Arthroscopic Treatment of a Massive Acromioclavicular Joint Cyst

A healthy 75-year-old man presented with a 9-month history of an enlarging painless shoulder mass. On examination, there was a 10 × 10 cm firm mass overlying the acromioclavicular (AC) joint. The active range of motion of the shoulder joint was 130° of forward elevation, 90° of abduction, 60° of abduction and internal rotation to the level of the waist. There was weakness of the rotator cuff. Plain radiographs showed degenerative changes of the AC joint with superior migration of the humeral head. Magnetic resonance imaging showed a large cyst arising from a degenerative AC joint with an associated major tear of both the supraspinatus and infraspinatus. Arthroscopy of the AC joint and debridement of the cyst was performed in the lateral decubitus position. The major rotator cuff tear of supraspinatus and infraspinatus was confirmed. A conservative subacromial decompression and AC joint excision arthroplasty was performed. As the superior AC ligament was opened, dark brown gelatinous material was seen emanating from the cyst. A thorough debridement of the cyst was performed until the lavage fluid was clear. At last follow-up 6 months after surgery, the shoulder remained asymptomatic with no evidence of recurrence of the cyst. Arthroscopic treatment of a massive AC joint cyst allows assessment of associated pathology, is minimally invasive, and allows early rehabilitation.