The effect of weak hip abductors or external rotators on knee valgus kinematics in healthy subjects: a systematic review.

CONTEXT: It has been postulated that subjects with weak hip abductors and external rotators may demonstrate increased knee valgus, which may in turn raise risk of injury to the lower extremity. Recent studies have explored the potential link between hip strength and knee kinematics, but there has not yet been a review of this literature.
OBJECTIVE: To conduct a systematic review assessing the potential link between hip-abductor or external-rotator strength and knee-valgus kinematics during dynamic activities in asymptomatic subjects. EVIDENCE ACQUISITION: An online computer search was conducted in early February 2011. Databases included Medline, EMBASE, CINAHL, SPORTDiscus, and Google Scholar. Inclusion criteria were English language, asymptomatic subjects, dynamometric hip-strength assessment, single or multicamera kinematic analysis, and statistical analysis of the link between hip strength and knee valgus via correlations or tests of differences. Data were extracted concerning subject characteristics, study design, strength measures, kinematic measures, subject tasks, and findings with regard to correlations or group differences. EVIDENCE SYNTHESIS: Eleven studies were selected for review, 4 of which found evidence that subjects with weak hip abductors or external rotators demonstrated increased knee valgus, and 1 study found a correlation to the contrary.
CONCLUSIONS: There is a small amount of evidence that healthy subjects with weak hip abductors and perhaps weak external rotators demonstrate increased knee valgus. However, due to the variation in methodology and lack of agreement between studies, it is not possible to make any definitive conclusions or clinical recommendations based on the results of this review. Further research is needed.