Biceps Femoris Muscle (Long Head): Anatomy, Origin, Insertion, Nerve and Blood Supply, Function, MRI & CT Imaging

Topic

Biceps femoris muscle (Long head)

The biceps femoris long head is one of the three hamstring muscles located in the posterior compartment of the thigh. It is the larger, medial component of the biceps femoris, running alongside the short head to form a common tendon. The long head spans both the hip and knee joints, making it a biarticular muscle involved in powerful hip extension and knee flexion. It plays a critical role in walking, sprinting, and stabilization of the pelvis.

Synonyms

Long head of biceps femoris
Hamstring biceps longus
Posterolateral hamstring

Origin and Insertion

Origin:
- Arises from the ischial tuberosity of the pelvis, via a common tendon with the semitendinosus muscle
Course:
- Fibers descend vertically along the posterior thigh
- Joins with the short head in the distal third of the thigh
Insertion:
- Inserts on the head of the fibula, sharing a common tendon with the short head

Nerve Supply

Tibial division of the sciatic nerve (L5–S2)

Arterial Supply

Perforating branches of profunda femoris artery
Inferior gluteal artery
Popliteal artery branches (distal portion)

Venous Drainage

Drains into the profunda femoris vein and popliteal vein → femoral vein

Function

Hip joint: Extension and external rotation of thigh
Knee joint: Flexion and external rotation of leg
Gait: Stabilizes pelvis during walking and running
Sports function: Important in sprinting and explosive movements; frequent site of hamstring injuries

Clinical Significance

Hamstring strains/tears: Common in athletes, especially at myotendinous junction
Avulsion fractures: At ischial tuberosity origin in adolescents and young adults
Entrapment: Close relation to sciatic nerve can complicate injuries
Surgical relevance: Important in tendon grafts for ACL reconstruction

MRI Appearance

T1-weighted images:

Normal muscle: low-to-intermediate signal intensity
Fat planes and septa: bright
Chronic fatty atrophy or infiltration: high signal

T2-weighted images:

Normal muscle: intermediate signal
Acute tears, edema, or inflammation: bright hyperintense areas

STIR (Short Tau Inversion Recovery):

Normal muscle: Intermediate signal
Pathology (strain, edema, hematoma): bright hyperintensity

T1 Fat-Sat Post-Contrast:

Normal muscle: mild uniform enhancement
Inflammation/myositis: diffuse or patchy enhancement
Abscess or tear with hematoma: rim enhancement with central non-enhancing area