Although most people think of the shoulder as one joint, 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 (AC) joint. The junction of the upper arm bone (humerus) with the shoulder blade (scapula) is called the glenohumeral joint. Both joints may be affected by arthritis. The treatment of shoulder arthritis depends on the level of pain and disability the arthritis causes, which joint is affected and which type of arthritis you have (osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis). Initial treatment may involve rest or a change in activities to avoid provoking pain, physical therapy, moist heat, and nonsteroidal anti-inflammatory medications, such as aspirin or ibuprofen, to reduce inflammation.