AC Joint Arthritis

Last Updated on October 30, 2023 by The SportsMD Editors

The acromioclavicular joint, or AC joint, is the joint formed between the collarbone (clavicle) and the top of the shoulder blade (acromion). Most people have a visible AC joint “bump” on the top of their shoulder where these two bones meet. Like most joints in the body, the AC joint is surrounded by a capsule and supported by several thick ligaments. The acromioclavicular ligaments are thickened portions of the joint capsule that surrounds the ends of the two bones. Inside the joint capsule, the end of each bone is lined with a smooth cartilage surface that, combined with a meniscus in between the two bones, allows the joint to glide easily. The coracoclavicular (CC) ligaments span from the coracoid to the clavicle and prevent superior (upward) instability of the AC joint.

Function of the AC joint

The AC joint is a direct connection between the arm and the axial skeleton and therefore all arm motion results in motion at the AC joint. The joint allows the clavicle to rotate and the acromion to slide and tilt with shoulder motion. Through this complex combination of motions, the AC joint acts as a pivot point around which the shoulder is able to elevate the arm overhead and across the body. Because most motions of the arm result in the shoulder blade and the clavicle moving as a unit, the AC joint only allows motion of about 5-8 degrees.

What is AC joint arthritis?

Arthritis of the AC joint results from degeneration of the cartilage at the ends of the clavicle and acromion. There are multiple causes of this degeneration: normal day-to-day activities that require repetitive arm motion that leads to cartilage loss (primary osteoarthritis) and cartilage degeneration after an injury to the joint (post traumatic arthritis). The central feature for both causes is that the normally smooth cartilage on the end of the bones as well as the meniscus in between the bones breakdown and creates an inflammatory response in the joint.

Symptoms of AC joint arthritis

The symptoms of AC arthritis are similar to arthritis in other joints. Pain and stiffness of the joint are common. Often patients complain of catching and “clicking” as well. Usually, these complaints are worst with overhead activity or with positioning the arm across the body. These are both common positions of the arm- from daily activities such as brushing your hair or reaching your back pocket to sports activities such as a golf swing.

Is AC joint arthritis common?

With years of repeated arm motion with large loads being placed across such a small surface area, AC joint degeneration is common. In fact, some experts feel that AC joint degeneration is a natural process that occurs with aging. Recent studies have demonstrated up to 50% incidence of AC joint arthritis on X-Ray or MRI in the elderly people with no symptoms. Symptomatic AC arthritis, however, is much less common.

What other conditions occur with AC arthritis?

AC arthritis can occur without any other shoulder problems, but there are other shoulder problems that can occur at the same time and obscure the proper diagnosis. For example, rotator cuff impingement, rotator cuff tears, and labral tears can occur with or be mistaken for AC arthritis.

Diagnosis for AC arthritis

An accurate diagnosis is made by obtaining a thorough history as well as physical examination. Most patients that have AC arthritis will complain of pain on top of their shoulder that may radiate into the trapezius muscle or even the base of the neck. The pain is usually worse when he or she crosses the affected arm to the opposite side of the body. This is extremely common in older recreational athletes. For example, a tennis player’s forehand or a golfer on follow through may experience this symptom. Shoulder range of motion is rarely affected and most patients will demonstrate full motion unless a concomitant injury is present. On examination, there can be a visible prominence of the arthritic AC joint and asymmetry from one side to the other. Additionally, there is often tenderness to palpation over the joint. The most reliable test for AC joint pain is the “Cross Body Adduction Test.” In this test, the patient places the affected arm across his or her body to the opposite shoulder. The examiner then grabs the elevated arm and adducts the arm across the body further. A positive test should replicate the patient’s symptoms.

Treatment for AC arthritis

Once the diagnosis of AC arthritis is confirmed, symptomatic treatment is initiated. The first phase of treatment is oral anti-inflammatory medications (NSAIDs) such as ibuprofen and activity modification. Often NSAIDs are sufficient to alleviate the pain and enable a return to activity. If oral medications are inadequate, injections of corticosteroids into the AC joint can be utilized to attempt to locally decrease the inflammation in the joint that is associated with arthritis. These injections offer both a therapeutic and diagnostic benefit. If all of a patient’s pain is relieved by the injection, then the diagnosis of isolated AC arthritis is likely; however, if the patient obtains no or only minimal relief, then additional or alternate diagnoses should be considered. If the steroid injections are effective, most patients will have relief of their symptoms for up to several months.

If the above mentioned non-operative treatments fail to provide relief enough to enable return to normal activities, surgical management is a reasonable option. Most often, AC arthritis pain is amenable to nonsurgical management. Further, as the arthritic changes in the joint progress, the motion in the joint decreases. When there is little or no motion left in the joint, the pain subsides as the bones no longer cause inflammation by rubbing against one another.

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AC Joint Surgery

If the pain is chronic and severe despite activity modification, NSAIDs and injections, then surgical excision of the distal clavicle can be performed. The goal of AC Joint Surgery is to increase the space between the ends of the collarbone and shoulder blade by removing a small portion of the collarbone so they do not grind against one another. This can be done through a small incision (open distal clavicle excision) or through several small incisions and with a camera (arthroscopic distal clavicle excision).

There are advantages and disadvantages to open and arthroscopic treatment, but both result in significant long term pain relief. Open resection of the distal clavicle allows for direct visualization of the joint and the resection. The amount of bone removed can be measured and excised completely and with ease. A small portion of the deltoid and trapezius muscle is often detached to provide access to the joint. This approach therefore may have increased pain postoperatively and require a longer period of recovery to allow healing of the muscles’ reattachment. Arthroscopic excision of the distal clavicle can be done with smaller incisions. Also, any other potential damage in the shoulder can be detected arthroscopically and treated at the same time. The final advantage is the potential of a quicker recovery and less pain postoperatively because there is no need to detach any muscle fibers. The disadvantages to arthroscopic excision are that it is a technically more demanding procedure that takes longer to perform. There is also a higher chance of an inadequate excision of the bone.

What imaging studies are used in diagnosing AC arthritis?

The first study obtained is generally a series of X-rays of the shoulder. While standard shoulder X-rays can be useful to evaluate the AC joint, a special view, called the Zanca view, can be obtained. This view provides a more complete look at the joint. Another imaging modality that can be utilized is Magnetic Resonance Imaging (MRI) scans. MRIs are not routinely recommended for AC arthritis because X-rays usually are sufficient for diagnosis. In addition, MRIs often show early signs of AC degeneration in patients who have no complaints of AC pain. It is generally accepted that MRIs are not a component of the routine AC arthritis workup. However, MRI can help evaluate any other shoulder conditions such as rotator cuff tears.

What is the usual recovery for a distal clavicle resection in athletes?

For both open and arthroscopic procedures, the patient is usually placed in a shoulder sling for 1-3 days for comfort. If an open resection was performed, most surgeons restrict active motion of the shoulder for up to 3 weeks to allow for deltoid and trapezial healing. With most rehabilitation protocols for isolated distal clavicle excision, a return to normal activity occurs at 3 months. If the procedure is performed arthroscopically, arm motion is not restricted after the surgery. Most overhead athletic activities (tennis serve, swimming, throwing) is discouraged for up to 3 weeks for pain control. Most patients return to full activities in 2 months. It is important to emphasize that if additional procedures are performed during the operation (e.g. rotator cuff repair), the postoperative recovery and rehabilitation will vary.

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