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Topic

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Hamstring muscles

The hamstring muscles are a group of powerful muscles located in the posterior compartment of the thigh. They are primary extensors of the hip and flexors of the knee and play a crucial role in walking, running, posture, and lower-limb stability.

They form a functionally and anatomically distinct group characterized by a common proximal origin from the ischial tuberosity, biarticular action across the hip and knee, and a shared role in locomotion.

Synonyms

  • Posterior thigh muscles

  • Hamstring group

Location

  • Situated in the posterior compartment of the thigh

  • Extend from the ischial tuberosity superiorly to the knee region inferiorly

  • Lie posterior to the femur

  • Deep to the fascia lata

  • Superficial to the posterior femoral cortex

Anatomical components

  • Biceps femoris:

    • Long head

    • Short head (often excluded from classic hamstring definition)

  • Semitendinosus

  • Semimembranosus

Relations

Superficially:

  • Skin and subcutaneous tissue

  • Deep fascia (fascia lata)

Deep:

  • Adductor magnus (medially)

  • Femur and linea aspera

Medially:

  • Gracilis

  • Adductor muscles

Laterally:

  • Iliotibial band

  • Vastus lateralis (anterior-lateral boundary)

Superiorly:

  • Ischial tuberosity

  • Gluteal fold

Inferiorly:

  • Popliteal fossa

  • Knee joint capsule

Individual muscles

Biceps femoris:

  • Lies laterally in the posterior thigh

  • Long head: originates from the ischial tuberosity

  • Short head: originates from the linea aspera

  • Forms the lateral boundary of the popliteal fossa

Semitendinosus:

  • Superficial medial hamstring muscle

  • Has a long distal tendon

  • Contributes to the pes anserinus

Semimembranosus:

  • Deep medial hamstring muscle

  • Broad proximal tendon

  • Forms part of the posterior knee capsule

Function

  • Hip extension: Powerful extension of the hip during gait and running

  • Knee flexion: Flexes the knee joint

  • Pelvic control: Stabilizes the pelvis during stance phase

  • Postural support: Controls forward trunk flexion

MRI appearance

T1-weighted images:

  • Normal muscle: Intermediate signal intensity

  • Intermuscular fat: High signal outlining muscle planes

  • Tendinous portions: Low signal intensity

T2-weighted images:

  • Normal muscle: Low-to-intermediate homogeneous signal

  • Tendons and aponeuroses: Low signal

  • Muscle architecture: Pennate and fusiform patterns visible

STIR:

  • Normal muscle: Intermediate-to-dark signal

  • Fascial planes: Clearly delineated by surrounding fat suppression

  • Useful for assessing muscle bulk and symmetry

CT appearance

Pre-contrast CT:

  • Muscle: Homogeneous soft-tissue density in the posterior thigh

  • Fascial planes: Preserved low-density fat planes between muscles

  • Tendons: Slightly higher density linear structures near attachments

  • Symmetry: Bilateral hamstring groups symmetric in size and density

CT image

Hamstring group

CT image

Hamstring muscles