['Medial collateral ligament tibial avulsion is rare. Consequently, diagnostic criteria and a treatment regimen for medial collateral ligament tibial side avulsions remain to be established. The purpose of this study is to clarify the clinical features of medial collateral ligament tibial side avulsions.', 'We performed a retrospective clinical and magnetic resonance imaging review of a consecutive series of 12 medial collateral ligament tibial side avulsions. All patients were treated operatively and the final diagnosis was made based on the intraoperative findings. Post-injury magnetic resonance imaging studies were reviewed to assess injury patterns with respect to the intraoperative findings.', 'Eleven of 12 cases (92%) had grade III valgus laxity (unstable to valgus stress at both 0° and 30° of flexion) on an examination under anesthesia. Concomitant anterior cruciate ligament tear was noticed in all cases. Intraoperative findings were classified into 3 types depending on the location of the ruptured end of the superficial medial collateral ligament with respect to the pes anserinus tendons. Magnetic resonance imaging depicted characteristic waving ("wave sign") of the superficial layer of medial collateral ligament in all cases.'] Is clinical features and injury patterns of medial collateral ligament tibial side avulsions : `` wave sign '' on magnetic resonance imaging essential for diagnosis?