As the knee went into external rotation and valgus, the anterior cruciate ligament became taut, acting as a fulcrum. The tibial collateral ligament was stressed and the lateral compartment of the knee compressed. As the force increased, the tibial collateral ligament was torn (Fig. 6.139A,B), as was the medial meniscus (Fig. 6.140C). Finally, the anterior cruciate ligament, which was taut, gave way (Fig. 6.140A,B).