Shear-Wave Elastography Supports That Muscle Stiffness Should Not Be Considered a Criterion to Determine the Presence of Myofascial Trigger Points in the Infraspinatus Muscle

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Abstract

Objective – This study aimed to determine latent myofascial trigger points and asymptomatic surrounding areas differences in pain pressure thresholds and shear-wave elastography metrics differences. Design – Latent myofascial trigger points and asymptomatic control points were identified within the infraspinatus muscle. A blinded examiner assessed the pain pressure thresholds and acquired three shear-wave elastography images of each location. Pain pressure threshold and shear-wave elastography scores were compared by location (myofascial trigger point and control) and gender. Finally, correlations among demographics, pain pressure thresholds, and shear-wave elastography data were calculated. Results – Forty participants were analyzed. Pain pressure thresholds were significantly lower in latent myofascial trigger points compared with control points in males (P = 0.003) and females (P < 0.001), and lower in females compared with males (myofascial trigger point P < 0.001; control point P = 0.006). No significant shear-wave elastography differences were found between myofascial trigger points and control points (P > 0.05) nor between males and females (myofascial trigger point and control points, P > 0.05). In contrast with the accepted myofascial trigger point definition, those areas with greater pain pressure thresholds exhibited greater stiffness via shear-wave elastography (P < 0.01). Conclusions – Although pain pressure threshold scores indicated significant differences in hyperirritability between latent myofascial trigger points and control points, shear-wave elastography measurements revealed no significant differences in muscle stiffness. Furthermore, muscle stiffness was significantly associated with greater pain pressure threshold scores, challenging the hypothesis that stiffer areas can be identified as myofascial trigger points or sources of pain.