Background Synovial inflammation plays an important role in knee osteoarthritis (OA), but the etiology is not well understood.
Objectives The aim of this cohort study was to investigate its clinical significant, natural history and related factors.
Methods A total of 406 subjects were randomly selected from the local community (mean 62 years, 50% female) at baseline and followed up 2.7 years later. Knee effusion-synovitis was determined using T2-weighted fat saturation magnetic resonance imaging (MRI) by measuring the maximum area of fluid-equivalent signals in the synovial joint. Reproducibility was excellent (intraclass correlation coefficients (ICCs): 0.81-0.60). Knee cartilage defects, cartilage volume, bone marrow lesions (BMLs) and meniscal lesions were assessed using MRI at baseline and follow-up. X-ray was used to assess radiographic osteoarthritis (ROA) at baseline. Dietary fats intake such as monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs) and saturated fatty acids (SFAs) were assessed at baseline.
Results At baseline, the mean (±SD) size of effusion-synovitis was 1.635 cm2 (±1.315 cm2), ranging from 0.035 cm2 to 8.914 cm2. Over 2.7 years follow-up, the mean size of effusion-synovitis was 1.746 cm2 (±1.293 cm2), 29% of participants (N=88) increased in size, 50% (N=201) remained stable and 22% (N=117) decreased in size. Baseline effusion-synovitis was associated with change in knee cartilage defects (adjusted β: 0.18, 95% CI: 0.08 to 0.29), cartilage volume (adjusted β: -0.45, 95% CI: -0.75 to -0.14) and BMLs (adjusted β =0.17, 95% CI: 0.04 to 0.30). Baseline structural changes were not significantly associated with change in effusion-synovitis area in adjusted analyses.
In the overall population, significant association was found between PUFAs and decrease in effusion-synovitis, after adjusted for age, gender, BMI, ROA, physical activity and energy intake (RR: 1.32 per 1 SD decrease, 95% CI: 1.03 to 1.69). In gender subgroup analyses, SFAs were significantly associated with decrease in effusion-synovitis size in males (RR: 0.62 per 1 SD decrease, 95% CI: 0.40 to 0.96). In female subjects, MUFAs and PUFAs were both negatively associated with increase in effusion-synovitis (RR: 0.48 and 0.67 per 1 SD increase, respectively), but not significant in overall sample and male subjects.
Conclusions In this older cohort, the proportion of effusion-synovitis increasing in size was similar to those decreasing in size with the rest half remaining stable. Change in cartilage and subchondral BMLs were predicted by effusion-synovitis, suggesting it could be a primary risk factor of structural changes. Dietary SFAs may be detrimental for effusion-synovitis progression but unsaturated fatty acids (UFAs) were rather beneficial.
Acknowledgements We especially thank the participants who made this study possible, and we gratefully acknowledge the role of the Tasmania Older Adult Cohort staff and volunteers in collecting the data, particularly research nurses Catrina Boon and Pip Boon. We also thank Dr Velandai Srikanth and Dr Helen Cooley assessed the radiographs.
Disclosure of Interest None declared