Normally, the head of the humerus moves smoothly in the glenoid cavity, a depression in the scapula. A shoulder is “frozen” when the capsule protecting the glenohumeral joint contracts and stiffens. Scar tissue (adhesions) may also form between the joint capsule and the head of the humerus. Sometimes freezing occurs because the shoulder has been immobilized for a long time by injury, surgery, or illness. In many cases the cause is obscure. Fortunately, the shoulder can usually be unfrozen, thoug