Iliotibial band syndrome is due to inflammation of the iliotibial band, a thick band of fibrous tissue that runs down the outside of the leg. The iliotibial band begins at the hip and extends to the outer side of the shin bone (tibia) just below the knee joint. The band functions in coordination with several of the thigh muscles to provide stability to the outside of the knee joint.
Iliotibial band syndrome (ITBS) occurs when there is irritation to this band of fibrous tissue. The irritation usually occurs over the outside of the knee joint, at the lateral epicondyle–the end of the femur (thigh) bone. The iliotibial band crosses bone and muscle at this point; between these structures is a bursa which should facilitate a smooth gliding motion. However, when inflamed, the iliotibial band does not glide easily, and pain associated with movement is the result.
As stated previously, the function of the iliotibial band is both to provide stability to the knee and to assist in flexion of the knee joint. When irritated, movement of the knee joint becomes painful. Usually the pain worsens with continued movement, and resolves with rest.