The rectus femoris is the only quadriceps head that crosses the hip joint, arising from the anterior inferior iliac spine and running straight down the anterior thigh to the patella. Its biarticular nature means it is length-dependent, becoming mechanically disadvantaged in positions of hip extension and knee flexion simultaneously, which limits its effectiveness as both a hip flexor and knee extensor in those ranges.
| Origin | Anterior inferior iliac spine (AIIS); Groove above the acetabular rim |
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| Insertion | Base of the patella and patellar tendon to the tibial tuberosity |
| Nerve Supply | Femoral nerve (L2, L3, L4) |
| Blood Supply | Lateral circumflex femoral artery |
| Actions | Extension of the knee; Flexion of the hip; The only biarticular quadriceps head, crossing both hip and knee |
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Its dual-joint function means that full hip extension stretches and reduces its knee extension torque, explaining why quadriceps strength tests should be performed with the hip in neutral rather than flexed position to avoid underestimating the other quadriceps heads.
The rectus femoris is the most commonly strained quadriceps muscle, typically at the proximal musculotendinous junction during kicking or sprinting. AIIS avulsion fractures at its origin are seen in adolescent athletes. The two-joint nature of the rectus femoris is clinically assessed by the Thomas test and the Ely test, where limited prone knee flexion combined with spontaneous hip flexion indicates rectus femoris tightness.
The rectus femoris runs centrally down the anterior thigh as the most superficial quadriceps head and is the easiest to palpate, becoming firm during resisted knee extension or hip flexion with the knee extended.
Proximal musculotendinous junction tear from explosive kicking or sprinting, producing anterior hip and proximal thigh pain with a palpable defect in severe cases.
Avulsion of the anterior inferior iliac spine at the rectus femoris origin in adolescent athletes during explosive sprinting, producing acute anterior hip pain with imaging showing the detached apophysis.
