Semitendinosus

The Semitendinosus arises in origin with the long head of the biceps femoris from the posteromedial surface of the ischial tuberosity. It is a hamstring muscle, and a constituent part of the tendon complex referred to as the pes anserinus (sartorius, gracilis, semitendinosus). When the knee is flexed, the semitendinosus becomes a good internal (medial) rotator of the leg.

The ischial bursa lies between the ischial tuberosity and the fascia at the inferior surface of the gluteus maximus. As a result of chronic irritation it can become inflamed in people who must sit on unpadded surfaces at work (weaver's knot, miner's knot).

Hamstring rupture and microvascular tears are all too familiar - these are painful and sometimes require a lengthy recovery period. The hamstrings cause extension of the thigh, flexion of the leg, and medial or lateral rotation of the flexed leg. The tibial nerve innervates the semimembranosus, semitendinosus, and the long head of the biceps femoris. A branch of the common fibular nerve innervates the short head of the biceps.