The popliteus is the 'key' that unlocks the knee from full extension. In terminal extension (the last 0-5 degrees), the tibia externally rotates under the femur (screw-home mechanism). To initiate flexion from full extension, the popliteus internally rotates the tibia, unlocking the screw-home mechanism. The popliteal hiatus in the lateral meniscus transmits the intra-articular popliteus tendon — this normal gap should not be mistaken for a lateral meniscal tear during arthroscopy.
| Origin | Popliteal groove of the lateral femoral condyle (intra-articular tendon passing through the popliteal hiatus in the lateral meniscus) |
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| Insertion | Posterior proximal tibial surface (triangular area above the soleal line) |
| Nerve Supply | Tibial nerve (L4, L5, S1) |
| Blood Supply | Inferior lateral geniculate artery |
| Actions | Unlocks the knee from full extension (internal tibial rotation — the reverse of the screw-home mechanism); Knee flexion initiation; Dynamic lateral meniscus protection (the popliteomeniscal fasciculi allow the lateral meniscus to retract during knee flexion) |
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Popliteus tendinopathy produces lateral knee pain during downhill running specifically — the popliteus decelerates the externally rotating tibia on the fixed foot during downhill loading. The popliteus is a key component of the posterolateral corner — its reconstruction is a critical step in anatomical PLC repair. Popliteomeniscal fasciculi tears allow lateral meniscal hypermobility.
The popliteus muscle is palpable posterior to the tibia in the popliteal fossa deep to the gastrocnemius medial head, becoming firm during resisted internal tibial rotation with the knee at 90 degrees of flexion.
Posterolateral knee pain during downhill running from popliteus tendon overload managed with eccentric loading and running technique modification.
