The purpose of this study was to investigate the causal relationship between quadriceps muscle strength and radiographic knee osteoarthritis (OA) in a longitudinal study.
The present study included 976 knees from 488 subjects who participated in both the 5th (2007) and 7th (2013) surveys of the Matsudai Knee Osteoarthritis Survey. Bilateral quadriceps strengths of each subject were measured using the quadriceps training machine (QTM-05F, Alcare Co., Ltd., Tokyo, Japan). Additionally, weight-bearing standing knee radiographs were obtained, and knee OA was graded according to the Kellgren-Lawrence classification system. The relationships between quadriceps strength and the incidence and progression of radiographic knee OA were assessed using multiple logistic regression analysis.
After adjusting for age and body mass index (BMI), both female and male knees in the lowest quantile of quadriceps strength had higher risk of the incidence of radiographic knee OA compared with the highest quantile of quadriceps strength (women: OR 2.414, 95% CI 1.098-5.311; men: OR 2.774, 95% CI 1.053-7.309). In contrast, after adjusting for age, BMI and femorotibial angle, both female and male knees in the lowest quantile compared with the highest quantile of quadriceps strength did not differ in risk of the progression of radiographic knee OA (women: OR 1.040, 95% CI 0.386-2.802; men: OR 2.814, 95% CI 0.532-14.898).
II.
Quadriceps muscle weakness was related to increased risk of the incidence of radiographic knee OA, but not its progression, in both women and men. Therefore, the clinically important finding of this study is that, in both women and men, maintaining higher quadriceps muscle strength may be one of the most effective prevention methods for incident radiographic knee OA.