Can a method to combine body mass index and handgrip strength improve body fat assessments compared to body mass index alone in individuals with symptomatic knee osteoarthritis?

Abstract Background: Knee osteoarthritis is a multifactorial joint disease characterized by cartilage degradation and joint space narrowing. Traditional anthropometric measures like body mass index and waist circumference are commonly used to estimate obesity-related risk in knee osteoarthritis. Still, they fail to capture muscle mass and fat distribution nuances. Emerging methods that combine anthropometric and functional methods may improve adiposity estimation in this population. Aim: This study aimed to determine whether a novel equation combining body mass index and handgrip strength (BMHG) enhances the estimation of body fat percentage and visceral fat area in individuals with symptomatic knee osteoarthritis compared to body mass index (BMI) or waist circumference (WC) alone.Methods: A cross-sectional analysis was conducted in 306 individuals (94 men, 212 women) with knee pain enrolled in the Halland osteoarthritis cohort. Body composition was assessed using bioelectrical impedance analysis (BIA). Field-based estimates were BMI, WC, and the BMHG equation, and these were compared against BIA-derived percent body fat and visceral fat area. Correlations were examined using Spearman's rank analysis, and results were reported separately by sex. Results: All three field-based estimates showed very strong and strong correlations with both percent body fat and visceral fat area. Among women, BMI had the highest correlation with visceral fat area (r = 0.92), while among men, WC correlated best (r = 0.92). The BMHG equation also showed comparably strong correlations for both sexes. No measure significantly outperformed the others, but each demonstrated strong agreement with bioelectrical impedance outcomes in percent body fat and visceral fat area. Conclusion: BMI, WC, and BMHG equation are equally valid for estimating adiposity in individuals with symptomatic knee osteoarthritis. While the BMI remains a practical and accessible tool, integrating handgrip strength could provide a low-cost enhancement that captures skeletal muscle mass, offering potential advantages in settings where advanced body composition tools are unavailable.