Acromioclavicular Joint Arthritis
The AC joint is formed as the synovial-type joint between the distal end of the clavicle and the acromion. This joint can become arthritic, as can any other joint in the body. When symptomatic, arthritis of the AC joint causes pain over the superior aspect of the shoulder. Occasionally, there is pain that radiates into the area of the trapezius. Pain is often worse with internal rotation, such as placing the arm behind the back. AC joint arthritis is often diagnosed by imaging studies, including anteroposterior radiography and MRI of the shoulder.
AC joint arthritis can be seen as an isolated lesion or can be associated with rotator cuff and other subacromial pathology. Clinically significant AC joint arthritis is defined as that associated with provocative maneuvers as well as specific tears over the AC joint. When associated with significant imaging changes of the arthritic process or cyst or spur formation, then the clinical diagnosis of AC joint arthritis is made. Injection of local anesthetic directly into the AC joint will temporarily relieve the pain associated with palpation or the provocative signs and help establish the AC joint as a sole or significant contributor to the shoulder pain. It should be understood that many patients have AC joint arthritic changes on radiographs and MR images and do not have clinically significant symptoms requiring treatment. It should also be understood that the symptoms and clinical findings of clinically significant AC joint related pain are very similar to those of rotator cuff pathologic process and often coexist in the same patient. If clinically significant pain is associated with the AC joint and it is not recognized as a problem separate from concomitant rotator cuff pathologic processes and not treated with the rotator cuff problem, then residual pain will occur even if the rotator cuff problem is successfully treated. Given the above, the physical examination and use of selective injection tests when it is not clear that the AC joint is involved as a pain generator are critical to making a complete diagnosis of the shoulder problem.
AC joint pain from arthritis can often be treated with anti-inflammatory medication, modification of activities, and, on occasion, cortisone injection specifically into the AC joint (see Plate 1-54). When these symptoms remain persistent and significant over a prolonged period of time, then arthroscopic removal of the distal end of the clavicle can be done by arthroscopic means. This treatment is termed resection arthroplasty and is very effective in relief of chronic symptoms associated with AC joint pathology. When done arthroscopically, there is minimal disruption of the AC capsular ligaments and no changes in the corticoclavicular ligaments. This results in a stable shoulder with relief of AC joint related pain.