Semimembranosus Tibial Insertion

insertiones musculi semimembranosi tibiales

The semimembranosus has a complex five-arm insertion at the posteromedial knee: the direct arm inserts on the posterior medial tibial condyle (the principal insertion); the reflected arm curves anteriorly beneath the MCL to insert on the medial tibial metaphysis; the capitate arm continues into the posterior capsule and medial gastrocnemius fascia; a fourth arm contributes to the oblique popliteal ligament (OPL) running obliquely across the posterior capsule; and a fifth arm contributes to the popliteal fascia.

Region: Knee

Clinical Relevance

Clinical Notes

The semimembranosus insertion complex is the primary structure of the posteromedial corner (PMC) of the knee, working with the deep MCL and the posterior oblique ligament to resist valgus and external rotation. PMC injuries in valgus-external rotation mechanisms produce medial knee instability with insufficiency of the semimembranosus insertion complex, MCL, and posterior capsule. The semimembranosus direct arm is protected during medial knee surgery; its reflected arm is identified in posteromedial approaches. In PM corner reconstruction, the semimembranosus insertional anatomy guides graft placement at the posteromedial tibial condyle.

Pathology

Common Injuries & Conditions

Posteromedial Corner Injury Disrupting Semimembranosus Complex

Valgus external rotation knee injury disrupts the semimembranosus insertion complex, MCL, and posteromedial capsule producing combined medial and posterolateral instability; isolated posteromedial reconstruction addressing the semimembranosus direct and reflected arm anatomy combined with MCL repair restores medial rotatory stability.