Misdiagnosis of an atypical cyclops lesion 4 years after single-bundle anterior cruciate ligament reconstruction.

Development of a cyclops lesion is a well described complication after anterior cruciate ligament (ACL) reconstruction. It commonly results in gradual extension loss during the early postoperative course, and magnetic resonance imaging (MRI) of the soft tissue nodule attached to the ACL graft is needed. Cyclops lesions are easy to diagnose based on the symptoms and MRI findings. Previous study showed that 78.6% of cyclops lesions had extension loss within 6 weeks postoperatively, and the diagnosis of 92.8% cases of cyclops lesions was established within 6 months.This article describes a case of misdiagnosis of a cyclops lesion 4 years after ACL reconstruction as a meniscal lesion combined with a meniscal cyst. The patient was asymptomatic for 4 years and then presented with a locked left knee and pain at the inferior pole of the patella during an attempt to gently extend the knee. Magnetic resonance imaging revealed a lateral meniscal cyst. The knee locking was released suddenly 2 days preoperatively. The authors had attributed the missed diagnosis to an atypical history and symptoms and an associated meniscal cyst.The purpose of this article is to help prevent misdiagnosis of atypical cyclops lesions. Cyclops lesions should be considered in the differential diagnosis of patients who present with gradual or sudden loss of extension after ACL reconstruction, regardless of how much time has passed postoperatively.