Ch. 21 Shoulder

Objectives• Name the three articulations that constitute the

shoulder girdle complex. • Describe how stability of the shoulder is

maintained. • Recite the names of the four muscles that come

together to form the rotator cuff. • Explain the anatomy of the shoulder complex.• Identify major injuries and conditions of the

shoulder.

Anatomy• Ball and socket joint• most mobile joint in

the body• Humerus• Clavicle- collar bone• Scapula- shoulder

bladeo Acromion processo Coracoid process

Joints and Movements• Glenohumeral Joint-

the actual shoulder joint

• Acromioclavicular Joint• Sternoclavicular Joint• Scapulothoracic Joint

• Flexion• Extension• Abduction• Adduction• Internal Rotation• External Roation• Elevation/Depression• Protraction/Retraction

Shoulder Flexion• Pectoralis Major • Coracobrachialis• Biceps brachii• Brachialis• anterior fibers of

deltoid

Shoulder Extension• latissimus dorsi • teres major• long head of triceps• posterior fibers of the

deltoid

Shoulder Abduction• True abduction:

supraspinatus (first 15 degrees), deltoid

• Upward rotation: trapezius, serratus anterior

Shoulder Adduction• Downward rotation:

pectoralis minor, pectoralis major, latissimus dorsi

• True Adduction: same as downward rotation with addition of teres major and the lowest fibers of the deltoid

Internal Rotation• Subscapularis• Latissimus dorsi• Teres major• Pectoralis major• Anterior fibers of

deltoid

External Rotation• Infraspinatus • Teres minor• Posterior fibers of

deltoid

Elevation/Depression• Elevation

o levator scapulaeo the upper fibers of the

trapezius

• Depressiono pectoralis minoro lower fibers of the trapeziuso subclaviuso latissimus dorsi

Protraction/Retraction• Protraction

o serratus anterioro pectoralis minor and major

• Retractiono rhomboid major and minor o trapezius

Rotator Cuff • Supraspinatus• Infraspinatus• Teres Minor• Subscapularis

Muscle Force Couple• Two equal forces acting in opposite directions to

rotate a part around its axis• During shoulder abduction, the rotator cuff is

pulling down on the humeral head while the deltoid is lifting the arm.

Muscle Weakness• Most athletes have

strong anterior shoulder muscles but weak posterior shoulder muscles

• This imbalance causes forward shoulder and other shoulder injuries