The shoulder can be thought of as three separate structures, the scapula or wing bone, the humerus or arm bone, and the clavicle or collar bone. When we move our shoulder, motion occurs between these three structures.
The scapula is next to the thorax and is held in place with muscles and ligaments. There is no cartilage between the scapula and the thorax to wear out. However, we have cartilage between the scapula and humerus which is called the glenohumeral joint and between the scapula and the clavicle which is called the AC joint. Both of these joints can wear out over time as the cartilage becomes thin and eventually erodes down to bone.
Shoulder arthritis frequently can be managed by medications, which include those taken by mouth as well as those applied topically. Sometimes injections about the shoulder joint can moderate symptoms. When the pain from shoulder arthritis persists and the person finds that it is difficult performing activities of daily living, surgery should be considered.
The glenohumeral joint is the main articulation of the shoulder and can cause sever pain and loss of function when it wears out. Like the hip and the knee, the glenohunmeral joint can be replaced. The type of replacement depends on the patient's condition. In some cases just the humeral head is replaced which is known as a hemi or partial arthroplasty. When the head and socket are worn out, a total shoulder replacement is performed. In circumstances where the rotator cuff is deficient, a more constrained design called a reverse shoulder replacement is used.
Shoulder replacements are also performed in some cases of complex fracture.
When the AC joint becomes arthritic and painful, orthopedists frequently treat the condition by removing the distal aspect of the clavicle. The bone is shortened just enough to prevent the distal clavicle from rubbing on the acromion. Fibous tissue fills in the defect left where the bone was removed and the patient no longer has the pain of bone rubbing on bone. The procedure is usually done using arthroscopic techniques as a day surgery and is very effective in relieving pain.