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The semispinalis muscle
Medical expert of the article
Last reviewed: 04.07.2025
The semimembranosus muscle (m.semimembranosus) begins on the ischial tuberosity with a flat, long tendon. The tendon plate continues downwards and, tapering distally, passes at the level of the mid-thigh into the muscle belly. This belly is located in front of the semitendinosus muscle and the long head of the biceps femoris. At the level of the knee joint, the muscle belly again continues into a flat tendon, which is attached by 3 bundles to the posterolateral surface of the medial condyle of the tibia. These tendon bundles of the semimembranosus muscle form the so-called deep pes anserinus. One bundle of the tendon continues downwards and joins the tibial collateral ligament. The second bundle, following downwards and laterally, is woven into the fascia of the popliteal muscle and is also attached to the line of the soleus muscle of the tibia. The third, largest bundle, is directed upward and laterally to the posterior surface of the lateral femoral condyle, forming the oblique popliteal ligament. Where the tendon of the semimembranosus muscle crosses the medial femoral condyle and comes into contact with the medial head of the gastrocnemius muscle, there is a synovial bursa of this muscle (bursa musculi semimembranosi).
The function of the semimembranosus muscle: extends the thigh and flexes the leg; when the leg is bent at the knee joint, it rotates it inward: pulls the capsule of the knee joint, protecting the synovial membrane from pinching.
Innervation of the semimembranosus muscle: tibial nerve (LIV-SI).
Blood supply of the semimembranosus muscle: circumflex femoral artery, perforating and popliteal arteries.
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