Although most people think of the shoulder as several joints, there are really two joints in the area of the shoulder. One is located where the collarbone (clavicle) meets the tip of the shoulder bone (acromion). This is called the acromioclavicular or AC joint. The junction of the upper arm bone (humerus) with the shoulder blade (scapula) is called the glenohumeral joint or scapulothoracic joint. Both joints may be affected by arthritis. To provide you with effective treatment, your physician will need to determine which joint is affected and what type of arthritis you have.
Three major types of arthritis generally affect the shoulder.
Osteoarthritis, or “wear-and-tear” arthritis, is a degenerative condition that destroys the smooth outer covering (articular cartilage) of bone. It usually affects people over 50 years of age and is more common in the acromioclavicular joint than in the glenohumeral shoulder joint.
Rheumatoid arthritis is a systemic inflammatory condition of the joint lining, or synovium. It can affect people of any age and usually affects multiple joints on both sides of the body.
Posttraumatic arthritis is a form of osteoarthritis that develops after an injury, such as a fracture or dislocation of the shoulder. Arthritis can also develop after a rotator cuff tear.