Background Corticosteroid injections are recommended as a safe and effective treatment for the relief of moderate to severe pain in knee osteoarthritis (OA). Though not firmly established, the mechanism of action is thought to be mediated in part by an anti-inflammatory effect on the synovium which may be detected by Ultrasound (US) examination.
Objectives To determine if US features suggestive of inflammation (effusion, synovial hypertrophy, power doppler signal (PDS) and popliteal cysts) change with improved knee pain following intra-articular cortico-steroid injection and a placebo in symptomatic osteoarthritic (SOA) knees.
Methods In a randomised, double-blind, within-patient cross-over study, 25 community participants with symptomatic knee OA received intra-articular injection of  methylprednisolone acetate (40mg) or  a saline placebo into the same knee in a random order. Assessments were carried out by a single (blinded) assessor at baseline, one week following each injection, and when pain had returned to its pre-injection severity. Assessments included: 100mm pain VAS, presence/absence of clinical effusion, WOMAC Index, ICOAP questionnaire and an Ultrasound (US) examination. US features (effusion, synovial hypertrophy, popliteal cysts and power Doppler (PD) signal within the synovium) were recorded as present/absent and grey-scale features were measured directly in mm.
No formal power calculations were determined. The primary outcome was change in pain VAS one week after injection. Response was defined as a decrease in pain VAS ≥ 15mm. Association between response and the presence of baseline US features was examined using simple logistical regression. Correlations between change in pain VAS scores and change in continuous US measures were explored using Spearman’s correlation rho.
Results Improvements in pain VAS were observed following both interventions (mean difference = -17.4mm SD (26.8), p=0.003 for steroid, -13.44mm SD(22.44), p=0.006 for placebo) but were not statistically different from each other. A small but statistically significant improvement was observed in synovial hypertrophy after 1 week for steroid injection (mean difference =-0.94mm SD (2.18), p=0.04), but not for placebo (mean difference = -0.98 SD (3.65) p=0.91). No association was found between pain response and the presence of US features at baseline. Furthermore, no correlation was found between change in pain VAS and change in direct US measures following either injection.
Conclusions Both steroid and placebo injection reduced pain in knee OA. However, the reduction was not associated with a reciprocal change in US features of synovial “inflammation”. Further larger studies are required to confirm the results.
Acknowledgements We are grateful to Arthritis Research UK for funding this work (AHP Training Fellowship Grant no.18861).
Disclosure of Interest None Declared