# Ultrasonographic Evidence of Synovitis Correlates with Synovial Citrate and TBARS in Equine Osteoarthritis

## TL;DR

This study shows that ultrasound findings in horse joints with osteoarthritis correlate with higher levels of citrate and oxidative stress markers in synovial fluid, suggesting these substances could help detect the disease early.

## Contribution

The study identifies citrate and TBARS as potential biomarkers for early equine osteoarthritis detection when combined with ultrasound.

## Key findings

- OA-affected joints had higher citrate and TBARS levels compared to healthy joints.
- Citrate and TBARS concentrations correlated strongly with ultrasound scores indicating synovitis.
- Ultrasonography detected synovitis earlier than radiography, with metabolic and oxidative stress markers supporting early diagnosis.

## Abstract

Osteoarthritis (OA) is a joint disease in horses that causes pain and reduced mobility, but it is difficult to detect in its early stages. Since ultrasound can detect earlier disease changes than radiography, this study evaluated whether substances present in the synovial fluid, which lubricates the joints, could help identify OA based on their concentrations and their relationship with ultrasonographic findings. The metacarpophalangeal joints of 26 horses, with and without OA, were examined using radiography and ultrasound. Synovial fluid samples were analyzed for markers related to inflammation, cartilage damage, and oxidative stress. Joints affected by OA showed higher levels of citrate and oxidative stress markers compared to healthy joints, and these levels were associated with more severe ultrasound changes. These results suggest that citrate and oxidative stress markers reflect early joint inflammation and metabolic changes, highlighting their potential as supportive tools for the early diagnosis of osteoarthritis in horses alongside ultrasonography.

Osteoarthritis (OA) is a degenerative joint disease that affects humans and animals worldwide. Its early diagnosis remains challenging due to subtle clinical signs and late radiographic changes. This study aimed to explore candidate biomarkers associated with spontaneous OA and to investigate their correlation with ultrasonographic scores to support early diagnosis. Clinical, radiographic, and ultrasonographic evaluations were performed on 52 equine metacarpophalangeal joints, with and without OA, allowing joint scoring and classification into osteoarthritis (OAG) and control groups. Synovial fluid samples were analyzed for cartilage degradation (C2C), untargeted 1H NMR-based metabolomics, and lipid peroxidation (TBARS). Statistical analyses included Student’s t-test, Mann–Whitney U test, univariate and multivariate metabolomic analyses, and Spearman’s correlation (p < 0.05). Ultrasonography revealed higher scores in the synovial fold, membrane, and fluid, indicating synovitis as the predominant finding in the acute phase. C2C and TBARS concentrations were significantly higher in the OAG. Seven metabolites differed between groups, with citrate and TBARS showing the strongest correlations with ultrasonographic scores. These findings suggest increased metabolic activity and lipid peroxidation in early OA and highlight citrate and TBARS as potential auxiliary biomarkers for early diagnosis associated with synovitis.