The biceps femoris is the lateral hamstring, consisting of a long head arising from the ischial tuberosity and a short head from the posterior femur, both inserting on the fibular head. It is the only hamstring with dual nerve supply, with the short head receiving the common peroneal nerve rather than the tibial nerve. Its insertion into the fibular head places it adjacent to the common peroneal nerve, which wraps around the fibular neck just distal to this attachment.
| Origin | Ischial tuberosity, shared with semitendinosus via the conjoined tendon; Lateral lip of the linea aspera and lateral supracondylar line of the femur |
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| Insertion | Head of the fibula and lateral condyle of the tibia |
| Nerve Supply | Tibial nerve (L5, S1, S2) for the long head; Common peroneal nerve (L5, S1, S2) for the short head |
| Blood Supply | Inferior gluteal artery; Perforating branches of the deep femoral artery |
| Actions | Flexion of the knee; Extension of the hip (long head only); External rotation of the tibia when the knee is flexed |
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The long head acts across both the hip and knee as a hip extensor and knee flexor, while the short head acts only at the knee. The external rotation of the tibia produced during knee flexion is important for the screw-home mechanism of knee locking.
Biceps femoris strains occur most commonly at the proximal long head musculotendinous junction, typically during sprinting or a sudden change of pace. The short head is the most common site of a complete hamstring tendon avulsion from the fibular head in contact sports. The common peroneal nerve runs immediately posterior to the biceps femoris tendon at the fibular neck and can be compressed or stretched when the tendon is avulsed or swollen.
The biceps femoris tendon is palpable as the prominent lateral cord in the popliteal fossa during resisted knee flexion with the tibia externally rotated. The fibular head insertion is a clear bony landmark at the lateral knee.
Proximal long head tear during sprinting producing posterior thigh pain and bruising, graded I to III by severity with complete tears showing a palpable defect and MRI confirming retraction.
Complete avulsion of the distal tendon from the fibular head in contact sport, producing posterolateral knee pain and instability with common peroneal nerve involvement in severe cases.
