What is one of the actions of the piriformis?

The piriformis muscle is primarily known for its significant role in hip movement. One of its primary actions is hip abduction, especially when the hip is flexed. This muscle originates from the sacrum and inserts into the greater trochanter of the femur, allowing it to exert a force that causes the hip to move away from the body's midline when the hip is in a flexed position.

When the hip is flexed, the orientation of the piriformis changes in such a way that it is well-positioned to facilitate abduction. This action contributes to stability during various movements and activities, particularly those requiring changes in direction or lateral movements.

The other choices relate to different movements involving the hip or knee but do not align with the primary function of the piriformis. For example, hip adduction and internal rotation do not accurately describe the primary actions of this muscle, especially since the piriformis primarily functions in abduction during flexion. Knee extension is not a movement associated with the piriformis at all, as it acts solely on the hip joint.