Abstract
OBJECTIVE: The objective of this study is to delineate disparities between patients with knee osteoarthritis (KOA) based on obesity status, investigate the interplay among body composition, physical activity and knee pain/function in patients with KOA and conduct subgroup analyses focusing on those with KOA and obesity. DESIGN: Cross-sectional study. SETTING: Residents of eight communities in Shijiazhuang, Hebei Province, China, were surveyed from March 2021 to November 2021. PARTICIPANTS: 178 patients with symptomatic KOA aged 40 years or older were included. MAIN OUTCOMES AND MEASURES: The primary outcome measure was knee pain, assessed using the Western Ontario and McMaster Universities Osteoarthritis Index-pain (WOMAC-P) scale. Secondary outcome measures included function, evaluated through the WOMAC-function (WOMAC-F) scale and the Five-Time-Sit-to-Stand Test (FTSST). Data analysis involved t-tests, Wilcoxon rank-sum tests, χ(2) tests, linear and logistical regression analysis. RESULTS: Participants (n=178) were 41-80 years of age (median: 65, P25-P75: 58-70), and 82% were female. Obese patients (n=103) had worse knee pain and self-reported function (p<0.05). In general patients with KOA, body fat mass was positively associated with bilateral knee pain (β=1.21 (95% CI 0.03 to 0.15)), WOMAC-P scores (β=0.25 (95% CI 0.23 to 1.22)), WOMAC-F scores (β=0.28 (95% CI 0.35 to 1.29)) and FTSST (β=0.19 (95% CI 0.03 to 0.42)), moderate-intensity to low-intensity physical activity was negatively associated with bilateral knee pain (β=-0.80 (95% CI -0.10 to -0.01)) and Skeletal Muscle Index (SMI) was negatively associated with WOMAC-F scores (β=-0.16 (95% CI -0.66 to -0.03)). In patients with KOA and obesity, SMI was negatively associated with FTSST (β=-0.30 (95% CI -3.94 to -0.00)). CONCLUSION: Patients with KOA and obesity had worse knee pain and self-reported function compared with non-obese patients. Greater fat mass, lower muscle mass and lower moderate-intensity to low-intensity physical activity were associated with increased knee pain and poor self-reported function. More skeletal muscle mass was associated with the improvement of objective function.