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Portrait of Popliteus

Anatomy · Muscles

Popliteus

The muscle that 'unlocks' the knee

Lower limb · knee, floor of the popliteal fossa

Popliteus is a small triangular muscle at the back of the knee, forming part of the floor of the popliteal fossa. It arises from the lateral femoral condyle and inserts on the back of the upper tibia. Its action is to unlock the fully extended knee at the start of flexion by rotating the femur on the tibia. It is supplied by the tibial nerve.

How to spot them

  • ▸Small triangular muscle across the back of the knee, deep in the popliteal fossa
  • ▸Arises from the outer side of the femur and inserts on the back of the tibia above the soleal line
  • ▸Its tendon passes inside the knee joint capsule
  • ▸Sits beneath the popliteal vessels and tibial nerve

What to know

The muscle that 'unlocks' the fully extended knee, starting the movement of flexion

Popliteus — by rotating the femur laterally on the fixed tibia.

A small muscle forming part of the floor of the popliteal fossa behind the knee

Popliteus.

It arises from the lateral femoral condyle by a tendon that lies inside the knee joint capsule

Popliteus.

It inserts on the posterior surface of the tibia above the soleal line

Popliteus.

A muscle supplied by the tibial nerve (L4–S1) whose name comes from the Latin for the hollow of the knee

Popliteus — from poples, the back of the knee.

The muscle that also rotates the tibia medially when the leg is free and the knee bent

Popliteus.

Key ideas

  • In the locked, fully extended knee the femur is medially rotated on the tibia; popliteus laterally rotates it to release the lock.
  • Popliteus also helps to retract the lateral meniscus during flexion.

Quick-fire facts

  • •Origin: lateral surface of the lateral femoral condyle, and the lateral meniscus.
  • •Insertion: posterior surface of the tibia above the soleal line.
  • •Nerve supply: tibial nerve (L4–S1).
  • •Action: unlocks the knee by lateral rotation of the femur on the tibia, or medial rotation of the tibia when the foot is free.
  • •It forms part of the floor of the popliteal fossa.
  • •Its tendon lies inside the knee joint capsule, but outside the synovial cavity.
  • •Popliteus comes from the Latin poples, the ham or hollow of the knee.

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