[Acromio-clavicular joint cyst. Surgical treatment].

A chronic cyst of the acromioclavicular joint was treated in 3 patients who were followed up for an average period of 26 months. All three were over 60 years old and presented with a massive rupture of the rotator cuff with a subnormal range of passive motion; active motion was variably affected and was painful. The patients underwent resection of one cm of the lateral end of the clavicle, together with resection of the cyst and synovectomy of the upper part of the pathologic humero-acromial joint; the coraco-acromial ligament was left in place. With a mean follow-up of 26 months, the 3 patients have significant pain relief and no cyst has recurred. The authors propose a mechanism to explain the persistence of the cysts in patients with massive rotator cuff tear: elevation of the arm brings the humeral head upwards and forces synovial fluid into the acromioclavicular joint through a perforation in the frayed capsule; this communication is later obstructed by synovial fringes which prevent drainage of the fluid. Excision of the synovium cures the problem.