Extension at the knee-quadriceps femoris extends the leg (rectus femoris and the vastus muscles) and helps flex the hip (rectus femoris). it is innervated by the femoral nerve, which is made from the contributions of l2, 3, and 4 in the lumbar plexus. if a patient could not adduct at the hip, the adductor muscles might be damaged. these are supplied by the obturator nerve, which also comes from l2, 3, and 4 in the lumbar plexus. if a patient could not extend at the hip or flex the leg, the hamstring muscles might be damaged. these muscles are supplied by the tibial nerve, a branch of the sciatic nerve. if a patient could not rotate the knee medially, popliteus might be injured. this muscle, which is innervated by the tibial nerve, allows the knee to twist and unlock from a fully extended position, as in erect stance.