Background Effect of quadriceps muscle strength on knee pain remains unclear.
Objectives To compare the effect of quadriceps muscle strength in knee pain with that of grip strength and muscle mass by using data from the large-scale population-based cohort Research on Osteoarthritis/osteoporosis Against Disability (ROAD) study.
Methods Among the 2,566 subjects who participated in the third visit of the ROAD study, 2,152 subjects who underwent X-ray examination of the knee and measurement of muscle strength and mass were enrolled in the present study. Knee osteoarthritis (OA) was graded according to the Kellgren-Lawrence (KL) grade. Knee pain was assessed by well experienced orthopedists. Grip strength was measured on the right and left sides using a TOEI LIGHT handgrip dynamometer (TOEI LIGHT CO. LTD., Saitama, Japan). Isometric knee extension muscle was estimated by using a quadriceps training machine (QTM) (QTM-05F; Alcare Co., Ltd., Tokyo, Japan). Skeletal muscle mass was measured via bioimpedance analysis by using a body composition analyzer (MC-190; Tanita Corp., Tokyo, Japan). The QTM and MC-190 have been validated.
Results Grip strength and quadriceps muscle strength were significantly different between subjects with and without pain in men (grip strength, 37.5±9.5 kgf and 35.1±9.0 kgf, respectively, p<0.05; quadriceps muscle strength, 32.9±12.5 kgf and 26.4±12.0 kgf, respectively, p<0.05) and women (grip strength, 24.1±5.8 kgf and 22.5±5.8 kgf, respectively, p<0.05; quadriceps muscle strength, 27.2±9.9 kgf and 23.2±9.5 kgf, respectively, p<0.05). After adjustment for age, sex, and BMI, the significant association with quadriceps muscle strength remained (p<0.05), while that of grip strength disappeared (p=0.31 and 0.10 in men and women, respectively). Muscle mass (kg)/height (m2) at the lower limbs was not significantly associated with knee pain (men: 2.95±0.44 kg/m2 and 3.03±0.47 kg/m2, respectively, p=0.89; women: 2.41±0.27 kg/m2 and 2.45±0.32 kg/m2, respectively, p=0.14). After adjustment for age, BMI, sex and KL grade, quadriceps muscle strength were significantly associated with knee pain (5 kgf increase; OR, 0.87; 95% CI, 0.82–0.92), indicating that the significant association of quadriceps muscle strength with knee pain is independent of obesity and knee OA. Next, to determine the prevalence of knee pain according to muscle strength, subjects were classified by quadriceps muscle strength (<10 kgf, ≥10 to <20 kgf, ≥20 to <30 kgf, ≥30 to <40 kgf, and ≥40 kgf). The prevalence of knee pain was 53.9%, 27.0%, 14.4%, 11.6%, and 9.8% in men and 41.0%, 31.0%, 23.7%, 16.3%, and 12.5% in women with muscle strength <10 kgf, ≥10 to <20 kgf, ≥20 to <30 kgf, ≥30 to <40 kgf, and ≥40 kgf, respectively. After the adjustment for age, BMI, and KL grade, the prevalence of knee pain was significantly higher in subjects with muscle strength <10 kgf and ≥10 to <20 kgf (p<0.05) compared to those with muscle strength ≥40 kgf.
Conclusions The present study revealed that muscle strength had a stronger association with knee pain than grip strength or muscle mass.
Disclosure of Interest None declared