Effect of Visual Feedback During Ultrasound-Guided Interfascial Injection for Myofascial Pain Syndrome: A Prospective, Multicenter, Observational Clinical Trial

Abstract

\n Background: Expectations for treatment have a favorable effect on the subsequent course of pain and behavior in patients. It is not known whether receiving interfascial injection while patients view their ultrasound image with doctors (visual feedback) is associated with positive treatment expectations. Methods: This was a prospective, multicenter, observational clinical trial. We evaluated whether visual feedback during ultrasound-guided interfascial injection affects treatment expectations and the subsequent course of pain in patients with myofascial pain syndrome. Treatment expectations were set as mediators of pain using path analysis. The primary endpoint was the proportion of patients who showed improvement in pain numerical rating scale score by 50% or more 14 days after initiation of treatment. Results: During 2019 and 2020, 136 outpatients received ultrasound-guided interfascial injection for myofascial pain syndrome. Of these, 65 (47.8%) patients received visual feedback during ultrasound-guided interfascial injection. Compared with the non-visual feedback group, the visual feedback group had higher expectations for treatment, immediately after interfascial injection, and their expectations were maintained at day 14 of treatment (p < .001). In the visual feedback group, 67.7% of patients showed improvement in pain numerical rating scale score by 50% or more at day 14 (95% confidence interval: 56.5–78.9), whereas such improvement was observed in only 36.6% of the non-visual feedback group (95% confidence interval: 25.3–47.9; p < .001). Path analysis revealed that visual feedback had the largest influence on pain numerical rating scale reduction at 14 days, which was indirectly via higher expectations for treatment (β = 0.434).Conclusions: Visual feedback during ultrasound-guided interfascial injection had a positive effect on the subsequent course of pain in patients with myofascial pain syndrome by increasing patients’ treatment expectations.Trial registration: UMIN000043160. Registered 28 January 2021 (registered retrospectively).