The popliteus is a small flat triangular muscle that sits in the back of the knee joint. Its primary motor roles are knee internal rotation (twist inwards) and assists with knee flexion, and it can also externally rotate the femur and leg when the foot is fixed on the ground.
Causes of injury
It is usually injured due to a large force on a weight bearing knee that may also injure ligaments and capsule leading to a potentially unstable knee.
The popliteus may also be injured due to repetitive compression and tension due to particular types of knee joint motions such as when practicing Brazilian Jujitsu (BJJ).