Ultrasound-guided transverse myofascial acupotomy for the tibialis posterior muscle in type II painful accessory navicular: a retrospective cohort study with 1-year follow-up

Abstract

Background

Type II painful accessory navicular (PAN II) commonly causes medial foot pain and functional limitation, and symptoms may persist when conservative care fails to reduce posterior tibial tendon traction on the accessory navicular synchondrosis. This study evaluated whether Ultrasound-Guided Transverse Myofascial Acupotomy for Tibialis Posterior (UG-MA-TP) is associated with better 1-year clinical and biomechanical outcomes than conventional conservative therapy.

Methods

This retrospective cohort study included 70 patients with PAN II treated between February 2022 and May 2024 at a single tertiary center. Patients were stratified according to treatment modality into the UG-MA-TP group (n=35) and the conventional therapy group (n=35). Outcomes included the 12-month clinical response rate and magnetic resonance imaging (MRI)-defined bone marrow edema resolution, serial Visual Analog Scale (VAS) pain scores and tibialis posterior/medial gastrocnemius muscle tone, American Orthopaedic Foot & Ankle Society (AOFAS) midfoot scores, surface electromyography-derived normalized root mean square relative values (nRMS-RV), Meary’s angle, and adverse events.

Results

The UG-MA-TP group showed significant improvements in VAS and AOFAS scores and a sustained reduction in tibialis posterior muscle tone after intervention (all P<0.05). In contrast, the control group showed transient improvement only at 1 month, followed by a return toward baseline. At 12 months, the UG-MA-TP group had a higher clinical response rate, lower VAS score, higher AOFAS score, higher MRI-defined bone marrow edema resolution rate (82.86% vs. 25.71%), and lower tibialis posterior muscle tone than the control group (all P<0.05). Medial gastrocnemius muscle tone and Meary’s angle remained stable in both groups (P>0.05). Tibialis anterior nRMS-RV was lower, whereas lateral gastrocnemius nRMS-RV was higher, in the UG-MA-TP group than in both the control group and baseline values (all P<0.05).

Conclusions

For PAN II, UG-MA-TP was associated with favorable mid-term (1-year) clinical and biomechanical outcomes compared with conventional therapy. It was associated with greater pain reduction, functional improvement, and tibialis posterior muscle tone regulation, with no recorded serious adverse events in this retrospective cohort. This treatment may be associated with favorable neuromuscular adaptations and may represent a minimally invasive option for selected patients with PAN II.

Introduction

The accessory navicular bone, an anatomical variant of the foot present in approximately 4–21% of the population, is frequently implicated in the etiology of medial foot pain and posterior tibial tendon (PTT) dysfunction (1). According to the Geist classification, the type II painful accessory navicular (PAN II) is frequently symptomatic and represents a significant clinical challenge (2). The pathogenesis is primarily driven by repetitive shear stress at the fibrocartilaginous junction, which under excessive loading induces chronic micro-trauma, leading to localized bone marrow edema and tendinopathic changes at the PTT insertion (3). This pathological cascade results in dynamic arch instability, medial foot pain, and progressive flatfoot deformity (pes planus). These symptoms significantly impair physical mobility and quality of life, particularly among adolescents and active athletes, representing a substantial burden of musculoskeletal disability in this demographic (4).

Current therapeutic management for PAN II remains a subject of debate, generally bifurcating into conservative and surgical strategies. Conservative modalities, including activity modification, custom orthoses, immobilization, physical therapy, and nonsteroidal anti-inflammatory drugs (NSAIDs) (5), serve as the first-line treatment. While these approaches may offer temporary symptomatic relief by reducing acute inflammation, they often fail to address the underlying biomechanical pathology. Consequently, recurrence rates remain high, primarily due to persistent mechanical tension exerted by the PTT on the compromised synchondrosis (6). Conversely, surgical interventions—such as the Kidner procedure (excision of the accessory ossicle with PTT readvancement), simple excision, or arthrodesis of the accessory navicular to the navicular body (2,7,8)—are reserved for refractory cases. However, surgery is not without significant drawbacks. Operative risks include wound complications, nerve entrapment, scar adhesion, postoperative tendon laxity, and a prolonged rehabilitation period of 6 to 12 months. This extended recovery timeline may be unacceptable for adolescent athletes who require a rapid return to sport (6). Thus, there remains a clinical need for minimally invasive options between conservative care and open surgical reconstruction.

In recent years, acupotomy—a specialized form of needle-knife therapy rooted in traditional Chinese medicine but modernized through anatomical guidance—has emerged as a promising minimally invasive technique for soft tissue disorders (9). Acupotomy can be regarded as a minimally invasive percutaneous release tool capable of dissecting adhesions and releasing high-tension fascial points without large incisions, and it has been increasingly reported in China for dividing fibrotic adhesions with limited soft-tissue trauma (9-11). However, traditional acupotomy approaches for PAN II have predominantly focused on longitudinal release directly at the tendon insertion site. Although this approach is theoretically intended to reduce tension, our clinical observations suggest that direct trauma to the already inflamed fibrocartilaginous junction may exacerbate postoperative pain and inflammation due to the region’s high sensitivity. Furthermore, this approach remains constrained by a localized perspective, neglecting the broader myofascial kinetics.

To overcome these limitations, we propose a shift from distal insertion release to proximal myofascial tension modulation. This study introduces a novel Ultrasound-Guided Transverse Myofascial Acupotomy for Tibialis Posterior (UG-MA-TP). This technique integrates the precision of high-frequency ultrasonography—which is recognized as a key tool for precise, minimally invasive guidance in myofascial interventions (10)—with myofascial biomechanics. Rather than incising the distal tendon insertion, we target the myofascial interface of the posterior tibial muscle belly proximally. We hypothesize that performing a transverse release of the deep fascia may lower the resting muscle tone and reduce the tensile load transmitted distally to the accessory navicular synchondrosis. This hypothesis is consistent with evidence that ultrasound-guided fascial interventions can relax muscle tension and alleviate pain (12). This proximal intervention aims to alleviate the mechanical driver of the disease while avoiding direct irritation of the painful distal pathology.

Despite the potential of this technique, systematic evidence regarding its mid-term efficacy and safety is lacking. Evidence regarding proximal ultrasound-guided myofascial acupotomy for PAN II remains limited. Our primary objective was to compare the 1-year clinical and functional outcomes of UG-MA-TP versus conventional therapy. Additionally, we utilized objective biomechanical markers, including muscle tone quantification (MyotonPRO) and surface electromyography (sEMG), to explore the potential neuromuscular mechanisms underlying this treatment. We present this article in accordance with the STROBE reporting checklist (13) (available at https://qims.amegroups.com/article/view/10.21037/qims-2026-0578/rc).

Methods

Study design and ethical considerations

The primary research question of this study was whether an ultrasound-guided proximal myofascial release of the tibialis posterior muscle is associated with superior and more sustained clinical and biomechanical improvements compared to conventional conservative therapy in patients with PAN II. This study was designed as a single-center, retrospective cohort study. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of The Bethune International Peace Hospital (No. 2026-KY-18). As this was a retrospective study, the requirement for study-specific informed consent was waived by the ethics committee.

Participants and grouping

This was a non-randomized, retrospective cohort study. Group allocation was dictated primarily by patient preference and clinical shared decision-making. Specifically, patients who firmly refused surgical intervention but were willing to undergo the ultrasound-guided minimally invasive procedure were allocated to the UG-MA-TP group, whereas those who opted strictly for non-invasive standard care formed the control group. To account for potential selection bias, baseline characteristics were compared between groups, and a propensity score matching (PSM) sensitivity analysis was conducted.

Inclusion and exclusion criteria

Inclusion criteria

Patients were eligible for enrollment if they met all the following criteria:

1. Clinical presentation of localized pain over the medial arch, with or without palpable tenderness or soft tissue edema;

2. Diagnosis of PTT dysfunction confirmed by high-frequency musculoskeletal ultrasound (14);

3. Radiographic confirmation of type II accessory navicular according to the Geist classification (15,16);

4. Magnetic resonance imaging (MRI) evidence of bone marrow edema at the synchondrosis on T2-weighted fat-saturated sequences, indicating active inflammation (17);

5. Documented refusal of surgical intervention despite chronic symptoms and a preference for conservative or minimally invasive management.

Exclusion criteria

Patients were excluded if they presented with:

1. Other types of accessory navicular (type I or type III);

2. Concomitant neurological or neuromuscular disorders (e.g., stroke, cerebral palsy, muscular dystrophy);

3. Fixed contracture of the gastrocnemius or Achilles tendon (positive Silfverskiöld test);

4. Active concurrent foot pathologies, such as fractures, acute infections, or tumors;

5. Severe systemic diseases [e.g., New York Heart Association (NYHA) Class III/IV heart failure, severe renal/hepatic insufficiency];

6. Psychiatric conditions or cognitive impairments affecting compliance;

7. Known contraindications or allergies to NSAIDs (for the control group).

Withdrawal criteria and safety analysis

For the efficacy analysis, a per-protocol complete-case analysis approach was adopted. This population was defined as enrolled patients who completed at least 80% of the scheduled protocol assessments, including Visual Analog Scale (VAS) scoring, American Orthopaedic Foot & Ankle Society (AOFAS) evaluation, muscle tone measurement, and sEMG detection. Specifically, missing key follow-up data was defined as failing to attend the 6-month or 12-month final evaluation, and incomplete baseline records meant missing initial MRI or functional scores. Subjects meeting any of the following conditions were withdrawn from the efficacy analysis but retained for safety analysis: (I) occurrence of grade ≥3 adverse events according to CTCAE v5.0 requiring hospitalization; (II) development of new comorbidities affecting foot function (e.g., traumatic re-injury); (III) protocol deviations exceeding 20% of assessments; (IV) patient-initiated withdrawal of consent. In this cohort, all 70 included patients completed the requisite follow-up assessments, resulting in a 100% completion rate for the efficacy analysis set.

Interventional procedures

All interventional procedures were performed by a senior orthopedic surgeon and a senior musculoskeletal ultrasonographer, both possessing over five years of specialized experience in ultrasound-guided interventions.

UG-MA-TP group protocol

Patients were positioned prone with the affected lower leg fully exposed and the ankle in a neutral position. Anatomical landmarks were identified, and three needle entry points were marked along the longitudinal midline of the posterior calf, targeting the proximal, middle, and distal thirds of the tibialis posterior muscle belly. The optimal entry points were predetermined by systematically scanning the posterior calf. The surgeon identified the maximal muscle belly cross-sections at the proximal, middle, and distal thirds of the tibialis posterior, specifically targeting high-tension myofascial zones with localized hyperechogenicity. Following standard sterile skin preparation and draping, a type I size 4 disposable acupotomy needle (Huacheng^®, diameter 1.0 mm × length 65 mm, with a flat distal blade) was utilized.

Under real-time ultrasound guidance (Mindray Resona R9, 6–11 MHz linear probe, 65 dB gain), the needle was inserted rapidly through the skin with the blade oriented parallel to the superficial gastrocnemius fibers to minimize injury. Upon reaching the dorsal aspect of the deep tibialis posterior myofascia, the needle was rotated 90 degrees to orient the blade perpendicular to the muscle fibers. Three controlled transverse release incisions (approximately 2 mm in depth) were performed specifically within the myofascial layer to release tension. The procedural details are illustrated in Figure 1A-1D. After needle withdrawal, manual compression was applied for 5 minutes to ensure hemostasis, followed by a sterile dressing. Patients were instructed to perform gentle functional exercises but avoid strenuous impact activities. The treatment regimen consisted of three sessions, performed at weekly intervals.

Figure 1.

Procedural details of the UG-MA-TP. (A) Patient positioning and surface marking: the patient is prone, and entry points are marked along the longitudinal midline of the posterior calf. (B) The specific acupotomy needle used (type I, size 4, 1.0 mm × 65 mm) featuring a flat distal blade. (C) Intraoperative photograph showing percutaneous insertion of the acupotomy needle at the marked target site (white arrow). (D) Intraoperative ultrasound image showing the hyperechoic needle track (arrowhead) targeting the deep fascia of the tibialis posterior muscle, sparing the neurovascular bundle. UG-MA-TP, Ultrasound-Guided Transverse Myofascial Acupotomy for Tibialis Posterior.

Conventional therapy group protocol

Patients in the control group underwent a structured non-operative protocol consisting of an intensive 3-week clinical phase followed by a 1-year home-based maintenance phase: (I) Activity modification: avoidance of high-intensity exercise (>3 metabolic equivalents) and use of loose-fitting, supportive footwear. (II) Physical therapy: local infrared radiation therapy (30 minutes/session, 3 times daily) to promote circulation. This clinical phase was administered in the outpatient rehabilitation clinic three times per week under physical therapist supervision. (III) Functional exercise: comprehensive functional exercises, including toe-grasping towel exercises, calf stretches, and TheraBand-resisted foot inversion to strengthen the intrinsic foot and posterior tibial muscles (10 repetitions/set, 3 sets daily). (IV) Pharmacotherapy: oral administration of celecoxib, with the dosage strictly modulated according to the patient’s body weight and gastrointestinal tolerance (e.g., 100–200 mg daily), primarily during acute flares. Compliance with the home-based program was monitored via a standardized patient daily logbook, which was reviewed during subsequent follow-up phone calls or clinic visits.

Outcome measures

Clinical response assessment

At the 12-month endpoint, two prespecified composite clinical outcomes were defined. Complete symptom resolution was defined as VAS ≤1 and AOFAS ≥90. Clinical response was defined as either complete symptom resolution or improvement meeting both a ≥30% reduction in VAS from baseline and an AOFAS score ≥70. Patients who did not meet either criterion were classified as non-responders. The clinical response rate was calculated as: (complete symptom resolution + improvement) / total cases × 100% (18,19).

Clinical and radiographic assessments

Subjective pain intensity was evaluated using the VAS (0–10), a commonly used pain outcome in foot and ankle studies (20,21). Functional status was assessed with the AOFAS Midfoot Scale (0–100) (22). Both measures were recorded at baseline and at multiple follow-up intervals up to 12 months. Baseline activity levels were evaluated using the Tegner Activity Scale (23). Meary’s angle was measured on weight-bearing lateral radiographs to assess flatfoot deformity (24). Follow-up MRI scans were utilized to assess the resolution rate of bone marrow edema at the 12-month endpoint.

Biomechanical assessment (muscle tone & sEMG)

Objective muscle tone of the tibialis posterior and medial gastrocnemius was quantified using the MyotonPRO device, which measures damped frequency (Hz) and has been validated for assessing muscle mechanical properties (25). Muscle tone was quantified at six specific timepoints (baseline, 1 day, 1 month, 3 months, 6 months, and 12 months). Neuromuscular activation patterns were analyzed using sEMG, with signals processed to obtain the normalized root mean square (nRMS) value (26). sEMG assessments were performed solely before treatment and at the 12-month endpoint. The raw RMS values of the selected lower-leg muscles were normalized to the peak RMS of the peroneus longus during the stance phase. Because the peroneus longus served as the normalization reference, its nRMS-RV was 1.00 by definition and was not included in between-group statistical testing.

Data collection and blinding

To minimize detection bias, the musculoskeletal radiologist evaluating the MRI scans for bone marrow edema, as well as the technicians performing the MyotonPRO and sEMG assessments, were strictly blinded to the patients’ treatment group allocations.

Statistical analysis

Data analysis was performed using SPSS version 25.0 (IBM Corp., USA). No a priori sample-size calculation was performed because this retrospective study included all eligible complete cases available during the study period. Therefore, the precision of key estimates was evaluated using effect sizes and 95% confidence intervals where appropriate. Continuous data were tested for normality using the Shapiro-Wilk test and presented as mean ± standard deviation (SD). For continuous longitudinal data with repeated measurements over time (VAS, AOFAS, and MyotonPRO), a repeated-measures analysis of variance (RM-ANOVA) with Bonferroni-adjusted pairwise comparisons was utilized to adjust for multiple comparisons. For two-timepoint continuous outcomes, including sEMG-derived nRMS-RV and Meary’s angle, within-group changes were analyzed using paired t-tests or Wilcoxon signed-rank tests, and between-group comparisons at the 12-month endpoint were analyzed using independent-samples t-tests or Mann-Whitney U tests, depending on data distribution. Categorical variables were analyzed via Chi-square tests or Fisher’s exact tests when the expected frequency in any given cell was less than 5. To further address potential selection bias inherent in the non-randomized design, a propensity score was estimated using age, sex, symptom duration, affected side, baseline VAS, baseline AOFAS, Tegner Activity Scale, and Meary’s angle. A 1:1 nearest-neighbor matching without replacement was performed. Covariate balance before and after matching was assessed using standardized mean differences (SMDs), with an SMD <0.10 considered acceptable balance. The full cohort was used for the primary analysis, and the propensity-score-matched cohort was used as a sensitivity analysis. Statistical significance was defined as a two-sided P value <0.05.

Results

Patient selection and baseline homogeneity

Between February 2022 and May 2024, a total of 78 patients diagnosed with symptomatic PAN II were initially screened for eligibility at our institution. Following the exclusion of 8 patients (3 for missing the final 12-month evaluation, 2 for missing initial MRI/functional scores, and 3 for transitioning to surgical or alternative injection therapies), 70 complete-case patients were included in the final per-protocol analysis. Participants were categorized based on their selected treatment modality into the UG-MA-TP group (n=35) and the conventional therapy group (n=35). Baseline demographic and clinical characteristics, including age, gender distribution, duration of symptoms, affected side, baseline VAS, baseline AOFAS, Tegner Activity Scale, and Meary’s angle, were comparable between the two groups (P>0.05 for all comparisons), suggesting baseline comparability in the full cohort (Table 1). After PSM, 28 patients were retained in each group, and the matched analysis was directionally consistent with the full-cohort analysis for the 12-month clinical response, VAS, and AOFAS outcomes.

Table 1. Baseline demographic and clinical characteristics of the study population.

Characteristic	UG-MA-TP group (n=35)	Control group (n=35)	P value
Age (years)	22.75±2.23	23.25±1.12	0.240†
Sex (male/female)	33/2	30/5	0.428‡
Symptom duration (months)	9.24±8.43	10.24±9.43	0.641†
Affected side (left/right)	19/16	20/15	0.809‡
VAS score (0–10)	5.56±1.21	5.22±1.62	0.324†
AOFAS score (0–100)	72.12±4.13	70.34±5.67	0.145†
Tegner Activity Scale (0–10)	4.82±1.15	4.91±1.24	0.748†
Meary’s angle (degrees)	4.65±1.82	4.78±1.95	0.771†

Data are presented as mean ± standard deviation or number of patients (n). ^†, calculated using independent samples t-test. ^‡, calculated using Chi-square test or Fisher’s exact test, as appropriate. AOFAS, American Orthopaedic Foot & Ankle Society; UG-MA-TP, Ultrasound-Guided Transverse Myofascial Acupotomy for Tibialis Posterior; VAS, Visual Analog Scale.

Clinical response at 1 year

Table 2 summarizes the primary clinical outcomes at the 12-month endpoint. The clinical response rate at 12 months was higher in the UG-MA-TP group than in the control group [85.71% (30/35) vs. 34.28% (12/35); risk difference 51.43 percentage points, approximate 95% CI: 31.89 to 70.97 percentage points; P<0.001]. The proportion of patients achieving complete symptom resolution was 57.14% (20/35) in the UG-MA-TP group and 8.57% (3/35) in the control group. Non-response occurred in 14.28% (5/35) and 65.71% (23/35) of patients, respectively.

Table 2. Summary of clinical response and key 12-month outcomes.

Outcome measure	UG-MA-TP group (n=35)	Control group (n=35)	P value
Clinical response rate	30 (85.71)	12 (34.28)	<0.001‡*
Complete symptom resolution (VAS ≤1, AOFAS ≥90)	20 (57.14)	3 (8.57)	–
Improved (VAS reduction ≥30%, AOFAS ≥70)	10 (28.57)	9 (25.71)	–
Non-responder	5 (14.28)	23 (65.71)	–
Final VAS score	1.54±1.02	4.85±1.35	<0.001†*
Final AOFAS score	86.22±3.23	72.15±4.58	<0.001†*
Bone marrow edema resolution rate	29 (82.86)	9 (25.71)	<0.001‡*

Data are presented as n (%) or mean ± standard deviation. ^†, calculated using independent samples t-test or Mann-Whitney U test. ^‡, calculated using Chi-square test or Fisher’s exact test, as appropriate. *, statistically significant. AOFAS, American Orthopaedic Foot & Ankle Society; UG-MA-TP, Ultrasound-Guided Transverse Myofascial Acupotomy for Tibialis Posterior; VAS, Visual Analog Scale.

Pain scores (VAS)

The longitudinal trajectory of pain scores is visually depicted in Figure 2A (detailed data in Table S1). In the UG-MA-TP group, VAS scores decreased from 5.56±1.21 at baseline to 2.22±0.85 at 1 day and 1.54±1.02 at 12 months (P<0.05 for post-treatment comparisons with baseline). In the control group, VAS scores decreased at 1 month (3.58±1.03, P<0.05) but returned toward baseline at later follow-up time points. At 12 months, the mean VAS score was lower in the UG-MA-TP group than in the control group (1.54±1.02 vs. 4.85±1.35; mean difference −3.31, 95% CI: −3.88 to −2.74; P<0.001).

Figure 2.

Longitudinal clinical efficacy outcomes over the 1-year follow-up period. (A) Comparison of VAS pain scores between the UG-MA-TP group and the control group. (B) Comparison of AOFAS midfoot scores. VAS and AOFAS trajectories are shown for both groups across the 12-month follow-up. *, P<0.05 vs. control. AOFAS, American Orthopaedic Foot & Ankle Society; UG-MA-TP, Ultrasound-Guided Transverse Myofascial Acupotomy for Tibialis Posterior; VAS, Visual Analog Scale.

Functional outcomes (AOFAS scores)

Functional outcomes are shown in Figure 2B (detailed data in Table S2). In the UG-MA-TP group, AOFAS scores increased from 72.12±4.13 at baseline to 86.22±3.23 at 12 months (P<0.05 for post-treatment comparisons with baseline). The control group had a smaller increase at 1 month (74.23±4.77), which was not sustained at the 3-, 6-, or 12-month follow-ups. At 12 months, the mean AOFAS score was higher in the UG-MA-TP group than in the control group (86.22±3.23 vs. 72.15±4.58; mean difference 14.07, 95% CI: 12.18 to 15.96; P<0.001).

Changes in tibialis posterior and medial gastrocnemius muscle tone

Quantitative muscle tone assessment using MyotonPRO is shown in Figure 3 (detailed data in Table S3). In the UG-MA-TP group, tibialis posterior muscle tone (damped frequency) decreased from 24.18±0.85 Hz at baseline to 20.13±0.23 Hz at 1 day and 19.24±0.61 Hz at 12 months (P<0.05 for post-treatment comparisons with baseline). In contrast, the control group showed no significant change in tibialis posterior muscle tone across follow-up time points (P>0.05) (Figure 3A). Neither group exhibited significant changes in medial gastrocnemius muscle tone (P>0.05 at all time points), suggesting that measurable changes in resting muscle tone were mainly observed in the tibialis posterior rather than the medial gastrocnemius (Figure 3B). Post-matching covariate balance and matched-cohort outcome estimates are provided in Table S4.

Figure 3.

Changes in objective muscle tone (damped frequency, Hz) measured by MyotonPRO. (A) Changes in tibialis posterior muscle tone over the 12-month follow-up. (B) Changes in medial gastrocnemius muscle tone over the 12-month follow-up; no significant changes were observed in either group. *, P<0.05 vs. control.

Neuromuscular adaptation (sEMG analysis)

Table 3 details the neuromuscular adaptations observed at the 12-month follow-up. Within the UG-MA-TP group, tibialis anterior nRMS-RV decreased from 1.14±0.21 at baseline to 0.93±0.21 at 12 months, whereas lateral gastrocnemius nRMS-RV increased from 0.92±0.33 to 1.41±0.31. At 12 months, tibialis anterior nRMS-RV was lower in the UG-MA-TP group than in the control group (0.93±0.21 vs. 1.19±0.22; P<0.001), and lateral gastrocnemius nRMS-RV was higher in the UG-MA-TP group than in the control group (1.41±0.31 vs. 0.94±0.38; P<0.001). The peroneus longus served as the normalization reference and was not included in between-group statistical testing.

Table 3. Neuromuscular adaptations: nRMS-RV of selected lower-leg muscles during gait at 12 months.

Muscle group	Pre-treatment (baseline)			12-month follow-up		P value (between groups at 12 months)
	UG-MA-TP	Control		UG-MA-TP	Control
Tibialis anterior	1.14±0.21	1.21±0.34		0.93±0.21*	1.19±0.22	<0.001**
Medial gastrocnemius	1.24±0.24	1.26±0.26		1.24±0.25	1.26±0.24	0.582
Lateral gastrocnemius	0.92±0.33	0.94±0.36		1.41±0.31*	0.94±0.38	<0.001**

nRMS-RV values are presented as mean ± standard deviation. The raw RMS values of selected lower-leg muscles were normalized to the peak RMS of the peroneus longus during stance; therefore, the peroneus longus served as the reference muscle and was not statistically tested. *, statistically significant difference compared with baseline within the UG-MA-TP group (P<0.05). **, significant differences between the UG-MA-TP group and the control group at the 12-month time point. nRMS-RV, normalized root mean square relative values; UG-MA-TP, Ultrasound-Guided Transverse Myofascial Acupotomy for Tibialis Posterior.

Radiographic and accessory navicular conditions at 1 year

Radiographic assessment revealed that the baseline Meary’s angle remained stable without significant flatfoot progression in both groups over the 1-year period (P>0.05). At the 12-month follow-up, the MRI-defined bone marrow edema resolution rate was higher in the UG-MA-TP group than in the control group [82.86% (29/35) vs. 25.71% (9/35); risk difference 57.14 percentage points, approximate 95% CI: 38.02 to 76.26 percentage points; P<0.001] (Table 2, Figure 4). This between-group difference should be interpreted as an association because causality cannot be inferred from this retrospective cohort.

Figure 4.

Resolution rate of bone marrow edema on MRI at 12 months. The MRI-defined bone marrow edema resolution rate at 12 months was higher in the UG-MA-TP group than in the control group. *, statistically significant. MRI, magnetic resonance imaging; UG-MA-TP, Ultrasound-Guided Transverse Myofascial Acupotomy for Tibialis Posterior.

Safety outcomes

Safety data were limited to adverse events documented in the medical records. No grade ≥3 adverse events or treatment-related hospitalizations were recorded in either group during the 12-month follow-up. In the UG-MA-TP group, no procedure-related infections, neurovascular injuries, tendon rupture, or persistent sensory abnormalities were documented. Because of the retrospective design, minor transient adverse events may have been under-recorded.

Discussion

This study presents a systematic, mid-term evaluation of UG-MA-TP for the management of PAN II. Our 1-year follow-up data suggest that this intervention was associated with greater pain reduction, functional recovery, and favorable neuromuscular adaptations compared with conventional conservative therapy. These findings support further investigation of a proximal myofascial-targeted strategy as a potential treatment approach for PAN II.

Breaking the cycle of chronic tension: superiority over conventional care

Conservative management remains the standard first-line treatment for PAN II. However, its efficacy is often disappointing, particularly in active young adults. Previous studies, such as Jegal et al. (27), reported low success rates of only 6.9% in athletes and 34% in the general population. Our control group results are consistent with these findings: while rest and NSAIDs provided transient relief at 1 month (VAS reduction), symptoms returned toward baseline by 3 months, resulting in a final clinical response rate of 34.28%. This pattern is consistent with the possibility that passive anti-inflammatory measures may be insufficient for some patients with persistent mechanical symptoms (28).

In contrast, the UG-MA-TP group achieved an 85.71% clinical response rate at 1 year. The observed effect was maintained over 12 months, with no significant regression in VAS or AOFAS scores over follow-up. Unlike surgical fusion or excision, which require prolonged immobilization and carry risks of arch collapse and other complications (2,6,29), UG-MA-TP allows for immediate functional rehabilitation. This intermediate therapeutic option may help address the clinical need between conservative care and invasive surgery (29). The procedure’s minimally invasive nature may facilitate rapid recovery and return to function, as supported by outcomes from similar ultrasound-guided percutaneous interventions (30).

Mechanistic insight: the proximal tension modulation hypothesis

A key feature of this study is the shift from longitudinal release at the insertion to transverse release at the muscle belly. A plausible explanation may involve two complementary mechanisms:

1. Biomechanical decompression: The posterior tibial muscle is the primary dynamic stabilizer of the medial arch (31). In PAN II, chronic repetitive traction may contribute to tibialis posterior hypertonicity. Our MyotonPRO data showed that UG-MA-TP was associated with a reduction in resting tone (damped frequency) of the tibialis posterior from approximately 24 to 19 Hz after treatment, an effect observed through one year (32). By transversely releasing the stiffened deep fascia, the procedure may disrupt pathological myofascial load transmission (33), thereby reducing the tensile load transmitted distally to the vulnerable accessory navicular synchondrosis (34,35). This mechanism may partly account for the observed early pain reduction without direct intervention at the symptomatic accessory navicular region.

2. Neurophysiological desensitization: Chronic pain is maintained by both peripheral and central sensitization (36). High-tension myofascial points are rich in nociceptors and mechanoreceptors. We hypothesize that the micro-trauma induced by acupotomy may potentially trigger a local healing response, which could help downregulate inflammatory mediators and promote desensitization of muscle spindles (37-39). The observed normalization of sEMG patterns (decreased tibialis anterior hyperactivity, increased lateral gastrocnemius recruitment) may reflect reduced pain-related guarding and a more physiological gait pattern (40).

Safety and precision via ultrasound guidance

Traditional blind acupotomy carries risks of neurovascular injury (41). By utilizing high-frequency ultrasound, the operator visualized the neurovascular bundle and the specific myofascial planes in real time. This may have helped confine the release to the tibialis posterior fascial plane (depth approximately 2 mm), sparing the gastrocnemius and the tibial nerve. No serious adverse events were recorded in this cohort. The absence of measurable changes in medial gastrocnemius tone is compatible with a relatively localized effect, although further imaging-based validation is needed.

Limitations

Several limitations warrant consideration. First, the retrospective and non-randomized design inherently limits causal inference; future multi-center prospective randomized controlled trials are needed to verify our hypotheses. Although we attempted to mitigate selection bias through PSM analysis, allocation was driven by patient preference, which may introduce uncontrolled confounding. Second, no a priori sample-size calculation was performed; therefore, the precision of the estimates should be interpreted using the reported effect sizes and confidence intervals, and the findings require confirmation in adequately powered prospective studies. Third, while a 1-year follow-up provides valuable mid-term insights, long-term observation (e.g., 5 years) is needed to monitor for potential flatfoot progression, although our current data show no signs of arch collapse. Fourth, the disparity in provider contact time between the interventional group (weekly clinic procedures) and the control group (transition to home-based care) may have introduced an attention bias or placebo effect. Fifth, safety data were limited to adverse events documented in the medical records, and minor transient adverse events may have been under-recorded. Finally, sEMG and MyotonPRO assessments were limited to the myotendinous junction due to anatomical depth; future studies using shear-wave elastography could provide more comprehensive muscle stiffness mapping. These design features may limit generalizability to centers with similar ultrasound-guided musculoskeletal intervention expertise and to patients who prefer minimally invasive alternatives to surgery.

Conclusions

In summary, UG-MA-TP was associated with favorable 12-month clinical and biomechanical outcomes and no recorded serious adverse events in this retrospective cohort of patients with PAN II. It was associated with greater pain relief and functional recovery compared with conventional therapy, potentially by modulating pathological muscle tone and neuromuscular balance. This technique may represent a minimally invasive option for selected patients, especially those seeking to avoid open surgery and return to activity rapidly.

Supplementary

The article’s supplementary files as

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of The Bethune International Peace Hospital (No. 2026-KY-18). As this was a retrospective study, the requirement for study-specific informed consent was waived by the ethics committee.

Data Sharing Statement

Available at https://qims.amegroups.com/article/view/10.21037/qims-2026-0578/dss

qims-16-08-642-dss.pdf ^{(80.8KB, pdf)}

DOI: 10.21037/qims-2026-0578