UCSF

OBJECTIVE: Hip abductors, important for controlling pelvic and femoral orientation during gait, may affect knee pain. Our objective was to evaluate the relation of hip abductor strength to worsened or new-onset frequent knee pain. Given previously noted associations of knee extensor strength with osteoarthritis in women, we performed sex-specific analyses. METHODS: We used data from the Multicenter Osteoarthritis study. Hip abductor and knee extensor strength was measured. Knee pain was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire and a question about frequent knee pain at baseline (144-month visit), and 8, 16, and 24 months thereafter. Knee pain outcomes were worsened knee pain (2-point increase in WOMAC pain) and incident frequent knee pain (answering yes to the frequent knee pain question among those without frequent knee pain at baseline). Leg-specific analyses tested hip abductor strength as a risk factor for worsened and new frequent knee pain, adjusting for potential covariates. Additionally, we stratified by knee extensor strength (high versus low). RESULTS: Among women, compared to the highest quartile of hip abductor strength, the lowest quartile had 1.7 (95% confidence interval [95% CI] 1.1-2.6) times the odds of worsened knee pain; significant associations were limited to women with high knee extensor strength (odds ratio 2.0 [95% CI 1.1-3.5]). We found no relation of abductor strength to worsening knee pain in men or with incident frequent knee pain in men or women. CONCLUSION: Hip abductor weakness was associated with worsening knee pain in women with strong knee extensors, but not with incident frequent knee pain in men or women. Knee extensor strength may be necessary, but not sufficient, to prevent pain worsening.