Objective: A localized form of anterior arthrofibrosis, the so-called cyclops lesion, has recently been reported to be a significant cause of loss of knee extension after reconstruction of the anterior cruciate ligament (ACL) of the knee. The purpose of this study was to characterize the MR appearance of this lesion.
Subjects and methods: Five patients who had arthroscopic verification of a focal nodule of fibrous tissue in the intercondylar notch anterior to the reconstructed ACL (the cyclops lesion) and who had an MR examination after ACL reconstruction but before repeat arthroscopy and excision of the cyclops lesion were included in this study. The MR images were evaluated for the presence of soft tissue in the intercondylar notch anterior to the reconstructed ACL. If present, this tissue was graded as 1, 2, or 3, depending on its anterior extent along the femoral condyle.
Results: MR images of all five patients showed abnormal soft tissue with signal characteristics consistent with fibrous tissue anterior to the reconstructed ACL in the intercondylar notch. The abnormal tissue was grade 2 or 3 in all patients.
Conclusion: MR imaging shows soft tissue with signal characteristics consistent with fibrous tissue anterior to the reconstructed ACL in the intercondylar notch in patients with localized anterior arthrofibrosis. Although the sensitivity and specificity of MR imaging for the cyclops lesion are yet to be determined, visualization of such fibrous tissue on MR images in a patient with clinical symptoms suggestive of localized anterior arthrofibrosis may be helpful in confirming the diagnosis.