Semimembranosus tendon !

The semimembranosus tendon is the hamstring tendon that wraps the back inner corner of the tibia and tightens the back of the knee capsule.

Official name: Tendon of semimembranosus

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What it is

The broad hamstring tendon wrapping the back inner corner of the tibia.

What it does

Helps bend the knee and turn the shin inward; supports the knee from the inner side.

Key facts

Attaches: Main insertion in the posterior groove of the medial tibial condyle; expansions to the oblique popliteal ligament, posterior capsule, medial meniscus and popliteus fascia
Function: Knee flexion and medial rotation; hip extension; stabilizes the posteromedial corner; the semimembranosus–gastrocnemius bursa between it and the medial gastrocnemius is where a Baker cyst forms
Tight in: Hip flexion with the knee extended

Relations

Superficial: Semitendinosus tendon, which lies on it
Lateral: Medial head of gastrocnemius, with the semimembranosus–gastrocnemius bursa between them; further out, the popliteal artery, popliteal vein and tibial nerve
Deep: Posterior knee joint capsule and the oblique popliteal ligament
Medial: Superficial MCL, under which its anterior (tibial) arm passes

How to find it

Prone with the knee bent against resistance, it is felt as the broad tendon on either side of and deep to the semitendinosus cord; its insertion is felt just below the joint line on the back of the medial tibial condyle.

On imaging

MRI shows its arms around the posteromedial corner, and insertional tendinopathy as thickening, high signal or bone oedema; axial images show a Baker's cyst between it and the medial gastrocnemius tendon.

Common problems

Strains or tendinitis, mostly in sports with sprinting or kicking.

How it is diagnosed

Physical exam; ultrasound or MRI if needed.

Treatment

Rest, ice and progressive physical therapy.

Clinical notes

Posteromedial corner injuries often accompany ACL tears; ramp lesions of the medial meniscus lie close to where its capsular arm attaches
A separate semimembranosus bursa, between the tendon and the tibia, can also swell and mimic a Baker's cyst

Test yourself

Think of the answer, then tap the question to see it.

Where is the main insertion of the semimembranosus tendon?

In the posterior groove of the medial tibial condyle, with expansions to the oblique popliteal ligament, posterior capsule and medial meniscus.

Through which gap does a Baker's cyst communicate with the knee joint?

Between the semimembranosus tendon and the tendon of the medial head of gastrocnemius.

What does the semimembranosus do to the medial meniscus as the knee bends?

Its arms tension the posteromedial capsule and pull the medial meniscus backward.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): musculus semimembranosus TA2 2642
Official Spanish (DeCS): Tendón del semimembranoso DeCS D013710
English (TA2): Tendon of semimembranosus
Also called: musculus semimembranaceus

Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Bony Pelvis and Lower Limb, Hamstring Muscle; Anatomy, Bony Pelvis and Lower Limb: Posterior Thigh Muscles.

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Representative model, for educational purposes only.

Semimembranosus tendon highlighted on the Durgical 3D model