Experimental Pain Model Based on Short‐Wave Diathermy Replicates the Intensity, Quality and Spatial Distribution of Chronic Shoulder Pain: A Parallel Group Validation Study

Abstract

Background: Several experimental pain models have been developed to better understand shoulder pain. However, most ofthese models do not accurately replicate characteristic features of clinical pain. The aim of this study was to assess whether theeffects of the short-wave diathermy (SWD) pain model mimic clinical shoulder pain in terms of intensity, quality, and spatialdistribution.Methods: Thirty-two patients with unilateral shoulder pain (USP) and thirty-two healthy volunteers participated in a singleexperimental session. SWD was applied to the dominant shoulder of healthy volunteers, until volunteers reached the tolerancethreshold for painful heat stimulation. Pressure pain thresholds (PPTs), pain intensity (using a visual analogue scale, VAS), painquality (using the McGill Pain Questionnaire) and spatial pain distribution were assessed 30 min after SWD application on theinfraspinatus muscle. The same assessments were performed in the USP group. Outcomes were contrasted using linear mixedmodels and independent sample t tests, and statistical equivalence was assessed using the TOST (two one-sided t tests) procedure.Results: PPTs on the painful side were statistically equivalent within a range of ±50 kPa. Pain intensities in both groups werestatistically equivalent within a range of ±2 VAS points. Both groups showed a similar spatial pain distribution, and describedthe pain as continuous, well-delimited, dull and bearable. However, USP patients more frequently used the stabbing and naggingdescriptors in contrast to volunteers in the SWD group, who chose hot and heavy instead.Conclusion: Experimental pain induced by SWD accurately reproduces many relevant characteristics of chronic shoulder pain.Significance Statement: Short-wave diathermy applied to the shoulder of healthy volunteers elicited equivalent pain intensity,quality and spatial distribution compared with clinical unilateral shoulder pain.