# Synovitis mediates cartilage outcomes during weight-loss in knee osteoarthritis – 4-year follow-up data from the Osteoarthritis Initiative

## TL;DR

Weight loss in people with knee osteoarthritis may help protect cartilage by reducing joint inflammation, but the effect is small.

## Contribution

This study shows that reduced synovitis partially explains improved cartilage outcomes during weight loss in knee osteoarthritis.

## Key findings

- Weight loss was associated with lower odds of increased synovitis (OR 0.72; p = 0.018).
- Synovitis reduction partially mediated the beneficial effect of weight loss on cartilage degeneration.
- The mediating effect of synovitis was small in slowing cartilage degeneration.

## Abstract

Weight loss can modify the progression of osteoarthritis (OA), and this may, in part, be achieved by decreased synovitis, a known accelerator of cartilage degeneration. The purpose of this study was to investigate whether change in synovitis mediates the beneficial effect of weight loss on longitudinal cartilage outcomes.

We analyzed right knees with baseline Kellgren & Lawrence grades 1–3 of 1153 obese and overweight participants of the Osteoarthritis Initiative (OAI) cohort with Whole Organ MRI Scores (WORMS) and semi-quantitative assessment of effusion synovitis and synovial proliferation scores form 3T MRIs at baseline and 48 months. There were 295 participants with weight-loss >5 ​% and 858 stable weight controls. Ordered logistic regression was used to assess the association of weight-loss status with concurrent changes in synovitis as well as cartilage WORMS scores; models were adjusted for age, gender, race, presence of radiographic OA, and abdominal circumference at baseline. A mediation analysis was used to determine whether change in overall cartilage degeneration was mediated by change in synovitis scores.

Individuals who lost weight had significantly lower odds for a higher grade on the scale assessing change in overall synovitis (OR 0.72; 95%CI 0.54, 0.95; p ​= ​0.018). Mediation analysis showed that slowing synovitis during weight loss had a small mediating effect on longitudinal cartilage outcomes.

Decreased cartilage degeneration during weight loss was partially mediated by concurrent deceleration in synovitis, showing that decreasing systemic inflammation during weight-loss may not be mirrored in imaging markers of joint inflammation.