Obesity Subtypes and Longitudinal Trajectories of Function Over Seven Years of Follow-Up: Data From the Multicenter Osteoarthritis Study

Abstract

Objective: Obesity, defined by body mass index (BMI) ≥30 kg/m2, is a risk factor for functional limitations in people with knee osteoarthritis (OA). However, function varies among such individuals. Our objective was to evaluate the implications of obesity subtypes on longitudinal patterns of physical functioning in people with or at risk for knee OA. Methods: We included participants from the Multicenter Osteoarthritis Study (MOST) with a BMI ≥30 kg/m2 and dual-energy x-ray absorptiometry–measured body composition. Three obesity subtypes were defined: (1) obesity with low muscle mass (OLM) and high fat mass; (2) obesity with cardiometabolic comorbidities (OCC) but without low muscle mass; and (3) uncomplicated obesity (UO), that is, neither OLM nor OCC. We examined the relation of these three obesity subtypes to self-reported Western Ontario and McMaster Osteoarthritis Index physical function at baseline and seven years using linear regression at both time points and to their longitudinal functional trajectory patterns using multinomial logistic regression. Results: Of the baseline sample (N = 1,211 individuals, 63% female, mean age 61.2 ± SD 7.6 years, mean BMI 35.0 ± SD 4.5 kg/m2), 49.1% were UO, 34.4% OLM, and 16.5% OCC. Compared to UO, the OLM and OCC groups had worse physical function at baseline. Five distinct trajectories of functioning were identified over seven years, with 23%, 38.5%, 26%, 4.5%, and 8% of the sample in groups 1 to 5, respectively. Compared to UO, OLM and OCC groups had higher odds of being in the persistent poorest functioning trajectory (odds ratio 1.9, 2.6, respectively). Conclusion: Individuals with obesity and concurrent low muscle or cardiometabolic comorbidities have persistent worse functioning over a seven-year period compared to those with obesity alone. Distinguishing obesity subtypes may enable personalized interventions to delay or avoid extended mobility disability.