The rectus femoris is a muscle in the front of the thigh. It is one of four muscles forming the quadriceps femoris group, which covers the front and sides of the femur. This muscle plays a role in leg movement and lower limb function. Its position allows it to act across both the hip and knee joints, distinguishing it from the other quadriceps muscles.
Anatomical Attachments
The rectus femoris originates from two points on the ilium, the largest bone of the pelvis. Its main origin is the anterior inferior iliac spine (AIIS). A smaller, reflected head also originates from a groove superior to the acetabulum, the hip socket.
From these origins, the muscle descends along the front of the thigh. Distally, it converges with the other three quadriceps muscles to form the common quadriceps tendon. This tendon crosses the knee joint and envelops the patella (kneecap), continuing as the patellar ligament. The patellar ligament inserts onto the tibial tuberosity, a bony bump on the front of the tibia (shin bone) below the knee. This arrangement transmits the force generated by the rectus femoris through the patella to the tibia, enabling knee movement.
Primary Actions
The rectus femoris performs two actions due to its attachments spanning both the hip and knee joints. One function is knee extension, which straightens the leg at the knee. This action is important for activities like kicking, standing, and the propulsive phase of walking or running. It works in concert with the other quadriceps muscles to achieve this extension.
It also contributes to hip flexion. This involves lifting the thigh towards the torso. This dual capability makes it important in movements requiring simultaneous hip and knee coordination, such as sprinting, jumping, and climbing stairs. The ability of the rectus femoris to act on two joints distinguishes it from the vastus muscles (vastus lateralis, vastus medialis, and vastus intermedius), which only cross the knee joint.
Clinical Relevance
Understanding the rectus femoris is important in clinical contexts, particularly in sports medicine and rehabilitation. Its dual-joint function makes it susceptible to injury, especially in activities involving explosive movements or rapid changes in direction. Muscle strains and tears, particularly at its proximal origin near the hip, are common among athletes in sports like soccer, football, and track and field. These injuries can cause pain and limit basic movements.
The rectus femoris also plays a role in knee conditions like patellofemoral pain syndrome. Imbalances or tightness in this muscle can alter patella tracking within the trochlear groove of the femur, leading to anterior knee pain. In rehabilitation, exercises targeting the rectus femoris are often incorporated to restore strength and flexibility following hip or knee injuries. Its contribution to hip and knee mechanics makes it a focus for therapists aiming to improve lower limb function and prevent future injuries.