Shoulder instability describes a condition in which the head of the humerus does not properly articulate with the glenoid. The humerus may slide either forward or backwards across the surface of the glenoid, although most slide forward. Mild cases of this motion are referred to as subluxation, and may be treated with restricted activities and physical therapy. In severe cases, the head of the humerus may slide almost completely off of the surface of the glenoid, resulting in a painful dislocated shoulder. The shoulder may dislocate with overhead activities or even while sleeping at night. Repeated dislocations may even cause degeneration of the cartilage on the head of the humerus, leading to degenerative arthritis.
Although the humerus is held in place by many tissues, the most common structures that fail to stabilize the shoulder joint are related to the glenoid labrum and the joint capsule, which attaches to the labrum. When the attachment of the labrum to the glenoid bone fails, the shoulder becomes unstable and the humerus slides forward.
A shoulder which has a torn labral attachment, will not heal without surgery to correct this condition. Secondarily, a shoulder which has had numerous dislocations will stretch the capsule, which will also need to be surgically corrected. Shoulder Instability Surgery