Long head of biceps femoris

At a glance

English

Long head of biceps femoris

Latin (TA2)

Caput longum musculi bicipitis femoris

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the long head of biceps femoris

Biceps femoris is the lateral muscle of the posterior thigh, and its long head is the part that belongs to the hamstring group proper. It starts on the pelvis, so it spans both the hip and the knee, whereas the short head starts on the femur and crosses the knee alone. The two heads fuse low in the thigh and finish on a single tendon that can be felt as the lateral hamstring cord at the back of the knee.

The long head springs from the medial facet on the back of the ischial tuberosity, sharing a short common tendon with semitendinosus, and it also takes fibres from the lowest stretch of the sacrotuberous ligament. Its spindle-shaped belly slants downwards and outwards, passing over the sciatic nerve, and ends on a broad aponeurosis on its posterior face. The short head joins the deep surface of that sheet, and the merged tendon splits around the fibular collateral ligament to attach mainly to the head of the fibula, with a smaller slip to the lateral tibial condyle and an expansion to the deep fascia of the leg.

Because it crosses two joints, the long head both flexes the knee and extends the hip. Its pull on either joint is weaker when the other is already in the shortened position: with the hip straight it is a poorer knee flexor, and with the knee bent it extends the hip less well. When the knee is partly bent, its oblique line of pull turns the leg slightly outwards. Its nerve is the tibial division of the sciatic nerve, the same as the other true hamstrings, while the short head is served by the common fibular division.

At the knee, the common fibular nerve runs down along the medial edge of the tendon, so it is at risk in injuries and surgery here. The long head is the hamstring most often strained in sprinting and other fast running, and violent knee bending can tear its tendon from the fibula. The muscle may show extra heads, a missing short head or a slip to gastrocnemius.

Attachments, action and supply

Origin

Medial facet on the back of the ischial tuberosity, by a tendon shared with semitendinosus, and the sacrotuberous ligament's lower end.

Insertion

Head of the fibula through the common biceps tendon, with a small slip to the tibia's lateral condyle and an expansion into the crural fascia.

Action

Flexes the knee and extends the hip; turns the leg outwards when the knee is partly bent.

Nerve supply

Tibial division of the sciatic nerve; roots L5 to S2.

Blood supply

Perforating branches of the deep femoral artery, with contributions from the inferior gluteal and popliteal arteries.