Further discussion of treatment options requires some basic knowledge of the anatomy of the shoulder joint. The shoulder is not a true ball and socket joint like the hip. The illustration here will give you a general idea of how the joint is shaped to help you visualize the anatomy. One side is round, and the other side is flat. The round side is called the humeral head, and the flat side is the glenoid. This comprises the shoulder joint. The bones that form the shoulder joint, because of their shape, do not provide much, if any, built in stability. The joint is often likened to a golf ball sitting on a tee.
The structures that do provide stability are the ligaments which surround the joint and are attached to the glenoid on one side and the humerus on the other side. These ligaments are most prominent in the front, underneath, and in the back of the joint. They are called the glenohumeral ligaments. There is also a thickened rim of cartilage which surrounds the bony glenoid and acts to deepen the surface to more of a saucer. This cartilage is called the glenoid labrum.
On the top of the shoulder, there is a group of tendons attached to muscles which are called the rotator cuff. These tendons that make up the rotator cuff are not generally involved in a shoulder that dislocates, except in older individuals. Overuse of the shoulder, such as with pitching, can lead to irritation of the rotator cuff muscles and tendons as well as weakness. Some athletes that do a lot of throwing or participate in overhead racquet sports develop subluxation or instability secondary to these activities. They develop a tendonitis of the rotator cuff as it tries to compensate for the instability of the shoulder. In this group of patients, the initial treatment should be to strengthen the rotator cuff musculature, to use nonsteroidal anti-inflammatory drugs, and to rest. Failure to improve and to respond positively to this treatment may lead to surgical recommendation to correct the instability.
For those of you who are interested in the anatomy of the shoulder, the names of the muscles and tendons that comprise the rotator cuff are the subscapularis in the front or anterior, the biceps tendon in the front and top of the shoulder, the subraspinatus which is more or less on top, and the infraspinatus and teres minor which comprises the posterior or back. The ligaments which provide stability to the joint are actually underneath the cuff tendons. These muscles and tendons do support the shoulder, but their main function is to move the arm and shoulder. Again, the ligaments, anterior (front), inferior (bottom), and posterior (back), give the joint stability.
A shoulder which dislocates or subluxes injures the ligaments and labrum in one of two different ways. In shoulders which sublux, the ligaments become torn and then heal in a stretched or elongated position. In shoulders which dislocate, the ligaments and glenoid labrum are torn from the glenoid (the flat bone socket of the shoulder joint). This detachment of the labrum usually heals in a position off the front of the bone and thereby allows greater motion and less restraint for the humeral head. Some patients have what is called multi-directional instability (MDI). These patients have loose ligaments all around the shoulder. The patient can sublux in any direction, anterior, inferior and posterior, but usually and most commonly anterior and inferior.