Introduction

Neck pain is a highly prevalent condition, affecting approximately 203 million people globally [1], and myofascial pain syndrome (MPS) is considered one of its major causes [2,3]. Pharmacological interventions, including nonsteroidal anti-inflammatory drugs (NSAIDs), muscle relaxants, and topical agents such as diclofenac patches and thiocolchicoside, have demonstrated varying degrees of efficacy in reducing pain in MPS [4]. Exercise [5] and physical therapy are central to the management of MPS. Adjunctive techniques, such as dry needling, myofascial release, and transcutaneous electrical nerve stimulation, have shown efficacy in achieving short- to medium-term pain reduction and functional improvement [6–8]. Although tissue ischemia has been implicated as a contributing factor in musculoskeletal pain (ischemic myalgia) [9], treatments specifically targeting the improvement of blood flow are rarely implemented. These findings suggest that approaches aimed at modifying blood flow may hold potential as causal therapies for chronic pain.

Ultrasound-guided fascia hydrorelease (US-FHR) has gained increasing attention, particularly in Japan, as a treatment modality for fascial pain (including myofascial pain) [10–12]. US-FHR involves injecting fluid to release “stacking” fascia, which appears on ultrasound as hyperechoic, strip-like lesions, similar to peeling apart thin layers of stacked paper. The term “release” refers to both the structural or morphological separation and the functional relaxation of the tissue [12]. Several studies have indicated that US-FHR is effective for a range of clinical conditions, including shoulder MPS [13], acute low back pain [14], and postoperative scar pain following arthroscopic knee surgery [15]. We previously reported that applying US-FHR to the coracohumeral ligament in patients with restricted shoulder range of motion resulted in a significant improvement in external rotation. Improvements in range of motion and pain were also observed in other directions [16]. Neck MPS frequently originates from myofascial structures such as the upper trapezius, levator scapulae, supraspinatus muscle, and rhomboid muscles, and US-FHR is typically applied to the fascia surrounding these muscles. Clinically, we have observed that US-FHR performed around arteries can enhance blood flow around the targeted artery and reduce pain within the corresponding vascular territories. However, the effects of periarterial US-FHR have not yet been formally investigated. We hypothesized that for pain originating from regions where stacking fascia is observed around the supplying arteries, the application of US-FHR to these perivascular areas would improve arterial blood flow and alleviate pain symptoms. We aimed to examine whether applying US-FHR to the transverse cervical or dorsal scapular artery—which supplies neck tissues, including the trapezius and supraspinatus muscles—can improve pain symptoms in patients with neck MPS.

Methods

This single-arm interventional trial is reported in accordance with the CONSORT 2025 statement, adapted for a single-arm non-randomized design (S1 CONSORT Checklist). Given its single-arm design and limited sample size, the study was conducted as an exploratory feasibility study intended to generate preliminary estimates and hypotheses for future controlled trials, rather than as a definitive efficacy trial.

Patient selection

We conducted a prospective, single-arm interventional study to assess the effectiveness of US-FHR in adult patients (aged >20 years) who presented with neck pain to the outpatient departments of Kimura Pain Clinic or Isesaki Municipal Hospital between May 1, 2024, and February 28, 2025.

The inclusion criteria were as follows: patients clinically diagnosed with MPS corresponding to chronic primary musculoskeletal pain (MG30.02 according to the International Classification of Diseases, 11th Revision criteria) for nonspecific chronic neck pain, a movement-related pain visual analog scale (VAS) score of ≥30 mm, and willingness to undergo FHR treatment. Patients were excluded if they: had been diagnosed with conditions that may cause secondary chronic neck pain, such as a history of head or neck trauma, neurological disorders, inflammatory diseases, or tumors; received an additional prescription for analgesics from 1 week before to 1 week after the FHR procedure; could not safely discontinue anticoagulant or antithrombotic therapy, had a bleeding tendency, or showed signs of infection at the planned FHR site; had difficulty in evaluating blood flow in the transverse cervical or dorsal scapular artery using ultrasound; and planned to undergo FHR at other anatomical sites during the study period. MPS was diagnosed clinically by pain physicians experienced in musculoskeletal ultrasound. The diagnosis required a palpable taut band or hardened area within the affected muscle, a localized tender spot that reproduced the patient’s familiar neck pain on palpation, and the absence of findings indicating an alternative cause, consistent with the criteria of Travell and Simons [17] and the fascial pain syndrome (FPS) framework [12]. Cervical radiculopathy, myelopathy, and other neurological disorders that may cause neck or arm symptoms were excluded by neurological examination, including assessment of motor power, sensation, and deep tendon reflexes; patients with positive findings were not enrolled. On ultrasound, stacking fascia was identified in accordance with the FPS classification criteria, as a high-echoic, strip-shaped lesion corresponding to high-density, adhesive, or cohesive fascia [12]. All diagnoses were made by experienced pain physicians, and a formal inter-rater reliability assessment of the clinical and ultrasonographic diagnosis was not performed. In each enrolled patient, US-FHR targeted the stacking fascia located in the interval between the trapezius and supraspinatus muscles, around the artery identified at this site; on tracing this vessel proximally under ultrasound, it corresponded to the transverse cervical or dorsal scapular artery. This perivascular stacking fascia was identified on ultrasound at the time of the procedure, and patients were not pre-screened to select a subgroup with this finding. The artery at this site was presumed to contribute to the perfusion of the symptomatic neck region, although this correspondence was not formally verified.

Fig 1 shows the flowchart of patient selection.

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Fig 1. Flow of participants through the trial.

CONSORT 2025-style flow diagram for this single-arm interventional trial. Patient 3 was excluded from the blood flow analysis owing to incomplete measurements at the post-procedure and 1-week time points but was retained for the pain VAS and PDI-5-J analyses. Abbreviations: PDI-5-J, 5-item Japanese version of the Pain Disability Index; US-FHR, ultrasound-guided fascia hydrorelease; VAS, visual analog scale.

https://doi.org/10.1371/journal.pone.0350882.g001

Intervention

Patients underwent US-FHR around the target artery during their first visit at Kimura Pain Clinic. Fig 2 illustrates the US-FHR procedure. Patients were positioned in the lateral decubitus position with the treatment site facing upward and the arm placed alongside the torso. US-FHR was performed using a Canon Aplio i700 ultrasound system (authentication number: 228ABBZX00022000) with an i18LX5 probe (frequency range: 4–18.3 MHz; authentication number: 228ABBZX00025000). The probe was placed medial to the acromion to visualize the trapezius and supraspinatus muscles, enabling identification of the artery located between them (Fig 2a, b). The arteries supplying the cervical tissues exhibit considerable anatomical variation; at this site, either the transverse cervical or dorsal scapular artery can be visualized. The artery closest to the pain source and most easily visualized was selected as the target for intervention. US-FHR was then performed at the stacking fascia surrounding the artery. A 27-gauge, 38-mm needle and a 10-mL syringe were used for the injection. Using the out-of-plane technique, the needle tip was visualized around the artery, and 2 mL of normal saline was injected into the stacking fascia around the artery (Fig 2c). Fig 3 illustrates the measurement of blood flow in the transverse cervical or dorsal scapular artery. After identifying the transverse cervical or dorsal scapular artery that supplies the cervical tissues, arterial blood flow was assessed before US-FHR (Fig 3a-1, 3a-2). The artery diameter and blood flow were reassessed at the same location 2 min after performing US-FHR (Fig 3b-1, Fig 3b-2). A video recording of each procedure was made (examples are provided in the S1 Video). Patients who were taking analgesics on a regular schedule were instructed to continue their usual medication regimen without interruption or dose modification.

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Fig 2. Probe position and visualization of the trapezius and supraspinatus muscles and the artery located between them.

(a) Probe and needle positions during US-FHR around the transverse cervical or dorsal scapular artery, demonstrated using one of the authors (T.H.) as a model. The model was positioned laterally, with the demonstration site facing upward and the arm positioned alongside the torso; the ultrasound probe was placed medial to the acromion. Written informed consent for publication of this image was obtained from the model (T.H., who is also an author of this manuscript). (b) Visualization of the trapezius and supraspinatus muscles and the artery located between them. The transverse cervical or dorsal scapular artery was visualized with the probe placed at the position shown in (a). A, trapezius; B, supraspinatus muscle; arrowheads, transverse cervical artery; asterisk: stacking fascia around the artery. (c) Ultrasound image of US-FHR around the transverse cervical artery. Normal saline (2 mL) was injected around the fascia of the transverse cervical artery, with continuous visualization of the needle tip (dagger) to maintain its position on the fascia around the transverse cervical or dorsal scapular artery throughout the injection. Post-injection, the fascia around the transverse cervical or dorsal scapular artery becomes irregularly edematous after the US-FHR, and this irregularity gradually resolves over a variable period depending on the participant. A, trapezius; B, supraspinatus muscle; arrowhead, transverse cervical artery, asterisk: release of stacking fascia around the artery, confirmed by the accumulation of injectate and the appearance of the characteristic “mille-feuille sign,” indicating separation of fascial layers. Note: In this case, blood flow measurement was performed on the transverse cervical artery. The fascia around the transverse cervical artery was released into a group of thin, strip-shaped lines (the full procedure is available in the S1 Video). Abbreviations: US-FHR, ultrasound-guided fascia hydrorelease.

https://doi.org/10.1371/journal.pone.0350882.g002

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Fig 3. Measurement of the blood flow of the transverse cervical or dorsal scapular artery.

In the presented case, blood flow was measured in the transverse cervical artery. (a-1) Identification of arterial blood flow using SMI mode and assessment of blood flow using PW mode before US-FHR. (a-2) Measurement of vessel diameter and calculation of arterial blood flow volume before US-FHR. The blood flow before US-FHR was measured at 14.94 mL/min (first row of the table in the upper left). (b-1) Identification of arterial blood flow using SMI mode and measurement of blood flow using PW mode 2 min after US-FHR. Deformation of the vessel may occur as a result of US-FHR; however, the vessel shape typically returns to normal within approximately 2 min; therefore, blood flow measurements were performed at that time. Because injecting normal saline into the fascia around the artery can cause the vessel to appear deeper and may slightly alter the probe position during the procedure, fine adjustments to the probe’s position and angle were required to ensure that measurements are obtained at the same site as before US-FHR. (b-2) Measurement of vessel diameter and calculation of arterial blood flow volume 2 min after US-FHR. The blood flow at 2 min after US-FHR was 21.828 mL/min (The entire procedure can be viewed in the S1 Video). Abbreviations: PW, Pulsed Wave; SMI, Superb Micro-vascular Imaging; US-FHR, ultrasound-guided fascia hydrorelease.

https://doi.org/10.1371/journal.pone.0350882.g003

Results

Table 1 summarizes the baseline characteristics of the patients. The median duration of neck pain was 10.0 years (IQR, 3.0–25.0), indicating that many participants had a long history of symptoms. Only 3 of the 13 patients were using analgesics (e.g., acetaminophen or NSAIDs). All 13 participants received the allocated US-FHR intervention as planned, with no protocol deviations. Adherence to post-procedure assessment time points was 100%.

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Table 1. Baseline patient characteristics.

https://doi.org/10.1371/journal.pone.0350882.t001

The primary outcome of this study was neck pain, assessed using the VAS during movement, measured 15 min after US-FHR, and compared with baseline. The median pain VAS during movement decreased from 49.0 mm (IQR, 44.5–64.0) before US-FHR to 22.0 mm (IQR, 14.5–31.5) 15 min after US-FHR, with a Hodges-Lehmann median difference of 30.5 mm (95% CI, 24.5 to 36.5; P < 0.001 vs. baseline). All 13 patients showed a reduction in the movement-related pain VAS at 15 min relative to baseline (individual reductions ranging from 14 to 43 mm). This improvement persisted at 22.0 mm (IQR, 14.0–34.0) 1 week later (Hodges-Lehmann median difference, 28.5 mm; 95% CI, 18.5 to 37.0; P < 0.001 vs. baseline; Fig 4a). The median pain VAS at rest also improved from 21.0 mm (IQR, 13.0–43.5) before US-FHR to 8.0 mm (IQR, 1.5–14.0) 15 min after US-FHR (Hodges-Lehmann median difference, 14.5 mm; 95% CI, 9.0 to 24.0; P = 0.001 vs. baseline). This improvement was maintained at 8.0 mm (IQR, 3.5–20.5) 1 week later (Hodges-Lehmann median difference, 13.5 mm; 95% CI, 6.0 to 21.0; P = 0.007 vs. baseline; Fig 4b).

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Fig 4. Median (interquartile range) and dot plots of pain VAS scores during neck movement (a) and at rest (b).

Abbreviations: US-FHR, ultrasound-guided fascia hydrorelease; VAS, visual analog scale.

https://doi.org/10.1371/journal.pone.0350882.g004

Arterial blood flow analysis was conducted in 12 patients, as measurements for Patient 3 were incomplete immediately after and 1 week following US-FHR. The median blood flow volume of the US-FHR-target artery increased from 11.2 mL/min (IQR, 4.5–14.4) before US-FHR to 17.2 mL/min (IQR, 6.1–23.7) immediately after US-FHR (Hodges-Lehmann median difference, + 4.1 mL/min; 95% CI, + 2.5 to +8.9; P = 0.001 vs. baseline). However, 1 week later, the median blood flow volume was 15.8 mL/min (IQR, 9.4–25.2), which was not significantly different from baseline (Hodges-Lehmann median difference, + 4.5 mL/min; 95% CI, −0.3 to +11.1; P = 0.128 vs. baseline; Fig 5a). Functional outcomes also improved. The PDI-5-J decreased from 17.0 (IQR, 10.5–23.0) before US-FHR to 13.0 (IQR, 4.0–17.5) 1 week after US-FHR (Hodges-Lehmann median difference, 5; 95% CI, 2–8; P = 0.004 vs. baseline; Fig 5b). Surface temperature data were acquired using a thermographic camera before, immediately after, and one week after US-FHR. However, reliable measurements could not be obtained because the painful region was difficult to localize on the thermographic images, and consistent thermal conditions could not be maintained before and after the procedure. Consequently, analysis of these data was not feasible.

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Fig 5. Median (interquartile range) and dot plots of blood flow volume of the US-FHR-target artery (a) and PDI-5-J (b).

Abbreviations: PDI-5-J, 5-item Japanese version of the Pain Disability Index; US-FHR, ultrasound-guided fascia hydrorelease.

https://doi.org/10.1371/journal.pone.0350882.g005

Regarding complications, one patient (Patient 11) experienced transient arterial bleeding following US-FHR, which was promptly controlled with compression. Hemostasis was achieved immediately, and blood flow measurements were successfully obtained without any issues. At the second visit, repeat blood flow assessment showed normal results, and both physical and ultrasound findings were unremarkable.

Discussion

US-FHR performed around the transverse cervical or dorsal scapular artery reduced both resting and movement-related neck pain, as measured by the VAS. The analgesic effect persisted for up to 1 week. US-FHR around the target artery also increased arterial blood flow immediately after the procedure and improved ADL performance 1 week later. Although further investigation is needed, these findings suggest a potential link between improved blood flow induced by FHR and pain reduction.

This study is the first to demonstrate that US-FHR performed around a target artery can simultaneously increase blood flow and alleviate pain symptoms associated with MPS in the affected region. Previous studies have shown that US-FHR can effectively treat various conditions, including MPS; however, those interventions primarily targeted the fascia, which is considered the primary source of pain [13,16]. In contrast, this study uniquely focused on the perivascular area supplying tissues suspected of generating MPS-related pain, representing a novel therapeutic target and approach.

Fascia actively contributes to chronic pain through mechanical, inflammatory, neurogenic, and circulatory pathways. Fibrotic and inflammatory changes alter viscoelasticity, sensitize nociceptors [20], and impair fascial mobility [21], whereas dense innervation sustains nociceptive signaling [22]. Furthermore, disturbances in extracellular hydration and local ischemia exacerbate hypoxia and increase pain sensitivity [23]. Although the detailed mechanisms underlying pain relief remain unclear, US-FHR is thought to ameliorate these pathophysiological changes by releasing abnormally “stacking” fascia.

The mechanism underlying the improvement in MPS symptoms observed in this study is likely distinct from those described above. Although a direct causal link between enhanced perfusion and pain reduction has not been confirmed, ischemia of muscular and fascial tissues may play a critical role [9]. Multiple mechanisms likely underlie the effects of US-FHR observed in this study, with the primary mechanism being the simple release of mechanical compression around the artery. Additionally, mechanical and chemical stimulation of the artery wall caused by the injection procedure, as well as enhanced arterial pulsation through smooth muscle stimulation, may have contributed to the observed hemodynamic changes. Furthermore, because the fascia contains a rich microvascular network [24,25], modulation of the vasa vasorum and compression of abnormal vessels due to increased perfusion pressure may contribute to pain relief. Okuno et al. identified abnormal neovascularization in patients with neck and shoulder pain, and reducing such abnormal blood flow—such as through vascular embolization—has been shown to relieve pain [26]. Future studies should clarify the hemodynamic changes induced by US-FHR using detailed vascular imaging.

Although the enhancement in blood flow was observed only immediately after US-FHR, the pain reduction effect persisted for up to 1 week. Furthermore, improvements in ADL performance were observed 1 week after the procedure. This mechanism may be explained by the hypothesis that MPS represents a type of ischemic pain, as well as by the possibility that US-FHR performed around the target artery reduces blood flow in abnormal vessels. Because the increase in blood flow was transient whereas the analgesia persisted, any causal interpretation remains speculative, and mechanisms other than perfusion may also contribute [27].

In this study, one case of bleeding requiring compression hemostasis was observed; however, hemostasis was easily achieved, and subsequent blood flow assessments were successfully performed. In all other cases, US-FHR was performed safely without complications. The procedure is effective when injecting agents, such as saline, via a fine needle. US-FHR offers significant advantages, including the absence of radiation exposure and a very low risk of adverse effects or allergic reactions from accidental intravascular injections of agents, making it a particularly safe therapeutic option.

This study had several limitations. First, the single-arm design without a control group may have increased the risk of bias and limited the ability to directly attribute the observed effects to the intervention. The results of this study cannot exclude the possibility that symptom improvement was due to placebo effects or natural progression. As a small, single-arm feasibility study, it was not designed to provide definitive efficacy estimates; the within-study reduction of the target sample size and the resulting small sample may have led to an overestimation of the true effect size (the so-called winner’s curse), so the magnitude of the reported estimates should be interpreted with caution. The cohort was also clinically heterogeneous, with a wide range of symptom duration, which further limits the precision and generalizability of the findings. Because the sample was too small for subgroup analysis, the possibility of heterogeneity in the treatment effect across patients could not be examined. Nevertheless, improvement in the primary outcome (movement-related VAS at 15 min) was observed consistently in all 13 patients. Moreover, the observed improvement cannot be attributed specifically to perivascular hydrorelease, because the injected saline may have spread to the surrounding fascial planes and the mechanical effect of needle insertion may also have contributed. In addition, the clinical diagnosis of MPS and the ultrasonographic identification of stacking fascia were made by experienced pain physicians but were not subjected to a formal inter-rater reliability assessment. To minimize confounding by analgesics, participants were instructed not to change their analgesic medication regimen during the study period. Additionally, outcome assessors were different from the US-FHR practitioners, and the anonymity of participants’ responses was emphasized to reduce response and desirability biases. The PDI-5-J questionnaire was administered as an anonymous, self-reported survey to further mitigate such biases. Conducting randomized controlled trials is challenging because the US-FHR procedure involves saline injection, and participants inevitably become aware of receiving the injection, thereby complicating effective blinding and randomization. Based on the findings of this study, future randomized controlled trials may be designed using control groups that undergo sham procedures or injections at alternative sites. Additionally, when US-FHR was performed on the target artery located between the trapezius and supraspinatus muscles, the intervention affected not only the area around the artery but also the fascia between these muscles. This indicates that, in addition to the effects of improved blood flow, traditional therapeutic mechanisms previously described for FHR may have also contributed to the observed outcomes, making it difficult to isolate the contribution of each mechanism. We demonstrated improvements in both pain and ADL 1 week after US-FHR treatment. However, the long-term effects of US-FHR on pain and ADL could not be evaluated within the scope of this study and remain to be clarified in future research. Although surface temperature measurements were initially planned and data were collected, the variability of the measurements was large, making reproducible evaluation and analysis difficult. This represents one of the limitations of the present study, and future research should aim to establish a more reliable and stable method for temperature assessment.

In conclusion, this single-arm feasibility study suggested that performing US-FHR around the target artery for cervical MPS was associated with an increase in arterial blood flow and with reduced neck pain 1 week after the procedure. Given the absence of a control group, these preliminary findings should be regarded as hypothesis-generating and warrant confirmation in controlled trials. US-FHR was found to be a safe and straightforward technique. By considering vascular supply and angiosome concepts in treatment planning, this approach may, pending confirmation in controlled studies, be applicable to other anatomical regions.

Supporting information

Acknowledgments

We thank Keiko Otani (nurse) for assisting with the US-FHR procedure, Masahiro Tajima (physical therapist) for measuring VAS scores and collecting patient profile data, and Erika Hirakawa (clinical laboratory technician) for operating the ultrasound machine. We also acknowledge Editage (www.editage.com) for English language editing.