note: images are not uniform in scale. One fiber bundle from each scan has been demarcated by a white

line (↔) with the length indicated above. A and B: Relaxed state. C and D: Contracted state (60° abduction

with neutral rotation). E and F: Contracted state (60° abduction with 80° external rotation). G and H:

Contracted state (60° abduction with 80° internal rotation). Skin (SK); subcutaneous tissue (SC); trapezius

muscle (TP); supraspinous fossa (SF); superficial part of anterior region (AS); middle part of anterior region

(AM); deep part of anterior region (AD); intramuscular tendon (○ ○); pennation angle (*)

88

n=34

Mean FBL (cm)

Mean PA (deg)

Relaxed Anterior region Posterior region

5.89±0.71a (4.68-7.63)

6.73±0.56b (5.61-7.77)

12.05±3.07a (6.74-21.68)

—

Contracted*: 0° rotation

Anterior region Posterior region

80° ER Anterior region Posterior region

80° IR Anterior region Posterior region

4.64±0.64c (3.17-6.12)

6.57±0.57b (5.46-7.79)

4.87±0.90c (2.96-6.74)

6.60±0.51b (5.72-7.80)

5.36±0.72d (3.91-7.32)

6.90±0.50b (5.86-8.06)

17.20±4.29b (8.05-26.62)

—

14.73±3.88c (8.03-22.75)

—

17.36±3.54b (9.67-26.62)

—

TABLE 5.6 Ultrasound investigation of normal supraspinatus: Architectural parameters of the anterior and posterior regions. Mean fiber bundle length (FBL), pennation angle (PA) ± standard deviation (range). Note: FBL of posterior

region includes acromial correction factor; *, in 60° abduction; ER, external rotation; IR, internal rotation.

Superscript letters are used to indicate the presence or absence of statistical significance between the

anterior and posterior regions and between relaxed and contracted states. If the superscript letters in a

column differ, then the result is statistically significant. If the letter is repeated, there is no statistical

significance.

89

n=34

Mean FBL

(cm)

Mean PA

(deg)

Relaxed Middle part Deep part

5.94±0.82a (4.69-8.13)

5.85±0.89a (3.78-7.91)

10.87±3.11a (5.48-20.51)

14.24±4.26b (6.78-25.33)

Contracted*: 0° rotation

Middle part Deep part

80° ER Middle part Deep part

80° IR Middle part Deep part

4.62±0.71bc (3.11-6.00)

4.68±0.72bc (3.30-6.42)

4.79±1.06cd (2.73-6.99)

5.04±0.87cd (2.90-6.98)

5.31±0.74d (3.91-7.34)

5.43±0.82ad (3.90-7.63)

16.23±3.97c (8.00-24.64)

18.80±5.26f (8.15-30.57)

13.38±4.22d (5.63-23.47)

17.29±5.50bf (7.31-29.79)

16.42±3.50ce (8.82-22.71)

19.23±4.73f (10.09-31.55)

TABLE 5.7 Ultrasound investigation of normal supraspinatus: Architectural parameters of the middle and deep parts of the anterior region. Mean fiber bundle length (FBL), pennation angle (PA) ± standard deviation (range); *, in 60° abduction;

ER, external rotation; IR, internal rotation. Superscript letters are used to indicate the presence or absence

of statistical significance between the middle and deep parts of the anterior region. If the superscript letters

in a column differ, then the result is statistically significant. If the letter is repeated, there is no statistical

significance.

5.4 Ultrasound investigation of pathological supraspinatus

5.4.1 Pre-scanning

Five of six recruited subjects were included in the study. One subject was excluded

because a full-thickness tear of the supraspinatus tendon was not found. On the contra-

lateral shoulder, a supraspinatus tendon tear with smaller dimensions was found in four

90

subjects. A summary of the tendon pathology found on the contra-lateral shoulder is

provided in Table 5.8.

Subject

Age

(gender)

Contra-lateral supraspinatus Pathology and tear (cm)

1

55 (F) • moderate tendinosis • full-thickness tear (0.9AP, 0.5 ML)

2 50 (M) • mild to moderate tendinosis • no tear

3 65 (F) • moderate tendinosis • partial thickness /bursal sided tear (1.5 AP, 0.8 ML)

4 69 (F) • moderate to severe tendinosis • partial thickness/ articular sided tear (0.8 AP, 1.6 ML)

5 57 (M) • moderate tendinosis, • full-thickness tear (1.0 AP, 1.0 ML)

TABLE 5.8 Ultrasound investigation of pathological supraspinatus: Summary of tendon pathology on the contra-lateral shoulder. AP= anterior posterior, ML=medial lateral

5.4.2 Intramuscular tendon

In all five subjects, the intramuscular portion of the anterior tendon was observed.

Fiber bundles of the AM and AD could be seen bilaterally in all subjects extending from

the supraspinous fossa to the deep surface of the intramuscular tendon. Similar to normal

subjects, TD (the distance between the intramuscular tendon and the superficial surface of

the muscle belly) was measured since individual fiber bundles of the AS could not be

visualized.

In the relaxed state, the mean TD in the pathological supraspinatus (0.30±0.8 cm) was

91

smaller than in the contra-lateral supraspinatus (0.39±0.15 cm). The difference, however,

was not statistically significant. In the contracted state, mean TD of the pathological

(0.44±0.15 cm) and contra-lateral supraspinatus (0.44±0.16 cm) were similar. For the

pathological supraspinatus, mean TD increased significantly on contraction (p<0.05).

However, for the contra-lateral supraspinatus mean TD did not change significantly on

contraction (Table 5.9).

n=5

Relaxed (cm)

Contracted (cm)

Pathological

supraspinatus

0.30±0.8a1 (0.18-0.39)

0.44±0.15b1 (0.21-0.56)

Contra-lateral supraspinatus

0.39±0.15a1 (0.21-0.62)

0.44±0.16a1 (0.22-0.66)

TABLE 5.9 Ultrasound investigation of pathological supraspinatus: Comparison of mean TD between pathological and contra-lateral supraspinatus. Mean distance between the intramuscular tendon and the superficial surface of the muscle belly (TD) ±

standard deviation (range). The superscript letters are used to indicate the presence or absence of statistical

significance between the relaxed and contracted state, and superscript numbers between the pathological

and contra-lateral supraspinatus. If the superscript letters/numbers differ, then the result is statistically

significant. If the letter/number is repeated, there is no statistical significance.

5.4.3 Muscle architecture

Fiber bundles on the contra-lateral supraspinatus were generally better defined than the

pathological supraspinatus (Figure 5.4).

92

FIGURE 5.4 Ultrasound investigation: Comparison of US scans of pathological and contra-lateral supraspinatus of same subject. A. Pathological supraspinatus (Full-thickness tendon tear) B. Contra-lateral supraspinatus

5.4.3.1 Muscle thickness:

The MT of supraspinatus, measured at the midpoint between the medial border of the

acromion and the most medial point of attachment of the muscle belly in the

suprascapular fossa, did not change significantly from the relaxed to the contracted state

in the pathological supraspinatus. However, MT of the contralateral supraspinatus

changed significantly (p<0.05) from the relaxed to contracted state. Muscle thickness in

the relaxed state of the pathological and contra-lateral supraspinatus did not differ

significantly. Muscle thickness in the contracted state also did not differ significantly

between the pathological and contra-lateral supraspinatus. A summary of MT is reported

A. B.

93

in Table 5.10.

n=5

Relaxed (cm)

Contracted (cm)

Pathological

supraspinatus

1.99±0.29a1

(1.57-2.34)

2.30±0.16a1

(2.10-2.54)

Contra-lateral supraspinatus

2.07±0.44a1

(1.46-2.61)

2.39±0.33b1

(1.98-2.71)

TABLE 5.10 Ultrasound investigation of pathological supraspinatus: Comparison of mean MT between the pathological and contra-lateral supraspinatus Mean muscle thickness (MT) ± standard deviation (range). The superscript letters are used to indicate the

presence or absence of statistical significance between the relaxed and contracted state, and superscript

numbers between the pathological and contra-lateral supraspinatus. If the superscript letters/numbers differ,

then the result is statistically significant. If the letter/number is repeated, there is no statistical significance.

5.4.3.2 Anterior region

The architectural parameters are presented in Tables 5.11 and 5.12. For both the

pathological and contra-lateral supraspinatus, the mean FBL was significantly shorter in

the contracted state than in the relaxed state (p<0.05). The percentage of shortening was

found to be 21.4% for the pathological supraspinatus and 27.4% for the contra-lateral

supraspinatus. The difference in mean FBL between the pathological and contra-lateral

supraspinatus in the relaxed and contracted state was not significant.

Mean PA was also found to significantly differ between the relaxed and contracted

states. The mean PA for the contracted state was significantly larger than the mean PA in

94

the relaxed state (p<0.05) for the pathological and contra-lateral supraspinatus. The

percentage change in mean PA between the relaxed and contracted states was found be

25.8% for the pathological supraspinatus and 42.4% for the contra-lateral supraspinatus.

The difference in mean PA between the pathological and contra-lateral supraspinatus for

both the relaxed and contracted states was not significant.

Comparing individual subject data, subject #1 had the smallest percentage change in

FBL, 3%, and the largest percentage change in PA, 49%. Both subjects #4 and #5 had the

largest percentage change in FLB of 29%; however, subject #4 had a 38% percentage

change in PA whereas subject #5 had a 21% percentage change in PA. Table 5.13

provides a summary of FBL and PA for each subject.

95

n=5

Relaxed (cm)

Contracted (cm)

%

change

Pathological shoulder

5.06±0.76a1 (4.13-6.14)

3.92±0.0.50b1

(3.27-4.42)

21.4%

Contra-lateral

shoulder

5.52±0.85a1 (4.79-6.58)

3.91±0.56b1 (3.48-4.79)

27.4%

TABLE 5.11 Ultrasound investigation of pathological supraspinatus: Comparison of mean FLB and percentage change of anterior region between pathological supraspinatus and contra-lateral supraspinatus. Mean fiber bundle length (FBL) ± standard deviation (range). The superscript letters are used to indicate

the presence or absence of statistical significance between the relaxed and contracted state, and superscript

numbers between the pathological and contra-lateral supraspinatus. If the superscript letters/numbers differ,

then the result is statistically significant. If the letter/number is repeated, there is no statistical significance.

n=5

Relaxed (deg)

Contracted (deg)

%

change

Pathological shoulder

11.93 ± 1.23a1 (10.52-13.09)

14.97 ± 2.24b1

(12.03-18.15)

25.8%

Contra-lateral

shoulder

13.0±1.98a1

(11.21-16.35)

18.40±3.55b1

(12.90-21.90)

42.4%

TABLE 5.12 Ultrasound investigation of pathological supraspinatus: Comparison of mean PA and percentage change of anterior region between pathological and contra-lateral supraspinatus. Mean pennation angle (PA), ± standard deviation (range). Superscript letters are used to indicate the

presence or absence of statistical significance between the relaxed and contracted state, and superscript

numbers between the pathological and contra-lateral supraspinatus. If the superscript letters/numbers differ,

then the result is statistically significant. If the letter/number is repeated, there is no statistical significance.

96

Subject Age (gender)

FBL (cm) % change

PA (deg) % change

relaxed contracted relaxed contracted

1

55(F) 4.13 4.0 3% 12.18 18.15 49%

2

50(M) 6.14 4.42 28% 10.76 12.03 12%

3

65(F) 5.02 4.38 13% 13.09 14.33 9%

4

69(F) 5.37 3.57 29% 10.52 14.52 38%

5

57(M) 4.63 3.27 29% 13.07 15.82 21%

TABLE 5.13 Ultrasound investigation of pathological supraspinatus: FBL and PA of anterior region for relaxed and contracted states and percentage change for each individual subject. Fiber bundle length (FBL), pennation angle (PA), male (M), female (F).

5.4.3.3 Posterior region

In four subjects, fiber bundles of the posterior region could be defined bilaterally but

in one subject (#4) fiber bundles could only be defined unilaterally in the contracted state.

The acromial correction factor (3.2cm) was added to each in vivo FBL measurement for

the deep part. The lateral attachment of fiber bundles were obscured by the acromion and

thus PA could not be measured.

The mean FBL for the deep part of the posterior region in the relaxed state was

5.84±0.64 cm (n=4). Mean FBL for the contracted state was slightly shorter 5.66±0.14

cm (n=5) but the difference was not significant. On the contra-lateral supraspinatus,

mean FBL in the relaxed state (5.88±0.84 cm) was the same as the mean FBL for the

97

contracted state (5.88±0.43 cm), with the relaxed state having a greater standard deviation

(Table 5.14).

When considering individual subjects, mean FBL for the deep part of the posterior

region shortened in two subjects (#2 and #5) and lengthened in two subjects (#1 and #3).

See Table 5.15.

Relaxed (cm)

Contracted (cm)

Pathological shoulder

5.84±0.64a1 (5.18-6.59)

n=4

5.66±0.14a1 (5.49-5.87)

n=5

Contra-lateral shoulder

5.88±0.84a1 (4.90-6.99)

n=5

5.88±0.43a1 (5.36-6.55)

n=5 TABLE 5.14 Ultrasound investigation of pathological supraspinatus: Comparison of mean FBL of posterior region between pathological and contra-lateral supraspinatus. Mean fiber bundle length (FBL) ± standard deviation (range). Note: FBL of posterior region includes

acromial correction factor. Superscript letters are used to indicate the presence or absence of statistical

significance between the relaxed and contracted state, and superscript numbers between the pathological

and contra-lateral supraspinatus. If the superscript letters/numbers differ, then the result is statistically

significant. If the letter/number is repeated, there is no statistical significance.

98

Subject

Relaxed (cm)

Contracted (cm)

1

5.18 5.60

2

6.14 5.87

3

5.48 5.72

4

- 5.49

5

6.59 5.62

TABLE 5.15 Ultrasound investigation of pathological supraspinatus: Mean FBL of posterior region for each individual subject. Fiber bundle length (FBL), - could not be measured.

5.5 Comparison of pathological and normal data

The architectural data of all five pathological subjects was compared with data from

five gender, age, and hand dominance matched normal controls.

5.5.1 Pre-scanning

The middle and deep parts of the anterior region in the pathological supraspinatus had

fewer well-defined fiber bundles than in the normal supraspinatus (Figure 5.5).

99

FIGURE 5.5 Ultrasound investigation: Comparison of US scans of normal and pathological supraspinatus. Right shoulder. A. Normal supraspinatus B. Pathological supraspinatus (full-thickness supraspinatus tendon

tear).

5.5.2 Intramuscular tendon

The mean TD in the relaxed state of the normal controls (0.36±0.09 cm) tended to be

larger than in the pathological supraspinatus (0.30±0.8 cm). In the contracted state, mean

TD of the pathological supraspinatus (0.44±0.15 cm) was slightly larger than in the

normal controls (0.41±0.1 cm). These differences, however, were not significant. Mean

A.

B. B.

100

TD did not significantly change between the relaxed and contracted state in the normal

controls, whereas in the pathological supraspinatus the mean distance did change

significantly (p<0.05).

n=5

Relaxed (cm)

Contracted (cm)

Normal

supraspinatus

0.36±0.09a1 (0.25-0.47)

0.41±0.1a1 (0.29-0.53)

Pathological

supraspinatus

0.30±0.8a1 (0.18-0.39)

0.44±0.15 b1

(0.21-0.56)

TABLE 5.16 Ultrasound investigation: Comparison of mean TD between normal controls and pathological supraspinatus. Mean distance between the intramuscular tendon and the superficial surface of the muscle belly (TD) ±

standard deviation (range). The superscript letters are used to indicate the presence or absence of statistical

significance between the relaxed and contracted state, and superscript numbers between the normal controls

and pathological supraspinatus. If the superscript letters/numbers differ, then the result is statistically

significant. If the letter/number is repeated, there is no statistical significance.

5.5.3 Muscle architecture

5.5.3.1 Muscle thickness

Mean MT between the normal controls and the pathological subjects did not differ

significantly in either the relaxed or contracted state. In the normal controls, mean MT in

the contracted state (2.07±0.38 cm) was significantly larger than in the relaxed state

(1.71± 0.34). In contrast, mean MT in the contracted state of the pathological

101

supraspinatus was not significantly larger than in the relaxed state. The percentage

change in mean MT between the relaxed and contracted states was 21.9% in the normal

controls, whereas it was 17.4% in the pathological supraspinatus (Table 5.17).

n=5

Relaxed (cm)

Contracted (cm)

% change

Normal

supraspinatus

1.71± 0.34a1 (1.28-2.14)

2.07±0.38b1

(1.59-2.54)

21.9%

Pathological

supraspinatus

1.99±0.29a1

(1.57-2.34)

2.30±0.16a1

(2.10-2.54)

17.4%

TABLE 5.17 Ultrasound investigation: Comparison of mean MT between normal controls and pathological supraspinatus. Mean muscle thickness (MT) ± standard deviation (range). Superscript letters are used to indicate the

presence or absence of statistical significance between the relaxed and contracted state, and superscript

numbers between the normal controls and pathological supraspinatus. If the superscript letters/numbers

differ, then the result is statistically significant. If the letter/number is repeated, there is no statistical

significance.

5.5.3.2 Anterior region

The mean FBL significantly changed between the relaxed and contracted state in both

the normal controls and pathological supraspinatus (p<0.05). In the relaxed state, the

mean FBL of the normal controls was 6.02±0.83 cm, and 4.30±0.83 cm in the contracted

state. The mean percentage change was 28.4%. In the pathological supraspinatus, the

mean FBL in the relaxed state was 5.06±0.76 cm, and 3.92±0.50 cm in the contracted

102

state. The mean percentage change was 21.4%. Mean FBL did not significantly differ

between the normal controls and pathological supraspinatus for either the relaxed or

contracted state. Table 5.18 summarizes these findings.

The mean PA also significantly changed between the relaxed and contracted state in

both the normal controls and pathological supraspinatus (p<0.05). In the normal controls,

mean PA in the relaxed state was 12.42º±1.89º and increased to 17.54º±2.59º in the

contracted state. The mean percentage change was 44.9%. In the pathological

supraspinatus, the mean percentage change was 25.8%. Mean PA in the relaxed state was

11.93º±1.23º and increased to 14.97º±2.24º in the contracted state. The difference in

mean PA between the normal controls and pathological supraspinatus in either the relaxed

and contracted state was not statistically significant (Table 5.19).

103

n=5

Relaxed (cm)

Contracted (cm)

% change

Normal

supraspinatus

6.02±0.83a1 (4.68-6.88)

4.30±0.83b1 (3.17-5.35)

28.4%

Pathological

supraspinatus

5.06±0.76a1 (4.13-6.14)

3.92±0.50b1

(3.27-4.42)

21.4%

TABLE 5.18 Ultrasound investigation: Comparison of mean FBL and percentage change of anterior region between normal controls and pathological supraspinatus. Mean fiber bundle length (FBL) ± standard deviation (range). The superscript letters are used to indicate

the presence or absence of statistical significance between the relaxed and contracted state, and superscript

numbers between the normal controls and pathological supraspinatus. If the superscript letters/numbers

differ, then the result is statistically significant. If the letter/number is repeated, there is no statistical

significance.

n=5

Relaxed (deg)

Contracted (deg)

% change

Normal

supraspinatus

12.42±1.89a1

(9.29-14.13)

17.54±2.59b1

(14.04-20.82)

44.9%

Pathological

supraspinatus

11.93 ± 1.23a1

(10.52-13.09)

14.97 ± 2.24b1

(12.03-18.15)

25.8%

TABLE 5.19 Ultrasound investigation: Comparison of mean PA and percentage change of anterior region between normal controls and pathological supraspinatus. Mean pennation angle (PA) ± standard deviation (range). Superscript letters are used to indicate the

presence or absence of statistical significance between the relaxed and contracted state, and superscript

numbers between the normal controls and pathological supraspinatus. If the superscript letters/numbers

differ, then the result is statistically significant. If the letter/number is repeated, there is no statistical

significance

104

5.5.3.3 Posterior region

Fiber bundle lengths of the deep part of the posterior region did not significantly

change between the relaxed and contracted state in the normal controls and pathological

supraspinatus. The difference between the mean FBL for the normal controls and

pathological supraspinatus was statistically significant in the contracted state (p<0.05) but

not in the relaxed state. See Table 5.20.

Relaxed (cm)

Contracted (cm)

Normal supraspinatus

6.70±0.33a1 (6.35-7.07)

n=5

6.47±0.59a1 (6.01-7.27)

n=4

Pathological

supraspinatus

5.84±0.64a1 (5.18-6.59)

n=4

5.66±0.14a2 (5.49-5.87)

n=5

TABLE 5.20 Ultrasound investigation: Comparison of mean FBL of posterior region between normal controls and pathological supraspinatus. Mean fiber bundle length (FBL) ± standard deviation (range). Note: FBL of posterior region includes

acromial correction factor. Superscript letters are used to indicate the presence or absence of statistical

significance between relaxed and contracted state, and superscript numbers between the normal controls

and pathological supraspinatus. If the superscript letters/numbers differ, then the result is statistically

significant. If the letter/number is repeated, there is no statistical significance.

5.6 Reliability and validity of measurements

5.6.1 Intra-rater reliability

No statistical difference was found between the two measurements for any variable at

105

any site (paired t-tests: p<0.05) for both the normal and pathological subject scans. The

Pearson product-moment correlation coefficients were calculated for FBL (r=0.93 normal

subjects; r=0.87 pathological subjects) and PA (r=0.88 normal subjects; r=0.84

pathological subjects), indicating a good correlation.

5.6.2 Inter-rater reliability

Paired t-tests were used to determine if measurements by investigator 1 and 2 were

significantly different. There was no statistical significant difference in measurements

(p<0.001). There was a good positive correlation between the measurements of the two

independent raters; FBL (r=0.74 normal subjects; r=0.87 pathological subjects) PA

(r=0.76 normal subjects; r=0.89 pathological subjects).

5.6.3 Validity

Table 5.21 shows US measurements and digitized data of FBL on the fresh male human

cadaver. Ultrasound measurements of FBL differed from digitized data by <0.1 cm.

106

US measurements Mean FBL (cm)

Digitized data Mean FBL (cm)

Anterior region

Middle part

Deep part

5.4±0.3

5.7±0.5

5.4±0.9

5.8±0.4

Posterior region

Deep part

3.0±0.2

3.0±0.2

TABLE 5.21 Summary of mean FBL measurements made on one male fresh cadaveric specimen: US scans and digitized data.

5.7 Summary of main findings

Cadaveric investigation:

• The supraspinatus muscle belly has two architecturally distinct regions that vary

significantly in their volumes (p<0.05).

• Within the anterior and posterior regions, there are three architecturally distinct

parts: superficial, middle and deep.

• Mean FBL for the entire anterior and posterior region were very similar.

• Within the anterior region, mean lateral PA for the middle part was significantly

less than the deep part (p<0.05).

US investigation of normal subjects:

• Mean FBL changes with active contraction and abduction to 60º differed between

the anterior and posterior regions.

107

• In the anterior region, mean FBL significantly shortened with active contraction

(p<0.05), but not in the posterior region.

• For the anterior region, the smallest percentage change in mean FBL between the

relaxed and contracted state was found when the arm was in the internally rotated

position.

• Mean PA significantly increased with active contraction in the anterior region

(p<0.05).

• The change in mean PA was significantly less in the externally rotated position

compared to the internally rotated and neutral positions (p<0.05).

• Within the anterior region, mean PA was significantly greater in the deep part than

in the middle part for the relaxed and all contracted states (p<0.05).

US investigation of pathological subjects:

• Muscle thickness did not change with active contraction on the pathological

supraspinatus.

• For the anterior region, the percentage change in mean FBL of the pathological

supraspinatus was less than the contra-lateral supraspinatus.

• A large difference in percentage change of mean PA was found between the

pathological and contra-lateral supraspinatus.

• Mean FBL of the posterior region did not significantly change with active

108

contraction and abduction to 60º.

Comparison of normal and pathological subjects:

• Mean TD in the relaxed state was smaller in the pathological supraspinatus than in

the normal controls.

• Mean FBL and PA were smaller in the pathological supraspinatus than in the

normal controls.

• Mean percentage change in FBL and PA varied between the pathological and

normal supraspinatus.

109

Chapter 6: Discussion

This cadaveric and in vivo study of the normal and pathological architecture of

supraspinatus is the first of its kind. The findings of this study show that supraspinatus

is a complex muscle; the fiber bundle architecture is not uniform throughout the muscle

volume and dynamic changes are affected by tendon pathology. In this chapter, the

findings of the cadaveric and in vivo investigation will be discussed relative to the

previous literature and the functional and clinical significance will be elaborated.

6.1 Cadaveric investigation of normal supraspinatus

6.1.1 Three-dimensional modeling

To date, no previous study has modeled the detailed musculotendinous architecture of

supraspinatus in situ throughout its volume. Computer modeling techniques that were

initially developed by Agur (2003) and Ng-Thow-Hing (2001) were specifically

customized for study of the supraspinatus. The enhanced technique enabled 1200-1600

fiber bundles spread throughout the muscle volume of supraspinatus and the intra- and

extra-muscular portions of the tendon to be captured in 3D.

Previous studies that have identified distinct regions relied on gross dissection or 2D

images (Roh et al., 2000; Vahlensieck et al., 2000). However, in this study, the

architecturally distinct regions could be defined precisely within the volume of the muscle

110

using the 3D model. The model allows for fiber bundles to be viewed individually, in

layers, and regionally. Furthermore, architecturally distinct parts within the anterior and

posterior regions that were not previously documented in the literature could also be

identified and defined.

6.1.2 Measurement of architectural parameters

This study is the first of its kind to quantify and document architectural parameters of

the supraspinatus, in situ, using 3D data. In previous cadaveric studies of supraspinatus,

architectural parameters have been quantified by sampling a small number of fiber

bundles, often from the superficial surface of the muscle.

Fiber bundle lengths were computed in this study by summating the distance between

closely digitized points, thus accounting for any fiber bundle curvature. In previous

studies, FBL was usually measured with calipers placed at each attachment site, which

does not capture fiber bundle curvature.

Pennation angle has been defined as the angle the fiber bundle creates at the

intersection with line of force (Murray et al., 2000). Since the line of force (the line that

intersects the centroids of cross-sections through the muscle volume) cannot be visually

determined on a specimen, previous cadaveric studies have measured the surface PA,

between the fiber bundle and its attachment sites to bone, tendon, or aponeurosis. In this

study, PA was measured, as initially defined, relative to the line of force. Using the 3D

111

computer model, the line of force could be computed mathematically from the digitized

data and used to determine PA.

The digitized data set could be sorted into separate files for the fiber bundles and

tendon, thus enabling calculation of MV using only fiber bundle data. On cadaveric

specimens, it is impossible to selectively remove the tendon alone without including some

of the fiber bundles. In addition, the digitized data of the fiber bundles could be easily

separated into regions based on attachment sites, FBL and PA. Roh et al. (2000)

separated the anterior and posterior regions by visual observation and dissection.

6.1.3 Comparison of architectural parameters

The results of this cadaveric study will be discussed and compared, when possible,

with data available in the literature.

6.1.3.1 Fiber bundle length

In this study, mean FBL for the entire muscle (6.7±0.64 cm) was found to be larger

than those reported in the literature (mean FLB ranged from 2.8-6.5 cm). The shorter

mean FBL reported by Itoi et al. (1995) and Ward et al. (2006) may be due to

normalization of data (Tables 2.4 & 5.2).

Roh et al. (2000) was the only study to report separate mean FBLs for the anterior and

posterior regions. The mean FBL for the anterior region found in this study was smaller

(6.7±0.7 cm) than what Roh et al. (2000) reported (8.3±0.9 cm). Mean FBL for the

112

posterior region found in this study (6.7 ± 0.5 cm) was similar with the mean Roh et al.

(2000) reported (6.5± 1.2 cm). It should be noted that mean FBL reported by Roh et al.

(2000) was based on “multiple representative muscle fibers excised from each muscle

belly” which could have resulted in differences in the mean FBL for the anterior region.

Unique to this study, architecturally distinct parts (superficial, middle, deep) were

observed within the anterior and posterior regions of the muscle belly. Within the

anterior region, the mean FBL among all the three parts did not differ significantly.

Within the posterior region, the shortest mean FBL was found in the deep part (6.2 ± 0.5)

and the longest in the middle part (7.0 ± 0.6 cm). The difference was significant

(p<0.05).

6.1.3.2 Pennation angle

In previous studies, PA was measured at only one attachment site relative to the

tendon. In this study, both the medial and lateral PA were computed for fiber bundles

relative to the line of force making comparison of results difficult. In this study, the

mean medial PA was significantly less than the lateral PA. This difference may be

explained by the orientation of the fiber bundles. The fiber bundles attach medially to a

large area of bone, i.e. supraspinous fossa, resulting in a small PA, whereas, laterally the

fiber bundles are more obliquely oriented and converge on the tendon.

113

6.1.3.3 Muscle volume

The combined volumes of the anterior and posterior regions in this study and the

study by Roh et al. (2000) were similar, 17.9 cm3 and 16 cm3 respectively. Muscle

volume of 39.3 ml reported by Wood et al. (1989) and 36 ml by Jensen et al. (1995) were

the largest, but these were based on only one male cadaveric specimen.

When compared to Roh et al. (2000) the volume of the anterior region found in this

study was larger (this study 15.4 ± 5.7 cm3; Roh et al. (2000) 12 ± 4 ml) and the posterior

region was smaller (this study 2.5 ± 0.7 cm3

In this study, as with previous studies, the length of the anterior tendon was found to be

greater than the posterior. The mean length of the anterior tendon (6.1 ± 0.7 cm) found

in this study was longer than the length Volk and Vangsness (2001) found (5.4 cm).

However, the mean length of the posterior tendon in this study (2.9±0.6 cm) was

; Roh et al. (2000) 4 ± 2 ml). These

differences may be explained by the manual techniques used by Roh et al. (2000) to

separate the anterior region from the posterior.

6.1.3.4 Tendon architecture

The anterior and posterior parts of the supraspinatus tendon were also documented by

Volk and Vangsness (2001) and Roh et al. (2000). These studies measured either tendon

length (Volk and Vangsness, 2001) or tendon width (Roh et al, 2000), but not both (Table

2.5).

114

comparable to data reported by Volk and Vangsness (2001) who found the length to be

2.8 cm. The mean length of the “intramuscular tendon” reported by Itoi et al. (1995)

was normalized to scapular length and was shorter than all other studies (4.08 ±1.03 cm).

The width of the anterior tendon found in this study (0.8±0.2 cm) was the same as that

found by Roh et al. (2000). The widths of the posterior tendon were similar (in this

study 1.6±0.3 cm; Roh et al. (2000) 1.3±0.3 cm). In this study, a small tendinous slip,

extending approximately 1 cm from the posterior tendon, was found in three of the

youngest (<50 years of age) specimens. Vahlensieck et al. (1993), in an MRI study of

subjects with a mean age of 40.5 ± 13.9 years, found similar tendinous slips. Other

cadaveric studies have not documented this structure. This may be explained by

differences in the mean age of specimens used in this study and in previous cadaveric

studies (Table 2.2). The mean age in this study was 61.9±16 years, whereas the mean

age was 78.9 and 82 years in the studies by Juul-Kristensen et al. (2000b) and Roh et al.

(2000). Furthermore, since the intramuscular tendinous slip was short and found deep to

the anterior region of the muscle belly it also could have been overlooked if the entire

muscle volume was not dissected.

6.2 Ultrasound investigation of normal supraspinatus

On longitudinal US scans of suprspinatus, the pennate pattern created by the

115

hyperechoic fibroapdipose septa of the perimysium surrounding the hypoechoic muscle

fiber bundles was visible. As Fornage et al. (1983) stated, the pennate pattern appeared

as “multiple parallel lines forming oblique angles with the echogenic myotendinous

junction”. Despite the visibility of the pennate pattern, US has not previously been used

to quantify architectural parameters.

This is the first US study in which architectural parameters (i.e. FBL, PA, MT and

TD) were quantified in vivo. The development of the US protocol would not have been

possible without the anatomical study which was integral in identifying the regions and

their subdivisions in vivo.

The musculotendinous architecture of supraspinatus was observed in four different

glenohumeral joint positions (0º abduction with neutral rotation, 60º abduction with

neutral rotation; 60º abduction with 80º external rotation; 60º abduction with 80º internal

rotation) with the contracted muscle working isometrically. Glenohumeral abduction of

60º was chosen because it is similar to the loose pack position (Trew & Everett, 2001).

The loose or “open” pack position is the position where the joint surfaces are least

congruent, where the ligaments are least tight, and where the greatest amount of joint play

is possible (Petersen, 2002). Thus, the loose pack position is a vulnerable position that

relies on the dynamic function of muscles such as the supraspinatus. Different degrees

of rotation at the glenohumeral joint in the loose pack position were investigated to gain

116

insight into the effect of joint position on musculotendinous architecture.

Shoulder abduction of 90º may have also been a good position to investigate since it is

a functional position in many sports. However, to ensure that architectural comparison

could be later made between the normal subjects and subjects with tendon pathology, this

position was not investigated. Shoulder abduction of 90º may have elicited discomfort

or pain in subjects with tendon pathology.

6.2.1 Measurement of architectural parameters

Since US has never been previously used to quantify FBL and PA of the

supraspinatus, the reliability and validity of measurements were rigorously tested. Intra-

and inter-rater measurements for FBL and PA in the normal and pathological subjects

were found to have good correlations (r=0.74 - 0.87 for FBL; r=0.76-0.89 for PA).

Validity of measurements was demonstrated by comparison of FBL measurements made

from US scans and digitized data of the same specimen. The measurement error was

found to be <0.1cm.

In this study, the location of the intramuscular tendon relative to the superficial

muscle belly surface (TD) was also measured. Similar to MT, TD can be used to assess

muscle atrophy. However, TD can provide insight into whether muscle atrophy has

occurred in the area above the intramuscular tendon. Meyer et al. (2005) suggested that

atrophy of the supraspinatus following tendon tears may not be uniform throughout the

117

muscle volume and that muscle atrophy is more likely to occur in the muscle volume

found above the intramuscular tendon.

6.2.2 Muscle architecture

The only architectural parameter that can be compared with previous US studies is

MT (Table 2.6). Mean MT in the relaxed state of normal subjects (1.74 ± 0.33 cm)

found in this study was similar to the reported mean by Juul-Kristensen et al. (2000) 2.0

cm. It should be noted that the mean age of subjects were similar (in this study

36.4±12.7 years; Juul-Kristensen et al. (2000) 39.8 years. The effect of aging on MT is

not clear. In a US study, Kubo et al. (2003) investigated 224 female subjects ranging in

20-79 years of age and found MT of vastus lateralis but not gastrocnemius and triceps

brachii to significantly decline with advanced aging.

Since there are no other in vivo studies that have quantified architectural parameters,

the findings from the cadaveric portion of this study will be compared with the findings

from the US portion. Mean FBL of the middle and deep parts of the anterior region in

vivo in the relaxed state, 5.94±0.82cm; 5.85±0.89cm respectively, were slightly shorter

than the mean FBLs found in the cadaveric specimens in this study (6.7±0.7cm for middle,

6.7±0.5 cm for deep). However, the mean FBL in vivo was still within the range of

mean FBL found in the cadaveric specimens (5.8-7.9 cm). For the deep part of the

posterior region, mean FBL in vivo in the relaxed state (6.73±0.56 cm) was slightly longer

118

than the mean found in the cadaveric specimens (6.2± 0.5cm) but was still within the

range of mean FBL (5.4-7.2cm).

On contraction, mean FBL significantly shortened for all positions in the anterior

region, whereas no significant shortening occurred in the posterior. Among the different

arm positions, mean FBL shortened the least in the internally rotated position and the

most in the neutral. On contraction, mean PA significantly increased for all positions but

was significantly less in the externally rotated position compared to the other contracted

positions. The functional implications of these findings are discussed in the following

section.

6.3 Functional implications of cadaveric and in vivo findings of normal subjects

To date, the dynamic function of supraspinatus has been inferred from static

architectural data most often obtained from cadaveric specimens. In this study, however,

the static and dynamic architecture were directly visualized and quantified. The muscle

architecture was investigated in vivo in the relaxed state (arm resting by the subjects’ side)

and three different contracted states (60˚ abduction; 60˚ abduction with 80˚ external

rotation; 60˚ abduction with 80˚ internal rotation) with the muscle working isometrically.

Making inferences on other glenohumeral positions and functional contexts which involve

119

different types of contraction, however, are limited. Furthermore, since the entire length

of fiber bundles from the posterior region could not be visualized, functional inferences of

the posterior region require further support with EMG analysis or possibly MRI analysis.

The anterior and posterior parts of the supraspinatus tendon allow for two distinct

fiber bundle arrangements to be found within the muscle volume. The long cord-like

anterior tendon allows for fiber bundles of the anterior region to be arranged in a pennate

fashion, whereas the broad posterior tendon allows for a more parallel arrangement of

fiber bundles in the posterior region. In a pennate muscle, fiber bundles are orientated

at an angle to the line of force, which allows for a greater number of fiber bundles to be

packed within a given volume. Thus, a pennate muscle can often produce greater forces

than a muscle of similar length with a more parallel arrangement. Based the overall

fiber bundle arrangements of the anterior and posterior regions, the anterior region is

more likely to be involved in force production.

The significantly larger volume of the anterior region of muscle belly also suggests

that much of the muscle’s force is produced by this region. As a result, the anterior

tendon may undergo greater stress than the posterior tendon during contraction. This

difference in volume and possible greater stress may explain the higher incidence of

anterior tendon tears (Huang et al., 2005).

Significant differences in PA between the middle and deep parts of the anterior region,

120

may suggest that stresses throughout the anterior tendon are heterogeneous.

Intratendinous shear has been found to occur within the supraspinatus tendon, and the

strain within the tendon has been found to increase as the joint angle increases (Bey et al.,

2002). Both Huang et al. (2005) and Fukada et al. (1994) found that there is higher

strain on the articular (deep) side of the tendon. Although joint position has been found

to have a pronounced effect on intratendinous strain, and shear within the tendon has been

thought to be responsible for pathogenesis of tendon injuries (Bey et al., 2002; Fukada et

al., 1994), the possible influence of the musculotendinous architecture on tendon shearing

has not been previously investigated or discussed. Based on the findings of this study,

the larger PA of the deep part when compared to the middle part of the anterior region

suggests that the middle part will generate greater force than the deep part under similar

activation conditions. As a result, the different contraction forces stressing the tendon

simultaneously may contribute to greater shear stresses to the articular surface of the

anterior tendon.

The results obtained in vivo indicate that the musculotendinous architecture of

supraspinatus significantly changes as a function of muscle contraction and that these

changes may not be uniform for the anterior and posterior regions. For example, mean

FBL and PA of the anterior region were different between the relaxed and contracted

states. The mean FBL was significantly shorter and the mean PA was significantly

121

greater in the contracted states compared to the relaxed state. Contrary to what was found

for the anterior region, the mean FBL of the posterior region did not significantly change

with muscle contraction.

Differences in the percentage of mean FBL shortening between the anterior and

posterior regions also suggest that these regions may have different functional roles. The

significantly greater percentage of fiber bundle shortening in the anterior region from the

relaxed to contracted states, in addition to volume differences previously discussed,

further suggests that the anterior region is more involved in force production than the

posterior region. In contrast, the small percentage of FBL change of the posterior region

from the relaxed to contracted states may suggest that this region has an important role in

maintaining tension on the tendon. In other words, the posterior region, which laterally

attaches to a wider portion of the tendon than the anterior region, may aid in maintaining

tension on the cuff and capsule to prevent impingement and help maintain joint stability.

To better elucidate the role of the posterior region further investigations are needed

such as US investigation with different glenohumeral joint positions. Fiber bundle

length may be found to significantly change with different joint positions.

Electromyography (EMG) analysis with needles placed within the posterior region may

also aid in better understanding the functional role. It would be interesting to investigate

FBL changes in 90º abduction with movement from external to internal rotation. This is

122

a functional position for overhead athletes who tend to have posterior tendon pathology

(Blevins, 1997). Finally, examination of the intramuscular innervation pattern of the

suprascapular nerve would provide important insight into whether the anterior and

posterior regions are independently innervated by separate branches of the nerve and thus

functionally distinct.

As found in the cadaveric specimens, mean PA in normal subjects in vivo was not

uniform throughout the anterior region. In the relaxed and all the contracted states, mean

PA of the middle part was significantly greater than the deep part. These differences in

mean PA between the middle and deep parts of the anterior region further suggest that

forces along the intramuscular tendon are heterogeneous. Since the mean PA of the

middle part was significantly smaller, the contracting force may be greater than the deep

part. This difference in resultant forces may result in shearing stresses along the

articular side of the intramuscular tendon which was previously discussed.

The musculotendinous architecture of supraspinatus also significantly changes as a

function of glenohumeral joint position with muscle contraction. For example, when the

muscle was contracted, the percentage of mean FBL shortening of the anterior region was

significantly less with the arm held in the internally rotated position than in the neutral or

externally rotated positions. In addition, mean PA was significantly smaller with the arm

held in the externally rotated position than in the neutral or internally rotated positions.

123

Architectural differences found between the various joint positions suggest that the

amount of force the supraspinatus is able to produce depends on the glenohumeral joint

position. Under similar activation conditions, the anterior region of the supraspinatus

may be able to produce less force in the internally rotated position than if the joint was

positioned in neutral or external rotation. In the internally rotated position, not only was

the mean PA greatest but the percentage of mean FBL shortening was also smallest.

6.4 Ultrasound investigation of pathological supraspinatus

The pennate pattern of the pathological supraspinatus was still visible on US scanning

although the sharp contrast between the muscle fiber bundles was often less distinct

compared to the normal subjects and to the contra-lateral supraspinatus.

It is not surprising that the contra-lateral supraspinatus tendon was found to have

pathology in four or the five subjects. In fact, Booth and Marvel (1975) state that “it is

unusual, by the fifth decade of life, to find rotator cuffs in which thinning and fibrillation

of the tendons has not begun.” Whether changes in the tendon precede or result in

changes of the muscle architecture remains unknown.

Ultrasound investigation of the pathological supraspinatus allowed for comparison of

architectural data not only between the pathological and contra-lateral shoulder but also

between age and gender matched normal controls. As the tendon pathology worsens (i.e.

124

partial thickness tear to full-thickness tear), the percentage change in MT, FBL and PA

with muscle contraction in the anterior region decreases. The impact was greatest to

the PA. For the posterior region, mean FBL changed very little from the relaxed to

contracted state for both the pathological and contra-lateral shoulder. This may be

related to the fact that the tear was located in the anterior not posterior tendon.

Comparison between the pathological and normal controls revealed more pronounced

differences in mean percentage change of MT, FBL and PA on contraction than between

the pathological and contra-lateral muscles of the same individual. Again, PA changes

were found to be impacted the most by the tendon pathology. Mean TD, the distance

between the intramuscular tendon and the superficial surface of the muscle belly, was

smallest in the pathological supraspinatus suggesting that muscle atrophy in this area of

the muscle had occurred.

Although the sample of pathological subjects was small (n=5), the results provide

preliminary data that suggest that architectural changes do occur with tendon pathology.

Quantification of architectural parameters with US of the pathological muscle in vivo may

provide additional functional and diagnostic information.

6.5 Functional implications of in vivo findings of pathological subjects

125

Differences in the percentage change in FBL and PA of the anterior region and MT on

contraction between the normal and pathological supraspinatus suggest that the muscle is

not functioning optimally. Since PA appears to be the architectural parameter that is

most affected by tendon pathology, changes in the force producing capabilities of the

anterior region are likely.

In the posterior region, the relatively small differences in the mean FBL on

contraction between the pathological, contra-lateral, and normal controls suggest that the

function of the posterior region, which is presently unclear, may be preserved with

anterior tendon tears.

As discussed earlier, shearing stresses along the intramuscular tendon may occur as a

result of significant differences in mean PA between the middle and deep parts of the

anterior region. If muscle atrophy that occurs with tendon pathology is not uniform and

affects the area of the muscle above the intramuscular tendon more than other areas, then

the contraction force generated by this area of the muscle will be less. Thus, in the

pathological supraspinatus, the shearing stress that may normally occur along the tendon

is likely to change.

126

6.6 Clinical implications

Rotator cuff tears involving the supraspinatus are one of the most common clinical

problems associated with the shoulder (Matsen, 2004). Unfortunately, as Harryman et

al. (2003) states, “the effectiveness and appropriateness of rotator cuff tear treatment

across multiple practices is essentially unknown.” The architectural data collected in

this study along with the US protocol has numerous clinical implications that may aid in

improving the outcome of rotator cuff treatment and in better understanding the etiology

of tendon tears.

Presently, therapeutic exercises for supraspinatus, such as the empty and full-can

exercises, aim at improving the force generating capability of the muscle. These exercises,

which involve shoulder abduction (0-90˚) with either internal or external rotation at the

glenohumeral joint, likely target the anterior region based on architectural changes seen

with US. Ultrasound investigation found significant changes in mean FBL in the

anterior region with active shoulder abduction but not in the posterior. Although further

investigation is needed to clarify the role of the posterior region, if the posterior region’s

role is more for proprioception and/or eccentric control, exercises that focus on these

aspects may be helpful to maximize functional properties.

The three-dimensional model of supraspinatus and the architecturally distinct region

and parts of the muscle could serve as an architectural map for future clinical studies.

127

For example, EMG analysis with accurately placed needles may be carried out to better

monitor the activity of distinct regions during different functional activities.

The US protocol developed in this study could be used as an outcome measure of

adaptive changes of muscle function following therapeutic exercises, athletic training, or

surgery. For example, although EMG and MRI studies have found the empty-can exercise

to be just as appropriate as the full-can exercise in activating supraspinatus, the in vivo

architectural data seems to suggest otherwise (Malanga et al., 1996; Takeda et al., 2002).

In the internally rotated position, which is the position of the glenohumeral joint with the

empty-can exercise, the in vivo architecture shows that the anterior region likely cannot

produce as much force as compared to the neutral or externally rotated positions.

Additionally, although athletes undergo rigorous training regimes that involve repetitive

overhead activities, little is known about the effects of training on the musculotendinous

architecture. Thus, a combination of US and EMG could be used to compare changes in

muscle architecture and make inferences regarding muscle function as a result of different

exercises and intensities of athletic training or surgery.

For patients with articular sided partial thickness tears, supraspinatus exercises within

the range of 60º of glenohumeral abduction may increase shearing stress on the articular

surface of the tendon caused by differences in PA between the middle and deep parts of

the anterior region. This is also supported by Bey et al. (2002) who found that

128

intratendinous strain “profoundly” increased with 60º abduction of the glenohumeral joint.

In these patients, avoiding exercises that involve abduction around or greater than 60º

may be important to prevent further progression of these kinds of tears.

In the case of more severe pathology of the supraspinatus tendon, US may also be

used by surgeons to determine the best intervention. Currently, the severity of the rotator

cuff tear and muscle atrophy are used to help determine the suitability for surgical repair

(Goutallier et al., 2003). However, as shown by Boehm et al. (2005), patients with an

identical clinical diagnosis (i.e. full thickness tears of the supraspinatus with the same

amount of fatty atrophy) can have significant variability in muscle contraction patterns.

Therefore, US investigation may assist surgeons detect muscles that may have atrophy but

still show potential to produce adequate forces based on quantitative analysis of

architectural parameters. Pre and post-operative investigation could also provide

surgeons with greater insight into how the repair of the tendon has influenced the

musculotendinous architecture and thus its function.

6.7 Summary

The supraspinatus is architecturally complex. In vivo investigation and

quantification of the musculotendinous architecture with US is feasible and can provide

important insight into the dynamic function of the normal and pathological muscle.

129

Traditionally, structural deficits of the tendon have been focused on to understand the

etiology of supraspinatus tendon tears (Rothman & Parke, 1965, Bigliani et al., 1990).

However, as shown in this study, quantification of architectural parameters of the muscle

belly may provide important insight into the pathomechanics, prevention, and treatment

of tendon pathology.

130

Chapter 7: Conclusions

The conclusions of this thesis are divided into three sections. The first section

outlines the conclusions derived from the cadaveric investigation, the second section from

the US investigation of normal subjects and the third from the US investigation of

pathological subjects.

Conclusions related to cadaveric investigation and three-dimensional modeling of

supraspinatus:

1. The supraspinatus muscle and tendon architecture is complex.

• The tendon has two distinct parts: an anterior tendon which is extra- and

intramuscular in its course; a posterior tendon which is entirely extramuscular.

The lengths of the anterior and posterior tendon are significantly different

(p<0.05).

• The muscle belly has two distinct regions: anterior and posterior. The

volume of each region is significantly different (p<0.05).

• Within the anterior and posterior regions, there are three distinct subdivisions:

superficial, middle, and deep.

• Mean PA between the middle and deep parts of the anterior region differ

significantly (p<0.05).

131

Conclusions related to US investigation of the normal supraspinatus:

1. Fiber bundle changes on contraction were not uniform throughout the muscle

volume.

• Fiber bundle length changes on contraction were significant (p<0.05) in the

anterior region but not in the posterior.

• Pennation angle changes on contraction in the anterior region were significant

(p<0.05).

• The mean PA between the middle and deep parts of the anterior region differed

even with muscle contraction and with different shoulder positions.

2. Fiber bundle architecture changes as a function of joint position. Among the

different positions investigated, the internally rotated position appears to be

the least optimal for force production.

132

Conclusions related to US investigation of the pathological supraspinatus:

1. The in vivo US protocol can be used to investigate and quantify the

musculotendinous architecture i.e. FBL, PA, MT and TD of supraspinatus in

subjects with a full-thickness anterior tendon tear.

2. Comparison of architectural parameters between the pathological and normal

controls suggests that the mean percentage change in FBL and PA on contraction

differ.

3. Based on differences between MT and percentage change in FBL and PA with the

normal controls, the pathological supraspinatus does not appear to be functioning

optimally.

4. The size of the tendon tear (i.e. partial thickness or full-thickness) appears to be

related to the mean MT and percentage change in FBL and PA on contraction.

The supraspinatus is a complex muscle that is architecturally partitioned. If

clinicians use the traditional perspective of a uniform muscle with an origin and insertion

as the only rationale to characterize supraspinatus function, it may limit optimal

evaluation and treatment of dysfunction associated with supraspinatus tendon tears.

133

Chapter 8: Future Directions

The findings of this study could be used as the basis for future anatomical,

biomechanical, imaging, and clinical studies. Below is an outline of some of the

possible future directions.

1. Use the architectural data base collected in this study to develop more advanced

computer models of supraspinatus such as a contractile model of the normal and

pathological supraspinatus that also accounts for tissue properties of muscle,

tendon and bone.

2. Use the architectural map to

a. Investigate correlation between the intramuscular innervation pattern of

the suprascapular nerve and architecturally distinct region of supraspinatus

b. Investigate and model the fiber type distribution throughout the muscle

volume of supraspinatus and discuss the functional and clinical

implications.

134

3. Use the US protocol developed in this study to investigate the musculotendinous

architecture of supraspinatus pre- and post- rotator cuff tendon repair surgery to

better understand the functional implications of surgical techniques.

4. Use the US protocol to investigate the musculotendinous architecture of

supraspinatus in other patient populations i.e. hemiplegic patients, overhead

athletes.

5. Plan EMG studies to investigate the activity of architecturally distinct regions of

supraspinatus with different exercise regimens.

6. Explore the feasibility of using other advanced imaging modalities i.e. MRI to

investigate the fiber bundle architecture of the posterior region of supraspinatus.

135

References

Agur, A. M., Ng-Thow-Hing, V., Ball, K. A., Fiume, E., & McKee, N. H. (2003). Documentation and three-dimensional modelling of human soleus muscle architecture. Clinical Anatomy (New York, N.Y.), 16(4), 285-293.

Agur, A. M. R. (2009). In Dalley A. F. (Ed.), Grant's atlas of anatomy (12th ed. ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.

Aluisio, F. V., Osbahr, D. C., & Speer, K. P. (2003). Analysis of rotator cuff muscles in adult human cadaveric specimens. American Journal of Orthopedics (Belle Mead, N.J.), 32(3), 124-129.

Basic biomechanics of the musculoskeletal system(2001). In Nordin M., Frankel V. H. (Eds.), (3rd ed. ed.). Philadelphia: Lippincott Williams & Wilkins.

Bassett, R. W., Browne, A. O., Morrey, B. F., & An, K. N. (1990). Glenohumeral muscle force and moment mechanics in a position of shoulder instability. Journal of Biomechanics, 23(5), 405-415.

Bey, M. J., Song, H. K., Wehrli, F. W., & Soslowsky, L. J. (2002). Intratendinous strain fields of the intact supraspinatus tendon: The effect of glenohumeral joint position and tendon region. Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society, 20(4), 869-874.

Bigliani, L. U., Dalsey, R. M., McCann, P. D., & April, E. W. (1990). An anatomical study of the suprascapular nerve. Arthroscopy : The Journal of Arthroscopic & Related Surgery : Official Publication of the Arthroscopy Association of North America and the International Arthroscopy Association, 6(4), 301-305.

Blevins, F. T. (1997). Rotator cuff pathology in athletes. Sports Medicine (Auckland, N.Z.), 24(3), 205-220.

Bodine, S. C., Roy, R. R., Meadows, D. A., Zernicke, R. F., Sacks, R. D., Fournier, M., (1982). Architectural, histochemical, and contractile characteristics of a unique biarticular muscle: The cat semitendinosus. Journal of Neurophysiology, 48(1), 192-201.

Boehm, T. D., Kirschner, S., Mueller, T., Sauer, U., & Gohlke, F. E. (2005). Dynamic ultrasonography of rotator cuff muscles. Journal of Clinical Ultrasound : JCU, 33(5), 207-213.

136

Booth, R. E.,Jr, & Marvel, J. P.,Jr. (1975). Differential diagnosis of shoulder pain. The Orthopedic Clinics of North America, 6(2), 353-379.

Chow, R. S., Medri, M. K., Martin, D. C., Leekam, R. N., Agur, A. M., & McKee, N. H. (2000). Sonographic studies of human soleus and gastrocnemius muscle architecture: Gender variability. European Journal of Applied Physiology, 82(3), 236-244.

Clemente, C. D. (2007). Anatomy : A regional atlas of the human body (5th ed.). Baltimore, MD: Lippincott Williams & Wilkins.

Codman, E. A. (1990). Rupture of the supraspinatus tendon. 1911. Clinical Orthopaedics and Related Research, (254)(254), 3-26.

Cole, G. K., van den Bogert, A. J., Herzog, W., & Gerritsen, K. G. (1996). Modelling of force production in skeletal muscle undergoing stretch. Journal of Biomechanics, 29(8), 1091-1104.

Conservative management of sports injuries(1997). In Gengenbach M. S., Hyde T. E. (Eds.), Baltimore: Williams & Wilkins.

Drake, R. L. (2005). In Vogl W., Mitchell A. W. M. and Gray H. (Eds.), Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone.

Dugas, J. R., Campbell, D. A., Warren, R. F., Robie, B. H., & Millett, P. J. (2002). Anatomy and dimensions of rotator cuff insertions. Journal of Shoulder and Elbow Surgery / American Shoulder and Elbow Surgeons ...[Et Al.], 11(5), 498-503.

Dupont, A. C., Sauerbrei, E. E., Fenton, P. V., Shragge, P. C., Loeb, G. E., & Richmond, F. J. (2001). Real-time sonography to estimate muscle thickness: Comparison with MRI and CT. Journal of Clinical Ultrasound : 29(4), 230-236.

Enoka, R. M. (2002). In Enoka R. M. (Ed.), Neuromechanics of human movement (3rd ed. ed.). Champaign, IL: Human Kinetics.

Fornage, B. D., Touche, D. H., Segal, P., & Rifkin, M. D. (1983). Ultrasonography in the evaluation of muscular trauma. Journal of Ultrasound in Medicine : Official Journal of the American Institute of Ultrasound in Medicine, 2(12), 549-554.

Fukuda, H., Hamada, K., Nakajima, T., & Tomonaga, A. (1994). Pathology and pathogenesis of the intratendinous tearing of the rotator cuff viewed from en bloc histologic sections. Clinical Orthopaedics and Related Research, (304)(304), 60-67.

Fukunaga, T., Ichinose, Y., Ito, M., Kawakami, Y., & Fukashiro, S. (1997). Determination of fascicle length and pennation in a contracting human muscle in vivo. Journal of Applied Physiology (Bethesda, Md.: 1985), 82(1), 354-358.

137

Ganong, W. F. (1993). Blood, pituitary, and brain renin-angiotensin systems and regulation of secretion of anterior pituitary gland. Frontiers in Neuroendocrinology, 14(3), 233-249.

Ganong, W. F. (2005). Review of medical physiology (22nd ed. ed.). New York: McGraw-Hill.

Gans, C. and W. J. Bock (1965). “The functional significance of muscle architecture - a theoretical analysis.” Ergebnisse Der Anatomie Und. Entwicklungsgeschichte 38: 115-142.

Gans, C., & Gaunt, A. S. (1991). Muscle architecture in relation to function. Journal of Biomechanics, 24 Suppl 1, 53-65.

Gladstone, J. N., Bishop, J. Y., Lo, I. K., & Flatow, E. L. (2007). Fatty infiltration and atrophy of the rotator cuff do not improve after rotator cuff repair and correlate with poor functional outcome. The American Journal of Sports Medicine, 35(5), 719-728.

Goldman, D., Evans, S., Boulter, J., Patrick, J., & Heinemann, S. (1987). Neural regulation of acetylcholine receptor gene expression. Annals of the New York Academy of Sciences, 505, 286-300.

Goutallier, D., Postel, J. M., Bernageau, J., Lavau, L., & Voisin, M. C. (1994). Fatty muscle degeneration in cuff ruptures. pre- and postoperative evaluation by CT scan. Clinical Orthopaedics and Related Research, (304), 78-83.

Goutallier, D., Postel, J. M., Gleyze, P., Leguilloux, P., & Van Driessche, S. (2003). Influence of cuff muscle fatty degeneration on anatomic and functional outcomes after simple suture of full-thickness tears. Journal of Shoulder and Elbow Surgery / American Shoulder and Elbow Surgeons ...[Et Al.], 12(6), 550-554.

Griffiths, R. I. (1991). Shortening of muscle fibres during stretch of the active cat medial gastrocnemius muscle: The role of tendon compliance. The Journal of Physiology, 436, 219-236.

Hamill, J. (2009). In Knutzen K. (Ed.), Biomechanical basis of human movement (3rd ed. ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams and Wilkins.

Harryman, D. T.,2nd, Hettrich, C. M., Smith, K. L., Campbell, B., Sidles, J. A., & Matsen, F. A.,3rd. (2003). A prospective multipractice investigation of patients with full-thickness rotator cuff tears: The importance of comorbidities, practice, and other covariables on self-assessed shoulder function and health status. The Journal of Bone and Joint Surgery.American Volume, 85-A(4), 690-696.

Harryman, D. T.,2nd, Mack, L. A., Wang, K. Y., Jackins, S. E., Richardson, M. L., & Matsen, F. A.,3rd. (1991). Repairs of the rotator cuff. correlation of functional results

138

with integrity of the cuff. The Journal of Bone and Joint Surgery.American Volume, 73(7), 982-989.

Herbert, R. D., & Gandevia, S. C. (1995). Changes in pennation with joint angle and muscle torque: In vivo measurements in human brachialis muscle. The Journal of Physiology, 484 ( Pt 2)(Pt 2), 523-532.

Hill, A. (1938). “The heat of shortening and the dynamic constants of muscle.” Proceedings of the Royal Society of. London Series. B: Biological Sciences 126: 136-195.

Holzbaur, K. R., Murray, W. M., Gold, G. E., & Delp, S. L. (2007). Upper limb muscle volumes in adult subjects. Journal of Biomechanics, 40(4), 742-749.

Howell, S. M., Imobersteg, A. M., Seger, D. H., & Marone, P. J. (1986). Clarification of the role of the supraspinatus muscle in shoulder function. The Journal of Bone and Joint Surgery.American Volume, 68(3), 398-404.

Huang, C. Y., Wang, V. M., Pawluk, R. J., Bucchieri, J. S., Levine, W. N., Bigliani, L. U., et al. (2005). Inhomogeneous mechanical behavior of the human supraspinatus tendon under uniaxial loading. Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society, 23(4), 924-930.

Huijing, P. A. (1998). Muscle, the motor of movement: Properties in function, experiment and modelling. Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology, 8(2), 61-77.

Human movement : An introductory text(2001). In Trew M., Everett T. (Eds.), (4th ed. ed.). New York: Churchill Livingstone.

Huxley, H. E. (1957). The double array of filaments in cross-striated muscle. The Journal of Biophysical and Biochemical Cytology, 3(5), 631-648.

Irlenbusch, U., & Gansen, H. K. (2003). Muscle biopsy investigations on neuromuscular insufficiency of the rotator cuff: A contribution to the functional impingement of the shoulder joint. Journal of Shoulder and Elbow Surgery / American Shoulder and Elbow Surgeons ...[Et Al.], 12(5), 422-426.

Itoi, E., Hsu, H. C., Carmichael, S. W., Morrey, B. F., & An, K. N. (1995). Morphology of the torn rotator cuff. Journal of Anatomy, 186 ( Pt 2)(Pt 2), 429-434.

Jensen, B. R., Jorgensen, K., Huijing, P. A., & Sjogaard, G. (1995). Soft tissue architecture and intramuscular pressure in the shoulder region. European Journal of Morphology, 33(3), 205-220.

139

Jensen, R. H., & Davy, D. T. (1975). An investigation of muscle lines of action about the hip: A centroid line approach vs the straight line approach. Journal of Biomechanics, 8(2), 103-110.

Johnson, G. R., Spalding, D., Nowitzke, A., & Bogduk, N. (1996). Modelling the muscles of the scapula morphometric and coordinate data and functional implications. Journal of Biomechanics, 29(8), 1039-1051.

Juul-Kristensen, B., Bojsen-Moller, F., Holst, E., & Ekdahl, C. (2000a). Comparison of muscle sizes and moment arms of two rotator cuff muscles measured by ultrasonography and magnetic resonance imaging. European Journal of Ultrasound : Official Journal of the European Federation of Societies for Ultrasound in Medicine and Biology, 11(3), 161-173.

Juul-Kristensen, B., Bojsen-Moller, F., Finsen, L., Eriksson, J., Johansson, G., Stahlberg, F., et al. (2000b). Muscle sizes and moment arms of rotator cuff muscles determined by magnetic resonance imaging. Cells, Tissues, Organs, 167(2-3), 214-222.

Katayose, M., & Magee, D. J. (2001). The cross-sectional area of supraspinatus as measured by diagnostic ultrasound. The Journal of Bone and Joint Surgery.British Volume, 83(4), 565-568.

Kawakami, Y., Abe, T., & Fukunaga, T. (1993). Muscle-fiber pennation angles are greater in hypertrophied than in normal muscles. Journal of Applied Physiology (Bethesda, Md.: 1985), 74(6), 2740-2744.

Kawakami, Y., Ichinose, Y., & Fukunaga, T. (1998). Architectural and functional features of human triceps surae muscles during contraction. Journal of Applied Physiology (Bethesda, Md.: 1985), 85(2), 398-404.

Keating, J. F., Waterworth, P., Shaw-Dunn, J., & Crossan, J. (1993). The relative strengths of the rotator cuff muscles. A cadaver study. The Journal of Bone and Joint Surgery.British Volume, 75(1), 137-140.

Keyes, E. L. (1933). Observations on rupture of the supraspinatus tendon: Based upon a study of seventy-three cadavers. Annals of Surgery, 97(6), 849-856.

Khoury, V., Cardinal, E., & Brassard, P. (2008). Atrophy and fatty infiltration of the supraspinatus muscle: Sonography versus MRI. AJR.American Journal of Roentgenology, 190(4), 1105-1111.

Kubo, K., Kanehisa, H., Azuma, K., Ishizu, M., Kuno, S. Y., Okada, M., et al. (2003). Muscle architectural characteristics in women aged 20-79 years. Medicine and Science in Sports and Exercise, 35(1), 39-44.

140

Lehman, C., Cuomo, F., Kummer, F. J., & Zuckerman, J. D. (1995). The incidence of full thickness rotator cuff tears in a large cadaveric population. Bulletin (Hospital for Joint Diseases (New York, N.Y.)), 54(1), 30-31.

Lemay, M. A., & Crago, P. E. (1996). A dynamic model for simulating movements of the elbow, forearm, an wrist. Journal of Biomechanics, 29(10), 1319-1330.

Lieber, R.L, Fazeli B.M. Botte, M.J. (1990) Architecture of selected write flexor and extensor muscles. Journal of Hand Surgery 15: 244-250

Lieber, R. L. (1993). Skeletal muscle architecture: Implications for muscle function and surgical tendon transfer. Journal of Hand Therapy : Official Journal of the American Society of Hand Therapists, 6(2), 105-113.

Lieber, R. L., & Friden, J. (2001). Clinical significance of skeletal muscle architecture. Clinical Orthopaedics and Related Research, (383)(383), 140-151.

Lindblom, K. (1939). On pathogenesis of ruptures of the tendon aponeurosis of the shoulder joint. Acta Radiologica, 20, 563-577.

Malanga, G. A., Jenp, Y. N., Growney, E. S., & An, K. N. (1996). EMG analysis of shoulder positioning in testing and strengthening the supraspinatus. Medicine and Science in Sports and Exercise, 28(6), 661-664.

Matsen, F. A. (2004). In Lippitt S. B., DeBartolo S. E. (Eds.), Shoulder surgery : Principles and procedures. Philadelphia, Pa.: Saunders.

McCully, S. P., Suprak, D. N., Kosek, P., & Karduna, A. R. (2006). Suprascapular nerve block disrupts the normal pattern of scapular kinematics. Clinical Biomechanics (Bristol, Avon), 21(6), 545-553.

McMahon, P. J., Debski, R. E., Thompson, W. O., Warner, J. J., Fu, F. H., & Woo, S. L. (1995). Shoulder muscle forces and tendon excursions during glenohumeral abduction in the scapular plane. Journal of Shoulder and Elbow Surgery / American Shoulder and Elbow Surgeons ...[Et Al.], 4(3), 199-208.

Mendez, J., Keys, A. (1960). Density and composition of mammalian muscle. Metabolism 9, 184-188

Meyer, D. C., Pirkl, C., Pfirrmann, C. W., Zanetti, M., & Gerber, C. (2005). Asymmetric atrophy of the supraspinatus muscle following tendon tear. Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society, 23(2), 254-258.

Moore, K. L. (2002). In Agur A. M. R., Moore K. L. and Agur A. M. R. (Eds.), Essential clinical anatomy (2nd ed. ed.). Philadelphia: Lippincott Williams & Wilkins.

141

Moore, K. L. (2006). In Dalley A. F., Agur A. M. R. (Eds.), Clinically oriented anatomy (5th ed. ed.). Philadelphia: Lippincott Williams & Wilkins.

Morse, C. I., Tolfrey, K., Thom, J. M., Vassilopoulos, V., Maganaris, C. N., & Narici, M. V. (2008). Gastrocnemius muscle specific force in boys and men. Journal of Applied Physiology (Bethesda, Md.: 1985), 104(2), 469-474.

Movement control : An interdisciplinary forum(1991). In Jacobs R., Rikkert W. E. I. (Eds.), . Amsterdam: VU University Press.

Murray, W. M., Buchanan, T. S., & Delp, S. L. (2000). The isometric functional capacity of muscles that cross the elbow. Journal of Biomechanics, 33(8), 943-952.

Narici, M. (1999). Human skeletal muscle architecture studied in vivo by non-invasive imaging techniques: Functional significance and applications. Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology, 9(2), 97-103.

Neer, C. S.,2nd. (1972). Anterior acromioplasty for the chronic impingement syndrome in the shoulder: A preliminary report. The Journal of Bone and Joint Surgery.American Volume, 54(1), 41-50.

Ng-Thow-Hing, V. (2001). Anatomically-based models for physical and geometric reconstruction of humans and other animals. Department of Computer Science. Toronto, University of Toronto (PhD Thesis).

Otten, E. (1988). Concepts and models of functional architecture in skeletal muscle. Exercise and Sport Sciences Reviews, 16, 89-137.

Otten, E. (1991). Modelling movement control. Movement Control. R. Jacobs and W. E. I. Rikkert. Amsterdam, VU University Press: Chapter 6. Oxorn, V., A. Agur, et al. (1998). Resolving discrepancies in image research: The importance of direct observation in the illustration of the human soleus muscle. Journal of Biomedical Communication 25(1): 16-26.

Petersen, C. M. (2002). In Foley R. A. (Ed.), Active and passive movement testing. New York: McGraw-Hill.

Petersen, C. M. (2002). In Foley R. A. (Ed.), Active and passive movement testing. New York: McGraw-Hill.

142

Powell, P. L., Roy, R. R., Kanim, P., Bello, M. A., & Edgerton, V. R. (1984). Predictability of skeletal muscle tension from architectural determinations in guinea pig hindlimbs. Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology, 57(6), 1715-1721.

Roh, M. S., Wang, V. M., April, E. W., Pollock, R. G., Bigliani, L. U., & Flatow, E. L. (2000). Anterior and posterior musculotendinous anatomy of the supraspinatus. Journal of Shoulder and Elbow Surgery, 9(5), 436-440.

Ross, M. H. (2006). In Pawlina W. (Ed.), Histology : A text and atlas with correlated cell and molecular biology (5th ed. ed.). Baltimore: Lippincott Wiliams & Wilkins.

Roy, R. R., Pierotti, D. J., Flores, V., Rudolph, W., & Edgerton, V. R. (1992). Fibre size and type adaptations to spinal isolation and cyclical passive stretch in cat hindlimb. Journal of Anatomy, 180 ( Pt 3)(Pt 3), 491-499.

Rothman, R. H., & Parke, W. W. (1965). The vascular anatomy of the rotator cuff. Clinical Orthopaedics and Related Research, 41, 176-186.

Segal, R. L., Wolf, S. L., DeCamp, M. J., Chopp, M. T., & English, A. W. (1991). Anatomical partitioning of three multiarticular human muscles. Acta Anatomica, 142(3), 261-266.

Sharkey, N. A., Marder, R. A., & Hanson, P. B. (1994). The entire rotator cuff contributes to elevation of the arm. Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society, 12(5), 699-708.

Silverstein, B., Welp, E., Nelson, N., & Kalat, J. (1998). Claims incidence of work-related disorders of the upper extremities: Washington state, 1987 through 1995. American Journal of Public Health, 88(12), 1827-1833.

Strobel, K., Hodler, J., Meyer, D. C., Pfirrmann, C. W., Pirkl, C., & Zanetti, M. (2005). Fatty atrophy of supraspinatus and infraspinatus muscles: Accuracy of US. Radiology, 237(2), 584-589.

Takeda, Y., Kashiwaguchi, S., Endo, K., Matsuura, T., & Sasa, T. (2002). The most effective exercise for strengthening the supraspinatus muscle: Evaluation by magnetic resonance imaging. The American Journal of Sports Medicine, 30(3), 374-381.

Thomazeau, H., Boukobza, E., Morcet, N., Chaperon, J., & Langlais, F. (1997). Prediction of rotator cuff repair results by magnetic resonance imaging. Clinical Orthopaedics and Related Research, (344)(344), 275-283.

143

Thompson, J. S. (1990). In Akesson E. J., Loeb J. A. and Wilson-Pauwels L. (Eds.), Thompson's core textbook of anatomy. (2nd ed. /|bElizabeth J. Akesson, Jacques A. Loeb, Linda Wilson-Pauwels. -- ed.). Philadelphia: Lippincott.

Vahlensieck, M., an Haack, K., & Schmidt, H. M. (1994). Two portions of the supraspinatus muscle: A new finding about the muscles macroscopy by dissection and magnetic resonance imaging. Surgical and Radiologic Anatomy : SRA, 16(1), 101-104.

Vahlensieck, M., Pollack, M., Lang, P., Grampp, S., & Genant, H. K. (1993). Two segments of the supraspinous muscle: Cause of high signal intensity at MR imaging? Radiology, 186(2), 449-454.

van den Bogert, A. J., Gerritsen, K. G., & Cole, G. K. (1998). Human muscle modelling from a user's perspective. Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology, 8(2), 119-124.

Van der Helm, F. C. and R. Veenbaas (1991). Modelling the mechanical effect of muscles with large attachment sites: Application to the shoulder mechanism. Journal of Biomechanics 24(12): 1151-63.

van der Linden, B. J., Koopman, H. F., Grootenboer, H. J., & Huijing, P. A. (1998). Modelling functional effects of muscle geometry. Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology, 8(2), 101-109.

Van Leeuwen, J. L., & Spoor, C. W. (1992). Modelling mechanically stable muscle architectures. Philosophical Transactions of the Royal Society of London.Series B, Biological Sciences, 336(1277), 275-292.

Veeger, H. E., Van der Helm, F. C., Van der Woude, L. H., Pronk, G. M., & Rozendal, R. H. (1991). Inertia and muscle contraction parameters for musculoskeletal modelling of the shoulder mechanism. Journal of Biomechanics, 24(7), 615-629.

Volk, A. G., & Vangsness, C. T.,Jr. (2001). An anatomic study of the supraspinatus muscle and tendon. Clinical Orthopaedics and Related Research, (384), 280-285.

Ward, A. D., Hamarneh, G., Ashry, R., & Schweitzer, M. E. (2007). 3D shape analysis of the supraspinatus muscle: A clinical study of the relationship between shape and pathology. Academic Radiology, 14(10), 1229-1241.

Ward, S. R., Hentzen, E. R., Smallwood, L. H., Eastlack, R. K., Burns, K. A., Fithian, D. C., et al. (2006). Rotator cuff muscle architecture: Implications for glenohumeral stability. Clinical Orthopaedics and Related Research, 448, 157-163.

144

Ward, S. R., & Lieber, R. L. (2005). Density and hydration of fresh and fixed human skeletal muscle. Journal of Biomechanics, 38(11), 2317-2320.

Webb, M. R., & Trentham, D. R. (1981). The mechanism of ATP hydrolysis catalyzed by myosin and actomyosin, using rapid reaction techniques to study oxygen exchange. The Journal of Biological Chemistry, 256(21), 10910-10916.

Werner, C. M., Weishaupt, D., Blumenthal, S., Curt, A., Favre, P., & Gerber, C. (2006). Effect of experimental suprascapular nerve block on active glenohumeral translations in vivo. Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society, 24(3), 491-500.

Wickham, J. B., & Brown, J. M. (1998). Muscles within muscles: The neuromotor control of intra-muscular segments. European Journal of Applied Physiology and Occupational Physiology, 78(3), 219-225.

Williams, P. E., & Goldspink, G. (1978). Changes in sarcomere length and physiological properties in immobilized muscle. Journal of Anatomy, 127(Pt 3), 459-468.

Winters, J. C., Sobel, J. S., Groenier, K. H., Arendzen, J. H., & Meyboom-de Jong, B. (1997). The course of pain and the restriction of mobility in patients with shoulder complaints in general practice. Rheumatology International, 16(6), 219-225.

Winters, J. M., Ed. (1990). Hill-based Muscle Models: A Systems Engineering Perspective. Multiple Muscle Systems: Biomechanics and Movement Organization, Springer- Verlag: 69-93.

Woittiez, R. D., Huijing, P. A., Boom, H. B., & Rozendal, R. H. (1984). A three-dimensional muscle model: A quantified relation between form and function of skeletal muscles. Journal of Morphology, 182(1), 95-113.

Wood, J. E., Meek, S. G., & Jacobsen, S. C. (1989). Quantitation of human shoulder anatomy for prosthetic arm control--II. anatomy matrices. Journal of Biomechanics, 22(4), 309-325.

Wuelker, N., Plitz, W., Roetman, B., & Wirth, C. J. (1994). Function of the supraspinatus muscle. abduction of the humerus studied in cadavers. Acta Orthopaedica Scandinavica, 65(4), 442-446.

Zahalak, G. I., & Ma, S. P. (1990). Muscle activation and contraction: Constitutive relations based directly on cross-bridge kinetics. Journal of Biomechanical Engineering, 112(1), 52-62.

Zuurbier, C. J., & Huijing, P. A. (1993). Changes in geometry of actively shortening unipennate rat gastrocnemius muscle. Journal of Morphology, 218(2), 167-180.

145

Appendix A Sample Size Calculation

Fiber bundle length was used to calculate the sample size because it is the most commonly

measured architectural parameter.

1. Null Hypothesis: Mean FBL (cm) of the anterior region of supraspinatus is the same

as the mean of the posterior region.

2. Alternative Hypothesis: Mean FBL (cm) of the anterior region of supraspinatus is

different from the mean of the posterior region.

3. Effect size = 0.651cm (10% X 6.51 cm)

4. Standard Deviation of fiber bundle length = 0.47 cm

5. Standardized effect size = effect size÷standard deviation = 0.651÷0.47= 1.38

6. α (two-sided) = 0.05; β= 1-0.80 =0.20

7. Therefore, sample size required is 17

146

Appendix B

Ethics Approval

147

148

149

150