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

Abstract

IntroductionClinicians 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. MethodThe 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. ResultsSignificant 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). ConclusionThe 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.