Although most people think of the shoulder as several joints, there are really two joints in the area of the shoulder. The shoulder complex is a ball and socket joint and is comprised of 4 main muscles, several bones, and several soft tissue structures. The scapula (shoulder blade), clavicle (collar bone), and humerus (upper arm bone) make up the bony components. The upper portion of your shoulder creates a joint between the clavicle and scapula called your AC joint – acromioclavicular. Your glenohumeral joint is created from the ball (head of the humerus) and socket (glenoid fossa). Covering of each bone consists of articular cartilage (white protective covering) that breaks down within this condition. When osteoarthritis the protective lining of the bone decreases it produces the bones to compress and rub.
There are several types of arthritis and your physician will need to determine which joint is affected and by which type of arthropathy. Osteoarthritis or “wear and tear” by definition is inflammation of a joint. Within the shoulder complex, this can occur at either your AC joint and or your glenohumeral joint. Osteoarthritis can occur in any active or non-active individual but usually affects individuals over the age of 50 but can be seen in earlier aged individuals depending on their occupation or their specific sport. When the process of cartilage breakdown begins and progresses, the joint will become stiff and painful.
Above the photo below is a shoulder without osteoarthritis. The space between the upper arm bone and socket still has a maintained joint space.
The picture below is a photo of end-stage osteoarthritis – no space between the upper arm bone and socket.