Immediate efficacy of low-intensity focused ultrasound versus planar ultrasound in patients with myofascial pain syndrome of upper trapezius: a randomized controlled clinical trial

Abstract

Background: Myofascial pain syndrome (MPS), a chronic musculoskeletal disorder characterized by myofascial trigger points (MTrPs), causes localized pain and dysfunction. The objective is to compare the immediate therapeutic effects of low-intensity focused ultrasound (LIFU) versus low-intensity planar ultrasound (LIPU) on pain and function in upper trapezius MPS.

Method: This study was designed as a single-blind, randomized controlled trial. The patients (20 ≤ aged ≤ 70) diagnosed with MPS of the upper trapezius were randomly allocated to either LIFU (study group; n = 20; 9 men, 11 women) or LIPU (control group; n = 20; 15 men, 5 women) treatments (1.5 W/cm², 1 MHz, 5 min, once a day, 3 days). The primary outcome was pain severity, assessed immediately post-treatment using the Visual Analog Scale (VAS; 0 ~ 10 cm), and served as the central efficacy endpoint. Secondary outcomes comprised supplemental assessments including: (1) multidimensional pain characterization via the Short-Form McGill Pain Questionnaire (SF-MPQ); (2) functional disability quantification through the Neck Disability Index (NDI); and (3) neuromuscular biomarkers measured by surface electromyography (sEMG) parameters (root mean square [RMS], median frequency [MF]). The outcomes were assessed before treatment and 10 min, 72 h after completing the third and final session of treatment.

Results: Pain intensity, as measured by the VAS, decreased significantly immediately after treatment in both the LIFU group (median difference [MD] = -2.0 cm; 95% confidence interval [CI]: -2.5 to -1.5 cm; p = 0.002) and the LIPU group (MD = -1.0 cm; 95% CI: -1.5 to -0.5 cm; p = 0.001), with these reductions maintained at 72 h post-treatment. Both SF-MPQ and NDI scores showed significant improvements following treatment in both groups. A significant reduction in RMS parameters was observed in the LIPU group immediately after treatment (MD = -15.3 µV; 95% CI: -20.0 to -10.5 µV; p = 0.028). No significant differences were observed between the groups in terms of pain alleviation, functional improvement, and alterations in neuromuscular electrophysiological activity (p > 0.05); however, moderate to large effect sizes suggest possible clinical relevance. No adverse events were reported.

Conclusion: Both LIFU and LIPU can be considered effective therapeutic options, offering immediate symptom relief in patients with upper trapezius MPS.

Trial registration: The protocol was registered at the Chinese Clinical Trial Register (ChiCTR2500097431) as a clinical trial on 19/02/2025 http://www.chictr.org.cn/ .

Keywords: Low-intensity focused ultrasound; Low-intensity planar ultrasound; Myofascial pain syndrome; Myofascial trigger points; Surface electromyography; Upper trapezius.

Fig. 1

The trial profile of CONSORT. A total of 46 patients have been consecutively enrolled from the rehabilitation medicine center, of which 6 patients were excluded according to exclusion criteria. The recruited 40 patients were randomly assigned at 1:1 to either the LIFU group or the LIPU group using the block randomization. Abbreviation: CONSORT, Consolidated Standards of Reporting Trials; LIFU, low-intensity focused ultrasound; LIPU, low-intensity planar ultrasound

Fig. 2

Comparison of immediate effect between LIFU versus LIPU on pain and physical function of MPS. A-C The VAS scores have been reduced after either LIFU or LIPU. D-F The SF-MPQ scores have been decreased after either LIFU or LIPU. G-I The disability index, NDI scores have been improved post-treament of either LIFU or LIPU. Abbreviation: LIFU, low-intensity focused ultrasound; LIPU, low-intensity planar ultrasound; NDI, neck disability index; SF-MPQ, McGill pain questionnaire; VAS, visual analog scale. Data presented as median and interquartile range. Post im: 10 min after treatment (after 3 session baseline); Post 72 h: 72 h after treatment (after 3 session baseline). *p < 0.05; **p < 0.001

Fig. 3

Comparison of immediate effect between LIFU versus LIPU on neuromuscular electrophysiological activity. (A-C) The abnormal time-domain features (RMS) induced by MTrPs were immediately readjusted following either LIFU or LIPU treatment. (D-F) The abnormal frequency-domain features induced by MTrPs were also immediately readjusted following either LIFU or LIPU treatment. Abbreviation: LIFU, low-intensity focused ultrasound; LIPU, low-intensity planar ultrasound; MF, median frequency; RMS, root mean square. Data presented as median and interquartile range. Post im: 10 min after treatment (after 3 session baseline); Post 72 h: 72 h after treatment (after 3 session baseline). *p < 0.05