Shoulder

From ArticleWorld

The shoulder is one of two matching joints that connect the upper extremities to the rest of the body. The shoulder has the ability to raise (abduct), to lower (adduct), and to rotate internally (toward the front) and externally (toward the back).

Anatomy

The joint in the shoulder is of the ball-in-socket type. The humerus has a ball-like joint surface in the shoulder and portions of the scapula together form the socket also called the “glenoid” socket. The acromioclavicular joint is a shoulder joint apart from the humerus and involves the connection between the clavicle and the acromion, which forms the highest point of the shoulder.

The shoulder joint and the acromioclavicular joint have supporting ligaments. The transverse ligaments of the humerus keep the ball and socket connected. The acromioclavicular joint has a band of connective tissue that holds it together as well. The coracoacromial ligament attaches the upper most acromion of the scapula and the lowermost coracoid process of the scapula. A joint capsule lines the joint and keeps synovial fluid, a lubricant into the glenohumeral joint.

Function

The shoulder joint is able to move by means of several muscles. The shoulder is able to be raised by the deltoid muscle that forms the smooth round outer surface of the shoulder. The trapezius muscle in the neck assists the deltoid when the shoulder is raised quite high. The latissimus dorsi muscle and the subscapularis muscle helps draw the shoulder joint forward across the chest wall.

The infraspinatous and teres minor muscles actually located in the back but are helpful in drawing back the shoulder muscle. The teres major muscle pulls the upper arm inward and settling the arm next to the body.

Conditions

Either the glenohumeral joint or the acromioclavicular joint can become traumatized and dislocate. The latter problem is easy to treat by resting the shoulder unless it is very severe. Dislocation of the glenohumeral joint usually is initially the result of a fall; however, once it dislocates the first time, damage to the joint ligaments result in recurrent dislocations involving no trauma at all. A glenohumeral joint dislocation is difficult to treat as the surrounding muscles often go into spasm and resist the relocation of the joint.