Elbow Joint - Biomech

8/8/2019 Elbow Joint - Biomech.

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ELBOW COMPLEX


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INTRODUCTION The elbow complex includes the elbow joint (humeroulnar and

humeroradial joints) and the proximal and distal radioulnar joints.

The elbow joint is considered to be a compound joint that functions as a

modified or loose hinge joint.

One degree of freedom is possible at the elbow, permitting the motions

of flexion and extension, which occur in the sagittal plane around a

coronal axis. A slight bit of axial rotation and side-to-side motion of the

ulna occurs during flexion and extension, and that is why the elbow is

considered to be a modified or loose hinge joint rather than a pure

hinge joint.


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Two major ligaments and five muscles are directly

associated with the elbow joint.

Three of the muscles are flexors that cross the anterioraspect of the joint.

The other two muscles are extensors that cross the

posterior aspect of the joint.

The proximal and distal radioulnar joints are linked and

function as one joint. The two joints acting together

produce rotation of the forearm and have 1 degree of

freedom of motion.

The radioulnar joints are diarthrodial uniaxial joints of

the pivot (trochoid) type and permit rotation

(supination and pronation), which occurs in the

transverse plane around a longitudinal axis.


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Six ligaments and four muscles are associated

with these joints. Two muscles are for

supination, and two are for pronation.

The elbow joint and the proximal radioulnar jointare enclosed in a single joint capsule but

constitute distinct articulations.


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ELBOW JOINT - ARTICULATION


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ARTICULATION HUMERORADIAL &

HUMEROULNAR JOINTS

The articulating surfaces on the anterior aspect of the distal

humerus are the hourglass-shaped trochlea and the spherical

capitulum.

These structures are situated between the medial and lateralhumeral epicondyles.

The trochlea, which forms part of the humeroulnar articulation, is

set at an angle on the medial aspect of the distal humerus and

lies slightly anterior to the humeral shaft.

A groove called the trochlear groove spirals obliquely around the

trochlea and divides it into medial and lateral portions.

The medial portion of the trochlea projects distally more than thelateral ortion and results in a val us an ulation of the forearm.


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The indentation in the humerus located just

above the trochlea is called the coronoid fossa

and is designed to receive the coronoid processof the ulna at the end of elbow flexion range of

motion (ROM).

The capitulum, which is part of the humeroradialarticulation, is located on the anterior lateral

surface of the distal humerus.

The capitulum, like the trochlea, lies anterior tothe shaft of the humerus. A groove called the

capitulotrochlear groove separates the

capitulum from the trochlea.


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The indentation located on the humerus just

above the capitulum is called the radial fossa

and is designed to receive the head of the radius

in elbow flexion.

Posteriorly, the distal humerus is indented by a

deep fossa called the olecranon fossa, which is

designed to receive the olecranon process of the

ulna at the end of elbow extension ROM.


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ARTICULATING SURFACES OF RADIUS

AND ULNA The articulating surfaces of the ulna and radius

correspond to the humeral articulating surfaces.

The ulnar articulating surface of the humeroulnarjoint is a deep semicircular concave surface called

the trochlear notch.

The proximal portion of the notch is divided intotwo unequal parts by the trochlear ridge, whichcorresponds to the trochlear groove on thehumerus.

The ulnar coronoid process forms the distal end ofthe notch, whereas the olecranon process projectsover the proximal end.


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The radial articulating surface of the

humeroradial joint is composed of the proximal

end of the radius, known as the head of theradius.

The radial head has a slightly cup-shaped

concave surface called the fovea that issurrounded by a rim.

The radial heads convex rim fits into the

capitulotrochlear groove.


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ARTICULATION

Articulation between the ulna and humerus at the

humeroulnar joint occurs primarily as a sliding

motion of the ulnar trochlear ridge on the humeral

trochlear groove.In extension, sliding continues until the olecranon

process enters the olcranon fossa .

In flexion, the trochlear ridge of the ulna slides alongthe trochlear groove until the coronoid process

reaches the floor of the coronoid fossa in full flexion.


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Articulation between the radial head and the

capitulum at the humeroradial joint involves

sliding of the shallow concave radial head overthe convex surface of the capitulum.

In full extension, no contact occurs between the

articulating surfaces. In flexion, the rim of the radial head slides in the

capitulotrochlear groove and enters the radial

fossa as the end of the flexion range is reached.


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JOINT CAPSULE

The humeroulnar and humeroradial joints and thesuperior radioulnar joint are enclosed in a single jointcapsule.

Anteriorly, the proximal attachment of the capsule is

just above the coronoid and radial fossae,and distallyit is inserted into the ulna on the margin of thecoronoid process.

The capsule blends with the proximal border of the

annular ligament except posteriorly, where thecapsule passes deep below the annular ligament toattach to the posterior and inferior margins of theneck of the radius


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Laterally, the capsules attachment to the radius

blends with the fibers of the lateral collateral

ligament (LCL).

Medially, the capsule blends with fibers of the

medial collateral ligament (MCL).

Posteriorly, the capsule is attached to the

humerus along the upper edge of the olecranon

fossa.


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The capsule is fairly large, loose, and weak

anteriorly and posteriorly, and it contains folds

that are able to unfold to allow for a full range of

elbow motion.

Laterally and medially, the capsule is reinforced

by the collateral ligaments.


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LIGAMENTS

The two main ligaments associated with the

elbow joints are the

medial (ulnar) and

lateral (radial) collateral ligaments.


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MEDIAL COLLATERALLIGAMENT

The MCL is considered to be the major soft tissuerestraint of valgus stress at the medial aspect of

the elbow.

The elbow joints normal valgus configuration

subjects the medial aspect of the joint to a high

degree of valgus stress, especially during

throwing and golfing activities. The MCL is described as consisting of two parts

(anterior and posterior)or three parts (anterior,

oblique or transverse, and posterior).


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The anterior part of the MCLextends from the

anterior aspect, tip, and medial edge of the

medial epicondyle of the humerus to attach on

the ulnar coronoid process.

Mechanoreceptors (Golgi organs, Ruffini

terminals, Pacini corpuscles, and free nerve

endings) are densely distributed near the

ligaments humeral and ulnar attachments.


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The anterior portion of the MCL is considered to

be the primary restraint of valgus stress from 20

to 120 degrees of elbow flexion.

Scientists the composition of the anterior portion

of the MCL as having an anterior band and a

posterior band that tighten in a reciprocalmanner as the elbow flexes and extends.

The anterior band of the anterior portion was

found by these authors to be the primaryrestraint of valgus at 30, 60, and 90 degrees of

flexion.


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The posterior portion of the MCL extends from

the posterior aspect of the medial epicondyle of

the humerus to attach to the ulnar coronoid and

olecranon processes.

The posterior MCLlimits elbow extension but

plays a less significant role than the anterior MCL

in providing valgus stability for the elbow.


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The oblique (transverse) fibers of the MCL

extend between the olecranon and ulnar

coronoid processes.

This portion of the ligament assists in providingvalgus stability and helps to keep the joint

surfaces in approximation.


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LATERAL COLLATERALLIGAMENT

The lateral collateral ligamentous complex

includes the LCL, the lateral ulnar collateral

ligament (LUCL)and the annular ligament.

The LCL is a fan-shaped structure that extends

from the inferior aspect of the lateral epicondyleof the humerus to attach to the annular ligament

and to the olecranon process.


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LUCL - Ligamentous tissue extending from the

lateral epicondyle to the lateral aspect of the

ulnar and the annular ligament, adheres closely

to the supinator, extensor, and anconeus muscles

and lies just posterior to the LCL.

Function ofLCL

1. stabilizes elbow against varus torque.


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2. stabilizes against combined varus and supination

torques.

3. reinforces humeroradial joint and assists in

providing some resistance to longitudinal

distraction of the articulating surfaces.

4. stabilizes radial head, thus providing a stable

base for rotation.

5. maintains posterolateral rotatory stability.


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6. prevents subluxation of humeroulnar joint by

securing ulna to humerus.

7. prevents forearm from rotating off of thE

humerus in valgus and supination during flexionfrom fully extended position.


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MUSCLES

Nine muscles cross the anterior aspect of theelbow joint.

3 have primary functions at the elbow :

B

rachialisBiceps brachii

Brachioradialis

Major functions at radioulnar joints :Supinator

Pronator teres


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Remaining muscles have primary functions at the

wrist, hand & finger joints but are considered to

be weak flexors at the elbow :

Flexor carpi radialis

Flexor carpi ulnaris

F

lexor digitorum superficialis

Palmaris longus


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The two extensors of the elbow are :

Triceps

Anconeus

In addition to the anconeus muscle, a number of

muscles with primary actions at the wrist and

fingers :

Extensor carpi radialis longus (ECRL)

Extensor carpi radialis brevis (ECRB)

Extensor digitorum communis (EDC)

Extensor carpi ulnaris (ECU)

Extensor digiti minimi (EDM)


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The ECRL, ECRB, and ECU are active in gripping ,

hammering, and sawing activities. Therefore, the

repetitive pull of these muscles during a patientsworkday could injure the common extensor

tendon.

The types of changes that might be seen in eithera patients tendon or his muscle, from

examinations of biopsy material from patients

with chronic lateral elbow pain diagnosed as

lateral epicondylitis (inflammation of the lateral

epicondyle and surrounding tissues).


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ELBOW JOINT FUNCTION AXIS OF

MOTION

An exact determination of the axis of motion at

the elbow is important because of the need to

position elbow prostheses in such a way that

they correctly mimic elbow joint motion.


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Screw displacement axis (SDA)

Screw displacement axes (SDAs) are used to

define the elbow axis accurately for proper

prosthesis positioning.

Location of the SDA is influenced by :

The type of flexion motion (active or passive)

By forearm position (pronation or supination)


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Intraindividual and interindividual variations in

the axes appear to be greater in the frontal

plane than in the horizontal plane.


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LONG AXIS OF THE HUMERUS &

FOREARM

In the anatomic position, the long axis of the

humerus and the long axis of the forearm

form an acute angle medially when they meet

at the elbow.

This normal valgus angulation is called the

carrying angle or cubitus valgus


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The average angle in full elbow extension is about 15

degrees.

An increase in the carrying angle beyond the average

is considered to be abnormal, especially if it occurs

unilaterally.

Normally, the carrying angle disappears when the

forearm is pronated and the elbow is in fullextension and when the supinated forearm is flexed

against the humerus in full elbow flexion.


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RANGE OF MOTION

A number of factors determine the amount of

motion that is available at the elbow joint. These

factors include :

The type of motion (active or passive),

The position of the forearm (relative pronation-supination).

Position of the shoulder.


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Type of motion (active/passive)

The range of active flexion at the elbow is usually

less than the range of passive motion, because

the bulk of the contracting flexors on the anterior

surface of the humerus may interfere with the

approximation of the forearm with the humerus.

Active flexion 135-145 degrees

Passive flexion 150-160 degrees


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Position of forearm (pronation/supination)

When the forearm is either in pronation or midprone

position, the ROM is less than it is when the forearm

is supinated.

Position of shoulder

Two joint muscles, such as the biceps brachii and the

triceps, that cross both the shoulder and elbowjoints may limit ROM at the elbow if a full ROM is

attempted at both joints simultaneously.


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The elbow has inherent articular stability at the

extremes of extension and flexion.

In full extension, the humeroulnar joint is in a

close-packed position. In this position, bony

contact of the olecranon process in the

olecranon fossa limits the end of the extension

range, and the configuration of the jointstructures helps provide valgus and varus

stability.


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Approximation of the coronoid process with the

coronoid fossa and of the rim of the radial head

in the radial fossa limits extremes of flexion.

S

welling and or pain also may limit the range ofelbow motion.


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MUSCLES OF ELBOW JOINT

Factors Affecting Elbow Muscle Activity :

Number of joints crossed by the muscle (one joint

or two joint muscles)

Physiologic cross-sectional area (PCSA)

Location in relation to joint

Position of the elbow and adjacent joints

Position of the forearm

Magnitude of the applied load


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Type of muscle action (concentric, eccentric,

isometric, isokinetic)

Speed of motion (slow or fast)

Moment arm (MA) at different joint positions

Fiber types


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Elbow Flexors

BRACHIA

LIS

Brachialis is considered to be a mobility muscle

because its insertion is close to the elbow joint

axis. It has a large strength potential.

Its MA is greatest at slightly more than 100

degrees of elbow flexion, at which its ability to

produce torque is greatest.

Because the brachialis is inserted on the ulna, it

is unaffected by changes in the forearm position

brought about by rotation of the radius.


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Being a one-joint muscle, it is not affected by the

position of the shoulder.

It also is active in all types of contractions

(isometric, concentric, and eccentric) during slow

and fast motions.


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BICEPSBRACHII

Also considered to be a mobility muscle because

of its insertion close to the elbow joint axis.

The long head of the biceps brachii has the

largest volume among the flexors.

The MA of the biceps is largest between 80 and

100 degrees of elbow flexion and, therefore, the

biceps is capable of producing its greatest torque

in this range.


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The MA of the biceps is rather small when the elbow

is in full extension, therefore, when the elbow is fully

extended, the biceps is less effective as an elbow

flexor than when the elbow is flexed to 90 degrees.

When the elbow is flexed beyond 100 degrees, the

translatory component of the muscle force is

directed away from the elbow joint and, therefore,

acts as a distracting or dislocating force.


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The functioning of the biceps is affected by the

position of the shoulder, if full flexion of theelbow is attempted with the shoulder in full

flexion, especially when the forearm is

supinated, the muscles ability to generate

torque is diminished.


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BRACHIORADIALIS

The brachioradialis is inserted at a distance from the

joint axis, and therefore the largest component of

muscle force goes toward compression of the joint

surfaces and hence toward stability.

The peak MA for the brachioradialis occurs between

100 and 120 degrees of elbow flexion.

The brachioradialis does not cross the shoulder

therefore unaffected by position of the shoulder.


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The position of the elbow joint was found to

affect brachioradialis muscle activity only duringvoluntary maximum eccentric contractions.

Elbow joint angle had no effect on concentric,

isometric, or isokinetic maximum voluntary

contractions.

The brachioradialis showed high levels of activity

during rapid alternating supination/pronation

motions.


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OTHER MUSCLES

The pronator teres, as well as the palmaris

longus, flexor digitorum superficialis, flexor carpi

radialis, and flexor carpi ulnaris, is a weak elbow

flexor with primary actions at the radioulnar and

wrist joints.


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Elbow extensors

The effectiveness of the triceps as a whole is

affected by changes in the position of the elbow

but not by changes in position of the forearm,

because the triceps attaches to the ulna and not

the radius.

Maximum isometric torque generation is at a

position of 90 degrees of elbow flexion.


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The triceps is active eccentrically to control

elbow flexion as the body is lowered to the

ground in a push-up.

The triceps is active concentrically to extend the

elbow when the triceps acts in a closed

kinematic chain, such as in a push-up.


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Superior & inferior radioulnar joints

The articulating surfaces of the proximal

radioulnar joint include the ulnar radial notch,

the annular ligament, the capitulum of thehumerus, and the head of the radius.

The articulating surfaces of the distal radioulnar

joint include the ulnar notch of the radius, the

articular disk, and the head of the ulna.


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Articular disk The articular disk is sometimes referred to as

either the triangular fibrocartilage (TFC) because

of its triangular shape or as a part ofthe

triangular fibrocartilage complex (TFCC) because

of its extensive fibrous connections.

The base of the articular disk is attached to the

distal edge of the ulnar notch of the radius.

The apex of the articular disk has twoattachments. One attachment is to the fovea on

the ulnar head. The other attachment is to the

base of the ulnar styloid process.


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The margins of the articular disk are thickened and

are either formed by or are integral parts of the

dorsal and palmar capsular radioulnar ligaments. 80% of the central portion of the articular disk is

avascular, in comparison with the peripheral area,

which was only 15% to 20% avascular.

The articular disk has two articulating surfaces:

The proximal (superior) surface and the distal

(inferior) surface.

The proximal surface of the disk articulates with theulnar head at the distal radioulnar joint, whereas the

distal surface articulates with the carpal bones as

part of the radiocarpal joint.


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RADIOULNAR ARTICULATION

The proximal and distal radioulnar joints are

mechanically linked; therefore, motion at one joint is

always accompanied by motion at the other joint.

The distal radioulnar joint is also considered to be

functionally linked to the wrist in that compressive

loads are transmitted through the distal radioulnar

joint from the hand to the radius and ulna.


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Pronation of the forearm occurs as a result of the

radiuss crossing over the ulna at the superioR

radioulnar joint.

Joint surface contact is optimal only with the

forearm in a neutral position between supination

and pronation.

In maximal pronation and supination, the

articulating surfaces have only minimal contact


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LIGAMENTS OF RADIOULNAR JOINTS

The three ligaments associated with the proximalradioulnar joint are the :

annular ligament

quadrate ligament

oblique cord

ANNULAR

LIGAM

ENT

The annular ligament is a strong band that forms

four fifths of a ring that encircles the radial head.

h l b d f h l l


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The proximal border of the annular ligament

blends with the joint capsule, and the lateral

aspect is reinforced by fibers from the LCL.QUADRATELIGAMENT

The quadrate ligament extends from the inferior

edge of the ulnas radial notch to insert in theneck of the radius.

Reinforces the inferior aspect of the joint capsule

and helps maintain the radial head in apposition

to the radial notch.

The quadrate ligament also limits the spin of the

radial head in supination and pronation.


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OBLIQUE CORD

The oblique cord is a flat fascial band on the

ventral forearm that extends from an attachmentjust inferior to the radial notch on the ulna to

insert just below the bicipital tuberosity on the

radius. May assist in preventing separation of the radius

and ulna.


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The dorsal and palmar radioulnar ligaments, as well

as the IOM, which stabilizes both proximal and distal

joints, reinforce the distal radioulnar joint.

The dorsal and palmar ligaments are formed by

longitudinally oriented collagen fiber bundles

originating from the dorsal and palmar aspects of

the ulnar notch of the radius.

The two ligaments extend along the margins of thearticular disk to insert on the ulnar fovea and base of

ulnar styloid process.


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The interosseous membrane (IOM), which is

located between the radius and the ulna, is acomplex structure consisting of the following

three components:

a central band,

a thin membranous portion, and

a dorsal oblique cord


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The central band is described as being a strong,

thick, ligamentous, or tendinous structure consisting

of bundles of fibers that run obliquely from the

radius to the ulna.

The central band has a very high collagen content.

In contrast to the central band, the membranous

portion is described as a soft and thin structure that

lies adjacent proximally and distally to the central

band.


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The dorsal oblique cord is considered to be part

of the IOM and should not be confused with the

oblique cord located on the ventral aspect of the

forearm, which is not considered to be part of

the IOM.

The dorsal oblique cord extends from the

proximal quarter of the ulna to the middle region

of the radius.

MUSCLE OF RADIOULNAR JOINTS


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MUSCLE OF RADIOULNAR JOINTS

The primary muscles associated with the

radioulnar joints are the

pronator teres,

pronator quadratus,

biceps brachii, and

supinator.


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FUNTION RADIOULNAR JOINT


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FUNTION RADIOULNAR JOINT

AXIS OF MOTION

The axis of motion for pronation and supination is

a longitudinal axis extending from the center ofthe radial head to the center of the ulnar head.

In supination, the radius and ulna lie parallel to

one another, whereas in pronation, the radius

crosses over the ulna.


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RANGE OF MOTION


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RANGE OF MOTION

The ROM of pronation and supination is assessed

with the elbow in 90 of flexion.

This position of the elbow stabilizes the humerus

so that radioulnar joint rotation may be

distinguished from rotation that is occurring at

the shoulder joint.

MUSCLE ACTION


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MUSCLE ACTION

1. The pronator teres has its major action at the

radioulnar joints.

Contributes some of its force toward stabilization of

the proximal radioulnar joint.

2. The pronator quadratus, a one-joint muscle, is

unaffected by changing positions at the elbow.

Active in unresisted and resisted pronation and in

slow or fast pronation.


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Pronators were found to be most efficient around

the neutral position of the forearm when the

elbow was flexed to 90 degrees.


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3. The supinator muscle may act alone during

unresisted slow supination in all positions of the

elbow or forearm.

The supinator also can act alone during unresisted fast

supination when the elbow is extended.

4. Activity of the biceps is always evident when

supination is performed against resistance and

during fast supination when the elbow is flexed to 90

degrees.


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The biceps has been found to exert four times as

much supination torque with the forearm in thepronated position than in other forearm

positions.

5. The anconeus muscle is active in supination and

pronation, and an elbow stabilization role has

been suggested to explain this activity.

STABILITY RADIOULNAR JOINT


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STABILITY RADIOULNAR JOINT

The ulnar head of the pronator teres may help bybinding the ulna to the radius while the humeral

head depresses the ulna during pronation.

The deep head of the pronator quadratus is active

throughout supination and pronation and therefore

is thought to provide dynamic stabilization for the

distal radioulnar joint.

A ti it i th ECU l t d i f


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Activity in the ECUmuscle exerts a depressive force

on the dorsal aspect of the ulnar head as the tendon

is stretched over the head during supination.

Tension in the tendon helps to maintain the position

of the ulnar head during both supination and

pronation.

The ECRBappears to act both as a stabilizer to the

forearm for gripping during pronation torques

(depending on forearm angle) and as a prime mover

for wrist extension for supination torques.

Th d l di l li t b t t i


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The dorsal radioulnar ligament becomes taut in

pronation, whereas the palmar radioulnar

ligament becomes taut in supination.

Radioulnar ligaments are able to prevent

separation of the radius from the ulna during

loading and also allow for force transmission

from the radius to the ulna through the distal

radioulnar joint.

Th ll i l 5 f l b h


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They allow approximately 5 mm of play between the

radius and ulna before providing resistance to

further distraction.

The radioulnar ligaments, the articular disk, and the

pronator quadratus maintain the ulna within the

ulnar notch and prevent the ulna from subluxating

or dislocating.

However, these ligaments allow a high degree of

mobility.

Th IOM id t bilit f th di t l j i t b


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The IOMprovides stability for the distal joint by

binding the radius and ulna together.

IOM in combination with the triangular

fibrocartilaginous complex provide important

longitudinal stabilization.

When the elbow was in the varus position (no

contact between the radial head and capitulum),

force was transmitted from the distal radius through

the IOM to the proximal ulna.

Wh th lb i th l iti


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When the elbow was in the valgus position

(contact between the radial head and the

capitulum), the force was transmitted through

the radius.

The articular disk acts as a cushion in allowing

compression force transmission from the carpals

to the ulna and acts as a stabilizer of the ulnar

side of the carpals.

MOBILITY & STABILITY ELBOW


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COMPLEX

FUNCTIONAL ACTIVITIES

A total arc of about 100 degrees of elbow flexion

(between 30 and 130) and about 100 degrees of

forearm rotation (50 supination and 50

pronation) is sufficient to accomplish simpletasks such as eating, brushing hair, brushing

teeth, and dressing.


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Using the telephone requires the largest arc of

motion in both flexion (92.8) and pronation and

supination (63.5).

Cutting with a knife requires the smallest arc of

flexion and of pronation/supination.

RELATIONSHIP OF THE HAND & WRIST


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RELATIONSHIP OF THE HAND & WRIST

The complete separation of the ulna from thecarpals by the articular disk and the formation of

a true diarthrodial joint lined with articular

cartilage are features that permit pronation and

supination to occur in every position of the hand

to the forearm.

Anatomically the hand and wrist muscles help


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Anatomically, the hand and wrist muscles help

reinforce the elbow joint capsule and contribute

to stability of the elbow complex.

The importance of compression or stabilization

of the elbow is that both the humeroradial and

humeroulnar articulations are subjected to

compressive forces during pulling activities and

that the MCL is heavily loaded.

EFFECTS OF AGE AND INJURY


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EFFECTS OFAGEAND INJURY

Age

Decrease in muscle strength with increasing age.

Injury

Injuries to the elbow are fairly frequent, and in

early adolescence the elbow is one of the mostcommon sites for apophysitis or strains at the

apophysis.

Compression Injuries


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Compression Injuries

Resistance to longitudinal compression forces at the

elbow is provided for mainly by the contact of bony

components; therefore, excessive compression

forces at the elbow often result in bony failure.

Falling on the hand when the elbow is in a close-

packed (extended) position may result in the

transmission of forces through the bones of the

forearm to the elbow.

If the forces are transmitted through the radius as may


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If the forces are transmitted through the radius, as may

happen with a concomitant valgus stress, a fracture of the

radial head may result from impact of the radial head on

the capitulum.

If the force from the fall is transmitted to the ulna, a

fracture of either the coronoid or olecranon processes

may occur from impact of the ulna on the humerus.

Ifneither the radius nor the ulna absorbs the excessive

force by fracturing, then the force may be transmitted to

the humerus and may result in a fracture of the

supracondylar area.

M l t ti l hi h


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Muscle contractions also may cause high

compression forces at the elbow.

Repetitive forceful contractions of the flexor carpi

ulnaris muscle may compress the ulnar nerve as it

passes through the cubital tunnel resulting in

cubital tunnel syndrome in which motion of the

fourth and fifth fingers is impaired.

Distraction Injuries


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Distraction Injuries

A tensile force of sufficient magnitude exerted on

a pronated and extended forearm may cause the

radius to be pulled inferiorly out of the annular

ligament. This injury is common in young

children younger than 5 years.

The injury is referred to as either nursemaids

elbow or pulled elbow.

Varus/Valgus Injuries


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If one side of the joint is subjected to abnormal

tensile stresses, the other side is subjected to

abnormal compressive forces.

The MCL is subjected to tensile stress during the

backswing or cock-up portion of throwing a ball.

If the stress on the MCL is repetitive, such as in

baseball pitching, the ligament may become lax and

unable to reinforce the medial aspect of the joint.

The resulting medial instability may cause anincrease in the normal carrying angle and excessive

compression on the lateral aspect of the joint so

that the radial head impacts on the capitulum.

If the abnormal compression forces on the


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If the abnormal compression forces on the

articular cartilage are prolonged, these forces

may interfere with the blood supply of thecartilage and result in avascular necrosis of the

capitulum.

The classic tennis elbow (epicondylitis of the

lateral epicondyle) appears to be caused by

repeated forceful contractions of the wrist

extensors, primarily the ECRB.

The tensile stress created at the origin of theECRB may cause microscopic tears that lead to

inflammation of the lateral Epicondyle.


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Elbow Joint - Biomech