Semimembranosus

Musculus semimembranosus

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The semimembranosus is the deepest and largest medial hamstring, named for the broad membranous tendon at its origin. It extends the hip, flexes the knee, and medially rotates the tibia, while its expansion into the oblique popliteal ligament reinforces the posteromedial knee capsule. Because it is a powerful hip extensor, it is heavily loaded during deadlifts and RDLs, and its knee-stabilizing attachments make it important for protecting the knee in deceleration and cutting.

Actions

Knee flexion, Hip extension, Medial rotation of the leg at the knee (when knee flexed), Medial rotation of the thigh (when hip extended)

Origin

Superolateral aspect of the ischial tuberosity, via a flat membranous tendon, lying deep and medial to biceps femoris and semitendinosus

Insertion

Posteromedial aspect of the medial condyle of the tibia, with fibrous expansions to the oblique popliteal ligament, popliteus fascia, and medial meniscus

Innervation

Tibial division of the sciatic nerve (L5-S2)

Blood supply

Perforating branches of the profunda femoris (deep femoral) artery and gluteal arteries

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