Background:​ Identification of mechanical factors associated with patellofemoral pain, the most prevalent running injury, is necessary to help in injury prevention, but unfortunately they remain elusive.

Hypothesis:​ Runners who develop patellofemoral pain have increased knee joint angular impulse in the frontal plane.

Study Design:​ Case control study;​ Level of evidence, 3.

Methods:​ A retrospective study compared knee abduction impulses of 20 patellofemoral pain patients with those of 20 asymptomatic patients. A second prospective study quantified knee angular impulses during the stance phase of running of 80 runners at the beginning of the summer running season. Epidemiologic data were then collected, recording the type and severity of injury of these runners during a 6-month running period.

Results:​ The patellofemoral pain patients in the retrospective study had significantly higher (P =. 026) knee abduction impulses (17.0 ± 8.5 Nms) than did the asymptomatic patients (12.5 ± 5.5 Nms). Six patients developed patellofemoral pain during the prospective study. The prospective data showed that patients who developed patellofemoral pain had significantly higher (P =. 042) knee abduction impulses (9.2 ± 3.7 Nms) than did matched patients who remained uninjured (4.7 ± 3.5 Nms).

Conclusion:​ The data indicate that increased knee abduction impulses should be deemed risk factors that play a role in the development of patellofemoral pain in runners.

Clinical Relevance:​ Footwear and running style can influence knee angular impulse, and the appropriate manipulation of these variables may play a preventive role for patients who are predisposed to patellofemoral pain.