Obese and overweight individuals have greater knee synovial inflammation and associated structural and cartilage compositional degeneration: data from the osteoarthritis initiative.

Objective: This work aims to study (i) the relationship between body mass index (BMI) and knee synovial inflammation using non-contrast-enhanced MRI and (ii) the association of synovial inflammation versus degenerative abnormalities and pain.

Materials And Methods: Subjects with risk for and mild to moderate radiographic osteoarthritis were selected from the Osteoarthritis Initiative. Subjects were grouped into three BMI categories with 87 subjects per group: normal weight (BMI, 20-24.9 kg/m), overweight (BMI, 25-29.9 kg/m), and obese (BMI, ≥ 30 kg/m), frequency matched for age, sex, race, Kellgren-Lawrence grade, and history of knee surgery and injury. Semi-quantitative synovial inflammation imaging biomarkers were obtained including effusion-synovitis, size and intensity of infrapatellar fat pad signal abnormality, and synovial proliferation score. Cartilage composition was measured using T relaxation time and structural abnormalities using the whole-organ magnetic resonance imaging score (WORMS). The Western Ontario and McMasters (WOMAC) Osteoarthritis Index was used for pain assessment. Intra- and inter-reader reproducibility was assessed by kappa values.

Results: Overweight and obese groups had higher prevalence and severity of all synovial inflammatory markers (p ≤ 0.03). Positive associations were found between synovial inflammation imaging biomarkers and average T values, WORMS maximum scores and total WOMAC pain scores (p < 0.05). Intra- and inter-reader kappa values for imaging biomarkers were high (0.76-1.00 and 0.60-0.94, respectively).

Conclusion: Being overweight or obese was significantly associated with a greater prevalence and severity of synovial inflammation imaging biomarkers. Substantial reproducibility and high correlation with knee structural, cartilage compositional degeneration, and WOMAC pain scores validate the synovial inflammation biomarkers used in this study.