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 blade Acromion process Coracoid process

Joints and Movements Flexion Extension Abduction Adduction Internal Rotation External Roation Elevation/Depression Protraction/Retraction Glenohumeral Joint- the actual shoulder joint Acromioclavicular Joint Sternoclavicular Joint Scapulothoracic Joint

Shoulder Flexion Pectoralis Major Coracobrachialis Biceps brachii 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 True abduction from arm to side to parallel with the ground

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 pectoralis minor lower fibers of the trapezius subclavius latissimus dorsi Elevation levator scapulae the upper fibers of the trapezius

Protraction/Retraction rhomboid major and minor trapezius Protraction serratus anterior pectoralis minor and major

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 Mirror muscles