Analysis of Different Kinds of Cyclops Lesions With or Without Extension Loss

Purpose: The purpose of this study was to retrospectively evaluate patients after anterior cruciate ligament (ACL) reconstruction in whom a cyclops lesion developed to seek the etiologic factors. Methods: From 1999 to 2005, we observed 48 cases of cyclops lesions in 311 cases arthroscopically while removing the internal fixation devices after ACL reconstruction. Before removing the hardware, the function of the knee was evaluated through symptoms, signs, radiography, and KT-2000 measurement (MEDmetric, San Diego, CA) in 311 cases. Histologic examination was performed on some of the resected lesions. Results: Of the 3 11 patients, 45 were found to have nodular formations in the anterior part of the knee; this caused extension loss in 6 patients. Extension loss occurred at 2 to 3 months after ACL reconstruction. Histologic results were available in 18 patients (6 complained of a loss of extension and 12 were asymptomatic). Microscopic examination of the resected fibrous nodules showed disorganized fibrous connective tissue. We found that 8 nodules (4 with extension loss and 4 without extension loss) contained chondroid tissues, but we did not find osseous tissue in the nodules. The histologic appearance was similar to hypertrophic, degenerative granulation tissue. Conclusions: Among 311 second-look arthroscopies after ACL reconstruction, 45 cyclops lesions were found with a typical histology indicating an inflammatory proliferation with disorganized fibrous tissue, with some having chondroid tissue. Clinically, 10 patients had not returned to sporting activities: 6 of 6 who had extension loss and 4 of 39 who had full range of motion. All 6 patients with extension loss had full motion after resection of the cyclops lesion.