The rectus femoris is a long, fleshy muscle located in the anterior compartment of the thigh. The rectus femoris is fusiform in shape with superficial fibers that are bipenniform and deep fibers that run straight (rectus) to the deep aponeurosis. The rectus femoris is the most superficial of the quadriceps muscles alongside the vastus lateralis, vastus intermedius, and vastus medialis. These four muscles conjoin to attach to the patella through the quadriceps tendon. The rectus femoris is located anteriorly, and it functions to flex the hip joint and extend the leg at the knee joint. The rectus femoris has two heads of origin: the direct (straight) head and indirect (reflected) head. The direct head arises from the anterior aspect of the inferior iliac spine (AIIS; site of avulsion), while the indirect head originates from the acetabular ridge. The two heads merge to become the conjoined tendon below their origin.
The rectus femoris is fusiform in shape with superficial fibers that are bipenniform and deep fibers that run rectus to the deep aponeurosis. The rectus femoris arises from two tendons that originate from the anterior inferior iliac spine and the other from the ridge of the acetabulum. The rectus femoris tendons conjoin at an acute angle spreading into the aponeurosis. The end of the muscle inserts into the base of the patella forming the patella tendon with the rest of the quadriceps muscles.
The rectus femoris antagonizes the hamstring muscles at the knee and the hip. The muscle flexes the hip along with the sartorius and iliopsoas and extends the lower leg at the knee alongside its quadriceps muscle counterparts. The rectus femoris is one of the weaker extensors of the knee when seated. The rectus femoris also can suffer from active insufficiency of hip flexing with the knee extended because the rectus femoris is already in a shortened state. Active insufficiency of the rectus femoris is also displayed in knee extension when the hip is flexed. Passive insufficiency is an issue with the rectus femoris because the muscle loses the ability to extend the knee and flex the hip when the rectus femoris is in a position of full hip extension and knee flexion.
During the fifth week of development, the lower limb bud appears originating laterally from the L2 through S2 spinal segments and containing all of the primary germ layers: ectoderm, endoderm, and mesoderm. The musculature of the rectus femoris comes from the myotomic portions of somites, while the skeletal elements supporting the lower limb comes from the lateral plate somatic mesoderm. During embryogenesis, the lower limb rotates 90 degrees medially about the longitudinal axis, bringing the knee to the anterior aspect of the fetus.
The femoral artery supplies the quadriceps muscle, but the descending branch of the lateral femoral circumflex artery specifically nourishes the rectus femoris. The venous drainage is by the same namesake vein as the arterial section and is via the femoral vein and its branches.
The lumbar aortic lymph nodes facilitate the lymphatic vessels of the lower limb including the rectus femoris muscle and the drainage will flow into the cisterna chyli.
The rectus femoris gets its innervation from the femoral nerve, along with the rest of the quadriceps muscles. The nerve roots for the rectus femoris are L2, L3, L4. The main nerve supply is from the L4 root of the femoral nerve. The neuronal mechanisms of the rectus femoris start at the apex of the precentral gyrus. The neuronal signal travels down the corticospinal tract to the central nervous system. The signal then travels across the lateral corticospinal tract until spinal root L4. At L4, is where the synapse from upper neurons to lower takes place. The neuronal synapse propagates from through the anterior root of L4 until it reaches the anterior rami of L4, where it exits the spinal cord by way of the lumbar plexus. The posterior section of the L4 root, also known as the femoral nerve supplies the rectus femoris along with the quadriceps muscle. Once the signal is received, the rectus femoris and other quadriceps muscles extend the knee and flex the thigh at the hip.
Accessory muscles can arise from the rectus femoris. These variations include a muscle slip from the acetabulum directly into the vastus lateralis. Variations in the origin of the rectus femoris can change from the upper anterior iliac spine to the lower anterior iliac spine with no acetabular origin in different individuals.
Distal rectus tear is more commonly associated with and involved in quadriceps tendon ruptures, and isolated tears are uncommon.
Proximal rectus femoris tears are typically managed conservatively at first, but surgically when conservative measures have failed (exceedingly rare). In keeping with the principles of the surgical tendon management, repair is attempted when avulsed, or torn tendon has a suitable tissue for surgical sewing - into either the tendon stump or into sutures that have been anchored into the bony origin (in the case of an avulsion). If the tendon edges are not suitable for repair, or more commonly, are not able to be properly mobilized (typical in chronic cases), then reconstruction with use of tendon allograft (that is, from a cadaver) is usually performed.
During intense exercise or trauma, the rectus femoris can be torn at either end resulting in a debilitating injury that correlates with severe pain.
The strain can be either a partial tear of the tendon at the patella or the muscle itself. This type of strain injury may occur during sprinting, kicking or jumping. It is most prevalent in football in its various forms around the world. When strain injury occurs, patients typically present with moderate to severe pain in the groin or anterior aspect of the hip. The individual may not be able to extend the knee when this occurs. MRI detects rectus femoral strains. Treatment of a partial tear is usually with conservative care, by way of activity modification (rest, crutch use) and positional restriction (a short, initial period of avoiding hip extension).
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