Semimembranosus

Anatomy

Origin:
Superolateral impression on ischial tuberosity.

Insertion:
Posteromedial surface of medial condyle of the tibia.

Key Relations:
-One of the three muscles of the posterior compartment of the thigh.
-Lies posteromedial to semitendinosus and the long head of biceps femoris.
-Along with semitendinosus forms the superomedial boundary of the popliteal fossa.

Functions

-Flexes the leg at the knee joint.
-Extends the thigh at the hip joint.
-Medially rotates the thigh at the hip joint when the hip is extended.
-Medially rotates the leg at the knee joint when the knee is semi-flexed.

Supply

Nerve Supply:
Tibial division of sciatic nerve (L5, S1, S2).

Blood Supply:
-Perforating arteries (branches of deep artery of thigh)
-Superior muscular branches of popliteal artery.

Clinical

‘Hamstring syndrome’ presents as pain near the ischial tuberosity, thought to be caused by tendinitis at the origin of the hamstrings – in some cases compression of the sciatic nerve may also be involved. It is common amongst athletes, especially those partaking in sports that involve sprinting or short bursts of acceleration. The pain associated with ‘hamstring syndrome’ often radiates down the posterior thigh and is exacerbated by actions that stretch the hamstrings.

In addition, the clinical examination of ‘hamstring syndrome’ may reveal tenderness over the ischial tuberosity, and percussion in that region may cause the pain to radiate down the posterior thigh in a pattern determined by the sciatic nerve. ‘Hamstring syndrome’ can be treated with rest, NSAIDs and steroid injections. Surgical exploration of the sciatic nerve may be required to release various bands.

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