Anterior internal impingement: An arthroscopic observation.

PURPOSE The source of pain in patients with a stable shoulder and clinical signs of impingement is traditionally thought to be subacromial or outlet impingement, as popularized by Neer. This report introduces the concept of anterior internal impingement in patients with signs and symptoms of classic impingement syndrome and arthroscopic evidence of articular-side partial rotator cuff tear. Contact that occurs between the fragmented undersurface of the rotator cuff and the anterosuperior labrum is the apparent source of pain in these patients. TYPE OF STUDY Case series. METHODS Ten patients with a primary symptom of pain and an arthroscopic finding of a partial rotator cuff tear were reviewed. Arthroscopic visualization of the subacromial space revealed no evidence of subacromial impingement or bursitis in any patient. All patients had clinical signs and symptoms of classic impingement. The initial part of the surgical procedure consisted of a complete diagnostic arthroscopy in a low-volume gas medium using a single posterior portal. While performing the Hawkins test, the locations of any areas of abnormal soft-tissue contact and impingement were observed directly. RESULTS There was anterior internal impingement in all 10 patients with partial-thickness rotator cuff tears. The abnormal and fragmented rotator cuff tissue made contact with the anterior superior labrum when the shoulder was visualized from the posterior portal while performing the Hawkins test. Preoperative magnetic resonance imaging correctly showed a partial-thickness rotator cuff tear in 20% of the cases. CONCLUSIONS Recognition of anterior internal impingement as a clinical entity is important because magnetic resonance imaging results are often misleading. This is of particular importance in young patients with isolated lesions in whom arthroscopic acromioplasty and capsular reefing procedures would be unnecessary. When anterior internal impingement is recognized as the source of unresolved shoulder pain, patient selection for surgery and procedure selection can be improved.