Objective: To determine whether baseline lower extremity muscle weakness is a risk factor for incident radiographic osteoarthritis (OA) of the knee.
Methods: This prospective study involved 342 elderly community-dwelling subjects (178 women, 164 men) from central Indiana, for whom baseline and followup (mean interval 31.3 months) knee radiographs were available. Lower extremity muscle strength was measured by isokinetic dynamometry and lean tissue (i.e., muscle) mass in the lower extremities by dual x-ray absorptiometry.
Results: Knee OA was associated with an increase in body weight in women (P = 0.0014), but not in men. In both sexes, lower extremity muscle mass exhibited a strong positive correlation with body weight. In women, after adjustment for body weight, knee extensor strength was 18% lower at baseline among subjects who developed incident knee OA than among the controls (P = 0.053), whereas after adjustment for lower extremity muscle mass, knee extensor strength was 15% lower than in the controls (P not significant). In men, in contrast, adjusted knee extensor strength at baseline was comparable to that in the controls. Among the 13 women who developed incident OA, there was a strong, highly significant negative correlation between body weight and extensor strength (r = -0.740, P = 0.003), that is, the more obese the subject, the greater the reduction of quadriceps strength. In contrast, among the 14 men who developed incident OA, a modest positive correlation existed between weight and quadriceps strength (r = 0.455, P = 0.058). No correlation between knee flexor (hamstring) strength and knee OA was seen in either sex.
Conclusion: Reduced quadriceps strength relative to body weight may be a risk factor for knee OA in women.