Unlocking of knee is caused by?

Ans. is 'd' i.e., Popliteus Locking and Unlocking of knee joint Locking is a mechanism that allows the knee to remain in the position of full extension as in standing without much muscular effo. Locking occurs as a result of medial rotation of the femur during the last stage of extension. The anteroposterior diameter of the lateral femoral condyle is less than that of the medial condyle. As a result, when the lateral condylar aicular surface is fully 'used up' by extension, pa of the medial condylar surface remains unused. At this stage the lateral condyle rotates backwards, i.e. medial rotation of the femur occurs, so that the remaining pa of the media condylar surface is also 'taken up'. This movement locks the knee joint. Locking is aided by the oblique pull of ligaments during the last stages of extension. When the knee is locked, it is completely rigid and all ligaments of the joint are taut. Locking is produced by continued action of the same muscles that produce extension, i.e. the quadriceps femoris, especially the vastus medialis pa. The locked knee joint can be flexed only after it is unlocked by a reversal of the medial rotation, i.e. by lateral rotation of the femur. Unlocking is brought about by the action of the popliteus muscle. Physiological locking ----> Qudriceps femoris Physiological unlocking --> Popliteus