Rectus femoris

 

 

The rectus femoris muscle is one of the four quadriceps muscles of the human body.

The others are the vastus medialis, the vastus intermedius (deep to the rectus femoris), and the vastus lateralis.

All four parts of the quadriceps muscle attach to the patella (knee cap) via the quadriceps tendon.

The rectus femoris is situated in the middle of the front of the thigh; it is fusiform in shape, and its superficial fibers are arranged in a bipenniform manner, the deep fibers running straight down to the deep aponeurosis.

 

Origin and insertion

It arises by two tendons: one, the anterior or straight, from the anterior inferior iliac spine; the other, the posterior or reflected, from a groove above the brim of the acetabulum.

The two unite at an acute angle, and spread into an aponeurosis which is prolonged downward on the anterior surface of the muscle, and from this the muscular fibers arise.

The muscle ends in a broad and thick aponeurosis which occupies the lower two-thirds of its posterior surface, and, gradually becoming narrowed into a flattened tendon, is inserted into the base of the patella.

 

Functions of the Rectus femoris

  • Hip flexion
  • Knee extension

The rectus femoris and sartorius are the only muscles in the quadriceps group that are involved in flexion of the hip, since they are the only ones that originate in the pelvis and not the femur. By crossing the pelvic femoral joint they can act as a lever to flex the leg at the hip.

The rectus femoris is a weaker hip flexor when the knee is extended because it is already shortened and thus suffers from active insufficiency. In essence: the action of raising a straightened leg will recruit more iliacus, psoas major, tensor fasciae latae, and the remaining hip flexors than it will the rectus femoris.

Similarly, the rectus femoris is not dominant in knee extension when the hip is flexed since it is already shortened and thus suffers from active insufficiency. In essence: the action of extending a leg from a seated position is primarily driven by the vastus lateralis, vastus medialis, and vastus intermedius, and less by the rectus femoris.

The rectus femoris is considered a direct antagonist to the hamstrings. The hamstrings oppose the rectus femoris at the hip joint through extension and at the knee joint through flexion.

The rectus femoris can be torn – which can be very painful.

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