The knee unlocker
Popliteus · musculus popliteus
A small muscle behind the knee that "unlocks" the straight knee so it can bend.
What it does
The popliteus runs from the outer side of the lower femur to the back of the upper tibia. When you stand with your knee fully straight, the joint locks; the popliteus rotates the bones slightly to unlock it so the knee can bend.
Surprising fact
Its job of unlocking the knee means it fires at the very start of every step from standing still.
Why it matters
It also helps keep the outer meniscus out of harm's way as the knee bends, and it can be strained by downhill running.
Nearby
Read more
Sources
Drafted with AI help; awaiting a human fact-check against these sources.
Open in the 3D atlas · Suggest a correction · Not medical advice.
3D models: Z-Anatomy & BodyParts3D (CC BY-SA 4.0 / 2.1 JP). Card text CC BY 4.0.