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

Abstract

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/m2), overweight (BMI, 25-29.9 kg/m2), and obese (BMI, ≥ 30 kg/m2), 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 T2 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 T2 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.

Keywords: Body mass index; Knee; Magnetic resonance imaging; Osteoarthritis; Synovitis.

Conflict of interest statement

Conflict of interest: All authors declare that they have no conflicts of interest.

Figures

Fig. 1

Patient selection from the OAI database. aHistory of rheumatoid arthritis or other inflammatory arthritis bHistory of knee arthroscopy for meniscectomy or ligament repair cHistory of other types of knee surgery (all subjects with arthroscopy excluded)

Fig. 2

MRI-synovial inflammatory biomarkers (A, B) and representative T2 maps (C, D) in overweight and obese subjects. (A) Mid-sagittal intermediate-weighted fat-suppressed image of a 47-year-old obese woman (Total WOMAC pain subscale = 5) with focal increased signal intensity within the IPFP (grade 2 for signal which is equal to cartilage and grade 1 for size with less than 33% IPFP involvement; asterisk), effusion-synovitis in the suprapatellar recess (grade 3 according to ACLOAS) and mild irregularity of the synovium with synovial thickening (grade 2 for synovial proliferation score; arrow). There is focal cartilage loss at the patella (WORM score = 2.5; arrowhead). The T2 color map is shown in (C) which shows heterogeneously increased T2 relaxation time throughout the entire medial femoral condyle and tibia (41.13 and 35.93 ms, respectively). (B) Axial reformatted 3D DESS image of a 62-year-old overweight man (Total WOMAC pain subscale = 4) demonstrating irregular and villonodular synovial thickening (grade 3 for synovial proliferation score; arrow), and effusion-synovitis (grade 2 according to MOAKS). Full thickness cartilage loss at the lateral facet of the patella was also noted (WORMS = 6; arrowhead). The T2 color map demonstrates heterogeneously elevated mean T2 relaxation time (34.12 ms) throughout the entire patella, highest near the cartilage defects (D)