The vastus intermedius is the deepest of the four quadriceps heads, lying directly on the anterior femoral shaft beneath the rectus femoris. It is the only quadriceps head that cannot be palpated directly. Its fibres blend into the deep portion of the quadriceps tendon and contribute to knee extension force without any distinct patellar attachment separate from the other heads.
| Origin | Anterior and lateral surfaces of the upper two-thirds of the femoral shaft |
|---|---|
| Insertion | Deep surface of the quadriceps tendon, joining the other heads above the patella |
| Nerve Supply | Femoral nerve (L2, L3, L4) |
| Blood Supply | Lateral circumflex femoral artery |
| Actions | Extension of the knee; Contributes to the patellofemoral joint reaction force |
|---|
Because it originates directly from the femoral shaft and inserts into the deep quadriceps tendon, it acts as a direct knee extensor without influencing patellar tilt, unlike the vastus lateralis and medialis which have specific lateral and medial patellar attachments.
The articularis genus muscle, a small slip arising from the lower vastus intermedius, prevents the suprapatellar pouch from being trapped during knee extension and is relevant in post-operative knee stiffness management. The vastus intermedius is assessed as part of overall quadriceps strength testing and cannot be isolated clinically. Its atrophy is detected by quadriceps bulk loss and dynamometric testing rather than visual assessment.
The vastus intermedius cannot be palpated because it lies deep to the rectus femoris. It is assessed indirectly through overall quadriceps bulk measurement and isokinetic dynamometry.
Tearing involving the deep quadriceps including the vastus intermedius from eccentric overload, producing deep anterior thigh pain with knee extension weakness and haematoma visible on MRI.
