Quadrizeps

Quadrizeps, or quadriceps femoris, is a large muscle group on the front of the thigh. It comprises four individual muscles: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The quadriceps are the primary knee extensors, enabling activities such as standing up, walking, and running. The rectus femoris also crosses the hip joint and contributes to hip flexion, giving the group a role in hip movement as well as knee extension.

Anatomy and connections: The rectus femoris originates from the anterior inferior iliac spine and the ilium above the acetabulum; vastus lateralis from the greater trochanter and the lateral lip of the linea aspera; vastus medialis from the intertrochanteric line and the medial lip of the linea aspera; and vastus intermedius from the anterior and lateral surfaces of the femoral shaft. All four heads unite to form the quadriceps tendon, which attaches to the patella. The patella vilifies the extensor mechanism and continues as the patellar ligament to insert on the tibial tuberosity. The muscles are supplied by branches of the femoral artery and are innervated by the femoral nerve (L2–L4).

Function and biomechanics: The quadriceps extend the knee, providing propulsion and stability during standing and movement. The vastus medialis and vastus lateralis help stabilize the patella within the femoral groove, contributing to smooth knee tracking. The group works in coordination with the hamstrings and other leg muscles during gait and athletic activities.

Clinical relevance: Common issues include quadriceps strains, contusions, tendinopathy, and, in some cases, rupture or atrophy after injury or disuse. Rehabilitation emphasizes progressive resistance training, neuromuscular control, and, when appropriate, eccentric loading to restore strength and knee function.