Anatomically, the iliotibial band (ITB) is a continuation of the tendinous portion of the tensor fascia lata (TFL) muscle with significant contributions from the gluteus maximus.  View image Distally, the ITB spans out and has attachments to the lateral border of the patella and lateral patellar retinaculum before its insertion on Gerdy's tubercle of the tibia. Anatomical dissections indicate a strong tendinous insertion at the lateral epicondyle of the femur with adipose tissue underneath (fat pad-like structure), and a ligamentous portion distally to Gerdy's tubercle.  During running, the posterior edge of the ITB impinges against the lateral femoral epicondyle of the femur just after foot strike. This impingement zone occurs at, or at slightly less than, 30° of knee flexion. View image Repetitive irritation can lead to chronic inflammation, especially beneath the posterior fibres of the ITB, which are thought to be tighter against the lateral femoral epicondyle than the anterior fibres.
Studies of female runners have demonstrated external rotation of the femur in stance phase running, resulting in an internally rotated knee.   Knee internal rotation may be a factor in tightening the Gerdy's tubercle portion of the ITB, adding to the tightening at the femoral epicondyle. Fatigue and segmental muscle coordination may be contributing factors to the excessive internal rotation at the knee and related issues at the hip.