REDUCED QUADRICEPS STRENGTH RELATIVE TO BODY-WEIGHT - A RISK FACTOR FOR KNEE OSTEOARTHRITIS IN WOMEN

Objective. To determine whether baseline lower extremity muscle weakne ss is a risk factor for incident radiographic osteoarthritis (OA) of t he knee. Methods. This prospective study involved 342 elderly communit y-dwelling subjects (178 women, 164 men) from central Indiana, for who m baseline and followup (mean interval 31.3 months) knee radiographs w ere available. Lower extremity muscle strength was measured by isokine tic dynamometry and lean tissue (i.e., muscle) mass in the tower extre mities by dual x-ray absorptiometry. Results. Knee OA was associated w ith 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 wei ght, knee extensor strength was 18% lower at baseline among subjects w ho developed incident knee OA than among the controls (P = 0.053), whe reas after adjustment for lower extremity muscle mass, knee extensor s trength was 15% lo vver than in the controls (P not significant). In m en, in contrast, adjusted knee extensor strength at baseline was compa rable to that in the controls. Among the 13 women who developed incide nt OA, there was a strong, highly significant negative correlation bet ween body weight and extensor strength (r = -0.740, P = 0.003), that i s, 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 stre ngth (r = 0.455, P = 0.058). No correlation between knee flexor (hamst ring) 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.