Association of Body Mass Index With Incidence and Progression of Knee Effusion on Magnetic Resonance Imaging and on Knee Examination

Objective. To determine the association of body mass index (BMI) with incidence and progression of knee effusion on magnetic resonance imaging (MRI) and physical examination (PE) in a longitudinal cohort with knee pain. Methods. A population-based cohort was assessed at baseline and 3 years (n = 163). BMI was categorized as normal (<25), overweight (25-29.9), and obese (>= 30). Knee effusion was graded as 0-3 (absent/mild/moderate/severe) on MRI and 0-1 (absent/present) on PE. Progression of MRI effusion (MRIeff) was an increase of >= 1 grade in those with grade 1 or 2 at baseline. Incident MRIeff and PE effusion (PEeff) were any effusion at followup (>0) in those with grade 0 at baseline. A second type of incident MRIeff was effusion grade >= 2 at followup in those with grade <2 at baseline. Exponential regression analysis was used, adjusted for age, sex, and radiographic severity. Results. Incident MRIeff >= 1, incident MRIeff >= 2, incident PEeff, and progression of MRIeff were seen in 14 of 73 (19%), 18 of 140 (13%), 26 of 127 (20%), and 18 of 86 (21%), respectively. There was a borderline statistical association of obesity with progression of MRIeff (hazard ratio [HR] 3.3 [95% confidence interval (95% CI) 1.0-11.2]) and with incident MRIeff >= 2 (HR 3.4 [95% CI 1.0-11.5]). BMI was not associated with incident MRIeff >= 1 (HR overweight 1.1 [95% CI 0.3-3.6], obese 1.0 [95% CI 0.2-5.0]). Overweight was associated with incident PEeff (HR 4.5 [95% CI 1.4-14.2]), while obesity was not statistically significant (HR 3.1 [95% CI 0.9-11.1]). Conclusion. Obesity was a risk factor for incident and progressive knee effusion in this population-based cohort. These findings highlight an important link between obesity and inflammation in knee osteoarthritis.