Background Synovial inflammation is commonly observed in osteoarthritis (OA). Vitamin D has showed anti-inflammatory properties in joint disorders which have not been reported in OA.
Objectives To examine the effect of vitamin D supplementation on synovial inflammation in patients with symptomatic knee osteoarthritis (OA) and low vitamin D levels over 24 months.
Methods In a multi-center, randomized, placebo-controlled and double-blind trial, symptomatic knee OA patients with a low 25-(OH)D level (12.5–60 nmol/l) were recruited. 413 patients (age 63.2±7.0 years, 208 females) were allocated to either a 50,000IU monthly vitamin D3 capsule (n=209) or placebo (n=204) for 24 months. In this post-hoc analysis, changes in knee effusion-synovitis volume and score (0–3) were assessed using MRI (fig 1). A least significant criterion (LSC) was used to define an increase of effusion-synovitis volume by correcting measurement errors.
Results At baseline, total effusion-synovitis volume was 8.0 ml with a prevalence of 47.7% (score ≥2). Over 24 months, the total effusion-synovitis volume remained stable in vitamin D group (mean: 0.26 ml, 95% CI: -0.82, 1.34) but increased significantly in placebo group (mean: 2.20 ml, 95% CI: 1.01, 3.38) (difference between groups: -1.94 ml, 95% CI: -3.54, -0.33). This effect was evident in those with baseline effusion-synovitis (difference: -2.04 ml, 95%CI: -3.83, -0.25) and in suprapatellar pouch (difference: -2.49 ml, 95%CI: -4.74, -0.25). Increases in total (relative risk: 0.66, 95%CI: 0.49, 0.90) and suprapatellar (relative risk: 0.64, 95%CI: 0.44, 0.93) effusion-synovitis volume were less in vitamin D than placebo group.
Conclusions Vitamin D supplementation over 24 months significantly reduced progression of effusion-synovitis in patients with knee OA and low 25-(OH)D level.
Acknowledgement We specially thank the participants who made this study possible, and we gratefully acknowledge the role of Vitamin D Effect on Osteoarthritis Study staff and volunteers in collecting the data. We thank the research assistants Jodi Barling, Kay Nguo, Judy Hankin and Alice Noone who were involved in the coordination of this study. Special thank to Yuelong Cao who wrote the study protocol. We also thank Rob Warren measured knee cartilage volume.
Disclosure of Interest None declared