A patient injured his knee while playing hockey 3 months ago. On examination, his knee was unstable during extension but was stable at 90 degrees of flexion. He is most likely suffering from

ACL primary restraint to anterior tibial displacement, accounts for 85% of resistance to the anterior drawer test when the knee is at 90deg of flexion and neutral rotation. Selective sectioning of the ACL has shown that the anteromedial band is tight in flexion, providing the primary restraint, whereas the posterolateral bulky poion of this ligament is tight in extension. The posterolateral bundle provides the principal resistance for hyperextension. Thus complete tear will have instability in both flexion and extension. Thus anteromedial tear will have instability in flexion only and posterolateral tear will have instability only in extension