Muscle · Lower limb
Vastus intermedius: origin, insertion, action and innervation
The vastus intermedius runs from the front of the femoral shaft to the patella and tibial tuberosity. It extends the knee and is supplied by the femoral nerve.
Quick answer
- Latin name
- Musculus vastus intermedius
- Origin
- Front and outer surfaces of the upper two thirds of the shaft of the femur
- Insertion
- Base of the patella through the quadriceps tendon, then the tibial tuberosity of the tibia through the patellar ligament
- Action
- Extends the knee
- Innervation
- Femoral nerve (L2-L4)
- Blood supply
- Lateral circumflex femoral artery and deep femoral artery
See it on the 3D body
The vastus intermedius lit on the 3D hip and thigh, as in the hip and thigh quiz. Turn the body, peel the layers, tap any structure for its name.
The vastus intermedius is the deepest of the four quadriceps muscles, lying directly on the front of the femur under the rectus femoris. It extends the knee through the shared quadriceps tendon and is supplied by the femoral nerve (L2-L4).
Where it is
The quadriceps femoris fills the front of the thigh with four heads: the rectus femoris in the middle, the vastus lateralis on the outer side, the vastus medialis on the inner side and the vastus intermedius underneath them all.
You cannot see or feel the vastus intermedius from the surface. It hugs the front and outer side of the femur, and the rectus femoris covers it like a lid. On each side, its edges blend with the two other vasti, so in a dissection it is hard to say exactly where one stops and the next begins. A useful picture is a cross-section of the thigh: the femur in the middle, the vastus intermedius wrapped over its front like a horseshoe, and the other three heads outside it.
A tiny muscle under its lower part, the articularis genus, is often blended with it. It pulls the synovial pouch above the knee upward when the knee straightens, so the pouch is not pinched. See the whole quadriceps on muscles of the thigh.
Origin and insertion
- Origin: the front and outer surfaces of the upper two thirds of the femoral shaft. The inner surface of the shaft is left bare, covered only by the vastus medialis lying against it.
- Insertion: the deep part of the quadriceps tendon, on the base of the patella. From there the patellar ligament carries the pull to the tibial tuberosity of the tibia.
The vastus intermedius forms the deepest layer of the quadriceps tendon, closest to the knee joint.
What it does
The vastus intermedius has one action: extension of the knee. It straightens the leg at the knee joint when you stand up from a chair, climb stairs, kick a ball or jump.
Unlike the rectus femoris, it does not cross the hip, so it does not flex the hip. That makes it a pure knee extensor, along with the vastus lateralis and medialis. When you hold a squat, all three vasti work together to stop the knee from buckling.
Innervation and blood supply
The vastus intermedius is supplied by the femoral nerve (L2-L4), the nerve of the whole anterior compartment of the thigh. Its branches enter the muscle from the front, after passing under the rectus femoris.
Its blood comes mainly from the lateral circumflex femoral artery and branches of the deep femoral artery.
How to remember it
- Intermedius means in the middle: it sits between the vastus lateralis and medialis, but deep, under the rectus femoris. Think "middle and bottom".
- Three vasti, one rectus: only the rectus femoris crosses the hip. All three vasti start on the femur and act on the knee alone.
- Hidden horseshoe: in a cross-section, the vastus intermedius is the horseshoe sitting directly on the femur.
- Femoral nerve, front of the thigh: every quadriceps head is supplied by the femoral nerve.
Test yourself in the hip and thigh quiz.
Frequently asked questions
What does the vastus intermedius do?
It extends the knee. It does not act on the hip.
Where is the vastus intermedius?
Deep in the front of the thigh, directly on the femur, under the rectus femoris and between the vastus lateralis and vastus medialis.
What nerve supplies the vastus intermedius?
The femoral nerve, from roots L2 to L4.
Is the vastus intermedius part of the quadriceps?
Yes. It is the deepest of the four quadriceps heads.
What is the articularis genus?
A small muscle under the lower vastus intermedius, often blended with it. It lifts the synovial pouch above the knee when the knee extends.
