Cyclops syndrome occurring after partial rupture of the anterior cruciate ligament not treated by surgical reconstruction.

Cyclops syndrome is one of the specific causes of loss of extension of the knee following anterior cruciate ligament (ACL) reconstruction. The syndrome is manifested by progressive loss of extension associated with pain and audible clunk at terminal extension caused by a pedunculated nodule of fibrovascular proliferative tissue usually arising from the graft. The entity has been described recently and has been reported exclusively as a complication of ACL reconstructions. We report the case of a patient with symptoms and arthroscopic and histological findings compatible with cyclops syndrome that developed after a partial ACL rupture that was not treated by surgical reconstruction. A different etiology and classical histological and immunohistological microscopic analysis of the nodule presented in this report may further clarify the pathogenesis of the cyclops syndrome.