Excessive friction of the distal iliotibial band (ITB) sliding over the lateral femoral epicondyle when the knee is in flexion and extension causes the friction and irritation. This can be the result of training factors that cause this excessive friction or intrinsic risk factors, and patients typically will have a combination of each. Runners predisposed to this injury are typically in a phase of over-training and often have underlying weakness of the hip abductor muscle.     The runner may describe a rapid progression in weekly mileage. 
Intrinsic factors that contribute to ITB tightness and muscle weakness (quadriceps and gluteus medius) include: genu varum (bow leg); pes cavus (high arch); prominent lateral femoral epicondyle; tight iliotibial tract (ITT), lateral retinaculum, tensor fascia lata (TFL), rectus femoris, and hamstrings.