The rectus femoris muscle is one of the four

quadriceps muscles The quadriceps femoris muscle (, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large ...

of the human body. The others are the

vastus medialis The vastus medialis (vastus internus or teardrop muscle) is an extensor muscle located medially in the thigh that extends the knee. The vastus medialis is part of the quadriceps muscle group. Structure The vastus medialis is a muscle present ...

, the

vastus intermedius The vastus intermedius () (Cruraeus) arises from the front and lateral surfaces of the body of the femur in its upper two-thirds, sitting under the rectus femoris muscle and from the lower part of the lateral intermuscular septum. Its fibers en ...

(deep to the rectus femoris), and the

vastus lateralis The vastus lateralis (), also called the vastus externus, is the largest and most powerful part of the quadriceps femoris, a muscle in the thigh. Together with other muscles of the quadriceps group, it serves to extend the knee joint, moving the ...

. All four parts of the quadriceps muscle attach to the

patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as ...

(knee cap) by the

quadriceps tendon In human anatomy, the quadriceps tendon works with the quadriceps muscle to extend the leg. All four parts of the quadriceps muscle attach to the shin via the patella (knee cap), where the quadriceps tendon becomes the patellar ligament. It att ...

. The rectus femoris is situated in the middle of the front of the

thigh In human anatomy, the thigh is the area between the hip ( pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of ...

; it is fusiform in shape, and its superficial fibers are arranged in a bipenniform manner, the deep fibers running straight ( la, rectus) down to the deep aponeurosis. Its functions are to

flex Flex or FLEX may refer to: Computing * Flex (language), developed by Alan Kay * FLEX (operating system), a single-tasking operating system for the Motorola 6800 * FlexOS, an operating system developed by Digital Research * FLEX (protocol), a comm ...

the thigh at the hip joint and to extend the

leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element ca ...

at the knee joint.

Structure

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 rim of the acetabulum. The two unite at an acute angle and spread into an aponeurosis that 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 that occupies the lower two-thirds of its posterior surface, and, gradually becoming narrowed into a flattened tendon, is inserted into the base of the

Nerve supply

The neurons for voluntary thigh contraction originate near the summit of the medial side of the precentral gyrus (the primary motor area of the brain). These neurons send a nerve signal that is carried by the corticospinal tract down the brainstem and spinal cord. The signal starts with the upper motor neurons carrying the signal from the precentral gyrus down through the internal capsule, through the cerebral peduncle, and into the medulla. In the medullary pyramid, the corticospinal tract decussates and becomes the lateral corticospinal tract. The nerve signal will continue down the lateral corticospinal tract until it reaches spinal nerve L4. At this point, the nerve signal will synapse from the upper motor neurons to the lower motor neurons. The signal will travel through the anterior root of L4 and into the anterior rami of the L4 nerve, leaving the spinal cord through the lumbar plexus. The posterior division of the L4 root is the femoral nerve. The femoral nerve innervates the quadriceps femoris, a fourth of which is the rectus femoris. When the rectus femoris receives the signal that has traveled all the way from the medial side of the precentral gyrus, it contracts, extending the knee and flexing the thigh at the hip.

Function

The rectus femoris, sartorius, and

iliopsoas The iliopsoas muscle (; from lat, ile, lit=groin and grc, ψόᾱ, psóā, muscles of the loins) refers to the joined psoas major and the iliacus muscles. The two muscles are separate in the abdomen, but usually merge in the thigh. They are usu ...

are the flexors of the thigh 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; the action will recruit more

iliacus The iliacus is a flat, triangular muscle which fills the iliac fossa. It forms the lateral portion of iliopsoas, providing flexion of the thigh and lower limb at the acetabulofemoral joint. Structure The iliacus arises from the iliac fossa on ...

psoas major The psoas major ( or ; from grc, ψόᾱ, psóā, muscles of the loins) is a long fusiform muscle located in the lateral lumbar region between the vertebral column and the brim of the lesser pelvis. It joins the iliacus muscle to form the iliop ...

tensor fasciae latae The tensor fasciae latae (or tensor fasciæ latæ or, formerly, tensor vaginae femoris) is a muscle of the thigh. Together with the gluteus maximus, it acts on the iliotibial band and is continuous with the iliotibial tract, which attaches to the ...

, and the remaining

hip flexors A flexor is a muscle that flexes a joint. In anatomy, flexion (from the Latin verb ''flectere'', to bend) is a joint movement that decreases the angle between the bones that converge at the joint. For example, one’s elbow joint flexes when one ...

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 the knee from a seated position is primarily driven by the

, and

, and less by the rectus femoris. In the other extreme, the muscle's ability to flex the hip and extend the knee can be compromised in a position of full hip extension and knee flexion, due to passive insufficiency. The rectus femoris is a direct

antagonist An antagonist is a character in a story who is presented as the chief foe of the protagonist. Etymology The English word antagonist comes from the Greek ἀνταγωνιστής – ''antagonistēs'', "opponent, competitor, villain, enemy, riv ...

to the

hamstring In human anatomy, a hamstring () is any one of the three posterior thigh muscles in between the hip and the knee (from medial to lateral: semimembranosus, semitendinosus and biceps femoris). The hamstrings are susceptible to injury. In quadrupe ...

s, at the hip and at the knee.

Clinical significance

Strain

Rectus femoris strain, referred to as hip flexor strain, is an injury commonly at the tendon that attaches to the patella or in the muscle itself. The injury is usually a partial tear, but could be a full tear. The injury is caused by a forceful movement related to sprinting, jumping, or kicking and is common in sports like football or soccer. The rectus femoris is prone to injury, since it crosses both the knee and the hip. Symptoms include a sudden sharp pain at the front of the hip or in the groin, swelling and bruising, and an inability to contract the rectus femoris with a full tear.

Avulsion fracture

The Rectus femoris tendon can cause a fragment of anterior inferior ilac spine of the hip (AIIS) to avulse in what is known as an

Avulsion fracture An avulsion fracture is a bone fracture which occurs when a fragment of bone tears away from the main mass of bone as a result of physical trauma. This can occur at the ligament by the application of forces external to the body (such as a fa ...

. This is due to forceful contraction of the muscle that generates a force greater than that which holds the bone together. This is a well recognized, but unusual

sports injury Sports injuries are injuries that occur during sport, athletic activities, or exercising. In the United States, there are approximately 30 million teenagers and children who participate in some form of organized sport. Of those, about three m ...

that can affect young athletes.

References

External links

PTCentral
{{Authority control Hip flexors Knee extensors Muscles of the quadriceps Anterior compartment of thigh Muscles of the lower limb