Pain Behind the Knee - Popliteus

There are many reasons for pain behind the knee. Your hamstring and gastroc both cross over the knee, so one of these muscles could be irritated. You could have a Baker’s cyst (benign), or have a lymphatic backup. One other possibility is an irritation of the popliteus. 

The popliteus is a small muscle with a big role. It’s a knee stabilizer, but it also can create rotation in both directions depending on the position of the leg. When the leg is planted on the ground (closed chain), it externally rotates the femur. When the leg is off the ground (open chain), it rotates the tibia internally. If you’ve heard of the screw home mechanism of the knee, it’s basically the opposite. The screw home mechanism is like a lock when the knee moves into extension (straightening). The popliteus basically unlocks it from this position and allows flexion (bending).

It has a few other functions. It is intracapsular and attaches to the lateral meniscus. It posteriorly retracts the meniscus so it doesn’t get pinched in the joint. It also prevents knee hyperextension. Because of this role, it can be provoked with excessive sprinting or downhill running. 

Here is a test for the popliteus:

Here is an exercise that may help the popliteus: