Ultrasound features of myofascial trigger points: a multimodal study integrating preliminary histological findings...

This study investigated the ultrasound and histological characteristics of myofascial trigger points (MTrPs) in the upper trapezius (UT) following dry needling (DN) therapy. Forty-nine participants with active MTrPs in one UT were included, with the contralateral healthy side serving as control. Ultrasound assessments (UT thickness, Young's modulus, vascular parameters including peak systolic velocity [PSV], resistance index [RI], and vascularity index [VI]) were performed: (1) pre-intervention, (2) 1-hour after DN. Pain levels were measured using the visual analog scale (VAS). Key findings showed affected UTs were initially thicker and stiffer than the healthy side (11.24 ± 1.81 mm, 32.28 ± 9.70 kPa vs. 10.00 ± 1.46 mm, 19.16 ± 6.39 kPa; p < 0.05), with greater deep fascia thickness (1.08 ± 0.14 mm vs. 0.92 ± 0.14 mm). Post-DN, the thickness and stiffness of the affected UTs decreased (9.64 ± 1.74 mm, 24.14 ± 5.31 kPa, P < 0.05). Perfusion improved, evidenced by a lower RI (0.78 ± 0.05 vs. 0.86 ± 0.03) and higher VI (12.90 ± 6.35 vs. 2.53 ± 1.69), while PSV remained unchanged. Eventually, VAS scores dropped from 7.86 ± 0.90 to 5.00 ± 1.29 (p < 0.05). Prior to DN, histological analysis (n = 5 biopsies) revealed characteristic MTrPs remodeling (muscle fiber atrophy, adipose tissue hyperplasia) without contraction knots. DN alleviates pain by reducing thickness and stiffness of muscle and enhancing perfusion, providing a mechanistic basis for its therapeutic effects in myofascial pain management.