The quadriceps femoris is actually a group of four muscles on the front of the thigh, rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius, that converge into the quadriceps tendon, pass over the patella as the patellar tendon, and attach to the tibial tuberosity to extend the knee. As the primary knee extensors, they are essential for every activity requiring the knee to straighten against load, squatting, stair climbing, jumping, and running. The rectus femoris is the only head that also crosses the hip, contributing to hip flexion.
| Origin | Anterior inferior iliac spine (AIIS) and groove above the acetabulum; Greater trochanter and lateral lip of the linea aspera of the femur; Medial lip of the linea aspera and medial supracondylar line of the femur; Anterior and lateral surfaces of the femoral shaft |
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| Insertion | Tibial tuberosity via the patellar tendon (all four heads unite into the quadriceps tendon, then the patellar ligament) |
| Nerve Supply | Femoral nerve (L2, L3, L4) |
| Blood Supply | Femoral artery branches |
| Actions | Extension of the knee, all four heads; Flexion of the hip, rectus femoris only (crosses both joints) |
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The four heads work collectively as the dominant knee extensor group, but the vastus medialis oblique (VMO) fibres have particular importance in keeping the patella tracking centrally in its groove, weakness here is directly implicated in patellofemoral pain syndrome.
Quadriceps inhibition, a reflex reduction in muscle activation triggered by knee joint swelling, is one of the primary obstacles in knee rehabilitation after injury or surgery. The vastus medialis oblique is consistently found to be relatively weaker than the vastus lateralis in patients with patellofemoral pain, contributing to lateral patellar maltracking. Quadriceps tendon ruptures, while less common than patellar tendon ruptures, tend to occur in older patients and require surgical repair to restore active knee extension.
The rectus femoris runs down the midline of the anterior thigh and is palpable with the hip flexed; the vastus lateralis and medialis flank it on either side and are easily felt during resisted knee extension. The quadriceps tendon is palpable above the patella, and the patellar tendon below it.
A tear within one of the quadriceps heads, most commonly the rectus femoris at the AIIS origin or musculotendinous junction, producing acute anterior thigh pain from explosive sprinting or kicking, with localised tenderness and a palpable defect in severe cases.
A multifactorial overuse syndrome involving pain at or around the patella, typically attributed to lateral patellar maltracking from quadriceps imbalance, training load errors, or hip weakness, worsening with stairs, squatting, and prolonged sitting.
A complete tear through the quadriceps tendon just above the patella, more common in middle-aged or older adults, causing inability to extend the knee, a palpable gap above the patella, and a downwardly displaced patella visible on imaging.
