Muscle · Hips

Semimembranosus

Musculus semimembranosus

Semimembranosus is the broad, deep inner hamstring that sits underneath and on either side of the semitendinosus rope. It starts on the sit bone by a wide flat sheet of tendon — the membrane it is named after — and ends on the back of the inner knee, where instead of stopping it fans out into the joint itself: expansions run into the capsule as the oblique popliteal ligament, over popliteus, and onto the medial meniscus. That fan is what makes it more than a mover. As the knee bends it pulls the medial meniscus backwards out of harm's way, and it stiffens the back inner corner of the joint. It is also the hamstring most often blamed for the deep ache at the back of the inner knee that is hard to point at.