The shoulder is a ball and socket type of joint with the ball being about twice the size of the socket. If it were not for the ligaments, muscles and tendons about the joint, the ball would constantly slide out of the socket. The socket being small when compared with the ball allows the shoulder joint to be capable of a large range of motion, however, the price we pay for such motion, is a greater potential for the ball to slide out of the joint. The socket is call the glenoid and the ball the humeral head.
The rotator cuff muscles functions to help contain the humeral head as we move our shoulder. The four muscles that make up the rotator cuff are the supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles originate from the scapula and converge to form a cuff of tendons that insert into the humeral head. The rotator alone cannot contain the humeral head.
The ligaments about the shoulder converge with the shoulder capsule to contain the humeral head. A sudden forceful injury can tear the ligaments and capsule and cause the humeral head to slide out of the glenoid resulting in a dislocation. Sever pain usually results from a dislocation and persists until the shoulder joint is reduced. After a dislocation, the ligaments and capsule rarely regain their original shape and strength and shoulder dislocates with less force in the future.
Younger people have a greater propensity to dislocate again than older people because of their greater activity level. In some cases, a forceful dislocation does not occur but the ligaments and capsule become stretched out over a period of time. When this happens, the humeral head does not completely dislocate from the joint, but partially slides out of place or subluxes which causes pain with certain activities, such as throwing or climbing.
Repairing an unstable shoulder requires suturing the capsule and a rim of cartilage called the labrum back to the bony socket called the glenoid. This procedure usually can be done completely through the arthroscope. In the picture a metal probe points to the repaired labrum.
Even though the procedure is a day surgery, the patient frequently requires the use of pain medicine after surgery for several days. Depending on the type of repair, many surgeons will have their patients wear a brace for several weeks to protect the tissues during healing.