In this condition the shoulder loses its normal ability to center the ball in the glenoid socket. In this condition there is usually nothing torn, but rather the stabilizing structures of the shoulder decompensate. Shoulder instability must be distinguished from other causes of shoulder dysfunction, such as arthritis, rotator cuff tear and snapping scapula. Rotator cuff tear results in shoulder weakness. In snapping scapula, the shoulder pops when the shoulder blade is moved on the chest wall.
Shoulder dislocations are among the most common conditions of the shoulder.
They are more likely to be found in people from 15 to 35 years of age. Individuals over the age of 40 who dislocate their shoulders are likely to also have a tear of the rotator cuff. Those who have instability of one shoulder are somewhat more likely to have instability of the opposite shoulder. People with loose joints are more likely to have atraumatic instability. The experienced shoulder surgeon can make a diagnosis of shoulder instability from the patient's history and from the physical examination.