Longitudinal change in thigh muscle strength prior to and concurrent with symptomatic and radiographic knee osteoarthritis progression: data from the Osteoarthritis Initiative.

OBJECTIVE: To investigate whether symptomatic and/or radiographic knee osteoarthritis (KOA) progression is associated with prior and/or concurrent change in thigh muscle strength in men or women.
DESIGN: Osteoarthritis Initiative (OAI) participants with isometric muscle strength measurements at baseline, 2- and 4-year follow-up (n = 1785: 1016 women) were grouped into 1) those with vs without symptomatic progression (i.e., increase ≥9 in WOMAC-pain [scale: 0-100]); and 2) those with vs without radiographic progression (i.e., decrease in minimum joint space width (JSW) ≥0.7 mm) between year-two and year-four follow-up. Sex-specific changes in thigh muscle strength concurrent (between year-two and year-four follow-up) and prior to (between baseline and year-two follow-up) symptomatic and radiographic progression were compared between groups (progression vs no progression) using analysis of covariance, with adjustment for age and body mass index.
RESULTS: In women, but not in men, loss in knee extensor and flexor strength was greater concurrent with symptomatic progression (extensors: -3.7%, 95% confidence interval [CI] -6.4, -0.9; flexors: -7.2% 95% CI -10.7, -3.7) than in women without symptomatic progression (extensors: -0.3%, 95% CI -1.9, 1.3, P = 0.030; flexors: -2.6%, 95% CI -4.7, -0.6, P = 0.018). No association was found between extensor or flexor strength loss concurrent to radiographic progression, in either men or women, nor any statistically significant association between prior change in muscle strength with symptomatic or radiographic progression.
CONCLUSION: These findings suggest that there is concurrent but not prior longitudinal association between loss in muscle strength and symptomatic KOA progression that is specific to women.