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May 2020

The MyotonPRO: a reliable and valid tool for quantifying the viscoelastic properties of a trigger point on the infraspinatus in non-traumatic chronic shoulder pain

Authors: Melanie Roch, Melanie Morin, Nathaly Gaudreault

Author information: Universite de Sherbrooke, Faculte de medecine et des sciences de la sante, Ecole de Readaptation, Centre de recherche du Centre hospitalier universitaire de Sherbrooke, 3001, 12e Avenue Nord, Sherbrooke, Quebec, Canada

Journal: Journal of Bodywork and Movement Therapies - May 2020, In Press, Journal Pre-proof (DOI: 10.1016/j.jbmt.2020.05.002)

  • There are currently no validated tools available in clinical practice to objectively measure a trigger point.
  • The MyotonPRO (Myoton AS, Tallinn, Estonia) is a portable hand-held myotonometer, it is non-invasive and provides a quantitative assessment of a muscle’s viscoelastic properties (stiffness, elasticity and tone).
  • The metrological properties of the MyotonPRO device for measuring the viscoelasticity of a localized area corresponding to a trigger point have so far never been studied.
  • The MyotonPRO device was able to measure a statistically significative difference (p<0.05) between a trigger point and an non-trigger point for all viscoelastic parameters (stiffness, elasticity and tone).
  • The measurements also showed excellent intra- and inter-evaluator reliability for the viscoelastic properties of a TP and good to excellent test-retest reliability.

 

Introduction: Clinicians rely on palpation for locating and diagnosing trigger points in muscles. Measuring a trigger point with clinical palpation remains a challenge. There are currently no validated tools available in clinical practice to objectively measure a trigger point.

Method: The presence of a trigger point within the infraspinatus muscle was identified on thirty-five individuals with non-traumatic chronic shoulder pain via palpation according to Travell and Simons criteria. Trigger and non-trigger points were marked within the same muscle and the viscoelastic properties of both points were independently measured twice with the MyotonPRO by two evaluators on two days.

Results: Significant differences were observed when the trigger and non-trigger point (discriminant validity) were compared. The trigger points showed greater tone and stiffness compared to the non-trigger points (tone: 15.30±1.99 Hz vs 13.57±1.76 Hz; stiffness: 270.20±46.96 N/m vs 227.86±43.44 N/m; p<0.05) and less elasticity (decrement of 1.13±0.21 vs 1.06±0.27; p<0.05).

The reliability of the three viscoelastic properties was found to be excellent for intra- and inter-evaluator reliability (ICC: 0.925-0.984 and 0.918-0.972, respectively) and good to excellent for test-retest reliability (between days) (ICC: 0.770-0.875).

Conclusion: The MyotonPRO can differentiate the viscoelastic properties of a trigger point from a non-trigger point. Our findings support the reliability of this myotonometer. This affordable and portable tool can be used to objectively measure viscoelastic properties of trigger points in the infraspinatus.

The MyotonPRO can discriminate the viscoelastic properties of a TP from an NTP located in the infraspinatus of individuals presenting with chronic, non-traumatic shoulder pain. The MyotonPRO is a reliable, affordable and portable tool that can objectively measure these properties in a clinical setting or for research purposes. This is an important breakthrough in the evaluation and treatment of musculoskeletal conditions associated with the presence of TPs, because as evidenced by Shah (2015), theories surrounding the pathogenesis, pathophysiology, and contribution of TPs in the diagnosis of myofascial pain syndrome have so far been mainly speculative.

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