[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Lower limb](https://durgical.com/en/anatomy/region/lower-limb/) › Semimembranosus [Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Lower limb](https://durgical.com/en/anatomy/region/lower-limb/) # Semimembranosus The semimembranosus is the deepest and broadest inner hamstring muscle at the back of the thigh; it bends the knee and extends the hip. Official name: Semimembranosus muscle [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=lower_limb&select=semimembranosus&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The deepest inner hamstring muscle, at the back of the thigh. ## What it does Bends the knee and extends the hip; helps control rotation of the knee. ## Key points - The deepest and broadest medial hamstring; it starts as a flat, membrane-like tendon lying deep to the conjoint tendon of the other hamstrings - Its distal tendon divides into several arms around the posteromedial knee, a key active stabilizer of the posteromedial corner - The bursa between it and the medial head of the gastrocnemius is where a popliteal (Baker) cyst arises - With the semitendinosus it forms the upper medial border of the popliteal fossa ## Key facts **Origin** Ischial tuberosity (superolateral impression) **Insertion** Posterior medial tibial condyle (direct arm); medial tibial condyle under the MCL (reflected arm); recurrent expansion forms the [oblique popliteal ligament](https://durgical.com/en/anatomy/oblique-popliteal-ligament/) **Action** Extends hip; flexes knee; medially rotates flexed knee **Nerve** Sciatic nerve, tibial division (L5–S2) **Blood supply** [Perforating arteries](https://durgical.com/en/anatomy/perforating-femoral-arteries/); [medial circumflex femoral artery](https://durgical.com/en/anatomy/medial-circumflex-femoral-artery/); popliteal artery branches ## Relations **Superficial** [Semitendinosus](https://durgical.com/en/anatomy/semitendinosus-muscle/), lying in a groove on its back surface **Deep** [Adductor magnus](https://durgical.com/en/anatomy/adductor-magnus/) above; at the knee, the medial head of the gastrocnemius and the posteromedial [joint capsule](https://durgical.com/en/anatomy/articular-capsule-of-knee-joint/), with the semimembranosus–gastrocnemius bursa between them **Lateral** [Sciatic nerve](https://durgical.com/en/anatomy/sciatic-nerve/) in the thigh; lower down, the [tibial nerve](https://durgical.com/en/anatomy/tibial-nerve/) and the [popliteal artery](https://durgical.com/en/anatomy/popliteal-artery/) and vein in the popliteal fossa **Medial** [Gracilis](https://durgical.com/en/anatomy/gracilis-muscle/), and the [sartorius](https://durgical.com/en/anatomy/sartorius-muscle/) near the knee **Below** Arms to the posteromedial capsule, the [popliteus](https://durgical.com/en/anatomy/popliteus-muscle/) fascia and, in many descriptions, the posterior horn of the [medial meniscus](https://durgical.com/en/anatomy/medial-meniscus/), which it draws back as the knee bends ## How to find it Prone with the knee bent against resistance, it is felt as a soft, fleshy mass on both sides of and deep to the [semitendinosus tendon](https://durgical.com/en/anatomy/tendon-of-semitendinosus/), best just above the inner back of the knee. ## Examination - Resisted knee flexion with the leg turned inward: pain at the posteromedial knee or in the medial hamstring belly suggests a semimembranosus strain or insertional tendinopathy ## On imaging On axial MRI or ultrasound of the knee, a popliteal (Baker) cyst is a fluid collection whose neck passes between the [semimembranosus tendon](https://durgical.com/en/anatomy/tendon-of-semimembranosus/) and the medial head of the gastrocnemius; this neck tells it apart from other masses of the popliteal fossa. ## Common problems - Hamstring strain, common in sprinting sports. - Rarely, the tendon pulls off the bone at the hip. ## How it is diagnosed Physical exam; MRI for severe strains. ## Treatment - Rest, then progressive stretching and strengthening; surgery only for complete tendon pull-offs. ## Clinical notes - Insertional tendinopathy causes posteromedial knee pain that can mimic a tear of the medial meniscus - Injuries of the posteromedial corner that come with anterior cruciate or medial collateral ligament tears often involve its capsular arms and add rotational instability ## Development From the ventral (flexor) muscle mass, and therefore supplied by the tibial division of the sciatic nerve. ## Related conditions - [Hamstring Strain](https://durgical.com/en/conditions/hamstring-strain/) - [Baker's (Popliteal) Cyst](https://durgical.com/en/conditions/baker-s-cyst/) ## Test yourself Think of the answer, then tap the question to see it. ## Between which two structures does a popliteal (Baker) cyst arise? In the bursa between the semimembranosus tendon and the medial head of the gastrocnemius; the cyst's neck passes between them on MRI or ultrasound. ## Which knee ligament is formed by an expansion of the semimembranosus tendon? The oblique popliteal ligament, which strengthens the back of the knee capsule. ## What role does the distal semimembranosus tendon play at the knee? It splits into several arms around the posteromedial knee and is a key active stabilizer of the posteromedial corner. ## Which knee problem can semimembranosus insertional tendinopathy mimic? A tear of the medial meniscus, because both cause posteromedial knee pain. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/semimembranosus-muscle/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** musculus semimembranosus TA2 2642 **Official Spanish (DeCS)** Músculo semimembranoso DeCS D000070633 **English (TA2)** Semimembranosus muscle **Also called** musculus semimembranaceus ## Related - [Semitendinosus](https://durgical.com/en/anatomy/semitendinosus-muscle/) - [Sciatic nerve](https://durgical.com/en/anatomy/sciatic-nerve/) - [Perforating arteries](https://durgical.com/en/anatomy/perforating-femoral-arteries/) - [Semimembranosus tendon](https://durgical.com/en/anatomy/tendon-of-semimembranosus/) - [Femur](https://durgical.com/en/anatomy/femur/) - [Tibia](https://durgical.com/en/anatomy/tibia/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=56253&filter=ths_termall&q=M%C3%BAsculos%20Isquiosurales); [Anatomy, Bony Pelvis and Lower Limb, Hamstring Muscle](https://www.ncbi.nlm.nih.gov/books/NBK546688/); [Anatomy, Bony Pelvis and Lower Limb: Posterior Thigh Muscles](https://www.ncbi.nlm.nih.gov/books/NBK542215/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/semimembranosus-muscle/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/semimembranosus-muscle/