To develop a measure of knee joint effusion-synovitis volume and to examine the effect of vitamin D supplementation on effusion-synovitis in people with knee osteoarthritis (OA) and low vitamin D levels over 24 months.
Symptomatic knee OA patients with low 25-(OH)D levels (12.5-60 nmol/l) were recruited for a multi-centre, randomised, placebo-controlled and double-blind trial. Participants (age 63 ± 7 years, 208 females) were allocated to either 50,000 IU monthly vitamin D
The reproducibilities of effusion-synovitis volume measurement were high with ICCs ranging from 0.93 to 0.99. Over 24 months, effusion-synovitis volume remained stable in the vitamin D group but increased in placebos with a significant between-group difference (-1.94 ml, 95% confidence interval (CI): -3.54, -0.33). This effect was evident in those with baseline effusion-synovitis and with suprapatellar effusion-synovitis. The proportion with an increase in effusion-synovitis volume was lower in the vitamin D group than placebo (risk ratio (RR): 0.87, 95% CI: 0.77, 0.97).
This highly reproducible effusion-synovitis volume measurement could be a promising outcome measure in OA trials. Vitamin D supplementation could retard the progression of effusion-synovitis which can potentially benefit people with an inflammatory OA phenotype.