Strain estimations of the plantar fascia and other

Graduate Theses and Dissertations Iowa State University Capstones, Theses and Dissertations

2021

Strain estimations of the plantar fascia and other ligaments of the Strain estimations of the plantar fascia and other ligaments of the

foot: Implications for plantar fasciitis foot: Implications for plantar fasciitis

Jeff Mettler

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Strain estimations of the plantar fascia and other ligaments of the foot: Implications for

plantar fasciitis

by

Jeffrey Howard Mettler

A dissertation submitted to the graduate faculty

in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

Major: Kinesiology

Program of Study Committee:

Timothy R. Derrick, Major Professor

Jason Gillette

Gary Mirka

Panteleimon Ekkekakis

Rick Sharp

The student author, whose presentation of the scholarship herein was approved by the program

of study committee, is solely responsible for the content of this dissertation. The Graduate

College will ensure this dissertation is globally accessible and will not permit alterations after a

degree is conferred.

Iowa State University

Ames, Iowa

2021

Copyright © Jeffrey Howard Mettler, 2021. All rights reserved.

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TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS ............................................................................................................. iv

ABSTRACT .....................................................................................................................................v

CHAPTER 1. GENERAL INTRODUCTION ................................................................................1 Purpose ...................................................................................................................................... 2 Significance of Research ........................................................................................................... 3 References ................................................................................................................................. 4

CHAPTER 2. LITERATURE REVIEW .........................................................................................6 Anatomy of the Plantar Fascia ................................................................................................... 6

Functions of the Plantar Fascia .................................................................................................. 6 Plantar Fascia Loading ......................................................................................................... 8

Anatomy and Functions of Other Ligaments of the Foot ........................................................ 10 Pathogenesis of Plantar Fasciitis ............................................................................................. 14

Etiology of Plantar Fasciitis .................................................................................................... 16 Foot Structure ..................................................................................................................... 16 1st MTP Joint Range of Motion ......................................................................................... 18

Posterior Leg Muscle Tightness and Ankle Dorsiflexion Range of Motion ...................... 19 Excessive Pronation ........................................................................................................... 20

Other Kinematic Factors .................................................................................................... 22

Multi-segment foot models ...................................................................................................... 22

Treatment of Plantar Fasciitis .................................................................................................. 24 Low-Dye Taping Technique & Variations .............................................................................. 24

Pain Reduction Following Low-Dye Taping ..................................................................... 25 Postural Effects of Low-Dye Taping.................................................................................. 26 Exercise Effects on Tape .................................................................................................... 27

Kinematic Effects of Low-Dye Taping .............................................................................. 28 References ............................................................................................................................... 28

CHAPTER 3. EFFECTS OF SPEED, INCLINE, AND SHOE STIFFNESS ON PEAK

PLANTAR FASCIA STRAIN DURING WALKING ..................................................................39 Abstract .................................................................................................................................... 39

Introduction ............................................................................................................................. 40 Methods ................................................................................................................................... 42

Participants ......................................................................................................................... 42 Data Collection Procedures ................................................................................................ 42

Data Analysis ..................................................................................................................... 43 Results ..................................................................................................................................... 44 Discussion ................................................................................................................................ 46 Conclusions ............................................................................................................................. 48 References ............................................................................................................................... 49

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Figures and Tables ................................................................................................................... 51

Appendix A: Institutional Review Board Approval ................................................................ 55 Appendix B: Modifications to the Musculoskeletal Foot Model ............................................ 56

CHAPTER 4. VALIDATION OF A SIX-SEGMENT MUSCULOSKELETAL MODEL OF

THE FOOT USED TO ESTIMATE LIGAMENT STRAINS ......................................................59 Abstract .................................................................................................................................... 59 Introduction ............................................................................................................................. 60 Methods ................................................................................................................................... 62

Data Collection Procedures ................................................................................................ 62 Data Analysis ..................................................................................................................... 63

Results ..................................................................................................................................... 65 Discussion ................................................................................................................................ 66

Conclusions ............................................................................................................................. 68 References ............................................................................................................................... 68

Figures and Tables ................................................................................................................... 70

CHAPTER 5. EFFECTS OF LOW-DYE TAPING ON PLANTAR FASCIA STRAIN AND

FOOT KINEMATICS IN INDIVIDUALS WITH PLANTAR FASCIITIS .................................78

Abstract .................................................................................................................................... 78 Introduction ............................................................................................................................. 79

Methods ................................................................................................................................... 82 Participants ......................................................................................................................... 82 Data Collection Procedures ................................................................................................ 83

Data Analysis ..................................................................................................................... 84

Results ..................................................................................................................................... 85 Discussion ................................................................................................................................ 87 Conclusions ............................................................................................................................. 91

References ............................................................................................................................... 91 Figures and Tables ................................................................................................................... 95

Appendix: Institutional Review Board Approval .................................................................. 101

CHAPTER 6. GENERAL CONCLUSIONS ...............................................................................103 Summary ................................................................................................................................ 103 Significance and Future Directions ....................................................................................... 105 References ............................................................................................................................. 105

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ACKNOWLEDGMENTS

As I think back on the path that I took to get here, I am incredibly grateful to the mentors

I had along the way. First of all, I need to thank Dr. Tim Derrick, my major advisor and primary

mentor during my dissertation. Your knowledge, your patience, and your support are all so

appreciated. You gave me help when I needed help and you gave me space when I needed to

learn on my own. You taught me how to be a skilled researcher and a caring professor by

demonstrating the qualities of a skilled researcher and a caring professor. I only hope I can

exhibit the same qualities to my own students. Next is Dr. Erin Ward, who became a second

mentor to me during my time at Iowa State University. The dedication that you showed to me

and my research has not gone unappreciated. I would have never accomplished the things I did

without your help, and for that I am so grateful. I also have to acknowledge my previous

advisors, Dr. Jae Yom and Dr. Mike Pohl, as they both played a vital role in my development as

a researcher. Dr. Yom, thank you for introducing me to the research process and filling me with

an excitement for the possibilities of research. Dr. Pohl, thank you for commitment to high-

quality research. You prepared me for this process, and for that I thank you.

Finally, I want to thank all my family and friends who have been with me

throughout this process. You all have provided me with support, encouragement, and patience,

and I am so humbled and grateful for your presence in my life.

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ABSTRACT

Plantar fasciitis is thought to occur due to excessive strain of the plantar fascia. There are

numerous anatomical, biomechanical, and environmental factors that affect plantar fascia strain.

Therefore, the first purpose of this dissertation was to investigate several biomechanical and

environmental factors thought to increase plantar fascia strain. Fifteen healthy participants

walked on a treadmill at two speeds, three inclines, and two shoe stiffness levels. A four-segment

musculoskeletal model of the foot was used to analyze the data, and a significant effect of speed

was found. Furthermore, the relationship between metatarsophalangeal (MTP) joint dorsiflexion

and arch collapse was investigated, and the amount that each contributed to total plantar fascia

strain was calculated. It was found that the increase in plantar fascia strain caused by MTP joint

dorsiflexion is counteracted by the increase in arch height that occurs with MTP joint

dorsiflexion, which is due to the function of the windlass mechanism.

The second purpose was to validate a six-segment musculoskeletal model of the foot that

estimates strains of several ligaments thought to assist the plantar fascia in arch support. Seven

fresh-frozen cadaver specimens were dissected and ligament strains were directly measured

using a manual digitizer. The directly-measured strains were compared to the model-estimated

ligament strains as a way to validate the use of the model for future studies.

The third purpose was to use the six-segment musculoskeletal model to determine the

effects of a taping procedure on plantar fascia strain. Fifteen individuals with plantar fasciitis

walked overground under two barefoot conditions: an untaped condition and a low-Dye taped

condition. The low-Dye taped condition decreased the amount of arch collapse exhibited by the

participants, and although the tape did not reduce peak plantar fascia strains during walking, it

significantly reduced plantar fascia strains during midstance. We suggest that the taping method

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is effective due to its ability to reduce cumulative strain across the entire stance phase rather than

peak strain.

The final purpose was to use the musculoskeletal model to determine the effects of the

low-Dye taped condition on several ligaments thought to assist the plantar fascia in arch support.

Significant reductions of strain in the spring ligament and long plantar ligament affirm the role of

these ligaments to provide support to the medial longitudinal arch.

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CHAPTER 1. GENERAL INTRODUCTION

The medial longitudinal arch is an evolutionary development of bipedal human gait.

There are several theories that aim to explain why the arch of the human foot evolved. First, it

increases the mechanical advantage of the ankle plantar flexors, giving them enough strength to

lift the weight of the body during stance phase [1]. Second, it gives the foot spring-like qualities,

allowing the foot to absorb and return elastic strain energy during gait [2].

The plantar fascia is an integral component of normal foot function, helping to support

the medial longitudinal arch and limit subtalar pronation. Normal function of the plantar fascia is

aided by the windlass mechanism. Because of its attachment on the proximal phalanges of the

toes, toe dorsiflexion causes the plantar fascia to wind around the metatarsal heads. In a closed-

chain environment, this increases the tension in the plantar fascia, which subsequently raises the

medial longitudinal arch and produces both rearfoot supination and tibial external rotation [3,4].

Dysfunction of the plantar fascia can be debilitating and reduce an individual’s quality of life [5].

Plantar fasciitis affects up to 10% of the population [6] and results in approximately one million

patient visits to office-based physicians and hospital outpatient departments each year [7].

However, the etiology of planter fasciitis is not well understood. While plantar fascia

dysfunction is multifactorial in nature, the development of the disorder is believed to be either

inflammatory or degenerative in nature [8–10]. Research shows that excessive strain in the

plantar fascia can produce microtears and inflammation at the insertion on the medial calcaneal

tubercle [10–13]. Consequently, research efforts have focused on ways to reduce excessive

strain.

While the plantar fascia provides a significant portion of the structural support of the

arch, it is not the only tissue that contributes to arch support [2,14]. There are numerous other

2

structures, namely the foot muscles and ligaments, that help to maintain the arch. Ligaments are

passive tissues that connect bone to bone and help to maintain the stability of a joint. They resist

joint motion either outside of that joint’s normal plane of motion or beyond that joint’s total

range of motion [15]. Ligaments are elastic and will return to their original length and shape

when relaxed as long as the tension is below the yield point. However, if tension greater than the

yield point is applied to a ligament, it displays plastic characteristics and will remain partially

elongated after tension is released [15,16]. Excessive strain applied to ligaments can increase the

resting length of the ligament, which may result in a decreased amount of support provided to the

joint [16,17]. The effects of decreased support of the medial longitudinal arch can result in the

development of a flatfoot condition [17,18], which is characterized by a reduction in the height

of the medial longitudinal arch. A flatfoot condition has been cited as a risk factor for plantar

fasciitis [19–21], so it is important to study the soft tissues that support the medial longitudinal

arch. The following dissertation describes three studies that investigate the strains applied to the

soft tissues that support the medial longitudinal arch. By using a combination of experimental

and musculoskeletal modeling techniques, the studies aim to provide insight into the

pathogenesis and etiology of plantar fasciitis, as well as the development of a flatfoot condition.

Purpose

Study 1

The purpose of the first study was to examine the effects of various walking conditions

on plantar fascia strain. All possible combinations of two walking speeds (preferred walking

speed and 20% greater than preferred walking speed), three inclines (0°, 5°, and 10°), and two

shoe forefoot bending stiffnesses (stiff and flexible midsole) were performed by participants on a

standard treadmill while lower extremity and foot kinematics were recorded. A four-segment

foot model (calcaneus, talus, forefoot, hallux) was created with the inclusion of the plantar

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fascia. Plantar fascia strain due to both the windlass mechanism of the 1st metatarsophalangeal

(MTP) joint and collapse of the arch was estimated and compared to previous literature to assess

the validity of the model.

Study 2

The purpose of the second study was to validate the use of a six-segment musxuloskeletal

foot model. To validate the model, several ligaments of the foot that are believed to provide

additional support to the arch were investigated, including the spring ligament, deltoid ligament,

bifurcate ligament, and cervical ligament. An axial load was applied to the tibia of cadaver

specimens, which resulted in arch collapse. Following the axial load application, ligament strains

were measured using a manual digitizer. Systematic increases in the axial load produced

corresponding increases in the amount of arch collapse, which allowed us to quantify the amount

of strain in each ligament due to arch collapse. Following the data collection, the ligament strain

results were incorporated into the six-segment musculoskeletal foot model, which was utilized in

the third and final study.

Study 3

The purpose of the final study was to investigate the effects of the low-Dye taping

method on plantar fascia and ligament strains in individuals with plantar fasciitis during walking.

Furthermore, the study examined the kinematic effects of the low-Dye taping method. The

validated six-segment musculoskeletal model of the foot was used, which included the calcaneus,

talus, navicular and cuneiforms, cuboid, metatarsals, and hallux.

Significance of Research

Walking is a very popular exercise to increase and maintain fitness, and physicians often

recommend it because it is a low-impact, low-cost exercise that can be done anywhere.

Unfortunately, plantar fasciitis can be debilitating and limit an individual’s activity level. The

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high prevalence of the disorder, as well as the lack of understanding of its etiology, makes

plantar fasciitis an important topic of research. This dissertation focuses on strains of the plantar

fascia and several other foot ligaments and their relationship to both plantar fasciitis and the

structural integrity of the medial longitudinal arch. It is hoped that the information learned in

these studies will lead to a better understanding of plantar fasciitis development and treatment, as

well as the soft tissue structures that provide support to the medial longitudinal arch during

walking.

References

[1] D.J. Morton, Evolution of the longitudinal arch of the human foot, J. Bone Jt. Surg. 6

(1924) 56–90.

[2] R.F. Ker, M.B. Bennett, S.R. Bibby, R.C. Kester, R.M. Alexander, The spring in the arch

of the human foot, Nature. 325 (1987) 147–149.

[3] J.H. Hicks, The mechanics of the foot. II. The plantar aponeurosis and the arch., J. Anat.

88 (1954) 25–30.

[4] P.A. Tansey, P.J. Briggs, Active and passive mechanisms in the control of heel supination,

Foot Ankle Surg. 7 (2001) 131–136.

[5] D.B. Irving, J.L. Cook, M.A. Young, H.B. Menz, Impact of chronic plantar heel pain on

health-related quality of life, J. Am. Podiatr. Med. Assoc. 98 (2008) 283–289.

[6] M. DeMaio, R. Paine, R.E. Mangine, D. Drez, Plantar Fasciitis, Orthopedics. 16 (1993)

1153–1163.

[7] D.L. Riddle, S.M. Schappert, Volume of Ambulatory Care Visits and Patterns of Care for

Patients Diagnosed with Plantar Fasciitis: A National Study of Medical Doctors, Foot

Ankle Int. 25 (2004) 303–310.

[8] S.C. Wearing, J.E. Smeathers, S.R. Urry, E.M. Hennig, A.P. Hills, The pathomechanics of

plantar fasciitis, Sport. Med. 36 (2006) 585–611.

[9] H. Lemont, K.M. Ammirati, N. Usen, Plantar Fasciitis: A Degenerative Process

(Fasciosis) Without Inflammation, J. Am. Podiatr. Med. Assoc. 93 (2003) 234–237.

[10] P. Kwong, D. Kay, R. Voner, M. White, Plantar fasciitis: Mechanics and pathomechanics

of treatment, Clin. Sports Med. 7 (1988) 119–126.

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[11] D.B. Thordarson, P.J. Kumar, T.P. Hedman, E. Ebramzadeh, Effect of Partial Versus

Complete Plantar Fasciotomy on the Windlass Mechanism, Foot Ankle Int. 18 (1997) 16–

20.

[12] G.C. Hunt, T. Sneed, H. Hamann, S. Chisam, Biomechanical and histiological

considerations for development of plantar fasciitis and evaluation of arch taping as a

treatment option to control associated plantar heel pain: A single-subject design, Foot. 14

(2004) 147–153.

[13] R. Puttaswamaiah, P. Chandran, Degenerative plantar fasciitis : A review of current

concepts, 17 (2007) 3–9.

[14] C. Cifuentes-De la Portilla, R. Larrainzar-Garijo, J. Bayod, Analysis of the main passive

soft tissues associated with adult acquired flatfoot deformity development: A

computational modeling approach, J. Biomech. 84 (2019) 183–190.

[15] M.L. Root, W.P. Orien, J.H. Weed, Normal and Abnormal Function of the Foot, Clinical

Biomechanics Corporation, 1977.

[16] T.G. McPoil, G.C. Hunt, Evaluation and management of foot and ankle disorders: Present

problems and future directions, J. Orthop. Sports Phys. Ther. 21 (1995) 381–388.

[17] H.B. Kitaoka, Z.P. Luo, K.N. An, Mechanical behavior of the foot and ankle after plantar

fascia release in the unstable foot, Foot Ankle Int. 18 (1997) 8–15.

[18] G.A. Arangio, C. Chen, W. Kim, Effect of cutting the plantar fascia on mechanical

properties of the foot, Clin. Orthop. Relat. Res. (1997) 227–231.

[19] I.S. Davis, R. Ferber, J. Hamill, C. Pollard, Rearfoot mechanics in competitive runners

who had experienced plantar fasciitis, in: Proc. 29th Annu. Meet. Int. Soc. Biomech.,

2003.

[20] B.L. Warren, C.J. Jones, Predicting plantar fasciitis in runners, Med. Sci. Sports Exerc. 19

(1987) 71–73.

[21] J.E. Taunton, M.B. Ryan, D.B. Clement, D.C. McKenzie, D.R. Lloyd-Smith, Plantar

fasciitis: A retrospective analysis of 267 cases, Phys. Ther. Sport. 3 (2002) 57–65.

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CHAPTER 2. LITERATURE REVIEW

Anatomy of the Plantar Fascia

The plantar fascia is a large fibrous band that extends from the plantar aspect of the

calcaneus to the proximal phalanges of the five digits. The anatomy of the plantar fascia has been

well-defined in the literature [1–4]. It is divided into three components: the medial, lateral, and

central components. The medial component is very thin and acts as the fascial covering of the

abductor hallucis muscle. The lateral component originates on the lateral margin of the medial

calcaneal tubercle. It extends towards the cuboid bone, where it bifurcates into two portions. The

medial portion inserts into the base of the fifth metatarsal and the lateral portion blends into the

fascia of the abductor digiti minimi. The central component is the largest portion of the plantar

fascia, and it is considered to be the most structurally and functionally important of the three

components. It originates on the medial calcaneal tubercle on the plantar aspect of the foot.

Approximately 1.5 to 2 cm wide at its origin, the central component of the plantar fascia fans out

as it extends distally, forming five distinct slips. Each slip consists of a deep component, which

crosses the metatarsophalangeal (MTP) joint to attach to the proximal phalanx, and a superficial

component, which anchors into the subcutaneous tissues and skin. Furthermore, at the level of

the MTP joint, the superficial component of the most medial slip of the central component inserts

into the sesamoid bones before anchoring to the skin.

Functions of the Plantar Fascia

The plantar fascia plays a significant role in the foot by providing support to the

longitudinal arch during static weight bearing and foot flat phases of stance during gait [5].

During these periods, the medial longitudinal arch has been compared to a truss, with the

calcaneus, midtarsal joint, and metatarsals acting as the arch and the plantar fascia acting as the

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tie-bar connecting the ends of the arch [6]. Under weight-bearing, the arch structure is

maintained due to tension placed on the plantar fascia [1,7]. The arch support function of the

plantar fascia has been documented in several cadaveric studies that investigated the effects of

plantar fascial release on arch structure [8,9]. Kitaoka, Luo, and An [9] reported an average arch

height decrease of 7.4 ± 4.1mm following plantar fascial release, while Murphy et al. [8]

reported a drop of 4.05 ± 1.73mm after release. A biomechanical model created to estimate the

effects of plantar fascia release on arch height found similar results. The model estimated a 17%

increase in total vertical displacement and a 15% increase in horizontal elongation of the arch

following plantar fascia release when the foot was placed under a constant load of 683N [10]. In

addition to the arch collapse that occurs in the sagittal plane, plantar fascia release also causes

alterations in the frontal and transverse plane. A finite element model that simulated release of

the plantar fascia found an increase in the talocalcaneal angle, which can be used as a measure of

foot pronation [11]. Pronation is a tri-planar motion consisting of a combination of dorsiflexion,

eversion, and abduction, and excessive pronation is often associated with an increased risk for

injury [12–14]. The results of the aforementioned finite element study [11] suggest that an

additional function of the plantar fascia is to prevent excessive pronation. The depiction of the

medial longitudinal arch as a truss is further supported by a study conducted by Kogler,

Solomonidis, and Paul [15], who found an increase in plantar fascia strain when an axial load

was placed on the tibia of seven cadaver feet. In addition to the longitudinal support provided by

the plantar fascia, significant transverse metatarsal head splaying in cadaver feet following

plantar fascial release suggests that the plantar fascia may also serve to provide support to the

transverse arch of the forefoot [16,17].

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The plantar fascia also plays an essential dynamic role during gait. Dorsiflexion of the

MTP joint activates the windlass mechanism of the plantar fascia [18–20]. When the toes are

dorsiflexed, the plantar fascia winds around the metatarsal heads. This increases the tension in

the plantar fascia and shortens the distance between the calcaneus and metatarsals, which causes

the arch to raise. The first digital slip produces the greatest amount of tension in the plantar

fascia due to the relatively large size of the first metatarsal head, as well as the presence of the

two sesamoid bones [21–23]. The windlass mechanism of the plantar fascia has been

demonstrated in a cadaveric study, where the arch height was raised following toe dorsiflexion

[5]. Furthermore, following plantar fascial release, the ability of toe dorsiflexion to increase arch

height is significantly attenuated [24] and the total toe dorsiflexion range of motion is increased

[25]. In a closed-chain environment, such as the propulsive phase during gait, the windlass

mechanism also produces rearfoot supination and tibial external rotation in addition to raising the

arch [18,26]. The windlass mechanism is also believed to increase the stability of the medial

longitudinal arch, as a study investigating first ray deformities found that the functional stability

of the arch was restored with correction of the deformity [27].

Plantar Fascia Loading

The load applied to the plantar fascia and corresponding strain values during both static

weight bearing and dynamic gait has been measured by several researchers. One of the first

studies to measure the peak strain on the plantar fascia measured plantar fascia load and strain in

tissue samples tested using a dynamometer. Wright and Rennels [28] found that the plantar

fascia could withstand a load between 890-1001N before failure, which was between 4-5%

strain. However, the authors conceded that the static measurements they collected in their study

could not be applied to dynamic conditions. Furthermore, failure of the tissue samples occurred

at the edges of the testing machine, so the authors did not consider their results to be true failure

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of the plantar fascia. A later study did measure higher loads of the plantar fascia before failure

[29]. The authors reported failure loads of 1189N, and it was noted that the majority of ruptures

occurred near the attachment of the plantar fascia on the medial calcaneal tubercle. Although the

plantar fascia was not loaded to failure in the study conducted by Kogler, Solomonidis, and Paul

[15], the authors reported strain values that were similar to Wright and Rennels [28] when they

measured plantar fascia strain relative to a given applied load in cadaver feet using a transducer

implanted directly into the plantar fascia. In contrast to these results, a later study by Gefen [30]

found significantly higher strain values relative to an applied load when radiographic

fluoroscopy was used to measure plantar fascia strain during walking. The author reported peak

fascial loads of approximately 1000N during walking with corresponding strain values between

9-12%. However, it is important to note that the study utilized a passive model of the foot and

ignored the intrinsic and extrinsic muscle contributions to loadbearing, which likely resulted in

an overestimation of strain values. Furthermore, the study only included the results of two

subjects. A methodologically similar study [31] reported an average peak fascial load of 488N

and an average peak strain of 4.8% when they used fluoroscopy to measure plantar fascia strains

during walking in eleven participants. The results of a gait simulation study using cadaver feet

also reported plantar fascia load values that were lower than the results from Gefen [30,32]. By

applying forces on the tendons of the extrinsic foot muscles to simulate the muscle action during

gait, the peak load applied to the plantar fascia during stance phase was significantly lower and

was approximately equal to bodyweight loads (538N) [32]. Finally, a study that utilized a rigid

body model to measure plantar fascia strain during walking found strain values that ranged

between 3.5-6% [22].

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An important factor that influences the load placed on the plantar fascia is the amount of

tension placed on the Achilles tendon. A tensile load placed on the Achilles tendon in a closed-

chain environment acts to produce calcaneal plantarflexion, which subsequently causes collapse

of the arch and an increased load placed on the plantar fascia. A cadaver study that investigated

the relationship between Achilles tendon tension, MTP dorsiflexion angle, and plantar fascia

strain found that dorsiflexion of the toes places more tension on the plantar fascia, which

increases the effect that a tensile force on the Achilles tendon has on plantar fascia strain [33]. In

other words, both an increase in MTP joint dorsiflexion and an increase in Achilles tendon

tension increases the strain on the plantar fascia. The same relationship between Achilles tendon

tension and plantar fascia strain has been reported using a gait simulator [32] and finite element

models of the foot [21,34]. Furthermore, a musculoskeletal model that considered both arch

collapse and MTP joint motion to estimate plantar fascia strain found that individuals running

barefoot demonstrated an average peak strain of 2.1% [35]. Interestingly, the authors also found

that the amount of total plantar fascia strain due to arch collapse was 2.0%, while the amount of

plantar fascia strain due to MTP joint dorsiflexion was 0.3%. The authors attributed their

relatively low strain values to their estimation of the plantar fascia resting length. While the exact

strain values may not be accurate, the results of the study helped to describe the relationship

between arch collapse, MTP joint motion, and plantar fascia strain, which exists regardless of the

specific strain values.

Anatomy and Functions of Other Ligaments of the Foot

As already mentioned, one of the functions of the plantar fascia is to provide structural

support to the medial longitudinal arch. However, the plantar fascia is not the only tissue that

helps to maintain the structural integrity of the arch [36–39]. There are many ligaments that

provide support to the arch and help to control excessive pronation. While considered passive

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tissues, ligaments can help to resist tensile forces that develop when a joint moves beyond its

normal range of motion [40]. Ligaments that help to support the arch and control excessive

pronation include the long and short plantar ligaments, the spring ligament, the cervical ligament,

the bifurcate ligament, and the deltoid ligament, among others.

Collapse of the medial longitudinal arch is believed to include all three planes of motion

[11]. This is supported by the results of a cadaver study by Kitaoka, Luo, and An [9]. The

authors found that sectioning the plantar fascia, long and short plantar ligaments, spring

ligament, and several other ligaments to induce an unstable foot affected joint rotations of the

foot. Importantly, there were kinematic effects in all three planes of motion, suggesting that these

structures may help to prevent excessive pronation. Furthermore, the process involves both the

subtalar joint, which is the articulation of the talus and calcaneus, and the talonavicular joint.

Therefore, ligaments that cross the subtalar and talonavicular joints, such as the spring ligament,

the cervical ligament, and the bifurcate ligament, are believed to provide structural integrity to

the medial longitudinal arch. The spring ligament is composed of two components. The

superomedial component originates along the anteromedial border of the sustentaculum tali on

the calcaneus. It courses anteriorly and superiorly to attach to the middle of the navicular [41,42].

The inferior component also originates on the sustentaculum tali, but it courses anteriorly to

attach to the inferior surface of the navicular [41,42]. The cervical ligament is the strongest

ligament to connect the talus and calcaneus bones. It originates on the anteromedial segment of

the sinus tarsi and courses anteriorly and medially to attach to the inferior aspect of the talar neck

[41]. The bifurcate ligament has two components, the lateral calcaneonavicular component and

the medial calcaneocuboid component. The calcaneonavicular component originates on the

anteromedial corner of the sinus tarsi, and the calcaneocuboid component origin is slightly

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lateral. The calcaneonavicular courses anteriorly, superiorly, and medially to attach to the lateral

navicular, while the calcaneocuboid courses anteriorly and inferiorly to attach to the dorsal

cuboid [41].

The involvement of the spring ligament in arch stability is supported by the results of

Cifuentes-De la Portilla, larrainzar-Garijo, and Bayod [11], who reported that the release of the

spring ligament increased arch collapse by 14.9% and increased the talocalcaneal angle by

53.3% in a finite element model of the foot. While no research has been conducted to investigate

the role of the cervical ligament or bifurcate ligament to control excessive pronation and

maintain arch stability, anatomical descriptions of the ligaments suggest that they may be

involved. Because subtalar joint motion is directly linked to pronation, the cervical ligament,

which crosses the subtalar joint, may help to prevent excessive pronation. Furthermore, the

bifurcate ligament crosses the subtalar and talonavicular joints, which suggests it may also help

to provide stability and support to the arch.

The long and short plantar ligaments, while not strong enough to support the arch on their

own, do provide secondary support to help maintain arch height [11]. The long plantar ligament

originates on the plantar calcaneus and divides into two components as it crosses the

calcaneocuboid joint. The deep component inserts on the cuboid, while the superficial

component splits into four slips and attaches to the 2nd, 3rd, 4th, and 5th metatarsal bases [41]. The

short plantar ligament originates on the anterior tuberosity of the calcaneus and fans out until it

attaches on the cuboid [41]. The contribution of both the long and short plantar ligaments to arch

support is highlighted by the effects of plantar fascia release. Using a finite element model, Tao

et al. [37] found that release of the plantar fascia resulted in an increase in tension of the long and

short plantar ligaments by 91% and 65%, respectively.

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The involvement of the long plantar ligament, short plantar ligament, and spring ligament

in arch stability is supported by a report from Ker et al [38], who quantified the amount of elastic

energy stored in the medial longitudinal arch as 17J. Further results in the study found that while

the stored elastic energy was reduced after sectioning of the plantar fascia, the arch continued to

store 13.3J due to the contributions of surrounding soft tissues. The authors listed the long

plantar ligament, short plantar ligament, and spring ligament as important in the maintenance of

the integrity of the arch. Another study measured the stiffness of the arch, and found that

sectioning of the plantar fascia decreased the stiffness by 25%, while sectioning the long and

short plantar ligaments and the spring ligament decreased the arch stiffness by 10% and 2%,

respectively [39]. Finally, sectioning of the plantar fascia has been demonstrated to increase

strains in the spring ligament and long plantar ligament. Under an axial load of 920N, the spring

ligament strain increased by 52% and the long plantar ligament strain increased by 94%

following plantar fascia release [43].

The anatomy of the deltoid ligament is complex and can be difficult to separate into

distinct components. It originates on the medial malleolus and fans out to attach to the navicular,

talus, and calcaneus bones. Its fan-like behavior and numerous attachments result in components

that course anteriorly, inferiorly, and posteriorly [41,44]. Consequently, the deltoid ligament

helps to stabilize the talus on the medial side of the foot [41]. The results of a study examining

the effects of dorsiflexion, plantarflexion, eversion, and inversion on ligament elongation support

the deltoid ligament’s role to provide stability to the foot and ankle [44]. The authors found that

the tibiotalar and tibiocalcaneal components of the deltoid demonstrated elongation under both

dorsiflexion and eversion, while the tibionavicular component of the deltoid demonstrated

elongation following ankle eversion [44]. A large portion of the eversion and dorsiflexion motion

14

in the study came from the ankle joint, but both the subtalar and talonavicular joints provided

additional motion as well. The elongation of the deltoid ligament due to dorsiflexion and

eversion suggests its involvement in preventing excessive pronation of the foot.

Research related to adult acquired flatfoot disorder can provide insight into the role of

ligaments in arch stability. Adult acquired flatfoot disorder is a disorder that results in functional

loss of the posterior tibial tendon. Because the disorder reduces the action of the posterior tibial

tendon as an invertor, the action of the peroneus brevis, its antagonist, is unopposed, which

increases rearfoot eversion and forefoot abduction [45]. Consequently, excessive stress is placed

on secondary ligaments and other soft tissues of the medial foot to oppose the rearfoot eversion

action of the peroneus brevis [46]. By comparing ligament degeneration using MRI between

individuals with adult acquired flatfoot disorder and controls, researchers found that the

superomedial component of the spring ligament demonstrated the most damage, suggesting it

plays a significant role in arch stability [46]. Furthermore, the inferior component of the spring

ligament and the tibionavicular component of the deltoid both showed degeneration as well,

suggesting that they also help control excessive pronation and provide stability to the arch.

Another study using MRI for diagnosis of adult acquired flatfoot disorder found a greater amount

of spring ligament injuries in the adult acquired flatfoot disorder group when compared to the

control group [47].

Pathogenesis of Plantar Fasciitis

Plantar fasciitis is estimated to affect two million people in the United States each year

[48], and up to 10% of the population will deal with the disorder at some point in their lives [49].

Planter fasciitis is defined by pain in the heel that is often localized at the insertion of the plantar

fascia on the medial calcaneal tubercle on the plantar aspect of the foot. It is frequently

associated with first step pain that lessens or resolves as the individual warms up. In more severe

15

cases, the pain may increase following prolonged standing or high levels of activity throughout

the day [50]. Several changes in the properties of the plantar fascia have been reported in

individuals with plantar fasciitis. An examination of 13 feet with plantar fasciitis and 40 healthy

feet using sonoelastography showed that individuals with plantar fasciitis exhibited plantar fascia

that were softer and less stiff than the age-matched individuals in the healthy group [51]. This is

notable as reduced elasticity in the plantar fascia makes it less resistant to strain, which may

increase the risk for injury [52]. Another effect of plantar fasciitis is a significant increase in

plantar fascia thickness near its insertion into the calcaneus [53–56]. For example, Gibbon and

Long [54] used high-resolution ultrasound to measure plantar fascia thickness in 48 healthy

volunteers and 190 patients with plantar fasciitis, and they found that the individuals with plantar

fasciitis displayed significant thickening of the plantar fascia. The authors noted the similarity in

the response at the plantar fascia to tendon injury, which results in thickening of the tendon due

to an inflammatory response. Plantar fasciitis is traditionally believed to be an inflammatory

disease, which is implied by the “-itis” suffix. The inflammation of the plantar fascia is believed

to occur due to excessive or repetitive tensile force applied to the tissue that produces

microscopic tears within the fascia, which subsequently leads to an inflammatory response

[24,49,57–59].

However, several authors have questioned the role of inflammation in the pathogenesis of

plantar fasciitis [4,60]. According to Lemont, Ammirati, and Usen [60], in addition to the

classical signs of inflammation of pain, heat, swelling, redness, and loss of function, histological

signs of inflammation, such as the presence of leukocytes, macrophages, lymphocytes and

plasma cells, should also be present. While the authors found several signs of fiber fragmentation

and degeneration in the plantar fascia of 50 individuals with chronic plantar fasciitis, they found

16

no histological signs of inflammation. Similar findings were reported by Tountas and Fornasier

[61] who analyzed 20 patients with subcalcaneal pain. Varying degrees of fascial degeneration

was found in the patients, but no signs of active inflammation were present. Consequently, this

has led some to theorize that plantar fasciitis does not result in an inflammatory response, but is

instead caused by degeneration of the fascia due to repetitive microtears that cannot be overcome

by the body’s ability to repair itself [4,50].

Etiology of Plantar Fasciitis

Despite uncertainty regarding the pathogenesis of plantar fasciitis, it is largely agreed that

the cause of plantar fasciitis is multifactorial in nature and includes anatomical, biomechanical,

and environmental factors. Several of the potential anatomical and biomechanical factors are

described below. However, environmental factors are beyond the scope of this literature review

and therefore will not be discussed.

Foot Structure

Foot structure has been theorized to contribute to plantar fasciitis risk [57,62,63]. A pes

planus foot structure is defined as a flat foot position. Consequently, a pes planus foot structure is

typically associated with excessive pronation generally defined by a collapsed arch and an

everted rearfoot position during static stance. Due to the pronated position associated with pes

planus, it is often cited as a risk factor for plantar fasciitis [57,63,64]. In 1987, Sarrafian [1]

discovered an increase in plantar fascial tension when the hindfoot and midfoot were in pronated

positions and the forefoot was in a supinated position. In this flat foot position, the medial

longitudinal arch of the foot is lower and the foot is longer. Therefore, it was concluded that a

foot in this position could place an increased tensile load on the plantar fascia, thereby increasing

the risk for microdamage and subsequent development of plantar fasciitis [57,65,66]. A study

conducted by Prichasuk and Subhadrabandhu [67] supported this conclusion, as they reported

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that 82 patients with plantar heel pain had a lower calcaneal pitch than 400 healthy subjects in

the control group. Huang et al. [66] also discovered a higher risk for plantar fasciitis in

individuals with flat feet. They found that ten out of the 23 individuals with flat feet in their

study had plantar fasciitis, while only two out of the 23 individuals with normal arched feet had

plantar fasciitis.

Alternatively, a pes cavus foot has also been theorized to place an individual at a greater

risk for the development of plantar fasciitis [57,63]. According to Krivickas [68], a cavus foot is

rigid and lacks the ability to absorb forces, which increases the amount of stress placed on the

plantar fascia. In fact, a study conducted by Di Caprio et al. [69] found that 57.1% of the patients

with plantar fasciitis had pes cavus feet, compared to 16.7% with pes planus feet and 23.2% with

normal arches. Similar results were reported by Warren and Jones [14], who found that the

participant group with current symptoms of plantar fasciitis had higher arches than both the

participant group with resolved plantar fasciitis and the healthy control group. However, the

authors did not provide any quantitative results in their study.

Despite the studies described above, results regarding the relationship between foot

structure and plantar fasciitis have overall been inconclusive. Several studies have reported no

significant differences in arch height between individuals with plantar fasciitis and healthy

individuals [65,70,71]. The complicated relationship between foot structure and plantar fasciitis

is further elucidated by the results of Taunton et al. [13]. The authors found that of the 267

individuals with plantar fasciitis who participated in the study, only 20 had pes planus and 27

had pes cavus, which only accounts for 7.5% and 10.1% of the study population, respectively.

The results of the preceding studies highlight the multifactorial nature of plantar fasciitis. Foot

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structure appears to play a role in the development of plantar fasciitis in some, but not all,

individuals.

In addition to the studies above that measured arch height, rearfoot eversion during static

stance can also be used as a measure of foot structure as it is an indirect measure of foot

pronation. A greater rearfoot eversion position during stance has been reported in individuals

with plantar fasciitis [14,72], which suggests a more pronated position and therefore a pes planus

foot. The results reported by Davis, Milner, and Hamill [72] support this relationship, as

individuals with plantar fasciitis in their study displayed a lower arch height in addition to

greater rearfoot eversion during static stance when compared to the healthy control group.

Rearfoot eversion also appears to have an indirect effect on plantar fascia tension. In a recent

study, Lee, Hertel, and Lee [73] reported that rearfoot eversion influences the amount of arch

collapse that occurs during gait, which consequently increases tension in the plantar fascia.

However, individuals with plantar fasciitis in the study conducted by Warren and Jones [14] had

higher arches than the control group even though they displayed a more everted rearfoot during

static stance, which suggests the relationship between arch height and rearfoot eversion is

complicated. Furthermore, studies by Allen and Gross [74] and Ribeiro et al. [75] reported no

differences in rearfoot eversion position during static stance between individuals with plantar

fasciitis and healthy individuals.

1st MTP Joint Range of Motion

Because the plantar fascia crosses the MTP joint to attach to the proximal phalanges, the

relationship between first MTP joint range of motion and plantar fasciitis has been investigated.

Creighton and Olson [76] discovered a decrease in passive extension range of motion of the first

MTP joint in runners with plantar fasciitis compared to runners without plantar fasciitis. Aranda

and Munuera [77] reported similar results in 50 individuals with plantar fasciitis when compared

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to 50 matched control individuals. These results suggest that the plantar fascia exhibits reduced

extensibility when an individual has plantar fasciitis. Alternatively, the reduced extensibility may

precede the pathology and contribute to the development of plantar fasciitis. In contrast to the

results of Creighton and Olson [76], Allen and Gross [74] reported no differences in passive

extension range of motion of the first MTP joint between individuals with plantar fasciitis and

healthy controls.

Posterior Leg Muscle Tightness and Ankle Dorsiflexion Range of Motion

Tightness of the gastro-soleus complex increases the tension on the plantar fascia

[33,34,78]. This tightness causes a reduction in ankle dorsiflexion range of motion, which has

been cited as a risk factor for plantar fasciitis [71,72,79,80]. Clinical assessment of 254 patients

with plantar fasciitis revealed that 83% demonstrated limited ankle dorsiflexion range of motion,

26% of which were due to tightness of the gastro-soleus complex and 57% of which were due to

isolated tightness of the gastrocnemius [81]. Slightly lower but similar statistics have been

reported in other studies as well [13,82]. Furthermore, it has been found that individuals with less

than 0° of ankle dorsiflexion range of motion had an odds ratio of 23.3 when compared to

individuals with greater than 10° of dorsiflexion range of motion. Furthermore, a dorsiflexion

range of motion between 1-5° and a dorsiflexion range of motion between 6-10° resulted in odds

ratios of 8.2 and 2.9, respectively, when compared to a dorsiflexion range of motion greater than

10° [80]. These results suggest that the risk for plantar fasciitis is greatly increased as the ankle

dorsiflexion range of motion is decreased due to tightness of the gastrocnemius or gastro-soleus

complex. This is supported by the results of several studies that found a reduction of passive

ankle dorsiflexion range of motion in individuals with plantar fasciitis when compared to

individuals without plantar fasciitis [14,71,72,79]. Cornwall and McPoil [83] suggest that a

limitation in ankle dorsiflexion range of motion leads to equinus of the foot. Foot equinus results

20

in premature heel rise during gait, which can lead to abnormal pronation and subsequent

increased stress placed on the plantar fascia.

Hamstring tightness has been proposed to increase tension on the plantar fascia and

therefore increase the risk for plantar fasciitis [84,85]. It is thought that increased hamstring

tightness causes early contraction of the posterior leg muscles during the gait cycle, which

decreases ankle dorsiflexion during gait [84,86]. Harty et al [84] investigated the relationship

between hamstring tightness and plantar fasciitis risk when they compared static knee extension

flexibility between individuals with plantar fasciitis and healthy individuals. They reported a

decreased knee extension angle in the plantar fasciitis group and suggested that the increased

knee flexion may produce a forward shift in plantar foot pressures during walking, which places

increased tension on the plantar fascia. Their conclusion was further supported when they placed

healthy individuals into knee braces to limit knee extension range of motion and found that the

healthy individuals demonstrated a forward shift in plantar foot pressures as their knee extension

range of motion decreased during walking. The possible role of hamstring tightness on plantar

fasciitis was reinforced by Labovitz, Yu, and Kim [85], who revealed that 62.0% of feet with

plantar fasciitis displayed hamstring tightness on the pathological side, while only 20.6% of feet

without plantar fasciitis displayed the same muscle tightness.

Excessive Pronation

Much of the research on foot kinematics and plantar fasciitis has focused on the role of

pronation, which has often been attributed as a risk factor for plantar fasciitis [12–14]. In support

of this, 54.7% of patients with plantar fasciitis exhibited excessive pronation according to a study

conducted on 267 individuals [13]. However, it is important to note that this assessment was

performed visually. Davis et al. [12] used rearfoot eversion as a measure of pronation and found

21

that runners with plantar fasciitis exhibited significantly greater maximum rearfoot eversion

during running when compared to healthy controls.

A relationship between excessive pronation and plantar fasciitis has not always been

found, leading some to question the role of pronation in the development of plantar fasciitis

[4,70,87,88]. Again using rearfoot eversion as a measure of pronation, Davis et al. [72]

conducted a prospective study in female runners and found that females who developed plantar

fasciitis displayed no difference in peak rearfoot eversion from females who stayed healthy over

the course of the study. A study conducted by Wearing et al. [55] that used arch height as a

measure of pronation also reported no differences in maximum arch angle or range of arch

motion between a group of individuals with plantar fasciitis and a healthy control group. While

the two-dimensional nature of the study by Wearing et al. [55] is a limitation, a more

comprehensive study utilizing a multi-segment foot model to compare the foot kinematics

between individuals with plantar fasciitis and healthy individuals also found no differences in

maximum arch angle or maximum rearfoot eversion between the groups [89]. The authors did

report significantly greater total rearfoot motion in the plantar fasciitis group than the control

group, as well as greater rearfoot eversion maximum velocity in the plantar fasciitis group that

trended towards significance [89], which suggests that a relationship between pronation and

plantar fasciitis may exist, albeit a more complicated relationship. Furthermore,

Bovonsunthonchai et al. [90] reported reduced peak forefoot-rearfoot dorsiflexion angles in

individuals with plantar fasciitis compared to healthy individuals, which means that the

individuals with plantar fasciitis displayed higher arch heights. Although the study by Chang et

al. [89] reported peak forefoot-rearfoot dorsiflexion angles to be the same between individuals

with plantar fasciitis and individuals without, they did note a greater forefoot-rearfoot

22

plantarflexion angle at initial contact in individuals with plantar fasciitis. The alterations in

forefoot-rearfoot angle may serve as a protective measure to reduce the stress placed on the

plantar fascia, as a flatter arch increases the tensile load on the plantar fascia [1].

Other Kinematic Factors

While not studied as extensively as pronation, several other lower extremity kinematic

differences have been noted between healthy individuals and individuals with plantar fasciitis.

One such measure that has been reported is peak 1st MTP dorsiflexion angle, which has been

found to be greater in individuals with plantar fasciitis compared to healthy controls during

walking [55,89]. In contrast to these results, Bauer [65] reported no differences in 1st MTP joint

range of motion between plantar fasciitis patients and healthy controls during running. It has

been established that increasing toe dorsiflexion produces a direct rise in plantar fascia tension

[21,33,91]. Therefore, an increase in peak 1st MTP dorsiflexion angle during walking may

contribute to an increased risk for plantar fasciitis. Other kinematic differences reported in the

literature include increased calcaneocuboid eversion range of motion in individuals with plantar

fasciitis [65], reduced peak forefoot inversion in individuals with plantar fasciitis [90], and

reduced total rearfoot frontal plane motion in individuals with plantar fasciitis [90].

Multi-segment foot models

Conventional gait analysis utilizes models that represent the human body as a system of

rigid segments. The simplest way to represent the foot is as a single rigid segment, in which

motion of the rearfoot is measured relative to the tibia. However, research has demonstrated both

kinematic and kinetic errors associated with single-segment models [92,93]. For example,

significant differences in sagittal and frontal plane angles were reported at the ankle joint when

comparing a single-segment model to a multi-segment model in children with flat feet [93].

23

The discovery of these errors has motivated researchers to create more sophisticated

models to better represent motion of the foot. One common model used is the Milwaukee Foot

Model, a three-segment model that divides the foot into rearfoot, forefoot, and hallux segments

[94–96]. The three-segment model allows for measurement of midtarsal joint motion, as well as

first MTP joint motion. A four-segment foot model proposed by Leardini et al. [97] further

divides the medial column of the foot by separating the foot into rearfoot, midfoot, forefoot, and

hallux segments. Such a configuration allows further quantitative assessment of structural

deformities in the medial column of the foot as well as kinematics during dynamic activities,

which is particularly important when analyzing populations with midfoot deformation or

dysfunction.

Previous research has reported considerable relative motion to occur between the

metatarsals during walking [98], which suggests that modelling the forefoot as a single rigid

segment may not be appropriate. To address this issue, the Jenkyn model is a four-segment foot

model that divides the foot into hindfoot, midfoot, medial forefoot, and lateral forefoot segments

[99]. The Ghent foot model is similar to the Jenkyn model, but it is a five-segment model that

also includes the hallux segment to allow for first MTP joint measurement. The KU-Leuven foot

model is an alternative five-segment model that includes the calcaneus, talus, midfoot, forefoot,

and toes [100]. Significant motion in the lateral column of the foot has been reported in the

literature [98,101]. Consequently, a six-segment model has been utilized by some researchers,

which includes the rearfoot, medial midfoot, lateral midfoot, medial forefoot, lateral forefoot,

and hallux [65,102]. The number of segments and the desired complexity of the foot model is

dependent upon the research question. Ultimately, the researcher should choose a model that is

24

sophisticated enough to answer the research question while still producing quality data based on

the technical capabilities of the research equipment.

Treatment of Plantar Fasciitis

There are several conservative treatment options for plantar fasciitis, including rest,

physical therapy, night splints, anti-inflammatory methods, pain reduction methods, and

mechanical methods [50,103]. Treatment using anti-inflammatory methods may consist of

NSAIDs or steroid injections [104,105], while pain reduction methods may consist of analgesics

or accommodative foot pads [106]. Mechanical treatment methods may consist of custom

orthotics, over the counter shoe inserts, or night splints [107]. Orthotics are proposed to reduce

the symptoms of plantar fasciitis. This is possibly due to the orthotic helping to maintain medial

longitudinal arch height [108], as plantar fascia strain has been found to be the lowest when

wearing orthotics that maintain medial longitudinal arch height [15].

Low-Dye Taping Technique & Variations

An alternative mechanical treatment option is taping. While it is often used as a way to

determine the potential success of custom orthotics [109,110], taping has also been used as a

treatment method [59,111]. The low-Dye taping method was designed to control excessive foot

pronation by preventing medial longitudinal arch collapse [112]. It consists of an anchor strip of

tape that originates on the lateral aspect of the fifth metatarsal head, wraps behind the calcaneus,

and attaches on the medial aspect of the first metatarsal head. Then, a series of stirrups are

applied on the plantar aspect of the foot, originating on the lateral side of the foot and attaching

to the medial side. Some tension is applied to the tape during the application of the stirrups to

oppose pronation. The stirrups begin below the medial longitudinal arch and are applied on the

plantar aspect of the foot in a proximal direction until the plantar calcaneus is covered.

25

Several authors have modified the low-Dye taping method. For example, Schulthies and

Draper [113] included figure-eight strips along with the low-Dye method described above, which

they did to allow the subtalar joint to remain in a neutral position. Following the application of

the anchor strip, a strip of tape is applied which originates at the first metatarsal head, crosses the

plantar foot, wraps behind the calcaneus, and attaches back on the first metatarsal head. Saxelby,

Betts, and Bygrave [111] utilized a similar method, but the figure-eight strips originated at the

first metatarsal head, crossed the plantar foot, wrapped behind the calcaneus, and then crossed

the plantar foot again to attach on the fifth metatarsal head. Finally, the augmented low-Dye

taping method was described by Vicenzino et al. [114]. In addition to the low-Dye technique, the

authors also include two calcaneal slings and three reverse sixes. The calcaneal slings originate

on the anterior tibia, run distally towards the medial malleolus and under the midfoot, then wraps

around the calcaneus until it attaches back on its origin. The reverse sixes originate at the medial

malleolus, run around the dorsum and under the midfoot, and then run vertically to cross the

origin and then attach on the medial tibia.

Pain Reduction Following Low-Dye Taping

Many studies have demonstrated the ability of low-Dye taping to reduce pain and

improve function in plantar fasciitis patients [103,115–117]. For example, Landorf et al. [116]

found that individuals with plantar fasciitis who received low-Dye taping for three to five days

saw a significant reduction in pain when compared to a control group who did not receive taping.

There are several proposed reasons for this, including altered plantar pressures [111,118–121],

altered surrounding muscular activity [121–123], altered posture, or altered kinematics. In

general, research has found an increase of plantar pressure under the lateral midfoot and a

decrease in plantar pressure under the medial midfoot [118,119,121]. The changes in plantar

pressure under the midfoot may be accompanied by changes under the rearfoot and forefoot as

26

well [111,118,120], but these findings have been inconsistent. Few studies have investigated the

effect of low-Dye taping on muscle activation during walking, although decreases in posterior

tibialis [122–124], anterior tibialis [122–124], peroneus longus [122], and medial gastrocnemius

[124] muscle activations have been reported in healthy individuals following low-dye taping.

Postural Effects of Low-Dye Taping

The postural effects of low-Dye taping have been investigated in greater detail. More

specifically, the effects of taping on navicular height [114,123,125–132] and rearfoot eversion

[125,129,133] during static stance have been measured. Holmes, Wilcox, and Fletcher [128]

investigated the effects of the low-Dye taping method described by Schulthies and Draper [113]

on navicular height in 40 healthy subjects with flat feet. They found that after taping, the

navicular height during neutral loaded standing was not significantly different from the navicular

height when the foot was placed in the unloaded subtalar neutral position. In contrast, Vicenzino

et al. [132] reported a significant increase in medial longitudinal arch height in 18 healthy

individuals following application of augmented low-Dye tape. Harradine, Herrington, and

Wright [133] utilized the Saxelby et al. [111] low-Dye taping method when they analyzed the

effects of taping on rearfoot eversion in 22 healthy participants. They reported a static rearfoot

angle that was significantly less everted following low-Dye taping.

The majority of the studies related to the postural effects of low-Dye taping have been

conducted on healthy individuals. However, Jamali et al. [125] investigated the effects of

windlass taping on 20 individuals with plantar fasciitis. The windlass taping method utilizes the

figure-eight strips that Schulthies and Draper [113] described, but it does not include the stirrups

along the plantar foot that is characteristic of low-Dye taping. Regardless, they found a small but

significant increase in navicular height, as well as a reduction of rearfoot eversion, in the taping

condition when compared to the barefoot condition. One study investigated the effects of the

27

augmented low-Dye taping method on tibial rotation and found a significant reduction in tibial

internal rotation following taping [134].

Exercise Effects on Tape

The effects of low-Dye taping methods on foot posture following exercise have been

detailed as well. Despite an immediate increase in navicular height and reduction of rearfoot

eversion following taping, exercise results in a reduction of these effects, which has been

attributed to a loss of tensile strength of the tape due to exercise [127]. For example, after 30

minutes of walking, Harradine et al. [133] found that that there was no significant difference of

the rearfoot eversion angle between the taped condition and the barefoot condition, which

indicates a loss of tensile strength of the tape. Holmes et al. [128] also reported a significant

reduction of navicular height after 10 minutes of walking with a taped foot. However, they found

that the navicular height after 10 minutes of walking during the taped condition was still

significantly higher than the navicular height during the barefoot condition, which suggests that

taping can still provide support, even after it has lost some of its tensile strength due to exercise.

Ator et al. [127] suggested that low-Dye taping may remain effective following exercise due to

its ability to prevent pronation at the extreme ranges of motion. Vicenzino et al. [130] provided

further support to the benefits of taping even after exercise when they included a control group in

their study. When analyzing the effects of the augmented low-Dye tape method, the authors

reported a significant decrease in navicular height following 10 minutes of exercise. Importantly,

they also reported a significant decrease in navicular height following 10 minutes of exercise in

the control group. Consequently, the navicular height between the taped group and the control

group was significantly different following exercise, which suggests the tape was able to

successfully maintain the navicular height despite losing some of its strength.

28

Kinematic Effects of Low-Dye Taping

Dynamic kinematics are also affected by low-Dye taping methods. O’Sullivan et al. [135]

found a significant reduction of subtalar joint pronation during walking as a result of low-Dye

taping. Vicenzino et al. [131] and Yoho et al. [136] also both reported significant increases in

arch height during walking following low dye taping methods when compared to a barefoot

condition. However, several studies have reported no kinematic effects of low-Dye taping on

rearfoot motion during walking [133,137] and running [138]. Keenan and Tanner [137] noted

that the low-Dye taping method increased the maximum inversion angle of the rearfoot but had

no effect on the maximum eversion angle. It is clear that more research needs to be conducted on

the effects of low-Dye taping on foot kinematics using a multi-segment foot model.

References

[1] S.K. Sarrafian, Functional characteristics of the foot and plantar aponeurosis under

tibiotalar loading, Foot Ankle. 8 (1987) 4–18.

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[138] C.L. Moss, B. Gorton, S. Deters, A comparison of prescribed rigid orthotic devices and

athletic taping support used to modify pronation in runners, J. Sport Rehabil. 2 (1993)

179–188.

39

CHAPTER 3. EFFECTS OF SPEED, INCLINE, AND SHOE STIFFNESS ON PEAK

PLANTAR FASCIA STRAIN DURING WALKING

Jeff H. Mettlera, Erin Wardb, Timothy R. Derricka

a Department of Kinesiology, Iowa State University, 534 Wallace Rd, Ames, Iowa, 50011,

United States b Central Iowa Foot Clinic, 1302 Warford St, Perry, Iowa, 50220, United States

Modified from a manuscript under review in Gait & Posture

Abstract

Plantar fascia strain is influenced by both metatarsophalangeal (MTP) motion and arch

collapse. However, the effects of walking speed, incline, and shoe stiffness on plantar fascia

strain are unknown. Therefore, the purpose of the study was to compare the effects of speed,

incline, and shoe stiffness on peak plantar fascia strain using a musculoskeletal model of the

foot. Fifteen healthy adults participated in a repeated measures study, in which they walked on a

treadmill at two speeds, three inclines, and two shoe stiffness levels. Foot kinematics were

collected and a musculoskeletal model of the foot was used to estimate plantar fascia strain due

to MTP and midtarsal joint motion. A 2x3x2 repeated-measures ANOVA was performed to

determine the effects of speed, incline, and shoe stiffness on plantar fascia strain. Further post-

hoc tests were conducted to investigate the individual contributions of MTP and midtarsal joint

motions to total plantar fascia strain. There was a significant main effect of speed, with increased

peak plantar fascia strain during fast walking. The MTP angle at peak plantar fascia strain was

more dorsiflexed during fast walking, which resulted in significantly increased peak plantar

fascia strain due to MTP dorsiflexion and significantly increased total peak plantar fascia strain.

An increase in MTP dorsiflexion angle was found with increasing incline, but the main effect for

incline was not significant. The main effect of shoe stiffness was also not significant, meaning

peak total plantar fascia strain was not affected by incline or shoe stiffness. Our findings

40

highlight the relationship between MTP dorsiflexion and arch collapse due to the windlass

mechanism. Although increased MTP dorsiflexion angle causes increased plantar fascia strain,

the action of the windlass mechanism raises the arch height, which subsequently reduces plantar

fascia strain.

Introduction

The plantar fascia is a large fibrous band extending from the plantar aspect of the

calcaneus to the proximal phalanges of the five digits. Dorsiflexing the metatarsophalangeal

(MTP) joints causes increased plantar fascia tension in what has been termed the windlass

mechanism [1]. The plantar fascia is an integral component of normal foot function, helping to

support the medial longitudinal arch and limit subtalar pronation. Excessive strain in the plantar

fascia can produce microtears and inflammation at the insertion on the medial calcaneal tubercle

[2–5], which is believed to lead to plantar fasciitis. This condition is most commonly

characterized by pain in the plantar heel and is estimated to affect two million people in the

United States each year [6]. There are several biomechanical factors attributed to its

development, such as a tight Achilles tendon, subtalar pronation and the windlass mechanism

[7].

Research conducted in both cadavers [8] and a finite element model of the foot [9] found

that plantar fascia tensile strain (PFS) increased with MTP dorsiflexion due to the windlass

mechanism of the plantar fascia. Similar results were reported by McDonald et al. [10] when

they created a musculoskeletal model of the foot to estimate PFS. The authors [10] also

described an increase in PFS due to arch collapse, which is caused by both ground reaction

forces and Achilles tendon forces [8].

The sesamoid bones are located below the head of the first metatarsal. They serve a

pulley function for the muscles that stabilize the hallux and consequently increase their

41

mechanical advantage during MTP dorsiflexion [11]. Studies have reported up to a 30% decrease

in the effective tendon moment arm of both the flexor hallucis brevis [12] and flexor hallucis

longus [13] with the excision of both sesamoids during MTP dorsiflexion, which demonstrates

the function of the sesamoid bones. The first digital slip of the plantar fascia also attaches to the

sesamoid bones [14], which suggests that the sesamoids may influence the moment arm of the

plantar fascia, thereby affecting PFS during MTP dorsiflexion. While research has shown the

contributions of PFS due to both MTP dorsiflexion and arch collapse in vivo, it is currently

unknown how the inclusion of dynamic sesamoid bones in the musculoskeletal model will affect

strain values.

Walking is a very popular exercise to increase and maintain fitness, and it is often

recommended to individuals by physicians because it is a low impact exercise and can be done

anywhere. Unfortunately, up to 10% of the population will experience plantar fasciitis [15],

which can limit exercise and prevent further fitness improvements. Consequently, it is important

to discover what walking conditions produce the lowest values of PFS, thereby reducing the risk

for developing plantar fasciitis. It has been shown that walking and running at various treadmill

inclines results in increased Achilles tendon strain [16]. Because an increase in PFS has been

reported due to increased tension at the Achilles tendon [8,9,17], it is possible that gait speed and

incline may affect PFS. In addition, research suggests that shoe flexion stiffness may contribute

to overall magnitude of PFS by decreasing MTP dorsiflexion and thereby reducing the windlass

effect [18]. Therefore, the purpose of the study was to create a musculoskeletal model with

realistic sesamoid movement to determine the contributions of MTP and midtarsal joint motion

to plantar fascia strain. A further purpose was to use the model to determine the effects of speed,

grade, and shoe stiffness on PFS. It was hypothesized that increased speed, incline, and shoe

42

flexibility would all increase peak plantar fascia strain during treadmill walking in healthy

individuals without plantar fasciitis.

Methods

Participants

A total of fifteen healthy participants (13 males, 2 females; age: 25.8±8.2yrs;

height: 1.8±0.1m; mass: 72.2±16.2kg) completed the study. Participants were between the ages

of 18-65 and fit into a men’s size 9-10 (women’s 10.5-11.5) shoe. Individuals were excluded

from participating if they had any current pain that might affect their walking or if they

previously had foot surgery.

Data Collection Procedures

After providing written informed consent using a form approved by the university

Institutional Review Board, anthropometric measurements were collected. Three marker triads

were attached to the participants’ right foot on the hallux, over the navicular tuberosity, and on

the calcaneus using cyanoacrylate [19]. Participants were provided with shoes that had portions

of the footwear upper cut out, which allowed marker triads to be attached directly to the skin in

order to more accurately define the locations of the anatomical landmarks.

The gait analysis was completed using an eight-camera motion analysis system (Vicon

MX, Vicon, Centennial, CO) and a standard treadmill. A standing calibration trial was captured,

and then participants performed a five-minute warmup at a self-selected walking speed on the

treadmill. Self-selected walking speed was operationally defined as a comfortable pace utilized

under normal circumstances. After the warmup, participants walked on the treadmill during

twelve conditions for one minute each. 30 seconds of marker trajectory data were collected and

tracked using Nexus software (Nexus 1.8.5, Vicon, Centennial, CO). The conditions included all

possible combinations of two speeds (preferred walking speed and 20% greater than preferred

43

walking speed), three inclines (0°, 5°, and 10°), and two shoe forefoot bending stiffnesses (stiff

and flexible midsole). Conditions were presented in a counterbalanced order within each shoe

condition, and shoe order was alternated between subjects. Two pairs of the same model of shoe

were utilized (New Balance, Boston, MA), with the only difference being a stiff thermoplastic

polyurethane layered between the midsole and outsole of one pair (stiff: 0.45 Nm/degree;

flexible: 0.075 Nm/degree).

Data Analysis

Raw 3D coordinate data were low-pass filtered at 6 Hz and input into Matlab software

(MathWorks, Inc., Natick, MA). A four-segment musculoskeletal model of the foot was created

by modifying a five-segment model [20]. Further modifications were done to include the plantar

fascia, sesamoid bones, and MTP motion that more closely followed the head of the first

metatarsal during flexion and extension (Figure 3.1). Translation and rotation of the sesamoids

were visually matched to follow the contour of the first metatarsal head, and movement was

calculated as a function of the first MTP joint angle. The insertion of the plantar fascia was

placed at the base of the first phalange to model the digital slip where the greatest strains occur

[9]. These modifications are detailed in Appendix B.

Movement of the model was driven by rotation about the mediolateral axis of the MTP

joint and 3D rotations at the midtarsal joint. Peak total PFS was calculated as the maximum

percent change in length of the plantar fascia from normal standing and was due to both the

windlass mechanism of the MTP joint and collapse of the arch (midtarsal joint movement). Peak

total PFS was found during each gait cycle, which occurred in the stance phase just prior to toe-

off (about 58% of the gait cycle). In addition, contributions to peak PFS from rotation about the

mediolateral axis of the MTP joint and all three axes of the midtarsal joint were estimated by

freezing all degrees of freedom in the model except the one of interest.

44

A 2x3x2 repeated-measures ANOVA (speed x incline x shoe stiffness) was performed to

analyze peak total PFS. Significance was set to α=0.05. Greenhouse-Geisser corrections were

applied whenever the assumption of sphericity was violated. A linear trend was used to identify

significance for incline. To further investigate contributions of movement of the MTP and

midtarsal joints on plantar fascia strain, post hoc analyses were conducted. 2x3x2 repeated-

measures ANOVAs were performed on peak PFS due to MTP joint motion, peak PFS due to

motion about the midtarsal mediolateral axis, peak PFS due to motion about the midtarsal

vertical axis, peak PFS due to motion about the midtarsal anteroposterior axis, MTP dorsiflexion

angle at peak total PFS, and midtarsal angle at peak total PFS. The same procedures mentioned

above were utilized. Generalized eta squared (ηG2) was calculated as a measure of effect size

[21,22]. All results are reported as means and 95% confidence intervals. All statistical analyses

were performed in SPSS (SPSS Inc., version 25; Chicago, IL).

Results

Plantar fascia strain throughout the gait cycle is negative at initial contact, indicating a

reduced strain magnitude relative to standing (Figure 3.2). Strain rapidly increases during foot

flat and then remains approximately zero or slightly negative during midstance. There is a rapid

increase in strain magnitude during late stance which decreases to a negative value during swing.

Therefore, peak PFS occurs immediately before toe-off at 56-60% of the gait cycle. At this point

nearly all of the strain in the plantar fascia is due to MTP joint dorsiflexion (2.8 to 3.7% strain

across all conditions). The midtarsal angle at peak PFS is generally negative, indicating the arch

was higher than normal standing (Figure 3.3). Therefore, the contribution of midtarsal joint

movement to peak planar fascia strain is very small to slightly negative (0.2% to -0.9% across all

conditions). Overall, the peak plantar fascia strain decreased from 2.8-3.7% to 2.0-2.4% when

both the MTP and midtarsal joints were included in the model (Table 3.1).

45

There were no statistically significant interactions between speed, incline, and shoe

stiffness. Mean values for peak total PFS are presented in Table 3.1. This table also contains

information concerning the contributions of the MTP and midtarsal joints to the resulting peak

PFS. There was a significant effect of speed, with greater total strain during fast walking

(preferred = 2.1±0.09%, fast = 2.4±0.08%; p = 0.02; ηG2 = 0.29) (Figure 3.2A). The main effect

of incline was not significant for peak total PFS (0° = 2.0±0.3%, 5° = 2.3±0.3%, 10° =

2.4±0.4%; p = 0.14; ηG2 = 0.10) (Figure 3.2B), nor was the main effect of stiffness (stiff =

2.1±0.4%, flexible = 2.4±0.4%; p = 0.4; ηG2 = 0.049) (Figure 3.2C).

Further analyses revealed a significant main effect of speed for MTP angle at peak PFS,

with a more dorsiflexed MTP angle at peak PFS for the fast walking condition compared to the

preferred walking condition (preferred = 13.2±0.9°, fast = 15.7±0.8°; p = 0.006; ηG2 = 0.34). This

resulted in increased PFS due to the MTP dorsiflexion (preferred = 3.0±0.2%, fast = 3.5±0.2%; p

= 0.004; ηG2 = 0.37). A significant linear trend was found for incline for both the MTP angle at

peak PFS (0° = 12.3±1.9°, 5° = 14.9±2.2°, 10° = 16.4±1.3°; p = 0.003; ηG2 = 0.21) and for PFS

due to MTP joint motion (0° = 2.8±0.4%, 5° = 3.3±0.5%, 10° = 3.7±0.3%; p=0.003; ηG2 = 0.23).

As the incline increased, the MTP angle at peak PFS increased, which caused the PFS due to

MTP joint motion to also increase. Finally, the main effect of stiffness for MTP angle at peak

PFS and for PFS due to MTP joint motion were trending towards significance, with a more

dorsiflexed MTP angle at peak PFS (stiff = 13.2±1.7°, flexible = 15.9±1.7°; p = 0.09; ηG2 = 0.18)

and greater PFS due to MTP joint motion (stiff = 2.9±0.4%, flexible = 3.6±0.4%; p = 0.08; ηG2 =

0.19) in the flexible shoe condition compared to the stiff shoe condition.

The main effects of speed, incline, and stiffness were not significant for the midtarsal

angle at peak PFS or for the peak PFS due to midtarsal joint motion.

46

Discussion

The results of the study supported the hypothesis that greater peak total PFS would be

observed in individuals walking at increased speeds. However, the hypotheses that greater

incline and increased shoe flexibility would produce greater peak plantar fascia strain were not

supported.

The trend of increased strain with increased MTP dorsiflexion angle from the current

study is consistent with results from previous studies [8,9,23]. In addition, the peak overall

strains estimated in the current study are similar to the strains reported by McDonald et al. [10],

who estimated peak strain values from their model ranging between 0.6-2.1% during a running

protocol. Therefore, it can be concluded that our model can be used to estimate plantar fascia

strains based on MTP and midtarsal joint movements.

The results of the current study demonstrate the function of the windlass mechanism. The

increased walking speed produces a greater MTP dorsiflexion angle at peak PFS, which tightens

the plantar fascia and acts to increase the total PFS [1,8,9,23]. However, the increased MTP

dorsiflexion angle also causes the arch to raise, as seen by the midtarsal angle about the

mediolateral axis (Figure 3.3) [1]. In contrast to the effect of increasing the MTP dorsiflexion

angle, the increase in arch height acts to reduce the total PFS, as indicated by the negative values

of PFS due to movement about the midtarsal mediolateral axis. While peak total PFS was only

significantly different between the preferred walking speed and the fast walking speed, the

relationship between the MTP angle and the midtarsal angle about the mediolateral axis and their

respective contributions to total PFS can be observed in all the walking conditions (Table 3.1).

In addition to raising the arch, the windlass mechanism also produces supination about

the midtarsal joint [1,14,24]. This supination motion, which is a combination of plantarflexion

about the mediolateral axis, adduction about the vertical axis, and inversion about the

47

anteroposterior axis, can be inferred by analyzing the PFS due to movements about the three

midtarsal axes. PFS due to movement about the midtarsal vertical axis is due to the adducted or

abducted position of the forefoot at the time of peak PFS. The negative values indicate that the

forefoot is in an adducted position about the midtarsal vertical axis at the time of peak PFS.

According to the results of our study, the contribution of the PFS due to movement about the

midtarsal vertical axis is -0.6 to -0.7% across all conditions. While this position acts to reduce

the total PFS, it does not appear to be affected by the various walking conditions, as seen by the

consistency of the values (Table 3.1).

PFS due to movement about the midtarsal anteroposterior axis is due to the inverted or

everted position of the forefoot at the time of peak PFS. The negative values indicate that the

forefoot was in an inverted position about the midtarsal anteroposterior axis at the time of peak

PFS. However, the contribution of the PFS due to movement about the midtarsal anteroposterior

axis was minimal (-0.002 to 0.2%) and not substantially affected by the various walking

conditions (Table 3.1).

Excessive and repeated strain on the plantar fascia is thought to contribute to the

development of plantar fasciitis [2–5]. Treatment strategies such as stiff midsole plates or rocker

soles are frequently used to limit MTP dorsiflexion, thereby reducing the windlass effect

[18,25,26]. The results of our model revealed that despite a reduction of MTP dorsiflexion due to

a stiff thermoplastic polyurethane in the midsole, there was no significant change in peak PFS.

Any reduction of MTP dorsiflexion that occurs with the stiffer midsole is mitigated by greater

arch collapse. Our findings are supported by the results of Greve et al. [27], who reported no

significant differences between peak PFS between stiff and flexible shoe conditions.

48

The results of our study suggest that both MTP dorsiflexion and arch collapse should be

considered when the reduction of peak PFS is the goal, as limiting MTP dorsiflexion may not be

enough to reduce excessive strain of the plantar fascia. It is possible that the efficacy of treatment

strategies such as stiff midsole plates or rocker soles may be due to reasons other than a

reduction in peak PFS. Therefore, these treatment strategies for plantar fasciitis should be

investigated further to determine their efficacy.

There are several limitations to the study. First, the current study used a static standing

position as the neutral reference system. Consequently, the estimated PFS is likely lower than the

true physiological strain that actually occurs during gait. Next, the arch was modelled by

securing a triad over the navicular, which was used to represent the entire forefoot segment.

Because the rigid body assumption was likely being violated in the forefoot segment [28–30], the

accuracy of the model may have been improved by including more segments into the foot model.

However, the current model was chosen to preserve the integrity of the shoe structure as much as

possible. Finally, participants were recruited for the study if they were healthy and fit into the

custom made men’s size 9-10 shoes. Convenience sampling resulted in many of the participants

being healthy, college-aged males. Caution must be taken when applying the results of the study

to other populations, such as females, other age groups, or pathological groups. These effects

should be investigated in a population with plantar fasciitis to further understand the interaction

between MTP dorsiflexion, arch collapse, and peak PFS while walking during different

conditions.

Conclusions

The results of this study show that greater speed produces an increase in peak plantar

fascia strain during walking. However, walking on varying inclines or wearing a stiff shoe does

not alter peak plantar fascia strain during walking. This can be attributed to the action of the

49

windlass mechanism, as reduced MTP dorsiflexion allowed for greater arch collapse. The

interaction between MTP dorsiflexion and arch collapse needs to be investigated further to

understand how they affect plantar fascia strain. In addition, investigating these effects on a

population with plantar fasciitis would provide further insight regarding the interaction between

these factors and how they may play a role in the development of plantar fasciitis.

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Effective Moment of the Flexor Hallucis Brevis, Foot Ankle Int. 15 (1994) 462–470.

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4379–4388.

[17] J.T.-M. Cheung, M. Zhang, K.N. An, Effect of Achilles tendon loading on plantar fascia

tension in the standing foot, Clin. Biomech. 21 (2006) 194–203.

[18] S.C. Lin, C.P. Chen, S.F. Tang, A.M. Wong, J.H. Hsieh, W.P. Chen, Changes in windlass

effect in response to different shoe and insole designs during walking, Gait Posture. 37

(2013) 235–241.

[19] R.G. Nielsen, M.S. Rathleff, C.M. Moelgaard, O. Simonsen, S. Kaalund, C.G. Olesen,

F.B. Christensen, U.G. Kersting, Video based analysis of dynamic midfoot function and

its relationship with Foot Posture Index scores, Gait Posture. 31 (2010) 126–130.




[21] R. Bakeman, Recommended Effect Size Statistic, Behav. Res. Methods. 37 (2005) 379–

384.

[22] S. Olejnik, J. Algina, Generalized Eta and Omega Squared Statistics: Measures of Effect

Size for Some Common Research Designs, Psychol. Methods. 8 (2003) 434–447.

[23] H.Y.K. Cheng, C.L. Lin, S.W. Chou, H.W. Wang, Nonlinear finite element analysis of the

plantar fascia due to the windlass mechanism, Foot Ankle Int. 29 (2008) 845–851.


Foot Ankle Surg. 7 (2001) 131–136.

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footwear adapted with rocker profiles — Evidence in the literature, Foot. 19 (2009) 165–

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[26] M.S. Mizel, J. V Marymont, E. Trepman, Treatment of plantar fasciitis with a night splint

and shoe modification consisting of a steel shank and anterior rocker bottom, Foot Ankle

Int. 17 (1996) 732–735.

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[27] C. Greve, D. Schuitema, B. Otten, L. van Kouwenhove, E. Verhaar, K. Postema, R.

Dekker, J.M. Hijmans, Biomechanical effects of rocker shoes on plantar aponeurosis

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Figures and Tables

Figure 3.1: Marker triads were placed on the calcaneus, navicular, and hallux. The four-

segment model of the foot allowed rotation about the mediolateral axis of the

metatarsophalangeal (MTP) joint and about all three axes of the midtarsal joint. In addition,

translation and rotation of the sesamoids followed the contour of the 1st metatarsal head and

were calculated as a function of the MTP joint angle.

X

Z

Z

Y

52

Figure 3.2: Mean ensemble curves of total plantar fascia strain for A) speed; B) incline; and C)

shoe stiffness, throughout the entire gait cycle. Toe-off is indicated by the vertical dashed line.

C)

-4

-2

0

2

0 20 40 60 80 100

PF

Str

ain

(%

)

0°5°10°

-4

-3

-2

-1

0

1

2

0 20 40 60 80 100

PF

Str

ain (

%)

Gait Cycle (%)

Stiff

Compliant

-4

-3

-2

-1

0

1

2

0 20 40 60 80 100P

F S

trai

n (

%)

Preferred

FastA)

B)

C)

53

Figure 3.3: The interaction between the metatarsophalangeal (MTP) and midtarsal joints about

the mediolateral axis demonstrates the function of the windlass mechanism. An increase in MTP

dorsiflexion tightens the plantar fascia, which raises the arch. Toe-off is indicated by the vertical

dashed line.

-15

-10

-5

0

5

10

15

20

25

0 20 40 60 80 100

An

gle

(°)

Gait Cycle (%)

MTP Angle

Midtarsal Angle

54

Table 3.1: Peak total plantar fascia strain (PFS) and the contributions to peak plantar fascia strain from rotation about the

mediolateral axis of the MTP joint and all three axes of the midtarsal joint (Mean ± 95% CI) are presented below. In addition, MTP

and midtarsal angles at peak total plantar fascia strain are also given.

* Denotes significance at the p < 0.05 level. # Denotes a significant linear trend at the p < 0.05 level.

Values at Peak Total PFS

Walking

Condition

Peak Total

PFS

MTP

Angle

Midtarsal

Angle (ML-

axis)

PF Strain

due to

MTP

PF strain due

to midtarsal

AP-axis

PF strain due to

midtarsal VERT-

axis

PF strain due to

midtarsal ML-

axis

Speed

Preferred 2.1 ±

0.09%*

13.2 ±

0.9°* -0.3 ± 1.0°

3.0 ±

0.2%* 0.004 ± 0.1% -0.6 ± 0.05% -0.2 ± 0.5%

Fast 2.4 ±

0.08%*

15.7 ±

0.8°* -1.7 ± 0.9°

3.5 ±

0.2%* 0.1 ± 0.1% -0.7 ± 0.04% -0.8 ± 0.4%

Incline

0° 2.0 ± 0.3% 12.3 ±

1.9°# 0.004 ± 1.8° 2.8 ±

0.4%# 0.02 ± 0.09% -0.6 ± 0.1% -0.1 ± 0.8%

5° 2.3 ± 0.3% 14.9 ±

2.2°# -1.7 ± 2.0° 3.3 ±

0.5%# 0.2 ± 0.3% -0.6 ± 0.07% -0.9 ± 1.0%

10° 2.4 ± 0.4% 16.4 ±

1.3°# -1.4 ± 0.7° 3.7 ±

0.3%# -0.002 ± 0.2% -0.7 ± 0.1% -0.6 ± 0.4%

Shoe Stiffness

Stiff 2.1 ± 0.4% 13.2 ±

1.7° -0.3 ± 1.0° 2.9 ± 0.4% -0.02 ± 0.2% -0.6 ± 0.1% -0.2 ± 0.5%

Flexible 2.4 ± 0.4% 15.9 ±

1.7° -1.7 ± 1.0° 3.6 ± 0.4% 0.1 ± 0.2% -0.6 ± 0.1% -0.9 ± 0.5%

55

Appendix A: Institutional Review Board Approval

56

Appendix B: Modifications to the Musculoskeletal Foot Model

Model Creation

The musculoskeletal model utilized in this study was based on the joint and muscle data of

Arnold et al. (2010) with foot and ankle modifications detailed in the KU Leuven foot model

(Malaquias et al., 2017). The addition of the KU Leuven model allowed midfoot and

metatarsophalangeal joint (MTP) to be defined. Four additions/changes were made to this

previously published model.

1. The first slip of the plantar fascia was added with an origin on the calcaneal tuberosity,

moving over the sesamoid bones and inserting onto the proximal first phalanx (Table 1).

2. Sesamoid bones were added at the head of the first metatarsal by creating translations and

sagittal plane rotation based on sagittal plane MTP movement (Table 2). Rotation and

translation of the sesamoids were visually matched to follow the contour of the 1st

metatarsal head (Figure 1).

3. The first slip of the plantar fascia was included to model the region where the greatest

plantar fascia strains occur. Therefore, motion of the first phalanx was optimized to

visually follow the non-spherical shape of the metatarsal head. The first phalanx was

translated in the anterior and medial directions as the MTP joint was dorsiflexed (Table

3).

4. Direct measurement of the talus was not possible due to external marker limitations.

Instead, inversion/eversion and abduction/adduction motions that occurred at the ankle

joint were attributed to the subtalar joint. Plantar/dorsiflexion was attributed to the

talocrural joint.

57

Table 3.2: Locations of the origin, via points, and insertion of the first slip of the plantar fascia.

Segment Anteroposterior

(m)

Vertical (m) Mediolateral (m)

Origin Calcaneus -0.0235 -0.0265 -0.0100

Via Point Sesamoids -0.0040 -0.0060 0.0000

Via Point Sesamoids 0.0040 -0.0070 -0.0010

Insertion Hallux 0.0159 -0.0100 -0.0311

Table 3.3: Sagittal plane rotation and translation of the sesamoids as a function of measured

MTP joint angle.

MTP

Angle (°)

Sagittal

Angle (°)

Anteroposterior

Translation (m)

Vertical

Translation (m)

Mediolateral

Translation (m)

-10 0.0 0.0562 -0.0200 -0.0250

0 0.0 0.0593 -0.0199 -0.0253

10 6.7 0.0620 -0.0198 -0.0256

20 13.3 0.0641 -0.0197 -0.0259

30 20.0 0.0656 -0.0196 -0.0262

40 23.3 0.0665 -0.0193 -0.0265

50 26.7 0.0668 -0.0189 -0.0268

60 30.0 0.0670 -0.0185 -0.0271

Table 3.4: Translation of the hallux as a function of the measured MTP joint angle.

MTP

Angle

(°)

Anteroposterior

Translation (m)

Mediolateral

Translation (m)

-10 0.0605 -0.0141

0 0.0612 -0.0141

10 0.0619 -0.0134

20 0.0626 -0.0127

30 0.0634 -0.0121

40 0.0641 -0.0114

50 0.0648 -0.0107

60 0.0655 -0.0100

58

Figure 3.4: A) rotation and translation of the sesamoids were visually matched to follow the

contour of the 1st metatarsal head. The effect of sesamoid rotation and translation on plantar

fascia strain and plantar fascia moment arm are depicted in B) and C).

A) B)

C)

59

CHAPTER 4. VALIDATION OF A SIX-SEGMENT MUSCULOSKELETAL MODEL

OF THE FOOT USED TO ESTIMATE LIGAMENT STRAINS




Modified from a manuscript to be submitted to Computer Methods in Biomechanics and

Biomedical Engineering

Abstract

In addition to the plantar fascia, there are several secondary ligaments that help to

provide support to the medial longitudinal arch. Because of their contribution to arch support,

these ligaments may influence the magnitude of the load placed on the plantar fascia, thereby

playing a factor in the development of plantar fasciitis. However, the nature of ligaments poses

limitations to the types of analyses that can be performed. To address this limitation,

musculoskeletal models can be used to provide information about in vivo kinematics and tissues

mechanics that would otherwise be impossible to measure directly. Therefore, the purpose of the

study was to validate a musculoskeletal model of the foot by comparing model-estimated

ligament strain values to directly-measured ligament strain values from seven fresh-frozen

cadaver specimens. The estimated ligament strains from the model were compared to the

directly-measured strains and evaluated using Pearson correlation coefficients and coefficients of

repeatability (CR). Results showed CR values between the ranges of 0.8-8.3% and statistically

significant Pearson’s R values in the inferior slip of the spring ligament (p = 0.0008) and the

tibionavicular slip of the deltoid ligament (p = 0.002), as well as nearly significant correlations in

the tibiocalcaneal slip of the deltoid ligament (p = 0.06) and the calcaneonavicular slip of the

bifurcate ligament (p = 0.05). The results indicate that the model can be used to estimate strains

60

of the ligaments that help to support the arch on the medial side of the foot. A secondary purpose

was to validate the use of skin-mounted markers in the musculoskeletal model, so bone pin

estimated ligament strains and skin marker estimated ligament strains were compared. Results

showed statistically significant Pearson’s R values in nearly all the ligaments and CR values that

were all between the ranges of 0.03-1.6%, indicating that skin markers can be used in the model.

Introduction

Ligaments are passive tissues that connect bone to bone and act to provide stability to a

joint. They can either resist excessive motion beyond a joint’s total range of motion or motion

outside of a joint’s normal plane of motion (Root, Orien, and Weed 1977). Along with the

plantar fascia, ligaments crossing the midfoot provide secondary support to the medial

longitudinal arch and help to control motions such as excessive pronation (Huang et al. 1993;

Ker et al. 1987; Kitaoka et al. 1997; Tao et al. 2010). Both arch collapse and excessive pronation

have been cited as risk factors for plantar fasciitis (Irving et al. 2007; Kwong et al. 1988;

Taunton et al. 2002; Warren and Jones 1987), potentially due to increased tensile load placed on

the plantar fascia (Bauer 2012; Kwong et al. 1988; Sarrafian 1987). Because the ligaments

crossing the midfoot provide structural support to the medial longitudinal arch, they may

influence the magnitude of load placed on the plantar fascia, thereby playing a role in the

development of plantar fasciitis. These ligaments include the long and short plantar ligaments,

the spring ligament, and the deltoid ligament. While no research has been conducted on them, the

orientation of the bifurcate and cervical ligaments suggest they may also help to support the

midfoot. However, despite the role that ligaments play in arch support and providing stability to

the foot, there is very little published information on the behavior of the ligaments in the foot. It

is currently unknown how many of the ligaments behave. Therefore, the primary purpose of this

study was to validate a six-segment modified musculoskeletal model of the foot by comparing

61

estimated ligament strain values from the model to directly measured strain values from loaded

cadaver specimens.

Musculoskeletal models provide information about kinematics and tissue mechanics

using a simplified representation of the system. They are made up of body segments connected

by joints with a defined number of degrees of freedom at each joint. Furthermore, the model may

include muscles and ligaments with specified origins and insertions that cross the joints.

Simplified musculoskeletal models of the foot have been created and validated in the past

(Kidder et al. 1996; Leardini et al. 1999; Myers et al. 2004). While they can provide useful

information, those models are not sophisticated enough to realistically replicate the complex

motions that occur in the foot during gait (Neptune, Wright, and van den Bogert 2000).

To address this limitation, Malaquias et al. (Malaquias et al. 2017) developed the KU

Leuven model, a five-segment model of the foot (talus, calcaneus, midfoot, forefoot, toes) with

five anatomical joints (ankle, subtalar, midtarsal, tarsometatarsal, and metatarsophalangeal)

based on CT scans used in OpenSim (Delp et al. 2007). The model included both intrinsic and

extrinsic muscles of the foot, as well as the major ligaments. While the kinematics were

validated by comparing to joint kinematics published in literature (Lundgren et al. 2008),

validation of the ligament strains estimated using the model was limited. The authors reported

physiologically acceptable values, as the average maximum elongation of the ligaments was

below the rupture threshold of 8% (Nordin and Frankel 2001). However, the authors

acknowledged that further refinement of their model in regards to the foot ligaments was needed.

Furthermore, the KU Leuven model treats the tarsals and metatarsals as single segments (midfoot

and forefoot, respectively), which may limit our understanding of the medial column of the foot

during walking. In addition, there are physiological differences in motion between the medial

62

and lateral columns of the foot (Lundgren et al. 2008), so it is important to model the medial and

lateral columns of the foot separately.

Skin-mounted markers are frequently used to estimate the position, velocity, and

acceleration of the underlying bones. However, previous research on the foot has reported

significant kinematic differences between bone pins and skin markers (Nester et al. 2007).

Furthermore, bone pins are invasive and impractical to use in many situations. Therefore, an

additional purpose of the study is to compare the estimated ligament strains between bone pins

and skin markers in order to validate the use of skin markers for our musculoskeletal model.

Methods


Seven fresh-frozen cadaver feet were analyzed for the study. An experienced podiatrist

dissected the foot to expose the two slips of the spring ligament (superior and inferior), three

slips of the deltoid ligament (tibionavicular, tibiocalcaneal, and tibiotalar), two slips of the

bifurcate ligament (calcaneocuboid and calcaneonavicular), and cervical ligament. Following

dissection, K-wire pins were placed at the origin and insertion of each ligament. Each cadaver

was placed on a portable force platform (Advanced Mechanical Technology, Inc., Watertown,

MA, USA) underneath a pneumatic actuator mounted on a frame (Figure 4.1). The actuator was

used in conjunction with the force platform to apply an axial load of 10N to the tibia of each

cadaver specimen. A manual digitizer (Microscribe G2, Revware Inc., Raleigh, NC, USA) was

used to define the origin and insertion of each ligament using the K-wire pins at the 10N load,

and this was considered the baseline length of each ligament.

Simultaneously, kinematic data were collected at 225 Hz using a 12-camera motion

analysis system (Qualisys Oqus 600+, Qualisys NA, Inc., Buffalo Grove, IL, USA). Intracortical

bone pins with reflective marker triads attached to the end were inserted into the calcaneus, talus,

63

navicular, 1st metatarsal, hallux, and cuboid (Figure 4.2). Marker trajectory data were collected

and tracked using QTM software (Qualisys Track Manager 2020.2, Qualisys NA, Inc., Buffalo

Grove, IL, USA). Following digitization of the ligaments and the kinematic collection during the

baseline condition, the axial load was increased to 250N, 500N, 750N, and 1000N, and the

digitization process was repeated at each load. The load condition was collected in the same

order for all specimens, and one of the researchers monitored the load to ensure the magnitude

stayed constant throughout the entire condition. The axial load resulted in arch collapse, and the

strain response of each ligament due to the collapse in the arch was measured.

Data Analysis

Raw 3D coordinate data were input into a custom Matlab script (MathWorks, Inc.,

Natick, MA, USA) and filtered at 8 Hz using a 2nd order low-pass Butterworth filter. An 11

degree of freedom (11DOF) musculoskeletal model of the foot was modified (Malaquias et al.

2017) to include six segments of the foot (calcaneus, talus, navicular and cuneiforms, cuboid,

metatarsals, and hallux) (Figure 4.3).

Furthermore, the sesamoids were separated from the metatarsal segment, and translation

and rotation of the sesamoids was achieved by moving them around the curvature of the first

metatarsal head as a function of the first MTP joint angle. The center of rotation of the

talonavicular joint was moved to the center of the talar head and visually adjusted so that the

navicular bone rotated about the articular surface of the talus. The calcaneocuboid joint center of

rotation was similarly adjusted so that it rotated about the proximal surface of the joint. Three-

dimensional helical segment and joint angles were calculated. Cadaver dissections were used to

define two slips of the spring ligament, three slips of the deltoid ligament, two slips of the

bifurcate ligament, and the cervical ligament. Strains of the spring, deltoid, bifurcate, and

cervical ligaments were estimated as the percentage change in length relative to the baseline 10N

64

load condition. Pearson’s correlation coefficients (r) were calculated to investigate the

relationship between ligament strains estimated from the model and the strains measured with

the digitizer, and were evaluated for significance at α = 0.05. Additionally, Bland-Altman plots

were utilized to compare the model-estimated ligament strains to the directly-measured ligament

strains, and the coefficient of repeatability (CR) for each ligament was assessed to test the

agreement (Giavarina 2015). CR represents the value in which 95% of the measurement

differences lie.

In addition to the bone pins that were inserted into the bones to directly measure

kinematics, reflective marker triads were also placed on the skin overlaying the calcaneus,

navicular, and hallux bones to measure foot kinematics captured by the skin markers (Figure

4.2). To accommodate the reduced number of skin markers on the foot, the model was further

modified by freezing all motions of the TMT and calcaneocuboid joints and estimating talus

motion, thereby creating a four-segment, 7DOF model (Figure 4.4). Talus motion was

considered to be the same as leg motion in the frontal and transverse planes and considered to be

the same as calcaneus motion in the sagittal plane. This allowed for a representation of both

subtalar and talonavicular joint motions, even when using skin markers which cannot be placed

over the talus. Movement of the model ankle joint using calcaneal and tibial markers was limited

to the sagittal plane, with frontal and transverse plane motions between these bones attributed to

the subtalar joint. Previous research regarding this assumption has shown that it is appropriate

for some individuals, although substantial variation was noted (Arndt et al. 2004; Engsberg,

Grimston, and Wackwitz 1988). The same four-segment model with the frozen TMT and

calcaneocuboid joint motion was used to measure foot kinematics captured by the bone pins, and

65

the data from the two methods were compared using Pearson’s correlation coefficients and tested

for agreement with CR using Bland-Altman methods (Giavarina 2015).

Results

Pearson’s correlation coefficients between the directly-measured and model-estimated

ligament strains using the six-segment model are presented in Figures 4.5 and 4.6. Ligament

strains estimated using the bone pins were significantly correlated to the directly-measured

ligament strains for the the inferior slip of the spring ligament (r = 0.99; p = 0.0008) and the

tibionavicular slip of the deltoid ligament (r = 0.99; p = 0.002), as well as nearly significant

correlations in the tibiocalcaneal slip of the deltoid ligament (r = 0.87; p = 0.06) and the

calcaneonavicular slip of the bifurcate ligament (r = 0.87; p = 0.05). Relatively weaker

correlations were noted for the superomedial slip of the spring ligament (r = 0.73; p = 0.16), the

calcaneocuboid slip of the bifurcate ligament (r = 0.68; p = 0.21), and the cervical ligament (r =

0.77; p = 0.13).

The CR values between the directly-measured ligament strains and the model-estimated

strains across the five loading conditions using the six-segment model are also presented in

Figures 4.5 and 4.6. CR values range from 1.2% at the calcaneonavicular slip of the bifurcate

ligament to 8.3% at the inferior slip of the spring ligament, which highlights the range of strain

magnitude differences between the model and the directly-measured values.

Using the four-segment model, the strains estimated using the bone pins and the skin

markers were compared, and Pearson’s correlation coefficients between the bone pin and skin

markers strain estimates are presented in Figures 4.7 and 4.8. Statistically significant correlations

were noted for both slips of the spring ligament (superomedial: r = 0.97, p = 0.008; inferior: r =

0.99, p = 0.002), the tibionavicular (r = 0.99; p = 0.002) and tibiocalcaneal (r = 0.99; p = 0.002)

slips of the deltoid ligament, the calcaneonavicular slip of the bifurcate ligament (r = 0.98; p =

66

0.005), and the cervical ligament (r = 0.94; p = 0.02). The CR values were also calculated and

are presented in Figures 4.7 and 4.8. The values range from 0.03 to 1.6, representing the

magnitude differences between ligament strains estimated by the bone pins and ligament strains

estimated by the skin markers.

Discussion

The primary purpose of the study was to validate the musculoskeletal model of the foot

by comparing the directly-measured ligament strains to the model-estimated ligament strains,

and the results of the study confirm the validation of the model. Significant correlations between

the directly-measured and model-estimated ligament strains indicate that the relationship

between arch collapse and ligament strain is adequately modelled for the ligaments on the medial

side of the foot in the musculoskeletal model. When the axial load applied to the tibia was

increased, the resultant arch collapse produced an increased strain response in the spring, deltoid,

bifurcate, and cervical ligaments. Similar estimated strain responses were noted in all the

modelled ligaments.

The magnitudes of the directly-measured and model-estimated strains are relatively

similar in some ligaments, such as the superomedial slip of the spring ligament, the

tibiocalcaneal slip of the deltoid ligament, the calcaneonavicular slip of the bifurcate ligament,

and the cervical ligament. However, in the remaining ligaments (inferior slip of the spring

ligament, tibionavicular and tibiotalar slips of the deltoid ligament, and calcaneocuboid slip of

the bifurcate ligament), the magnitudes are substantially different (Figures 4.5 and 4.6). These

results are quantified in the reported CR values. There are several possible explanations for this

discrepancy. First, the material properties of the soft tissues in the cadaver specimens may have

been altered by the freezing and thawing process, or due to drying out. Furthermore, while the

age of the specimens were unknown, often cadaver specimens come from elderly individuals.

67

Material properties of ligaments are known to change with age (Woo, Ohland, and Weiss 1990),

so it is possible that the age of the cadaver specimens affected the measured strain values. For

example, the directly-measured and model-estimated strains of the tibionavicular slip of the

deltoid ligament follow nearly identical strain responses, but the directly-measured strains are

consistently between 3.6-4.1% higher (Figure 4.6A). This may be due to altered material

properties of the soft tissues of the cadaver specimens, leading to higher strain magnitudes. Next,

assumptions made in the model may have influenced the estimated ligament strains. For

example, the directly-measured strains of the tibiotalar slip of the deltoid ligament exhibited

strains of up to 5.5%, while the modelled ligament displayed estimated strains of approximately

zero (Figure 4.6E). This is due to the inability of the model to directly measure talus motion.

Because of this limitation, motion of the talus was assumed to be identical to the motion of the

tibia in the frontal and transverse planes. Consequently, the low strain magnitudes estimated in

the ligament are due to sagittal plane motion of the ankle joint, which was minimal in the study.

The secondary purpose of the study was to compare the model-estimated strains using

bone pin markers and skin markers as a way to validate the use of skin markers for the model,

and the results support the use of skin markers. Correlations between the bone pin and skin

marker estimated strains were very high and were statistically significant for nearly all of the

ligaments (Figures 4.7 and 4.8). The tibiotalar slip of the deltoid ligament exhibited a Pearson’s

R correlation of 0.6, which is likely due to the model assumptions of the ankle and subtalar joints

described previously. Furthermore, CR values were generally low, indicating similar magnitudes

of ligament strains between the two methods of segment measurement. Estimations of ligament

strains using the bone pins and skin markers can be seen in Figures 4.7 and 4.8. It should be

noted that a possible limitation of the study was the static nature of the data collection. A main

68

source of error when using skin-mounted markers is due to skin movement artefact, in which the

skin moves relative to the underlying bones during dynamic movements (Nester et al. 2007;

Westblad et al. 2002). This artefact has been shown to be affected by type of movement, with

greater errors demonstrated in a cutting motion when compared to walking (Benoit et al. 2006).

However, the pattern of error between skin-mounted markers and bone pins appears to be

inconsistent, as several studies have reported no systematic error patterns between the conditions

(Nester et al. 2007; Westblad et al. 2002).

Conclusions

The results of the current study show that the six-segment, modified musculoskeletal

model is satisfactorily able to estimate the ligament strain response due to arch collapse

following an axial load on the tibia. Furthermore, the comparison of the estimated ligament

strains between the bone pin model and the skin marker model showed that skin markers can be

used for the model. Therefore, it can be concluded that the model can be used in many different

scenarios, including on humans and in dynamic situations.

References

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during the Stance Phase of Walking.” Foot & Ankle International 25(5): 357–64.

Bauer, Robin Lee. 2012. “The Effects of Plantar Fasciitis on Multi-Segment Foot Running Gait

Kinematics.”

Benoit, Daniel L. et al. 2006. “Effect of Skin Movement Artifact on Knee Kinematics during

Gait and Cutting Motions Measured in Vivo.” Gait & Posture 24(2): 152–64.

Delp, Scott L. et al. 2007. “OpenSim: Open-Source Software to Create and Analyze Dynamic

Simulations of Movement.” IEEE Transactions on Biomedical Engineering 54(11): 1940–

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Pronated Foot Type May Increase the Risk of Chronic Plantar Heel Pain: A Matched Case-

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Ker, R. F. et al. 1987. “The Spring in the Arch of the Human Foot.” Nature 325(6100): 147–49.

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Analysis of Foot and Ankle Kinematics during Gait.” IEEE Transactions on Rehabilitation

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Kitaoka, Harold B., Tae-Kun Ahn, Zong Ping Luo, and Kai-Nan An. 1997. “Stability of the Arch

of the Foot.” Foot & Ankle International 18(10): 644–48.

Kwong, PK, D Kay, RT Voner, and MW White. 1988. “Plantar Fasciitis: Mechanics and

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Leardini, A. et al. 1999. “An Anatomically Based Protocol for the Description of Foot Segment

Kinematics during Gait.” Clinical Biomechanics 14(8): 528–36.

Lundgren, P. et al. 2008. “Invasive in Vivo Measurement of Rear-, Mid- and Forefoot Motion

during Walking.” Gait and Posture 28(1): 93–100.

Malaquias, Tiago M. et al. 2017. “Extended Foot-Ankle Musculoskeletal Models for Application

in Movement Analysis.” Computer Methods in Biomechanics and Biomedical Engineering

20(2): 153–59.

Myers, Kelly A, Mei Wang, Richard M Marks, and Gerald F Harris. 2004. “Validation of a

Multisegment Foot and Ankle Kinematic Model for Pediatric Gait.” IEEE Transactions on

Neural Systems and Rehabilitation Engineering 12(1): 122–30.

Neptune, R. R., I. C. Wright, and A. J. van den Bogert. 2000. “A Method for Numerical

Simulation of Single Limb Ground Contact Events: Application to Heel-Toe Running.”

Computer Methods in Biomechanics and Biomedical Engineering 3(4): 321–34.

Nester, C. et al. 2007. “Foot Kinematics during Walking Measured Using Bone and Surface

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Root, Merton L., William P. Orien, and John H. Weed. 1977. Normal and Abnormal Function of

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Figures and Tables

Figure 4.1: The cadaver specimens were placed on the force platform underneath the pneumatic

actuator, which applied an axial load on the tibia.

71

Figure 4.2: Bone pins with reflective marker triads attached to the end were inserted into the

calcaneus, talus, navicular, cuboid, 1st metatarsal, and hallux. In addition, skin marker triads

were placed on the calcaneus, navicular, and hallux.

72

Figure 4.3: The 11DOF model included six segments of the foot, including the calcaneus, talus,

navicular and cuneiforms, cuboid, metatarsals, and toes. In addition, the sesamoid bones were

separated from the metatarsals segment and modelled to rotate about the curvature of the first

metatarsal head as a function of the first MTP joint angle.

73

Figure 4.4: The 7DOF model included four segments of the foot, including the calcaneus, talus,

midfoot and forefoot, and toes. In addition, the sesamoid bones were separated from the

metatarsals segment and modelled to rotate about the curvature of the first metatarsal head as a

function of the first MTP joint angle.

74

Figure 4.5: Directly-measured (blue line) and model-estimated (orange line) ligament strains

at each axial load for the A) spring – superomedial, C) spring – inferior, E) bifurcate –

calcaneonavicular, and G) bifurcate – calcaneocuboid ligaments. Bland-Altman plots for the

B) spring – superomedial, D) spring – inferior, F) bifurcate – calcaneonavicular, and H)

bifurcate – calcaneocuboid ligaments. The solid black lines represent the bias in the mean

differences between the measurements, the dotted lines represent the 95% limits of agreement,

CR represents the coefficient of repeatability, and CV represents the coefficient of variation.

0

4

8

12

0 250 500 750 1000

Str

ain

(%

)

Load (N)

0

4

8

12

0 250 500 750 1000

Str

ain (

%)

Load (N)

0

4

8

12

0 250 500 750 1000

Str

ain (

%)

Load (N)

0

4

8

12

0 250 500 750 1000

Str

ain

(%

)

Load (N)

r = 0.73 (p = 0.16)

r = 0.99 (p = 0.0008)*

r = 0.87 (p = 0.05)

r = 0.68 (p = 0.21)

A) B)

H) G)

F) E)

C) D)

75

Figure 4.6: Directly-measured (blue line) and model-estimated (orange line) ligament strains

at each axial load for the A) deltoid – tibionavicular, C) deltoid – tibiocalcaneal, E) deltoid –

tibiotalar, and G) cervical ligaments. Bland-Altman plots for the B) deltoid – tibionavicular,

D) deltoid – tibiocalcaneal, F) deltoid – tibiotalar, and H) cervical ligaments. The solid black

lines represent the bias in the mean differences between the measurements, the dotted lines

represent the 95% limits of agreement, CR represents the coefficient of repeatability, and CV

represents the coefficient of variation.

0

4

8

12

0 250 500 750 1000

Str

ain

(%

)

Load (N)

0

4

8

12

0 250 500 750 1000

Str

ain

(%

)

Load (N)

0

4

8

12

0 250 500 750 1000

Str

ain (

%)

Load (N)

0

4

8

12

0 250 500 750 1000

Str

ain

(%

)

Load (N)

r = 0.87 (p = 0.06)

r = 0.99 (p = 0.002)*

r = 0.81 (p = 0.1)

r = 0.77 (p = 0.13)

A) B)

H) G)

F) E)

C) D)

76

Figure 4.7: Model-estimated ligament strains using bone pins (orange line) skin markers

(green line) at each axial load for the A) spring – superomedial, C) spring – inferior, E)

bifurcate – calcaneonavicular, and G) bifurcate – calcaneocuboid ligaments. Bland-Altman

plots for the B) spring – superomedial, D) spring – inferior, F) bifurcate – calcaneonavicular,

and H) bifurcate – calcaneocuboid ligaments. The solid black lines represent the bias in the

mean differences between the measurements, the dotted lines represent the 95% limits of

agreement, CR represents the coefficient of repeatability, and CV represents the coefficient of

variation.

0

4

8

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ain (

%)

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r = 0.97 (p = 0.0008)*

r = 0.99 (p = 0.002)*

r = 0.98 (p = 0.005)*

r = 0.83 (p = 0.08)

A) B)

H) G)

F) E)

C) D)

77

Figure 4.8: Model-estimated ligament strains using bone pins (orange line) skin markers

(green line) at each axial load for the A) deltoid – tibionavicular, C) deltoid – tibiocalcaneal,

E) deltoid – tibiotalar, and G) cervical ligaments. Bland-Altman plots for the B) deltoid –

tibionavicular, D) deltoid – tibiocalcaneal, F) deltoid – tibiotalar, and H) cervical ligaments.

The solid black lines represent the bias in the mean differences between the measurements, the

dotted lines represent the 95% limits of agreement, CR represents the coefficient of

repeatability, and CV represents the coefficient of variation.

0

4

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r = 0.99 (p = 0.002)*

r = 0.99 (p = 0.002)*

r = 0.60 (p = 0.29)

r = 0.94 (p = 0.02)*

A) B)

H) G)

F) E)

C) D)

78

CHAPTER 5. EFFECTS OF LOW-DYE TAPING ON PLANTAR FASCIA STRAIN

AND FOOT KINEMATICS IN INDIVIDUALS WITH PLANTAR FASCIITIS




Modified from a manuscript to be submitted to Clinical Biomechanics

Abstract

The low-Dye taping method has been found to be effective at reducing pain and

increasing function in individuals with plantar fasciitis. While there are several proposed reasons

for this, the true reason for the reduction of pain following the taping procedure is unknown.

Therefore, the purpose of the study is to investigate the effect of the low-Dye taping method on

plantar fascia strain in individuals with plantar fasciitis. Fifteen adults with plantar fasciitis

participated in a repeated measures study, in which they walked barefoot at a self-selected speed

while untaped and while their pathological foot was taped using the low-Dye taping method.

Statistical Parametric Mapping (SPM) was used to compare plantar fascia strain between the two

conditions across stance phase. Significantly greater plantar fascia strain was found during the

untaped condition between 57-86% of stance phase (p = 0.008), which does not include the time

during stance phase when peak strain was reached. Post-hoc SPM analyses were conducted on

several foot joint motions to help explain the reported difference in plantar fascia strain, and the

low-Dye taping method reduced the amount of talonavicular joint dorsiflexion during 47-86% of

stance phase (p = 0.004), which represents a reduction in arch collapse. Finally, exploratory SPM

analyses were conducted on several secondary ligaments thought to assist the plantar fascia in

arch support. It was found that the low-Dye taping method reduced strains of the superomedial

and inferior slips of the spring ligament from 5-84% (p < 0.001) and 19-60% (p < 0.001) of

79

stance phase, respectively, and the 2nd and 3rd slips of the long plantar ligament from 70-85% (p

= 0.021) and 73-85% (p = 0.026) of stance phase, respectively. Our findings suggest that the

low-Dye taping method is effective at reducing pain in individuals with plantar fasciitis due to its

ability to reduce cumulative strain across the entire stance phase, which occurs due to the

reduction in arch collapse.

Introduction

Plantar fasciitis affects up to 10% of the population [1] and results in approximately one

million patient visits to office-based physicians and hospital outpatient departments each year

[2]. Unfortunately, the etiology of planter fasciitis is not well understood. While the etiology is

multifactorial in nature, the development of the disorder is believed to be caused by excessive

strain at the insertion of the plantar fascia on the calcaneal tubercle that produces microdamage

and/or inflammation [3–6]. Overpronation has often been cited as a risk factor for plantar

fasciitis [5,7,8], and the collapse of the medial longitudinal arch that occurs with pronation may

place an increased amount of strain on the plantar fascia [5]. Excessive pronation has been

reported in individuals with plantar fasciitis, although the measures were assessed visually [8].

Rearfoot eversion, a surrogate measure of pronation, has also been found to be altered in

individuals with plantar fasciitis. Although Chang et al. [9] reported no differences in peak

rearfoot eversion between healthy individuals and individuals with plantar fasciitis, they found

that individuals with plantar fasciitis displayed greater total rearfoot eversion when walking.

However, there have also been studies reporting no differences in rearfoot pronation between

individuals with plantar fasciitis and healthy controls [10,11]. Therefore, it is important to further

investigate the relationship between pronation and plantar fasciitis. Multi-segment foot models

are a valuable tool to accomplish this because they can be used to assess the complex interactions

of joint motions in the foot, as well as estimate strains of the plantar fascia and other ligaments

80

directly. While the plantar fascia provides much of the support of the medial longitudinal arch,

there are also several ligaments that have been shown to provide support under static conditions,

such as the spring ligament, portions of the deltoid ligament, long and short plantar ligaments,

bifurcate ligament, and cervical ligament [12–17]. However, more information is needed

regarding the role that these ligaments play in the support of the medial longitudinal arch during

dynamic activities.

There are several conservative treatment options for plantar fasciitis, including anti-

inflammatory methods such as NSAIDs or steroid injections, pain reduction methods such as

analgesics or foot pads, and mechanical methods [18]. Mechanical methods include custom

orthotics, over the counter shoe inserts, and night splints [19]. Orthotics are proposed to reduce

the symptoms of plantar fasciitis. This is possibly due to the orthotic helping to maintain medial

longitudinal arch height [20], as plantar fascia strain has been found to be the lowest when

wearing orthotics that maintain medial longitudinal arch height [21]. An alternative mechanical

treatment option is taping. While it is often used as a way to determine the potential success of

custom orthotics [22,23], taping can also be used as a treatment method [4,24]. Much like the

mechanism of orthotics, the low-Dye taping method is designed to control excessive foot

pronation by preventing medial longitudinal arch collapse [25]. It consists of an anchor strip of

tape that begins on the lateral aspect of the fifth metatarsal head, wraps behind the calcaneus, and

attaches on the medial aspect of the first metatarsal head. Then, a series of stirrups are applied on

the plantar aspect of the foot, beginning on the lateral side of the foot and attaching to the medial

side. Tension is applied to the tape during the application of the stirrups to oppose pronation. The

stirrups begin below the medial longitudinal arch and are applied on the plantar aspect of the foot

in a proximal direction until the plantar calcaneus is covered (Figure 5.1).

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Many studies have demonstrated the ability of low-Dye taping to reduce pain and

improve function in plantar fasciitis patients [18,26–28]. There are several proposed reasons for

this, including altered plantar pressures, altered surrounding muscular activity, or altered

kinematics. Research has reported a decrease in plantar pressures under the medial midfoot and

an increase in plantar pressures under the lateral midfoot following low-Dye taping [29,30],

which suggests this taping may help to support the medial longitudinal arch. Reductions in

tibialis posterior and tibialis anterior activity following taping have also been reported [31,32],

although the results are not consistent enough to make definitive conclusions. Finally,

individuals with plantar fasciitis have demonstrated increased medial longitudinal arch height

and reduced rearfoot eversion during static stance following a taping technique similar to the

low-Dye method [33]. Similar results have also been found in healthy individuals considered to

be excessive pronators [34,35].

There are few studies that have considered the effects of low-Dye taping on lower

extremity kinematics during gait, and none to the author’s knowledge have researched the effects

in a clinical population. A reduction in peak rearfoot eversion following low-Dye taping has

been reported in healthy subjects [36], although no significant differences in peak rearfoot

eversion during walking has also been reported [34,37]. Furthermore, Vicenzino et al. [38] and

Yoho et al. [39] both reported a significantly higher medial longitudinal arch height in healthy

subjects following low-Dye taping methods when compared to the untaped condition. At this

point, the kinematic effects of low-Dye taping on individuals with plantar fasciitis during

walking have not been investigated. Therefore, the purpose of the study is to determine the

effects of low-Dye taping on plantar fascia strain in individuals with plantar fasciitis during

walking. It was hypothesized that the low-Dye taping method would result in reduced levels of

82

plantar fascia strain during walking in individuals with plantar fasciitis. Previous studies have

limited their kinematic analysis of the foot to medial longitudinal arch height and rearfoot

eversion. Therefore, an additional exploratory purpose of the study is to investigate the effects of

low-Dye taping on the kinematics of the foot using a multi-segment foot model. Finally, there is

limited knowledge regarding other ligaments besides the plantar fascia that help to support the

arch during dynamic activities. Therefore, the effects of low-Dye taping on strain during walking

in several ligaments of the foot will be investigated using the multi-segment foot model.

Methods

Participants

To investigate the effects of low-Dye taping on foot kinematics and ligament strains, data

were collected on individuals who currently had plantar fasciitis. Participants were included in

the study if they had been diagnosed by a physician, if they had been experiencing pain for at

least three months, if they had no arthritis or other concurrent lower extremity or back injuries,

and if they had received no steroid injections within the last three months. Other treatments such

as taping, shoe inserts, custom orthotics, and NSAIDs were acceptable. Treatment for the plantar

fasciitis patients must have been consistent for a period of three months before they were

allowed to participate in the study.

A power analysis using the results from Vicenzino et al. [38] was used to calculate the

required sample size for a repeated measures study assuming α=0.05 and β=0.20. The study

measured the effects of augmented low-Dye taping on the sagittal plane midfoot angle during

gait in seventeen healthy individuals. The results of the power analysis revealed that a sample of

ten participants was required to yield sufficient statistical power. Eventually, fifteen participants

with plantar fasciitis were recruited for the study (11 males, 4 females; age: 38.3±15.8yrs;

height: 1.8±0.1m; mass: 78.4±12.3kg).

83


Following the informed consent procedure, participants were screened by a licensed

podiatrist to ensure they met the inclusionary criteria for plantar fasciitis. Static measures of arch

height index [38,40] and arch rigidity index [41] were obtained before taping the pathological

foot (10 right feet analyzed, 5 left feet analyzed). For plantar fasciitis patients who displayed

bilateral plantar fasciitis, the foot that displayed greater symptoms was used for analysis.

Statically, arch height index measures were taken while the participant stood with equal weight

on both limbs. The arch height index was calculated by dividing the arch height by the truncated

foot length, which is the distance from the posterior heel surface to the first metatarsophalangeal

(MTP) joint line. The same measures were taken while the participant sat in a chair with equal

weight on both limbs, and the arch rigidity index was then calculated by dividing the arch height

index during standing by the arch height index during sitting (standing AHI = 0.38±0.04, seated

AHI = 0.40±0.04, ARI = 0.95±0.03). Following the static measures, a standing calibration trial

was captured. A support was provided to the participant to allow them to offload their

pathological foot while keeping contact with the ground. Participants then walked overground on

the force platforms at a self-selected barefoot walking speed (untaped = 1.26±0.15m/s; taped =

1.25±0.16m/s) while kinematics and ground reaction forces were collected. Each participant

performed ten trials in each of two conditions: barefoot and barefoot with low-Dye tape on the

pathological foot. Participants were taped with rigid sports tape with zinc oxide adhesive (Henry

Schein, Inc., Melville, NY, USA) by a licensed podiatrist with extensive experience performing

the low-Dye taping method. The conditions were counterbalanced, and half the participants

started with the untaped condition while the other half started with the taped condition. Five

marker triads were placed on the calcaneus, navicular, cuboid, 1st metatarsal, and hallux of the

taped foot. A curved base of each triad was fitted to the bone. The triads were attached with

84

double-sided tape on the base and secured with athletic tape over the top. Anatomical markers

were placed on the sacrum, ASIS, greater trochanter, medial and lateral knee, and medial and

lateral malleoli, and tracking markers were placed on the thigh and shank on the taped side to

measure additional kinematics while walking during both conditions. Anthropometric

measurements and marker placements were performed by the same researchers for all

participants.

Data Analysis

Raw 3D coordinate data were low-pass filtered at 8 Hz and input into a custom Matlab

script (MathWorks, Inc., Natick, MA). The ground reaction force data were used to determine

stance phase, which was defined as a vertical ground reaction force greater than 20N. The six-

segment, modified musculoskeletal model [42] that was described in chapter four was utilized to

analyze the data and provide estimates of plantar fascia and ligament strains. Talus motion was

considered to be the same as calcaneus motion in the sagittal plane and considered to be the same

as leg motion in the frontal and transverse planes. This assumption allowed for a representation

of both subtalar and talonavicular joint motions, even when using skin markers which cannot be

placed over the talus. Movement of the model ankle joint using calcaneal and tibial markers was

limited to the sagittal plane, with frontal and transverse plane motions between these bones

attributed to the subtalar joint. A further modification of the model included the addition of four

slips of the long plantar ligament and one slip of the short plantar ligament (Figure 5.2), as both

have been found to provide support to the medial longitudinal arch [13,15].

Plantar fascia strain during stance phase was analyzed using one-dimensional statistical

parametric mapping (SPM) (spm1d, version M.0.4.7 for Matlab, http://spm1d.org). SPM is a

procedure that was originally developed to analyze cerebral blood flow in 3D PET and fMRI

images [43,44], but it has also been utilized to analyze spatiotemporal biomechanical data [45].

http://spm1d.org/

85

SPM takes into consideration the time-dependent nature of biomechanical variables such as joint

kinematics or ligament strains and performs a statistical comparison across the entire

spatiotemporal profile, rather than analyzing a discrete time point. Specifically, plantar fascia

strain was compared between the untaped and taped conditions using an SPM two-tailed

dependent t-test. First, the SPM{t} statistic was calculated for each data point during the stance

phase of gait. Random field theory was then used to determine the critical threshold in which the

SPM{t} statistic must cross to be considered significantly different at the α = 0.05 level. Tests

for normality using the D’Agostino-Pearson K2 test. Violations of normality were defined by a

significant K2 test statistic at the α = 0.05 level. In cases where violations of normality occurred,

non-parametric SPM analysis was conducted.

To further investigate the effects of low-Dye taping on plantar fascia strain, post hoc

analyses were conducted. The multi-segment foot model was used to explore kinematic variables

to help explain differences in plantar fascia strain. SPM procedures were utilized to analyze the

sagittal plane kinematics of the ankle joint, talonavicular joint, tarsometatarsal (TMT) joint, and

MTP joint, as well as the frontal and transverse plane kinematics of the subtalar joint. Finally,

strains in the spring, deltoid, long plantar, short plantar, bifurcate, and cervical ligaments during

stance phase were analyzed using the same SPM procedures utilized for the plantar fascia.

Results

At initial contact, there was a small spike in plantar fascia strain, which indicates an

increased strain magnitude relative to the offloaded standing calibration trial. Following the

initial spike, strain reduced to approximately 1-1.5% during midstance. This is followed by a

much larger spike in strain magnitude during late stance that corresponds to the push-off phase

of the gait cycle (Figure 5.2A).

86

Statistical parametric mapping revealed a significant difference in plantar fascia strain

between the untaped and taped conditions because the SPM{t} statistic crossed the critical

threshold at α = 0.05 (p = 0.008). More specifically, differences between plantar fascia strain

were present between 57-86% of stance phase, with lesser strain present in the taped condition

(Figure 5.2B).

Subsequent analyses revealed a significant difference in talonavicular joint motion

between the untaped and taped conditions (p = 0.004) from 47-86% of stance phase (Figure 5.3A

and 5.3B). The taped condition displayed a smaller degree of talonavicular joint dorsiflexion,

indicating a reduced amount of arch collapse in the taped condition. A significant difference was

also found in the transverse plane subtalar joint motion from 15-17% (p = 0.047) and 33-65% (p

= 0.013) of stance phase, with the taped condition exhibiting greater subtalar abduction (Figure

5.3C and 5.3D). Analyses of the ankle, TMT, MTP, and frontal plane subtalar joint revealed no

statistical differences between the conditions.

Exploratory investigation of ligament strains revealed several significant differences due

to the walking conditions. Both slips of the spring ligament displayed lower magnitudes of strain

during the taped condition. The superomedial slip displayed significantly lesser strain (p < 0.001)

during the taped condition from 5-84% of stance phase (Figure 5.4A and 5.4B), while the

inferior slip displayed significantly lesser strain (p < 0.001) during the taped condition from 19-

60% of stance phase (Figure 5.4C and 5.4D). Finally, the 2nd and 3rd slips of the long plantar

ligament displayed higher magnitudes of the untaped condition, with the 2nd slip exhibiting

significantly greater strain (p = 0.021) during the untaped condition from 70-85% of stance phase

(Figure 5A and 5B) and the 3rd slip exhibiting significantly greater strain (p = 0.026) during the

untaped condition from 73-85% of stance phase (Figure 5C and 5D). However, no significant

87

differences were found in the deltoid, 4th slip of the long plantar, deep component of the long

plantar, short plantar, bifurcate, or cervical ligaments.

Discussion

The results of the study supported the hypothesis that the low-Dye taping method results

in reduced levels of plantar fascia strain in individuals with plantar fasciitis when walking. The

levels of plantar fascia strain estimated by the model ranged from approximately 0.5-1.5% strain

during midstance to nearly 6% strain during late stance. These values are similar to Caravaggi et

al. [46], who reported peak strain magnitudes that ranged between 3.5-6.0% in a group of healthy

individuals when using a rigid body model to estimate plantar fascia strains during walking. The

study conducted by Fessel et al. [47] also provides support to the strain values estimated by this

study’s model. In it, the researchers reported a mean peak plantar fascia strain value of 4.8%

when they used fluoroscopy to measure plantar fascia strains during walking.

It is believed that excessive strain in the plantar fascia produces microtears and

inflammation at the insertion of the plantar fascia on the medial calcaneal tubercle, which leads

to plantar fasciitis [3–6]. A reduction in pain following the application of low-Dye tape has been

shown in individuals with plantar fasciitis [18,26–28]. The results of our study revealed a

reduction of plantar fascia strain during the taped condition from 57-86% of stance phase, which

may help to explain the ability of the low-Dye taping method to reduce pain in individuals with

plantar fasciitis. Interestingly, there was no difference between the conditions at the time of peak

plantar fascia strain, which occurred at approximately 90% of stance phase. These results suggest

that the reduction in pain from the low-Dye taping method is not due to a reduction in peak

plantar fascia strain, but instead due to a cumulative reduction in strain across the entire stance

phase.

88

The low-Dye taping method may also reduce pain in plantar fasciitis patients by affecting

the function of the windlass mechanism. Previous studies have demonstrated the function of the

windlass mechanism by showing that an increase in MTP joint dorsiflexion causes the plantar

fascia to wind around the metatarsal heads, which increases the tension of the plantar fascia

[46,48,49]. Additionally, it has previously been reported that plantar fascia strain is moderated

by both MTP joint motion and arch collapse [50,51]. The results of this study support the strong

relationship between the windlass mechanism and plantar fascia strain, as the rapid increase of

MTP joint dorsiflexion during late stance corresponds to a similar rapid increase of plantar fascia

strain. However, the rapid increase of plantar fascia strain during the push-off phase occurred

slightly later during the taped condition. This suggests that the arch support provided by the

taping method acts to delay the engagement of the windlass mechanism by keeping the

talonavicular joint closer to neutral. The relative slackness of the plantar fascia in the taped

condition due to the increased arch height requires a greater amount of MTP joint dorsiflexion to

engage the windlass mechanism. Furthermore, the reduction in talonavicular dorsiflexion angle

helps to explain the decreased magnitude of plantar fascia strain during midstance. Increased

arch collapse (represented in this study by an increased talonavicular dorsiflexion angle)

increases the total distance between the calcaneus and the hallux, which increases the overall

strain in the plantar fascia.

The reduced arch collapse demonstrated by the individuals with plantar fasciitis in our

study was supported by the results found by Vicenzino et al. [38] and Yoho et al. [39], who

reported similar results in healthy individuals. In addition to the significant reduction of

talonavicular dorsiflexion caused by low-Dye taping, the participants in the current study also

demonstrated significantly greater subtalar abduction. While electromyographic data were not

89

collected in the study, it is possible that the application of the low-Dye tape affected activity of

the tibialis posterior and peroneus brevis muscles. The tibialis posterior is a subtalar inverter,

while the peroneus brevis is an everter [52]. The action of the low-Dye tape to prevent subtalar

eversion may reduce activity of the tibialis posterior, thereby increasing the action of its

antagonist, the peroneus brevis. In contrast to these results, a previous study conducted by

O’Sullivan et al. [36] reported reduced subtalar pronation following low-Dye taping. However, it

is important to note that the authors utilized a different method of subtalar joint measurement,

which may explain the differences in results. Furthermore, pronation is a tri-planar motion used

to describe a combination of dorsiflexion, eversion, and abduction, but previous research has

shown that motions of the subtalar joint often do not occur in the tri-planar pattern mentioned

above during closed-chain activities [53,54].

The decrease in arch collapse following application of the low-Dye tape can also explain

the decreased strains of the superomedial and inferior slips of the spring ligament, as well as the

2nd and 3rd slips of the long plantar ligament. Both the spring ligament and the long plantar

ligament provide support to the medial longitudinal arch [12,16], and the current study shows

that an increase in arch collapse increases the strain in the spring and long plantar ligaments.

Research has shown that release of the spring ligament increased arch collapse by 14.9% [15],

and a finite element model has shown that tension in the long plantar ligament increased by 91%

following release of the plantar fascia [13]. The results of the current study provide further

evidence of the roles that the spring and long plantar ligaments play in the maintenance of medial

longitudinal arch support. However, caution must be taken when interpreting the results of these

ligaments, as statistically significant differences found when the strains are negative may have

90

little physiological significance. More research needs to be conducted to better understand the

true physiological strains of these ligaments during dynamic activities such as walking.

The current study demonstrates the ability of the low-Dye taping method to reduce

plantar fascia strain during walking during a short time. The long-term effects of the low-Dye

taping method were not considered in this study, so caution must be taken when interpreting the

results of the study. Additionally, several limitations of the study must be considered. First, the

inability to directly measure talus motion may have affected measurements of the subtalar and

talonavicular joints. Because markers cannot be placed on the talus bone, the model was

modified to attribute frontal and transverse plane motions of the ankle joint to the subtalar joint.

A study that inserted bone pins in the foot to measure ankle and subtalar joint motion found that

plantarflexion/dorsiflexion occurred mainly around the ankle joint, while inversion/eversion and

abduction/adduction occurred equally across both joints [55]. However, it must be noted that the

study was only conducted on three participants, and the researchers concluded that the

assumption is appropriate for some individuals. While the visual recreation of the walking trials

with the musculoskeletal model appeared reasonable, it is possible that the inability of the model

to measure true motions of the subtalar joint affected the estimated strain magnitudes of the

plantar fascia and other ligaments. However, the similarity of the plantar fascia strain magnitudes

in the current study to strain magnitudes reported in other studies [21,46] provides support to the

validity of the current model. Another limitation of the study was the use of markers mounted on

the skin to represent the underlying motion of the foot bones, as previous research has reported

significant kinematic differences between bone pins and skin markers [56]. However, the

validation results reported in chapter four support the use of skin markers to represent the bones

of the foot during walking.

91

Conclusions

The results of this study show that the low-Dye taping method is effective at reducing

plantar fascia strain during walking. While it does not reduce the magnitude of peak plantar

fascia strain, it causes the increase in strain due to activation of the windlass mechanism to occur

later in the stance phase. The reduction in plantar fascia strain can be attributed to the significant

positive effect that the low-Dye taping method has on arch collapse, represented by talonavicular

motion in this study. Finally, this study shows that support to the medial longitudinal arch is

provided by both the spring and long plantar ligaments.

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Figures and Tables

Figure 5.1: The low-Dye taping procedure is designed to prevent medial longitudinal arch

collapse. Reprinted from “Arch-taping techniques for altering navicular height and plantar

pressures during activity,” by T. Newell, J. Simon, and C. Docherty, 2015, Journal of Athletic

Training, 50(8), 827. [57]

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Figure 5.2: The model described in chapter four was modified to include the long plantar

ligament and short plantar ligament.

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Figure 5.2: A) Mean plantar fascia strain during stance phase across all participants during

untaped (black line) and low-Dye taped (blue line) walking conditions. B) The critical threshold

of 2.716 was exceeded from 57-86% of stance phase, indicating significantly lesser (p = 0.008)

plantar fascia strain during the taped condition.

A) B)

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Figure 5.3: A) Mean sagittal plane talonavicular angle and C) mean transverse plane subtalar

angle during stance phase across all participants during untaped (black line) and low-Dye taped

(blue line) walking conditions. B) For the talonavicular joint, the critical threshold of 2.535 was

exceeded from 47-86% of stance phase, indicating significantly lesser (p = 0.004) talonavicular

joint dorsiflexion during the taped condition. D) For the subtalar joint, the critical threshold of

2.213 was exceeded from 15-17% and from 33-65% of stance phase, indicating significantly

greater (p = 0.047 and p = 0.013, respectively) subtalar joint abduction in the taped condition.

C) D)

A) B)

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Figure 5.4: Mean strain of the A) superomedial and C) inferior slips of the spring ligament

during stance phase across all participants during untaped (black line) and low-Dye taped (blue

line) walking conditions. B) For the superomedial slip, the critical threshold of 2.339 was

exceeded from 5-84% of stance phase, indicating significantly lesser (p < 0.001) strain during

the taped condition. D) For the inferior slip, the critical threshold of 2.783 was exceeded from

19-60% of stance phase, indicating significantly lesser (p < 0.001) strain in the taped condition.

C) D)

A) B)

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Figure 5.5: Mean strain of the A) 2nd and C) 3rd slips of the long plantar ligament during stance

phase across all participants during untaped (black line) and low-Dye taped (blue line) walking

conditions. B) For the 2nd slip, the critical threshold of 2.823 was exceeded from 70-85% of

stance phase, indicating significantly greater (p = 0.021) strain during the untaped condition. D)

For the 3rd slip, the critical threshold of 2.864 was exceeded from 73-85% of stance phase,

indicating significantly greater (p = 0.026) strain in the untaped condition.

C) D)

A) B)

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Appendix: Institutional Review Board Approval

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103

CHAPTER 6. GENERAL CONCLUSIONS

Summary

The overall purpose of this dissertation was to investigate strains in the plantar fascia and

other ligaments that help to support the medial longitudinal arch with a specific goal to provide

insight into the injury mechanism of plantar fasciitis.

The first study examined several environmental factors thought to influence plantar fascia

strain. The effects of speed, incline, and shoe stiffness on peak plantar fascia strain during

walking were analyzed in healthy participants using a four-segment musculoskeletal model. It

was found that increased speed caused an increase in peak plantar fascia strain, while incline and

shoe stiffness did not affect peak strains. Furthermore, the study examined the interaction

between metatarsophalangeal (MTP) joint motion and arch collapse to help explain the results, as

both have been found to moderate plantar fascia strain [1–3]. The function of the windlass

mechanism was demonstrated; the results showed that MTP joint dorsiflexion during the push-

off phase contributed to an increase in plantar fascia strain. However, the MTP joint dorsiflexion

was accompanied by an increase in arch height, which contributed to a decrease in the plantar

fascia strain, thereby resulting in no significant differences in peak plantar fascia strain between

inclines or shoe stiffnesses.

The second study was conducted to validate a six-segment musculoskeletal model of the

foot that was created to generate estimations of ligament strains. In addition to the plantar fascia,

several ligaments also provide support to the medial longitudinal arch and help to control

motions such as excessive pronation [4–7]. Because of their contribution to arch support, these

ligaments may influence the magnitude of the load placed on the plantar fascia, which may be a

factor in the development of plantar fasciitis. The spring, deltoid, bifurcate, and cervical

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ligaments were dissected on seven cadaver specimens, and strains were directly measured using

a manual digitizer and estimated using the musculoskeletal model while an axial load was placed

on the tibia. While there were some limitations to the results, strong correlations were reported in

several ligaments. Furthermore, many ligaments exhibited low coefficients of repeatability.

Therefore, the model was deemed appropriate to use in the subsequent study.

The final study examined the effects of the low-Dye taping method on plantar fascia

strain during walking in individuals with plantar fasciitis. The study also utilized the six-segment

musculoskeletal model to estimate the effects of the low-Dye taping method on ligament strains.

The low-Dye taping method helps to support the arch, and research has shown it is effective at

reducing pain and improving function in individuals with plantar fasciitis [8–11]. It was found

that the taping method reduced plantar fascia strain during midstance, although there was no

reduction of peak plantar fascia strain. The function of the windlass mechanism was also affected

by the taping method. The rapid increase of plantar fascia strain during the push-off phase

occurred slightly later, which suggests that the arch support provided by the taping method acts

to delay the engagement of the windlass mechanism by reducing talonavicular joint dorsiflexion.

Consequently, the increased arch height in the taped condition required a greater amount of MTP

joint dorsiflexion to overcome the relative slackness of the plantar fascia and engage the

windlass mechanism. The musculoskeletal model also revealed a significant decrease in spring

ligament and long plantar ligament strain during the taped condition. As both ligaments have

been shown to provide support to the medial longitudinal arch [4,12], these results suggest that

these ligaments may play a role in the development of plantar fasciitis by affecting the

magnitude of the load placed on the plantar fascia. However, more research needs to be

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conducted on these tissues, as there is very little published information on the behavior of the

ligaments in the foot during dynamic activities.

Significance and Future Directions

In summary, this dissertation provides information about the plantar fascia strain

response under several different conditions. The results from this dissertation that examined

effects of speed, incline, shoe stiffness, and taping on plantar fascia strain affirm the contribution

of the windlass mechanism to plantar fascia strain, as both MTP joint motion and arch collapse

interact to influence plantar fascia strain magnitudes during walking. Furthermore, the spring and

long plantar ligament provide support to the medial longitudinal arch, and the way they influence

the magnitude of strains in the plantar fascia needs to be investigated further. Finally, the results

suggest that it may be the accumulation of strain rather than peak strain that plays a role in the

development and perpetuation of plantar fasciitis. This finding has implications, both in our

understanding of the disorder and in the treatment of the disorder. Further research is necessary

to better understand the plantar fascia strain response, as it is hoped that understanding the role

of plantar fascia strain in the etiology of plantar fasciitis will enable effective treatment and

prevention of the disorder.

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Documents

Strain estimations of the plantar fascia and other