Glossary
Popliteus
Quick answer
The popliteus is a small, flat muscle at the back of the knee. It unlocks the fully straightened knee so it can start to bend, and its tendon, running to the outer femur, is a key part of the posterolateral corner, explains Dr. Pablo Gelber, knee surgeon at Aman Hospital in Doha.
What it is
The muscle lies deep behind the knee on the back of the upper tibia. Its tendon travels upwards and outwards inside the joint capsule, passing next to the lateral meniscus, to attach to the outer side of the femur. Fibres also connect it to the lateral meniscus and the fibula, the latter forming the popliteofibular ligament.
When you stand with the knee locked straight, the popliteus rotates the bones slightly to unlock it. It also resists the shin rotating outwards and helps guide the lateral meniscus.
Why it matters for patients
Overuse of the popliteus, popliteus tendinopathy, causes pain at the back or outer side of the knee, often in runners and hikers, especially going downhill or on slopes. It can be confused with IT band syndrome, a lateral meniscus tear or a Baker's cyst.
The tendon can also be torn in significant twisting or hyperextension injuries, usually as part of a posterolateral corner injury. In that setting it matters for knee stability, and surgeons check it carefully, sometimes reconstructing it alongside other ligaments.
Frequently asked questions
Why does the back of my knee hurt walking downhill?
Downhill walking loads the popliteus as it controls rotation. Popliteus tendinopathy is one possible cause; others include meniscus tears and a Baker's cyst.
Is a popliteus injury serious?
An overuse problem usually settles with load adjustment and physiotherapy. A tear from a significant injury may be part of a wider ligament injury and needs specialist assessment.
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