Causes / typical injury mechanism: The iliotibial band is a fibrous structure that runs down the lateral thigh from the iliac crest to the anterolateral tibia just below the knee (Gerdy's tubercle). Iliotibial band syndrome (ITBS), also called iliotibial band friction syndrome, is the second most common injury in runners and is the most common cause of lateral knee pain in runners. The cause of ITBS is thought to be multifactorial and variable, leading to friction between the distal iliotibial band and the lateral femoral epicondyle during repetitive flexion and extension of the knee (eg, from running, cycling). This causes irritation and pain at the distal iliotibial band region.

Classic history and presentation: This overuse injury is most commonly seen in individuals who have recently increased activities that require repetitive knee flexion and extension, most commonly running and cycling. Runners with ITBS may have begun running for the first time, more often, or for longer distances. Patients initially complain of vaguely localized aching over the lateral aspect of the knee without a specific point of tenderness. With continued activity, the pain may progress to become sharper and more localized to the lateral femoral condyle. Patients may initially report that the pain only occurs after or towards the end of a run. As the condition progresses, symptoms may occur soon after starting a run or even at rest.

Prevalence:

• Age – There is no definitive data published regarding prevalence of ITBS by age group.
• Sex / gender – Both sexes are affected, although it is thought to be more common in women.

Risk factors: There is limited evidence to support any major biomechanical or anatomic risk factors for ITBS. However, weak hip abductors lead to increased hip adduction and knee internal rotation ("knock knee"), increasing friction between the iliotibial band and the lateral femoral condyle. Additionally, genu varum ("bowleg") or increased hindfoot supination may stress the iliotibial band as it stretches over the lateral femoral condyle, predisposing it to friction and irritation.

Extrinsic risk factors include downhill running, a sudden increase in running or cycling mileage, and running with excessively long strides, all of which increase distal iliotibial band strain.

Pathophysiology: Although the exact pathophysiology of ITBS is unclear, it is considered a combination of repetitive strain at the distal iliotibial band and friction against the lateral femoral condyle, which causes local irritation, pain, and possibly inflammation.

Grade / classification system: A symptom-based grading system for ITBS in runners was proposed by Lindenberg et al (1984).

• Grade I: Pain occurs after running without limitation on running distance or speed
• Grade II: Pain occurs during running without limitation on running distance or speed
• Grade III: Pain occurs during running and distance or speed is limited
• Grade IV: Pain prohibits running