People who participate in intense physical training, such as runners, cyclists, and military recruits, are most susceptible to IT band syndrome. They may notice a sharp pain that comes and goes at the outside of the knee. Over time, the pain may become more pronounced.

See Common Running Injuries


What Is the Iliotibial Band?

The iliotibial band is a wide strip of fibrous tissue that extends down the outside of the upper leg. It begins at the top of the pelvis, at a boney prominence called the iliac crest, and travels down the outside of the thigh, continuing over the outside of the knee joint. The bottom of the IT band attaches to the top of the tibia (shinbone). One of its functions is to help stabilize the knee joint.

See Knee Injuries

Depending on where you look, sources define the iliotibial band as a large tendon, a ligament, or an area of thickened fascia. (Fascia is a normally thin membrane that envelops muscles and organs.)

Interestingly, each definition is valid. The IT band connects muscle to bone (like tendons), connects bone to bone (like ligaments), and integrates with the thigh’s fascia. Moreover, tendons, ligaments and fascia are made of the same type of fibrous tissue. To avoid confusion, this article will only use the terms iliotibial band or IT band.

What Causes Iliotibial Band Syndrome?

Where it passes over the outside, top of the knee joint, the iliotibial band is often just a millimeter or two thick. 1 Goh LA, Chhem RK, Wang SC, Chee T. Iliotibial band thickness: sonographic measurements in asymptomatic volunteers. J Clin Ultrasound. 2003 Jun;31(5):239-44. PubMed PMID: 12767018. , 2 Gyaran IA, Spiezia F, Hudson Z, Maffulli N. Sonographic measurement of iliotibial band thickness: an observational study in healthy adult volunteers. Knee Surg Sports Traumatol Arthrosc. 2011 Mar;19(3):458-61. doi: 10.1007/s00167-010-1269-z. Epub 2010 Oct 2. PubMed PMID: 20890700. Though thin, the IT band is a common source of pain.

Exactly how it causes pain is debated among experts. Theories of how the IT band causes pain include:

  • The IT band rubs uncomfortably against the rounded bump at the bottom of the thighbone, called the lateral femoral epicondyle. This theory is the most common.
  • The IT band rubs against and/or compresses other soft tissue near the knee joint, such as a bursa or fat deposits near the knee, causing painful irritation.
  • IT band itself becomes inflamed or otherwise injured.

It may be that one or all of these theories are correct, or that some other forces are at play. No matter what the cause, doctors generally agree on the condition’s symptoms and how to diagnosis it. Patients usually recover with non-surgical treatments.

Dr. Christian Foglar is an orthopedic surgeon specializing in sports medicine and trauma and reconstructive surgery. He practices at Advanced Orthopaedics in San Jose, CA, and is a lieutenant colonel in the U.S. Army Reserves.