Definition [edit]. Iliotibial band syndrome is one of the leading causes of lateral knee pain in runners. The iliotibial band is a thick band of fascia on the lateral aspect of the knee, extending from the outside of the pelvis, over the hip and knee, and inserting just below the knee.The band is crucial to stabilizing the knee during running, as it moves from behind the femur to the front of the femur during activity.he iliotibial band is a thick band of fascia on the lateral aspect of the knee, extending from the outside of the pelvis, over the hip and knee, and inserting just below the knee.