Objective: To explore the relationship between lower extremity weakness and the progression of established radiographic changes of knee osteoarthritis (OA).
Methods: The study cohort of 342 elderly subjects was recruited from central Indiana by random digit dialing. We analyzed 79 subjects who had definite radiographic changes of unilateral or bilateral knee OA at baseline and for whom baseline data for lower extremity muscle strength and lean tissue mass and baseline and followup assessments of knee pain were available. Radiographs were graded for severity of OA at baseline and again about 2.5 years later (mean 31.5 months). Knee pain was evaluated at the same examination. Strength of the knee flexors and extensors was assessed bilaterally at baseline by isokinetic dynamometry and lower extremity muscle mass by dual energy x-ray absorptiometry.
Results: Mean peak knee extensor strength of women with progressive OA, before and after adjustment for lower extremity muscle mass, was about 9% lower than that in those with stable radiographic changes, but this difference was not statistically significant. No difference was apparent between the 2 groups with respect to knee flexor (hamstring) strength. The decrease in quadriceps strength among women with progressive OA, relative to those with stable OA, did not appear to be attributable to knee pain, and knee extensor strength at baseline bore no apparent relationship to the development or progression of knee pain among those with OA.
Conclusion: We have shown previously that quadriceps weakness may be of etiologic importance in development of knee OA. The absence of a significant difference in quadriceps strength between subjects with radiographically stable OA and those whose joint damage progressed suggests that factors other than quadriceps weakness are more important determinants of OA progression.