Shoulder
The shoulder joint is a very mobile ball and socket joint similar to the hip joint, except, unlike the hip, the socket (glenoid) is very shallow. The glenoid is part of the shoulder blade (scapula). The ball (humeral head) is held to the glenoid by ligaments and the joint capsule. A rubbery cartilage called the labrum surrounds the edge of the glenoid and serves to deepen the socket and keep the head centered on the glenoid. A smooth layer of articular cartilage covers the head of the humerus and face of the glenoid, and is nourished and lubricated by joint fluid.
Four muscles (the rotator cuff) surround the joint capsule and serve as the primary movers of the shoulder joint. These muscles are attached to the head of the humerus by tendons. Injury to these tendons from trauma, repetitive throwing, and the effects of aging will cause pain and difficulty raising the arm. The articular cartilage on the humeral head and glenoid surface is also prone to degeneration, resulting in thinning and eventual loss of the protective covering over the underlying bone. This condition called osteoarthritis can be very painful and debilitating.
In addition to injuries to the rotator cuff and arthritis of the joint, there are several other conditions that affect the shoulder. A thorough history, physical examination, and appropriate x-rays are critical to making the proper diagnosis. Most conditions can be successfully treated with conservative measures, including rest, anti-inflammatory medication, and specific shoulder exercises, but sometimes surgery is necessary.
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