Ans. is 4d' i.e., Fibular collateral ligament injury [Ref: Apleys 9k/ep. 876}o The most common mechanism of ligament disruption of knee is adduction (valgusj, flexion and internal rotation of femur on tibia which usually occur in sports in which the foot is planted solidly on the ground and leg is twisted by rotating body (i.e., foot ball, soccer, basket ball, skiing).o The medial structures medial (tibial) collateral ligament (MCL) and medial capsular ligament are first to fail, followed by ACL tears, if the force is of sufficient magnitude. The medial meniscus may be trapped between condyles and have a peripheral tear, thus producing unhappy triad of O' Donoghue.