Muscle
Biceps femoris
Two-headed muscle along the outer posterior thigh
High-yield
Both heads act at the knee, but only the long head crosses and extends the hip. Their nerve supply also differs: tibial division for the long head and common fibular division for the short head.
Overview
Biceps femoris approaches the knee from the outer side of the posterior thigh. Its long head starts on the pelvis and crosses the hip; its short head begins on the femur and joins the distal tendon system.
Reference facts
- Origin
- Long head from the ischial tuberosity with semitendinosus; short head from the lateral linea aspera, lateral supracondylar line and intermuscular septum
- Insertion
- Mainly the fibular head, with additional connections around the lateral tibial condyle and fibular collateral ligament
- Action
- Flexes the knee and externally rotates the flexed leg; the long head also extends the hip
- Innervation
- Long head: tibial division of the sciatic nerve; short head: common fibular division. Hamstring motor roots are commonly summarized as L5-S2
- Blood supply
- Mainly profunda femoris perforating branches, with proximal inferior gluteal and distal popliteal muscular contributions
Clinical correlation
A distal tendon avulsion can occur with other injuries around the outer knee. The nearby common fibular nerve may also be damaged or displaced, potentially causing weakness in lifting the foot; this is a possible complication rather than an inevitable result.
Frequently asked questions
What does the biceps femoris do?
Flexes the knee and externally rotates the flexed leg; the long head also extends the hip.
What nerve innervates the biceps femoris?
Long head: tibial division of the sciatic nerve; short head: common fibular division. Hamstring motor roots are commonly summarized as L5-S2.
Where does the biceps femoris attach?
Origin: Long head from the ischial tuberosity with semitendinosus; short head from the lateral linea aspera, lateral supracondylar line and intermuscular septum. Insertion: Mainly the fibular head, with additional connections around the lateral tibial condyle and fibular collateral ligament.
What is the blood supply of the biceps femoris?
Mainly profunda femoris perforating branches, with proximal inferior gluteal and distal popliteal muscular contributions.