Semitendinosus Tendon

tendo musculi semitendinosi

The semitendinosus has the longest tendon relative to its muscle belly of any hamstring muscle, its tendon beginning in the lower thigh and inserting at the pes anserinus on the medial tibial surface. This long tendon makes it the preferred hamstring for ACL reconstruction graft harvest, often used alongside the gracilis to create a four-strand hamstring graft. The regenerated semitendinosus after harvest is detectable on MRI as a reformed but smaller muscle-tendon unit by 12 months.

Region: Thigh

Biomechanics

Function & Actions

Knee flexion and internal tibial rotation; pes anserinus contribution to medial knee stability

Clinical Relevance

Clinical Notes

Semitendinosus harvest for ACL reconstruction produces temporary hamstring weakness that normalises over 12 to 18 months as the muscle regenerates from the remaining proximal belly. Some studies show persistent hamstring strength deficits at 2 years, particularly for knee flexion strength at low flexion angles. Tendon regeneration appears to occur in 80 to 90 percent of patients based on MRI follow-up studies.

Pathology

Common Injuries & Conditions

Semitendinosus Strain

Proximal musculotendinous junction injury during explosive activities producing posterior thigh pain, managed conservatively with progressive loading rehabilitation.