Anatomy:

Your shoulder is made up of three bones: your upper arm bone (humerus), your shoulder blade (scapula), and your collarbone (clavicle). The head of your upper arm bone fits into a rounded socket in your shoulder blade. This socket is called the glenoid. A combination of muscles and tendons keeps your arm bone centered in your shoulder socket. These tissues are called the rotator cuff.

The AC joint is located where the clavicle meets the tip of the shoulder blade (acromion). This is called the acromioclavicular (AC) joint.

Common Causes:

Osteoarthritis (OA)
Also known as “wear-and-tear” arthritis, osteoarthritis is a condition that destroys the smooth outer covering (articular cartilage) of bone. As the cartilage wears away, it becomes frayed and rough, and the protective space between the bones decreases. During movement, the bones of the joint rub against each other, causing pain. OA is more common in the AC joint than in the glenohumeral shoulder joint.

Posttraumatic Arthritis
Posttraumatic arthritis is a form of osteoarthritis that develops after an injury, such as a fracture or dislocation of the shoulder.

Imaging:

X-rays of an arthritic shoulder will show a narrowing of the joint space and the formation of bone spurs (osteophytes) at the AC joint. Occasionally, an MRI will be ordered to evaluate for additional problems inside the shoulder that are not visible on x-rays.

Treatment:

Nonsurgical Treatment

As with other arthritic conditions, initial treatment of arthritis of the shoulder is nonsurgical. Your doctor may recommend the following treatment options:

• Rest or modifying your activities to avoid aggravation of symptoms.
• Physical therapy exercises to try and improve the range of motion in your shoulder.
• Nonsteroidal anti-inflammatory medications (NSAIDs), such as Aleve or ibuprofen, to reduce inflammation and pain. 
• Corticosteroid injections in the shoulder can dramatically reduce the inflammation and pain. However, the effect is often temporary.
• Heat and/or ice for 20-30 minutes at a time.

Surgical Treatment

If your AC joint arthritis symptoms are not relieved with nonsurgical treatment, then surgical treatment to remove the arthritis may be indicated.

• Arthroscopy: Cases of mild AC joint arthritis may be treated with minimally invasive arthroscopy. During arthroscopy, the surgeon inserts a small camera, called an arthroscope, into the shoulder joint. Because the arthroscope and surgical instruments are thin, the surgeon can use very small incisions (cuts), rather than the larger incision needed for standard, open surgery. During the procedure, your surgeon can debride (clean out) the inside of the AC joint to remove the arthritis and create a larger space inside the joint. 
• Open: For more severe cases of AC joint arthritis, Dr. Fleager may need to make a small incision on the top of your shoulder to remove a small amount of bone from the end of the collarbone, to remove the arthritis and create more space within the AC joint.