The cyclops lesion: A cause of diminished knee extension after rupture of the anterior cruciate ligament

Four patients presented with persistent diminution of knee motion after rup ture of the anterior cruciate ligament with a novel lesion as the cause, Ea ch had participated in an aggressive rehabilitation program for a minimum o f 2 months with emphasis on regaining full range of knee motion. Because ch ronic impairment of knee extension can be disabling, in those who did not r egain full range of motion, arthroscopy of the knee ensued. All had a lesio n in the intercondylar notch near the tibial insertion of the anterior cruc iate ligament that acted as a mechanical obstruction to full knee extension . Grossly and histologically, these were similar to the cyclops lesion that also has been shown to cause loss of knee extension after anterior cruciat e ligament reconstruction. Arthroscopic debridement of the cyclops lesion a nd manual manipulation of the knee under anesthesia lead to restoration of full knee extension in all knees. In 1 other knee with chronic instability after anterior cruciate ligament rupture, the cyclops lesion was present bu t was Very small and was not associated with diminished knee extension. Whe n loss of full extension persists for 2 months after anterior cruciate liga ment disruption despite aggressive rehabilitation, the presence of a cyclop s lesion should be considered.