Biceps femoris (short head) !

The short head of biceps femoris is the shorter part of the outer hamstring, starting on the femur; it bends the knee.

Official name: Short head of biceps femoris

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What it is

The short head of the outer hamstring, starting on the femur.

What it does

Bends the knee.

Key facts

Origin: Lateral lip of linea aspera; lateral supracondylar line of femur
Insertion: Head of fibula (with long head)
Action: Flexes knee; laterally rotates flexed knee
Nerve: Sciatic nerve, common fibular division (L5–S2)
Blood supply: Perforating arteries; popliteal artery branches

Relations

Superficial: Long head of the biceps femoris, which covers it
Lateral: Lateral intermuscular septum and, beyond it, the vastus lateralis
Medial: Sciatic nerve and, lower down, the common fibular nerve, which runs along the medial border of the biceps femoris
Below: Joins the long head in a common tendon above the knee

How to find it

It cannot be separated from the long head by touch. With the knee bent against resistance, its fleshy fibres are felt on the outer back of the lower thigh, deep to the long head and reaching closer to the knee. Ultrasound and MRI show it lying on the femur, deep and lateral to the long head.

Examination

Needle EMG of the short head: denervation places the lesion in the thigh or higher (sciatic nerve, its fibular division or the L5–S1 roots); a normal short head with abnormal leg muscles points to the fibular neck

On imaging

Axial MRI and ultrasound show it in the lower back of the thigh, deep and lateral to the long head, arising from the linea aspera and reaching close to the knee. It is strained less often than the long head. In foot drop, denervation oedema in the short head on MRI places the lesion in the sciatic nerve (fibular division) above the knee, not at the fibular neck.

Common problems

Hamstring strain, common in sprinting sports.
Rarely, the tendon pulls off the bone at the hip.

How it is diagnosed

Physical exam; MRI for severe strains.

Treatment

Rest, then progressive stretching and strengthening; surgery only for complete tendon pull-offs.

Clinical notes

In sciatic nerve injuries from hip surgery, hip dislocation or a misplaced gluteal injection, the fibular division is often hit harder, so foot drop may dominate
Injured together with the long head in posterolateral corner trauma; isolated strains are uncommon

Development

Usually taught as a dorsal muscle mass derivative that joined the long head secondarily: this is why it alone receives the common fibular division of the sciatic nerve.

Hamstring Strain

Test yourself

Think of the answer, then tap the question to see it.

Why is the short head of the biceps femoris not strictly a true hamstring?

It does not cross the hip: it arises from the linea aspera and lateral supracondylar line of the femur and only flexes the knee.

Which nerve supplies the short head of the biceps femoris?

The common fibular division of the sciatic nerve; it is the only hamstring component supplied by that division.

How does needle EMG of the short head of the biceps femoris localize a foot drop?

Denervation places the lesion in the thigh or higher (sciatic nerve or L5–S1 roots); a normal short head with abnormal leg muscles points to the fibular neck.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): caput breve musculi bicipitis femoris TA2 2640
Official Spanish (DeCS): Cabeza corta del músculo bíceps femoral DeCS D000070633
English (TA2): Short head of biceps femoris

Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Bony Pelvis and Lower Limb, Hamstring Muscle; Anatomy, Bony Pelvis and Lower Limb: Posterior Thigh Muscles.

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Representative model, for educational purposes only.

Biceps femoris (short head) highlighted on the Durgical 3D model