Attachments
Quadriceps femoris has four heads that converge on one tendon above the patella.
| Head | Origin | Notes |
|---|---|---|
| Rectus femoris | Straight head from the anterior inferior iliac spine; reflected head from the ilium just above the acetabulum | The only head crossing the hip, so it also flexes the hip |
| Vastus lateralis | Upper intertrochanteric line, greater trochanter, lateral lip of the linea aspera | The largest head |
| Vastus medialis | Lower intertrochanteric line, spiral line, medial lip of the linea aspera | Its lowest, near-horizontal fibres (vastus medialis obliquus) pull the patella medially |
| Vastus intermedius | Front and lateral surfaces of the femoral shaft | Deepest; a few fibres (articularis genus) pull up the suprapatellar bursa |
The quadriceps tendon is layered: rectus femoris forms the superficial layer, vastus medialis and lateralis the middle layer, and vastus intermedius the deep layer. It inserts on the upper border of the patella, and its superficial fibres continue over the front of the bone.
The patella is the largest sesamoid bone in the body. It holds the tendon away from the femur and increases the lever arm of quadriceps. Its back carries a larger lateral facet and a smaller medial facet.
The patellar ligament (patellar tendon) runs from the apex of the patella to the tibial tuberosity. It is roughly as long as the patella itself. Expansions from the vasti pass beside the patella to the tibial condyles as the medial and lateral patellar retinacula.
Relations
The extensor mechanism lies directly in front of the knee joint, separated from it by fat and bursae. The suprapatellar bursa lies under the quadriceps tendon and opens into the joint. The infrapatellar fat pad sits behind the patellar ligament, and the deep infrapatellar bursa lies between the ligament and the upper tibia. The prepatellar and superficial infrapatellar bursae lie under the skin.
The patella glides in the patellar groove between the femoral condyles. The lateral condyle's front surface stands higher, and together with vastus medialis obliquus and the medial patellofemoral ligament it stops the patella slipping laterally. Deep to the mechanism, once it is reflected, the tibial plateaus and menisci come into view.
Blood supply and innervation
Quadriceps is supplied mainly by the lateral circumflex femoral artery, with branches from the profunda femoris and femoral arteries. The patella receives blood from a ring of genicular vessels around its margins, entering mostly at the front and lower pole. The femoral nerve (L2–L4) supplies all four heads. Tapping the patellar ligament stretches quadriceps and produces the knee jerk, which tests the L3 and L4 roots.
Clinical relevance
Any break in the extensor chain leaves the patient unable to lift the straight leg off the couch or hold the knee extended against gravity.
- Quadriceps tendon rupture: usually over the age of 40, often with steroid use, renal failure or diabetes. A gap is felt above the patella, which sits low (patella baja).
- Patellar ligament rupture: usually under 40, often in jumping sports. The patella rides high (patella alta).
- Patellar fracture: a displaced transverse fracture with torn retinacula abolishes active extension and needs fixation; if the retinacula are intact the patient may still extend weakly.
- Lateral patellar dislocation: favoured by a shallow groove, a high patella, a wide Q angle and weak vastus medialis obliquus. The medial patellofemoral ligament tears.
- Traction apophysitis: Osgood–Schlatter disease at the tibial tuberosity and Sinding-Larsen–Johansson disease at the lower pole of the patella, in active adolescents.
- Patellar tendinopathy ('jumper's knee'): pain at the lower pole of the patella.
- Graft source: the central third of the patellar ligament with bone blocks from the patella and tibia is a standard ACL reconstruction graft.
On the specimen
The station shows the front of an opened knee, with the extensor mechanism and the lateral side of the joint exposed. Trace the chain from above down: the broad band above the patella is the quadriceps tendon; the triangular bone in it is the patella; the thick band below is the patellar ligament; and the rough bump it reaches on the front of the tibia is the tibial tuberosity.
The other two markers lie deeper. The lateral femoral condyle is the outer knuckle of the femur, whose front surface forms the high lateral wall of the patellar groove. The lateral meniscus is the nearly circular crescent on the lateral tibial plateau, identified by its rounder shape and by its two horns, which attach close together in the middle of the plateau.