The Iliotibial band (ITB) is something of a mystery: what’s its function, why does it get irritated and how can we avoid injury?

your expert

Sarah Milner is a specialist musculoskeletal physiotherapist at Pure Sports Medicine (puresportsmed.com). Sarah particularly enjoys working with runners, focusing on rehabilitation, injury prevention and performance enhancement.

The ITB is a long, thin tendon-like structure, a thickening of fascia, which is an elastic layer of connective tissue that encloses muscles, connects muscles to bone and compartmentalises muscles that serve a similar function. The ITB is the largest piece of fascia in the human body, and runs down the outside of your thigh from the tensor fascia latae (the TFL, the muscle in front of the hip joint) and gluteus maximus down to the side of the knee, attaching to your tibia (shin bone) and the femoral condyle on the lower outside portion of the thigh bone.

It slides forwards and backwards across this bony point at the knee with movement. The repetitive sliding can create excess friction, especially when the knee is bent at 30 degrees, which commonly happens just as your foot strikes the ground when running. This region of 30 degrees knee flexion is called an ‘impingement zone’. Iliotibial band friction syndrome is common in runners presenting with knee pain and for many it’s the source of a nagging and painful injury.