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Muscle Thigh

Semitendinosus Detail

musculus semitendinosus detail

The semitendinosus has an exceptionally long thin tendon (relative to its belly) making it ideal for tendon graft harvest. It is one of the components of the pes anserinus, along with gracilis and sartorius.

An expanded entry for Semitendinosus.

Anatomical Data

Origin, Insertion & Supply

OriginIschial tuberosity, medial facet, shared with the long head of biceps femoris
InsertionSuperomedial tibia, pes anserinus (along with gracilis and sartorius)
Nerve SupplyTibial nerve (L5, S1, S2)
Blood SupplyPerforating branches of the profunda femoris
Biomechanics

Function & Actions

Actions
  • Flexes the knee, the most superficial medial hamstring
  • Extends the hip
  • Medially rotates the tibia when the knee is flexed
  • Contributes to pes anserinus tendon complex stability

It extends the hip, flexes the knee, and medially rotates the tibia, contributing to medial knee stability.

Clinical Relevance

Clinical Notes

The semitendinosus tendon (with gracilis) is the most commonly harvested graft for ACL reconstruction (quadrupled hamstring graft, 4-strand STSG). The long tendon allows harvesting with a tendon stripper. After harvest, the semitendinosus regenerates a new tendon over 12-24 months from the remaining muscle belly.

Palpation

Palpated as the prominent posteromedial knee tendon at the medial hamstring, the most palpable of the three hamstring insertions.

Pathology

Common Injuries & Conditions

Semitendinosus Harvest for ACL Reconstruction

Semitendinosus tendon harvesting (with gracilis) for quadrupled hamstring ACL graft, with the tendon regenerating over 12-24 months post-harvest.

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