Progressive loss of knee extension after injury. Cyclops syndrome due to a lesion of the anterior cruciate ligament.

Cyclops syndrome has been defined as a loss of knee extension due to impingement of a pedunculated proliferative tissue mass after anterior cruciate ligament reconstruction. We describe four patients who were operated on for progressive loss of knee extension after minor knee injury. During the arthroscopic procedure, the consistent finding was a fibrous pedunculated nodule adhering to the anterolateral aspect of the original anterior cruciate ligament, obstructing extension by impingement in the anterior aspect of the knee. At least part of the anterior cruciate ligament was intact in all cases. These patients were compared with seven patients who developed cyclops syndrome after anterior cruciate ligament reconstruction. Clinical and arthroscopic findings were the same in both groups. An arthroscopic excision of the nodule, performed an average of 12 weeks after knee trauma or after reconstruction, gave very good results. Histologic examination of the excised nodules from both groups showed fibroelastic connective tissue proliferation, thromboangiitis, and areas of necrotic bone and foreign body giant cell granuloma. On the basis of our observations, we conclude that formation of a fibrous pedunculated nodule may occur after an anterior cruciate ligament injury as well as after surgical reconstruction of the anterior cruciate ligament.