Immediateefficacyoflow-intensityfocusedultrasoundversusplanarultrasoundinpatientswithmyofascialpainsyndromeofuppertrapezius:arandomizedcontrolledclinicaltrial

Myofascial pain syndrome (MPS) is a chronic musculoskeletal condition that affects up to 85% of people at some point in their lives. It is characterized by myofascial trigger points (MTrPs) in muscles, which cause localized pain, stiffness, spasms, and restricted movement. The upper trapezius muscle is one of the most commonly affected areas, particularly in people who work at computers. While various treatments exist, including medications that can cause side effects and invasive procedures like dry needling or acupuncture that carry risks of bleeding and pain, therapeutic ultrasound offers a non-invasive alternative.

Two types of low-intensity therapeutic ultrasound exist: low-intensity planar ultrasound (LIPU), which disperses energy across a broad area, and low-intensity focused ultrasound (LIFU), which concentrates energy at a specific target. Previous studies had shown benefits for each type separately, but no direct comparison of their immediate effects on MPS had been conducted, particularly regarding changes in neuromuscular electrical activity.

The researchers conducted a single-blind randomized controlled trial at West China Hospital, Sichuan University, enrolling 40 patients aged 20 to 70 with diagnosed MPS of the upper trapezius. Participants were randomly assigned to receive either LIFU (20 patients: 9 men, 11 women) or LIPU (20 patients: 15 men, 5 women). Both groups received three treatment sessions, once daily for three consecutive days, with each session lasting 5 minutes using the same parameters: 1.5 W/cm² intensity, 1 MHz frequency, in continuous mode. The ultrasound transducer was moved in circular motion over the trigger point area.

Patients were blinded to their group assignment through the use of light-blocking goggles, opaque partitions, and positioning that prevented them from seeing the device. Assessments were conducted before treatment, immediately after the third session (10 minutes post-treatment), and 72 hours later.

The primary outcome was pain intensity measured by the Visual Analog Scale (VAS, 0-10 cm). Secondary outcomes included the Short-Form McGill Pain Questionnaire (SF-MPQ, 0-45 points) for multidimensional pain assessment, the Neck Disability Index (NDI, 0-50 points) for functional status, and surface electromyography (sEMG) measuring root mean square (RMS) and median frequency (MF) to assess neuromuscular activity.

Both treatment groups experienced significant pain reduction. In the LIFU group, VAS scores decreased by a median of 2.0 cm immediately after treatment (95% CI: -2.5 to -1.5 cm; p = 0.002), with further improvement maintained at 72 hours. The LIPU group also showed significant immediate reduction of 1.0 cm (95% CI: -1.5 to -0.5 cm; p = 0.001), also sustained at 72 hours. However, there was no statistically significant difference between the two groups in pain reduction at any time point (p > 0.05).

Both groups also showed significant improvements in SF-MPQ and NDI scores, with no significant between-group differences.

For neuromuscular activity, the LIPU group showed a significant immediate reduction in RMS parameters (MD = -15.3 µV; 95% CI: -20.0 to -10.5 µV; p = 0.028), while the LIFU group did not show significant sEMG changes. At 72 hours, a significant between-group difference in MF parameters was observed (MD = 3.9 Hz; 95% CI: 0.8 to 6.5 Hz; p = 0.033), but no other intergroup differences in sEMG measures. Importantly, no adverse events were reported in either group.

The researchers noted that while no statistically significant differences were found between groups, moderate to large effect sizes (ranging from 0.40 to 0.65 for various comparisons) suggested possible clinical relevance that might be detectable with larger sample sizes.

This study provides evidence that both LIFU and LIPU are safe, effective options for immediate pain relief in upper trapezius myofascial pain syndrome. For patients, this means there is a non-invasive, drug-free treatment option that can provide rapid pain reduction without the side effects associated with medications or the risks of invasive procedures. The comparable efficacy between the two ultrasound types gives clinicians flexibility to choose based on practical factors like equipment availability, cost, and technical resources rather than concerns about effectiveness.

The findings support using ultrasound therapy as a first-line non-pharmacological option, particularly for patients who cannot or prefer not to use medications. The short 3-session protocol achieving meaningful immediate and sustained relief suggests potential for efficient, cost-effective treatment courses that reduce patient burden and healthcare costs. The sEMG findings, while showing limited significant differences, suggest both modalities may help normalize abnormal muscle electrical activity associated with trigger points, providing objective biomarkers that could complement traditional pain and function assessments in monitoring treatment response.

However, the lack of a sham control group means some improvement may reflect natural symptom resolution or placebo effects. The short follow-up period and single-center design with a small sample limit conclusions about long-term durability and generalizability. Future research with larger samples, longer follow-up, and placebo-controlled designs is needed to confirm these findings and clarify whether the moderate to large effect sizes translate to clinically meaningful between-group differences.