A muscle in the quadriceps, the rectus femoris muscle is connected to the hip, and helps extend or raise the knee. This muscle also used to contract the thigh. The rectus femoris is the only muscle that can flex the hip. Injury to the rectus femoris muscle may be attributed to muscle overuse in kicking or sprinting. Inflammation of the muscle causes pain in the groin during physical exercises that use this muscle. The patient may experience pain during knee raises when the muscle is ruptured or inflamed. An operation may be necessary if the muscle is torn. Some patients with cerebral palsy may have an irregular stride due to problems related with the rectus femoris. In this case, surgery may be performed to transfer the rectus femoris onto a knee flexor. This surgery improves the patient's knee extension. Although research has shown that this surgery can improve the knee flexion, other studies have shown that rectus femoris muscle transfer surgery is best performed in combination with other surgeries.