Semitendinosus muscle

The semitendinosus is one of the three hamstring muscles located in the posterior compartment of the thigh, along with the biceps femoris and semimembranosus. It is a long, fusiform muscle distinguished by its elongated tendon that extends distally down the medial aspect of the posterior thigh.

The semitendinosus crosses both the hip and knee joints, contributing to hip extension, knee flexion, and medial rotation of the leg. It also plays a vital stabilizing role in maintaining postural balance during standing and gait.

Origin

• Arises by a common (conjoined) tendon with the long head of the biceps femoris from the inferomedial aspect of the ischial tuberosity of the pelvis.

• The origin lies deep to the gluteus maximus and lateral to the semimembranosus.

Course and insertion

• The semitendinosus muscle descends vertically and medially in the posterior thigh, superficial to the semimembranosus.

• In the distal third of the thigh, the fleshy belly tapers into a long, round tendon that descends on the posterior surface of the medial side of knee. Here it forms the superomedial boundary of the popliteal fossa.

• The round tendon expands distally to insert onto the medial surface of the superior tibia, just below the medial condyle.

• Together with the tendons of sartorius (anteriorly) and gracilis (posteriorly), it forms the pes anserinus (goose’s foot).

• A bursa (pes anserine bursa) separates these tendons from the underlying tibial collateral ligament.

Nerve Supply

• Tibial division of the sciatic nerve (roots L5–S2) → Derived from the lumbosacral plexus.

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