Ultrasonographic and Electromyographic Evaluation of the Effects of Deep Versus Superficial Dry Needling on Myofascial Trigger Points in Patients with Neck Pain: A Triple-Blind Randomized Clinical Trial

Background: The physiological differences between deep dry needling (DDN) and superficial dry needling (SDN) for myofascial trigger points (MTrPs) remain unclear. This randomized clinical trial compared the impact of DDN and SDN on ultrasonographic, surface electromyographic (sEMG), and clinical outcomes in patients with non-specific neck pain and upper trapezius MTrPs. Methods: Forty-four participants were randomly allocated to DDN (50 mm) or SDN (13 mm), with 22 participants in each group. Participants received four treatment sessions over 2 weeks. Ultrasonographic outcomes included upper trapezius stiffness, thickness, and blood-flow parameters. sEMG outcomes included maximum voluntary isometric contraction (MVIC), root mean square (RMS), and median frequency (MDF). Pain intensity was measured using the Visual Analogue Scale (VAS) and disability using the Neck Disability Index (NDI). Outcomes were assessed at baseline, following 2 weeks of intervention, and during the 6-week follow-up. Results: No statistically significant between-group differences were detected for the ultrasonographic outcomes. For sEMG, the time-specific contrast for active RMS at the 6-week follow-up was nominally significant (DDN minus SDN: 1.09, 95% CI 0.06–2.13; p = 0.039), whereas the remaining between-group sEMG comparisons were not statistically significant. A small within-group reduction in muscle stiffness was observed in the SDN group at 2 weeks (−0.09, 95% CI −0.17 to −0.001). MVIC increased in both groups at 6 weeks, and active RMS decreased within the SDN group. Both groups showed reductions in pain and disability; adjusted VAS changes ranged from −3.04 to −3.35 cm and adjusted NDI changes ranged from −4.5 to −6.5 points across groups and follow-up assessments. The isolated p = 0.039 finding is interpreted cautiously because multiple outcomes were examined without formal multiplicity adjustment. Conclusions: Both DDN and SDN were associated with improvements in pain and disability, with no statistically significant between-group differences detected for these clinical outcomes in this sample. Most ultrasonographic and sEMG between-group comparisons were also non-significant, although a nominal difference in active RMS was observed at 6 weeks. Because this trial was not designed as an equivalence or non-inferiority study, the findings should not be interpreted as establishing therapeutic equivalence. The absence of consistent ultrasonographic changes suggests that mechanisms beyond measurable local structural or vascular changes may contribute to the observed clinical improvements; such mechanisms were not directly measured in this study.