In patients with established osteoarthritis (OA), synovial inflammation may result from joint structural abnormalities, according to a post hoc analysis published in The Journal of Rheumatology.1

The study evaluated data from a randomized controlled trial conducted in Australia on 413 patients (age 49 to 80 years; mean age, 63 ± 7; 50.4% women) with symptomatic knee OA.1 The aim of the study was to describe the association between effusion-synovitis and joint structural changes in patients with knee OA over 24 months.

Knee effusion-synovitis volume and score, cartilage defects, cartilage volume, and bone marrow lesions (BMLs) were assessed with magnetic resonance imaging. Joint space narrowing (JSN) and presence of osteophytes were evaluated using knee radiographs. Change in effusion-synovitis volume was calculated from baseline to 24 months. A least significant change criterion was used to define an increase or a lack of increase (defined as a stable or reduced volume) in effusion-synovitis volume. The participants’ serum 25-hydroxy vitamin D levels were also measured.  

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Total effusion-synovitis volume increased modestly from baseline (8.0 ± 8.5 mL) to follow-up (9.0 ± 10.5 mL). Baseline BMLs, cartilage defects, JSN, and osteophyte scores were significantly associated with changes in effusion-synovitis volume (P <.05). Baseline cartilage defects and JSN were also significantly associated with changes in effusion-synovitis scores (P <.05). In contrast, neither baseline effusion-synovitis scores nor their volume consistently predicted changes in the above structures, with the exception of cartilage volume.

In the mixed-effects model, knee effusion-synovitis was positively associated with BMLs (volume: β =1.19 mL/grade; score: odds ratio [OR] =1.75/grade) and cartilage defects (volume: β =1.87 mL/grade; score: OR =2.22/grade), and negatively associated with cartilage volume loss. In addition, change in effusion-synovitis volume was significantly associated with changes in knee pain and stiffness scores (P <.05 for each).

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The results of this study indicate that, although knee cartilage and subchondral bone abnormalities were predictive of changes in effusion-synovitis, effusion-synovitis was not predictive of structural changes of the knee. According to the investigators, synovial inflammation is likely to result from joint structural abnormalities in patients with established OA.

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Wang X, Jin X, Blizzard L, et al. Associations between knee effusion-synovitis and joint structural changes in patients with knee osteoarthritis [published online September 1, 2017]. J Rheumatol. doi: 10.3899/jrheum.161596