The purpose of this study was to confirm the efficacy of arthroscopic findings for the diagnosis of posterolateral rotatory instability (PLRI) of the knee.

We retrospectively evaluated 27 patients (28 cases) who had been operated upon for PLRI between February 1998 and June 2001. All patients underwent preoperative or intraoperative arthroscopic examinations including anterior/posterior cruciate ligament, popliteus tendon, inferior and superior popliteomeniscal fascicle, popliteofibular ligament, lateral meniscus, instability and abnormal popliteomeniscal motion for internal and external rotation.

Instability, which means popliteal hiatus widening during internal rotation of the tibia, was identified in all cases (100%). Tear of the inferior and superior popliteomenical fascicle was identified in 24 cases (86%) and abnormal popliteomeniscal motion during rotation was identified in 20 cases (71%). Popliteus tendons were abnormal in 18 cases (65%) with 5 cases (19%) of complete tear and 13 cases (46%) of partial tear or elongation.

These results suggest that arthroscopic evaluation of the popliteal hiatus structures in the patients suspected for PLRI of the knee is helpful for diagnosis and the determination of treatment modality.