Background/Purpose: Synovial inflammation is associated with knee osteoarthritis (KOA) progression. Body mass index (BMI) has also been associated with KOA progression. Yet, it is unclear whether synovial inflammation mediates the association of BMI with KOA progression. Here, we examined the mediating effect of synovitis in the association between BMI and progression of radiographic KOA in the Osteoarthritis Initiative (OAI) cohort.

Methods: We conducted a case-control study within the OAI. Cases (n = 315) were right knees with an increase of ≥ 1 Kellgren-Lawrence (K-L) from baseline to 48 months of follow-up. Controls (n = 315) were right knees that had no K-L change over 48 months. Cases and controls were matched by age, gender, race and baseline K-L. MRI Osteoarthritis Knee Score (MOAKS) was used for a semi-quantitative evaluation (0-3) of effusion synovitis and Hoffa-synovitis at baseline. The SPSS PROCESS macro was used to test the mediating effects.

Results: The mean age of participants was 61 years, 70.8% were women, and 87% were white. Baseline knee KL was as follows: 36.8% grade 0, 30.2% grade 1, 25.1% grade 2 and 7.9% grade 3. 24.9% were normal weight (BMI < 24.9 kg/m2), 37.1% were overweight (BMI 25-29.9 kg/m2) and 37.0% were obese (BMI ≥ 30 kg/m2). Average BMI was 28.63 ± 4.8. 49.8% had synovitis effusion with a score of 0.56 ± 0.6, and 51.9% had Hoffa synovitis with a score or 0.61 ± 0.66. Compared with controls, cases had higher BMI (29.1 ± 4.7 vs 28.2 ± 4.9,p< 0.05), and were more likely to be obese (41.5% vs. 34.3%) than controls (p < 0.05). At baseline, cases had higher prevalence of both synovitis effusion and Hoffa-synovitis than controls (59.6% vs 40.1%, p< 0.01 for synovitis-effusion and 61.9% vs 42%, p< 0.01, for Hoffa synovitis respectively). Yet, in the mediation analysis, neither synovitis effusion nor Hoffa synovitis mediated the relationship between BMI and KOA progression.

Conclusion: Preliminary findings from mediation analysis showed that neither synovitis effusion nor Hoffa synovitis mediated the relationship between BMI and progression of radiographic KOA over a 4-year period. A longer duration of follow-up may be required to determine if synovitis mediates the association between BMI and progression of KOA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/synovitis-does-not-mediate-the-relationship-between-body-mass-index-and-progression-of-radiographic-knee-osteoarthritis-data-from-the-osteoarthritis-initiative/