The semimembranosus has five distinct insertional expansions, including the oblique popliteal ligament which reinforces the posterior knee capsule. Its broad insertion provides medial and posteromedial knee stability.
| Origin | Ischial tuberosity — superolateral facet (separate from the semitendinosus/biceps femoris origin) |
|---|---|
| Insertion | Posterior medial tibial condyle — primary insertion, with 5 secondary expansions including the oblique popliteal ligament and medial meniscus |
| Nerve Supply | Tibial nerve (L5, S1, S2) |
| Blood Supply | Perforating branches of the profunda femoris |
| Actions | Flexes the knee; Extends the hip; Medially rotates the tibia when the knee is flexed; Provides posteromedial knee stability via its multiple insertions |
|---|
Semimembranosus tendinopathy produces posteromedial knee pain. The oblique popliteal ligament (a semimembranosus expansion) is the posterior medial knee landmark in PCL and posterolateral corner surgery. Semimembranosus bursitis (posterior medial) is distinguished from popliteal Baker's cyst by location.
Palpated at the posteromedial knee as the most medial and deep of the three hamstring tendons during resisted knee flexion.
Degeneration of the semimembranosus at its tibial insertion producing posteromedial knee pain on knee flexion resistance, managed by eccentric strengthening and targeted injection.
