Pathomechanics of Shoulder II

Dr .Manal Radwan SalimFall 2013-2014

14-12-2013

Muscles acting on shoulder girdles and their impairements

They are grouped into three groups according to their attatchements

a) Axiohumeral muscles:

b) Axioscapular and axioclavicular muscles:

c)Scapulhumeral muscles:

a) Axiohumeral muscles: These muscles attach

thorax to humerous thus their fibers crosses all four joints of shoulder girdle their role is providing additional strength to the shoulder girdle functions

1- Pectoralis Major: 2- Latismus Dorsi

1- Pectoralis major: Effect of Weakness:

Decrease strength in medial rotation, adduction, horizontal adduction and depression.

Effect of tightness: limited ROM in shoulder lateral rotation, horizontal abduction, also shoulder flexion range. Seen following thoracic surgery or breast surgery

Latismus Dorsi Effect of

Weakness: Decrease strength in

extension, adduction,

internal rotation

and depression.Effect of tightness: limited ROM in shoulder lateral rotation, and perhaps abduction, also may lead to flexion of upper thoracic spine.

Upper extremity weight bearing

The ground reaction force in upper extremity weight bearing is in upward direction that tend to elevate shoulders up, so shoulder depressors muscle are required to act and depress shoulder so fix it in position.

Scapulohumeral muscles:

They provide motion and dynamic stabilization to the glenohumeral joint.

Composed of: 1- Deltoid

2- Teres major 3- Coracobrachialis

4-Supraspinatus (RC) 5-Infras spinatus(RC) 6- Teres minor (RC) 7- Subscapularis (RC)

1-Deltoid Composed of three

parts

A)Anterior Deltoid:Effect of weakness:weakness in shoulder flexion, medial rotation, abduction and horizontal adduction

Effect of tightness: limited shoulder range in external rotation and extension

A)Posterior Deltoid:Effect of weakness: weakness in shoulder extension strength.Effect of tightness: limited shoulder range in flexion adduction.A)Middle Deltoid:Effect of weakness: moderate weakness in shoulder abduction strength and may be flexion strength also.

Rotator cuff muscles

1- Suprapinatus:Effect of weakness: weakness in shoulder abduction initiation and strength Effect of tightness: unlikely only

with surgical repair of rotator cuff so following surgery avoid adduction or medial rotation with hyper extension of shoulder as they stretch the tendon

2- Subscapularis

-Anterior instability of shoulder

Effect of tightness: tightness in lateral rotation

Effect of weakness: -weakness in shoulder medial rotation.

c) Axioscapular and axioclavicular muscular groups

Their role is to position scapulae or clavicle by movements of sternoclacicular and scapulothoraci joints. With resultant motion of the acromioclavicular joint. They work in team to hold the scapula to the chest wall.

They are:1-Trapezius2-Serratus Anterior3-Levator Scapuli4-Rhomboid Major5-Rhumboid Minor6-Pectoralis Major7-Pectorlais Minor picture p

151, 152

Trapezius Muscle

its strength is a vector summation of forces from the upper, middle and lower trapezius musclesas a whole trapezius adduct and upwardly rotates scapulae.

The two opposing forces of upper and lower trapezius muslce make “ anatomical force couple” which allows scapula to rotate upwardly without being displaced superiorly or inferiorly on the thorax.

Balance between upper and lower trapezius muscles:

Serratus Anterior Effect of

weakness:Weakness in

scapular abduction, upward rotation and to some extent scapular elevation. Its weakness appears in push up exercises as medial winging of scapula.

Interaction between trapezius and serratus anterior muscles

both trapezius and serratus anterior make a force couple with both muscles producing upward rotation of scapula while they counteract each other in abduction and adduction of scapula.

Medial winging of scapulais a protrusion of medial border of

scapula away from the thorax *If caused by weakness in serratus

anterior; the protrusion appear in shoulder elevation (flexion/ abduction) or resisted scapular abduction.

*While if medial winging of scapula was found at rest of passive movements of shoulder, it is a sign of restricted ROM at glenohumeral joint or posture abnormality. As during activities as reaching for back pocket

Levator scapuli, rhumboid major, rhumboid minorEffect of

weakness:It leads to

impairment in activities that need pulling as open doors and rowing also causes adduction and depression of scapulae as reaching to back pocket.

Pectoralis Minor

Effect of weakness:

Difficulty in controlling shoulder girdle especially in weight bearing activities as crutch walking.

In it the pectoralis moinor exerts a downward force on the scapulae to stabilize it against the reaction force of a crutch that is directed upward

Effect of tightness:

Pull scapula in anterior tilt and causes rounded shoulder . As when the pectoralis minor contract it pulls the coracoid process anteriorly causing the scapula to elevate

Interaction between pectoralis minor and rhumboid muscles

There is a force couple which is formed by the rhumboids muscles, the levator scapulae, and the pectoralis minor. The pectoralis minor abducts the sacpula and balances the adduction pull of the rhomboids major and minor and levator scapulae as all four muscles rotate scapula downward.