Popliteus muscle

At a glance

English

Popliteus muscle

Latin (TA2)

Musculus popliteus

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the popliteus muscle

Popliteus is a flat, triangular muscle lying deep at the back of the knee, forming the lower part of the floor of the popliteal fossa. It belongs to the deep group of the posterior leg, yet of all the muscles at the back of the leg it alone works on the knee while leaving the ankle untouched. Its job is small but specific: it starts knee bending from the fully straightened, locked position.

It begins inside the knee joint capsule as a cord-like tendon from a pit on the outer surface of the lateral femoral condyle. The tendon runs back and down between the lateral meniscus and the fibular collateral ligament, with some fibres attaching to the meniscus and to the arcuate popliteal ligament. Emerging below the capsule, the fibres spread out downwards and medially into a fleshy triangle that attaches to the back of the tibia above the soleal line.

When the knee straightens fully with the foot on the ground, the femur turns slightly inwards on the tibia, tightening the ligaments and locking the joint so that standing needs little muscle effort. To bend the knee from here, popliteus turns the femur outwards on the fixed tibia, unlocking the joint; with the foot free it instead turns the tibia inwards. It also helps flex the knee and draws the lateral meniscus back during flexion so that it is not caught between the bones. It is active in squatting and in rising from a chair.

The nerve to popliteus is a branch of the tibial nerve, which winds round its lower border to enter the deep surface. Its blood comes mainly from the inferior medial genicular branch of the popliteal artery and from the posterior tibial artery. The popliteal vessels lie directly on the muscle. Injury to its tendon can occur with other damage at the posterolateral corner of the knee, giving instability with rotation. A small sesamoid may rarely be found in the tendon.

Attachments, action and supply

Origin

Lateral surface of the lateral femoral condyle, inside the knee joint capsule, with fibres from the lateral meniscus and arcuate popliteal ligament.

Insertion

Posterior surface of the tibia above the soleal line.

Action

Unlocks the extended knee by turning the femur laterally on the fixed tibia, or medially rotating the free tibia; assists knee flexion and pulls the lateral meniscus back.

Nerve supply

Tibial nerve (L4, L5, S1).

Blood supply

Inferior medial genicular artery from the popliteal artery, and the posterior tibial artery.