Main extensor of knee:

Ans. (b) Quadriceps femorisRef : Maheshwari 5th ed. /145* Quadriceps is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the great extensor muscle of the knee. It is subdivided into four separate portions or 'heads', which have received distinctive names: Rectus femoris occupies the middle of the thigh, covering most of the other three quadriceps muscles. It originates on the ilium. It is named from its straight course.# The other three lie deep to rectus femoris and originate from the body of the femur, which they cover from the trochanters to the condyles: Vastus lateralis is on the lateral side of the femur (i.e on the outer side of the thigh). Vastus medialis is on the medial side of the femur (i.e. on the inner part thigh). Vastus intermedius lies between vastus lateralis and vastus medialis on the front of the femur (i.e. on the top or front of the thigh), but deep to the rectus femoris. Typically, it cannot be seen without dissection of the rectus femoris.* Quadriceps femoris is the main and only extensor of knee.# It produces locking action as a result of medial rotation of the femur during the last stage of extension.# To reverse this lock popliteus muscle comes into action and does so by the lateral rotation of femur* Remember: Lock is: Quadriceps femoris muscle and,Key is popliteus muscle.