Background & Aims

Shoulder pain is a highly prevalent musculoskeletal condition, and a number of experimental pain models have been developed in order to better understand it. However, most of these models do not replicate the clinical experience of pain (Ford et al., 2019). We developed a novel experimental pain model based on the application of short-wave diathermy (SWD), which showed to be a simple and non-invasive alternative for eliciting muscle pain (Mista et al., 2019). The aim of this study was to assess whether the application of SWD on healthy volunteers accurately mimics the clinical experience of shoulder pain, including topographical pain distribution, and pain intensity and quality.

Methods

A quasi-experimental study was conducted to compare the effects of SWD application as a shoulder experimental pain model with the clinical experience of chronic unilateral shoulder pain (USP). Thirty-two volunteers with USP and thirty-two healthy volunteers participated in a single experimental session. SWD was applied three times to the dominant shoulder of healthy volunteers at a fixed stimulation intensity, until volunteers reached the tolerance threshold for painful heat stimulation. Applications were separated by 2-3 min intervals. Pain intensity (using a visual analogue scale, VAS), pain quality (using the McGill Pain Questionnaire), pressure pain thresholds (PPT) and topographical pain distribution were assessed before and 30 min after SWD application on the infraspinatus muscle. The same assessments were performed in the USP group. Outcomes were contrasted using linear mixed models, and statistical equivalence was assessed using the TOST (two one-side t tests) procedure.

Results

Volunteers with USP presented higher pain intensity than healthy volunteers after SWD (5.67±0.97 vs. 4.45±1.09 respectively, p<0.001), and the scores were statistically equivalent within a range of ±2 VAS points (TOST, p?0.002). PPTs were lower on the painful side in both groups (228±72.2 kPa vs. 312±81.9 kPa respectively, p<0.001). PPTs on the painful side were not significantly different between groups (238.0 ± 58.1 kPa vs. 218.0 ± 83.8 kPa respectively, p=0.276), and they were statistically equivalent within a range of ± 50 kPa (TOST, p?0.05). USP patients reported larger areas with high pain intensity (24.7% vs 4.9% with high, 49.9% vs 38.2% with medium, and 25.3% vs 56.9% with low pain intensity). The frequency of pain quality descriptors was similar between USP patients and healthy volunteers after SWD: continuous (68.7% vs 62.5%), heavy (51.3% vs 75%), well-localized (75% vs 46.9%), unbearable (50% vs 65.6%), respectively, except for hot (25% vs 62.5%).

Conclusions

Experimental shoulder pain induced by SWD on infraspinatus muscle elicited a topographical pain distribution similar to that observed in clinical USP. Healthy volunteers reported muscle soreness, moderate pain intensity, and showed a decrease in PPT after SWD application. These outcomes were statistically equivalent to the USP group. Overall, the experimental pain induced by SWD accurately reproduce the quality of the clinical experience of shoulder pain.

References

Mista CA, Laugero SJ, Adur JF, Andersen OK, Biurrun Manresa JA. A new experimental model of muscle pain in humans based on short-wave diathermy. Eur J Pain. 2019;23(9):1733-1742. doi:10.1002/ejp.1449
Ford B, Cohen M, Halaki M, Diong J, Ginn KA. Experimental shoulder pain models do not validly replicate the clinical experience of shoulder pain. Scand J Pain. 2019;20(1):167-174. doi:10.1515/sjpain-2019-0055

Presenting Author

José. A. Biurrun Manresa

Poster Authors

Leonardo Intelangelo

MSc

University Center for Assistance, Teaching and Research (CUADI), University of Gran Rosario

Lead Author

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Christian Mista (PhD)

Institute for Research and Development in Bioengineering and Bioinformatics (IBB) CONICET-UNER

Lead Author

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Mauro Barone (PhD)

University Center for Assistance, Teaching and Research (CUADI), University of Gran Rosario (UGR)

Lead Author

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Fernando Imaz (PhD)

University Center for Assistance, Teaching and Research (CUADI), University of Gran Rosario (UGR)

Lead Author

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Silvio Laugero (MSc)

National University of Entre Ríos (UNER)

Lead Author

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Javier Adur (PhD)

National University of Entre Ríos (UNER)

Lead Author

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Ole Kæseler Andersen

Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), Aalborg University

Lead Author

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José Biurrun Manresa

National Scientific and Technical Research Council (CONICET)

Lead Author

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Topics

  • Models: Musculoskeletal