Shoulder Instability
The shoulder joint has no intrinsic stability, as its structure can be likened to a golf ball perched on a golf tee. The shoulder joint is entirely dependant upon the surrounding soft tissues (muscles and tendons) for its stability. Typically in a young sportsperson who falls on to their shoulder and forcibly dislocates the shoulder, the rim ( labrum ) of the glenoid is torn off. This may heal but this is unusual. More often the labrum does not heal or heals in the wrong place resulting in looseness ( laxity ) of the ligaments at the front of the shoulder joint. When the arm is placed in the critical position (approaching 90° abduction and external rotation) the shoulder can dislocate without any further injury. The treatment for this is to repair the injury to the labrum, which can be performed arthroscopically. The risk of recurrent instability is greater the younger the person is at the time of the first traumatic dislocation. Traumatic dislocations occurring in persons in their teen years carry a >80% risk of re-dislocation. Every dislocation increases the risk of the development of osteoarthritis. In older people who dislocate their shoulder instability can occur as a result of tearing of the rotator cuff tendons, which is a difficult problem to resolve and retain function in the shoulder after such surgery. A final scenario of instability is where abnormal shoulder girdle muscle control and coordination results in dislocations of the shoulder joint without injury. This problem is usually corrected by prolonged specialist shoulder physiotherapy to alter the abnormal muscle patterns and stabilise the shoulder. Surgical intervention is unusual and usually the last resort.
