Positive pivot shift test in knee is because of injury to -
Posterior cruciate ligament
Anterior cruciate ligament
Medial meniscus
Lateral meniscus
COLLATERAL LIGAMENT INJURY

The most common mechanism of ligament disruption of knee is abduction (valgus), 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.
The medial structures medial (tibial) collateral ligament (MCL) and medial capsular ligament are first to fail, followed by ACL tear, 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 0’ Donoghue.
Main test for MCL (medial collateral ligament) is valgus (abduction) stress in 30° of knee flexion. (Because in full extension it is indicative of combined MCL, posterior oblique ligament injury and posterior cruciate ligament injury).
Varus (Adduction) stress test in 30° flexion (removes the lateral stabilizing effect of iliotibial band so that the lateral collateral ligament can exclusively be examined).
Apleys distraction test is used for collateral ligaments.