Semitendinosus

Where is the semitendinosus?

It arises from the inner border of the ischial tuberosity, from the inner border of the tendon of the long head of biceps femoris and from the proximal aponeurosis. (StatPearls, Thigh Semitendinosus Muscle)

It stays fleshy until below the middle of the thigh, then becomes a long tendon that forms the inner border of the popliteal fossa. (StatPearls, Thigh Semitendinosus Muscle)

Semimembranosus lies deep to it and is the most medial muscle of the back of the thigh. (StatPearls, Thigh Semitendinosus Muscle)

Where does the semitendinosus insert?

Its tendon curves over the pes anserine bursa, which lies over the medial collateral ligament, and inserts on the upper inner front of the tibia, behind the tendons of sartorius and gracilis. (StatPearls, Thigh Semitendinosus Muscle)

It is the longest muscle of the hamstrings, averaging 44.3 cm, against 42.0 cm for the long head of biceps femoris. (StatPearls, Hamstring Muscle)

An aponeurosis about 7 cm long joins it to the long head of biceps femoris below the ischial tuberosity. (StatPearls, Hamstring Muscle)

What does the semitendinosus do?

With the other hamstrings it extends the hip and flexes the knee, and it helps the popliteus rotate the leg medially. (StatPearls, Thigh Semitendinosus Muscle)

When the gluteus maximus extends the hip with force, as in climbing stairs, it works with semitendinosus and semimembranosus. (StatPearls, Gluteus Maximus Muscle)

What supplies the semitendinosus?

The tibial nerve, a branch of the sciatic nerve, supplies it, as it does every muscle of the back of the thigh except the short head of biceps femoris. (StatPearls, Thigh Semitendinosus Muscle)

It and the long head of biceps femoris each receive two nerve branches; semimembranosus and the short head usually receive one. (StatPearls, Hamstring Muscle)

Perforating branches of the deep femoral artery supply it, and perforating veins drain it to the femoral vein. (StatPearls, Thigh Semitendinosus Muscle)

Does the semitendinosus vary?

In one reported case it sent an extra tendon slip to the gracilis tendon, and the gracilis sent one back, making a double pes anserinus. Other reports have its tendon ending in the fascia of the leg. (StatPearls, Thigh Semitendinosus Muscle)

Where the sources differ

Sources differ on the roots of the sciatic nerve that carries its supply: L4 to S2 in the StatPearls semitendinosus article, L4 to S3 in its hamstring article. (StatPearls, Thigh Semitendinosus Muscle and Hamstring Muscle)