The role of the acromioclavicular joint in impingement syndrome.

Although AC pathology usually represents a late manifestation of outlet impingement, it typically presents as a cause of pain that is resistant to nonoperative and operative measures designed to treat purely anterior acromial pathology. The bursitis that occurs with AC joint impingement may be indistinguishable from anterior acromial impingement on clinical presentation; however, physical examination, diagnostic injection, and radiographic evaluation are generally sufficient to establish the diagnosis of AC joint impingement. Nonoperative measures are indicated for the treatment of acute bursitis, although operative intervention may be necessary in cases of large, distally projecting osteophytes in the presence of AC joint degeneration. Acromioclavicular pathology, when present, should be addressed at the time of subacromial decompression, and may involve distal clavicular resection, beveling of the AC joint, or excision of marginal osteophytes. The results of surgery to address the AC contribution to impingement are generally favorable; future investigation may further clarify the role of coplaning and its potential contribution to continued postoperative AC pain and symptomatic instability.