Iliotibial band syndrome is a repetitive strain injury that occurs when the iliotibial band (ITB) becomes inflamed causing knee pain. The ITB is a thick band of fibrous tissue that runs down the outside of the leg. It attaches at the hip and to the tensor fascia latae muscle, and extends down the leg, inserting on the outer side of the tibia (shin bone), just below the knee joint.

The band functions in coordination with several of the thigh muscles to provide stability to the knee and to assist in flexion of the knee joint. The main problem occurs when the tensor fascia latae muscle and iliotibial band become tight. This causes the tendon to rub against the outside of the knee, at the lateral epicondyle, which results in inflammation and pain. ITB syndrome can be caused by overload, as is the case with endurance athletes or those who rapidly increase their activity levels, or by biomechanical inefficiencies, such as uneven leg length, tight or stiff muscles in the leg or hip, muscle imbalances, foot structure problems, or gait and running problems.