<prompt> Physiological locking involvesInternal rotation of femur over stabilized tibiaInternal rotation of tibia over stabilized femurExternal rotation of tibia over stabilized femurExternal rotation of femur over stabilized tibia  <response>: A i.e. Internal rotation of femur over stabilized tibia Physiological locking occurs in last 30 degree of extension, when femur rotates medially internally over stabilized tibiaQ. This very stable position is caused by quadriceps femoris muscle. Unlocking needed to initiate flexion is carried out by popliteus muscle, which moves femur laterally on stabilized tibia. 