Acromioclavicular joint arthritis
What is it?
Some joints in the body are more likely to develop problems from normal wear and tear. Degeneration causes the cartilage that cushions the joint to wear out. This type of arthritis is called osteoarthritis. The acromioclavicular (AC) joint in the shoulder is a common spot for osteoarthritis to develop in middle age. Degeneration of the AC joint can be painful and can cause difficulty using the shoulder for everyday activities.
What is the AC joint?
The shoulder is made up of three bones: the scapula (shoulder blade), the humerus (upper arm bone), and the clavicle (collarbone). The part of the scapula that makes up the roof of the shoulder and connects with the clavicle is called the acromion. The joint where the acromion and the clavicle join is the AC joint. In some ways, the AC joint is like any other joint. It has two bones that need to connect but be flexible as well. The ends of the bones are covered with articular cartilage. Articular cartilage provides a slick, rubbery surface that allows the bones to glide over each other as you move. Cartilage also functions as sort of a shock absorber.
What causes it?
We use our shoulder constantly. The resulting strain makes AC joint osteoarthritis a common disorder. The AC joint is under constant stress as the arm is used overhead. Weightlifters and others who repeatedly lift heavy amounts of weight overhead tend to have an increased incidence of the condition, and often at a younger age. AC joint osteoarthritis may also develop following an injury to the joint, such as an AC joint separation. This injury is fairly common. A separation usually results from falling on the shoulder. The shoulder does heal, but many years later degeneration causes the AC joint to become painful.
What are the symptoms?
In its early stages, AC joint osteoarthritis usually causes pain and tenderness in the front of the shoulder around the joint. The pain is often worse when the arm is brought across the chest, since this motion compresses the joint. The pain is vague and may spread to include the shoulder, the front of the chest, and the neck. If the joint has been injured in the past, there may be a bigger bump over the joint on the affected shoulder than on the unaffected shoulder. The joint may also click or snap as it moves.
How is it diagnosed?
Your doctor will want to get a detailed medical history, including questions about your condition and how it is affecting you. You will need to answer questions about past injuries to your shoulder. You may be asked to rate your pain on a scale of one to ten. Your doctor will also want to know how much your pain affects your daily tasks. Diagnosis of AC joint osteoarthritis is usually made by physical examination. The AC joint is usually tender. A key finding is pain as the joint is compressed. To test for this, your arm is pulled gently across your chest. Your doctor may inject a local anesthetic such as lidocaine into the joint. If the AC joint is the problem, the injection will temporarily reduce the pain. Your doctor may want to take X-rays of the AC joint. X-rays can show narrowing of the joint and bone spurs around the joint, which are signs of degeneration.
What is the treatment?
Initial treatment for AC joint osteoarthritis usually consists of rest and anti-inflammatory medications such as aspirin or ibuprofen. A rehabilitation program may be directed by a physical or occupational therapist. If the pain doesn't go away, an injection of cortisone into the joint may help. Cortisone is a strong medication that decreases inflammation and reduces pain. Cortisone's effects are often temporary, but it can give very effective relief in the short term.
If nonsurgical measures fail to relieve your pain, your doctor may recommend surgery. The most common procedure for AC joint osteoarthritis is resection arthroplasty. A resection arthroplasty involves removing a small portion of the end of the clavicle. This leaves a space between the acromion (the piece of the scapula that meets your shoulder) and the cut end of the clavicle, where the joint used to be. Your surgeon will take care not to remove too much of the end of the clavicle to prevent any damage to the ligaments holding the joint together. Usually only a small portion is removed, less than one cm. As your body heals, the joint is replaced by scar tissue. The scar tissue allows movement but stops the bone ends from rubbing together.
Today, it is more common to do this procedure using the arthroscope. An arthroscope is a slender tool with a tiny TV camera on the end. It lets the surgeon work in the joint through a very small incision. This may result in less damage to the normal tissues surrounding the joint, leading to faster healing and recovery. The older, open method of performing this operation is done by making a small incision, less than two inches long, over the AC joint.