BackgroundSynovitis occurring frequently in osteoarthritis (OA) may be a targeted outcome. There are no data examining whether synovitis changes following intra-articular intervention.MethodsPersons aged 40 years and older with painful knee OA participated in an open label trial of intra-articular steroid therapy. At all time points they completed the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire. They had a contrast-enhanced (CE) MRI immediately prior to an intra-articular steroid injection with a repeat scan within 20 days. Response status was assessed using the Osteoarthritis Research Society International (OARSI) response criteria. OARSI responders were followed until their pain relapsed either within 20% of baseline or 6 months, shortly after which a third MRI was performed. Synovial tissue volume (STV) was measured on postcontrast knee images. We looked at changes in the STV and in pain, and their association.Results120 subjects with preinjection and postinjection CE MRI were followed. Their mean age was 62.3 years (SD=10.3) and 62 (52%) were women. The median time between injection and follow-up scan was 8 days (IQR 7–14 days). 85/120 (71%) were OARSI responders. Pain decreased (mean change in KOOS=+23.9; 95% CI 20.1 to 27.8, p<0.001) following steroid injection, as did mean STV (mean change=−1071 mm3; 95% CI −1839 mm3 to −303 mm3, p=0.01). Of the 80 who returned for a third MRI, pain relapsed in 57, and in the 48 of those with MRI data, STV increased between follow-up and final visit (+1220 mm3; 95% CI 25 mm3 to 2414 mm3, p=0.05). 23 were persistent responders at 6 months and, in these, STV did not increase (mean change=−202 mm3; 95% CI −2008 mm3 to 1604 mm3, p=0.83). Controlling for variation over time, there was a significant association between synovitis volume and KOOS pain (b coefficient—change in KOOS pain score per 1000 mm3 change in STV=−1.13; 95% CI −1.87 to −0.39, p=0.003), although STV accounted for only a small proportion of the variance in change in pain.ConclusionsSynovial tissue volume in knee OA shrinks following steroid therapy, and rebounds in those whose pain relapses. It can be considered a treatment target in symptomatic knee OA.Trial registration numberISRCTN07329370.

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Objective. IA steroid injections (IASIs) have been shown to relieve pain in knee OA and are widely used in clinical practice. There is, however, evidence of some variation in response. Knowledge of predictors of response could aid in the selection of patients for this therapy. The aim of this systematic review was to determine factors associated with response to IASI in knee OA.Methods. Medline, Embase, AMED, CINAHL, Web of Science and Cochrane Central Registers for Controlled Trials up to January 2012 were searched with additional hand searches of relevant articles. Studies included were those that involved adults diagnosed with knee OA in whom IASIs were administered and factors that predicted treatment response were investigated.Results. Eleven publications meeting these criteria were reviewed and relevant information extracted. It was not possible to pool the results because of the different predictors studied, variable outcome measures, different criteria for symptom change and missing data. Given the relative paucity of data and small heterogeneously designed studies, it was difficult to identify predictors of response. Data from individual publications, although not consistent across studies, suggest that the presence of effusion, withdrawal of fluid from the knee, severity of disease, absence of synovitis, injection delivery under US guidance and greater symptoms at baseline may all improve the likelihood of response to IASI.Conclusion. Further larger-scale studies using standardized methods are required to characterize predictors of response and should focus on synovitis, effusion, pain and structural severity of disease. Such data would help in better targeting therapy to those most likely to benefit.