Catheter‐Based Sacral Nerve Block Versus Pudendal Nerve Block in the Treatment of Pudendal Neuralgia: A Randomized Double‐Blinded Controlled Trial

ABSTRACT

Background

Pudendal neuralgia (PN) severely impacts quality of life, particularly sitting. Uncertainty exists whether catheter‐based sacral nerve block with daily intermittent bolus (SNB) or pudendal nerve block (PNB) is more effective. This trial compared their efficacy over 6 months.

Methods

A prospective, randomized, double‐blinded trial in China enrolled 90 PN patients. Patients were randomized to CT‐guided catheter‐based PNB near the pudendal nerve or SNB through the third posterior sacral foramen. In both groups, the catheter remained in place for 7 days, and 10 mL of 0.2% ropivacaine was administered once daily as an intermittent bolus, with compound betamethasone administered on Day 7. Primary outcome was pain intensity (VAS) over 6 months; secondary outcomes included patient‐reported global outcomes and maximum sitting time at 6 months.

Results

The SNB group had significantly lower VAS scores at 1 month (2.98 ± 1.47 vs. 3.72 ± 1.08, p = 0.04), 3 months (3.36 ± 1.14 vs. 4.17 ± 1.19, p = 0.02), and 6 months (3.85 ± 1.04 vs. 4.95 ± 1.08, p < 0.0001). Significantly more SNB patients reported excellent/good outcomes at 1 month (83.88% vs. 63.40%, p = 0.04) and 6 months (75.61% vs. 37.50%, p = 0.002). Maximum sitting time at 6 months was longer with SNB (68.56 ± 21.61 vs. 37.65 ± 16.25 min, p < 0.0001). No severe complications occurred.

Conclusions

SNB provided superior and sustained pain relief, functional improvement, and patient satisfaction compared to PNB over 6 months in PN patients. Broader sacral root (S2‐4) coverage by SNB may enhance efficacy by targeting pudendal neuropathy and central sensitization. SNB may be considered as an intermediate minimally invasive option for selected refractory PN patients in experienced centers, pending larger safety and feasibility studies.

Significance Statement

This first RCT directly comparing catheter‐based nerve blocks for pudendal neuralgia demonstrates that sacral nerve block (SNB targeting S2‐4) provides significantly superior and sustained pain relief, functional gains (doubled sitting tolerance), and patient satisfaction over pudendal nerve block (PNB) at 6 months. Its broader root coverage likely addresses central sensitization alongside neuropathy. Catheter‐based sacral nerve block with daily intermittent bolus may represent an intermediate minimally invasive option for selected patients with refractory PN in experienced centers capable of structured catheter monitoring. Because this trial was not powered to estimate rare infectious complications and required a 7‐day inpatient protocol, larger multicenter studies are needed to define safety, feasibility, cost‐effectiveness, and the potential for outpatient adaptation.

1. Introduction

Pudendal neuralgia (PN) is a complex condition characterized by intense pain in the innervated regions of the pudenda, which includes the vaginal orifice, clitoris root, labia, urethral orifice, and surrounding tissues (Andiman et al. 2025; Conic et al. 2025). Despite estimates from the International Pudendal Neuropathy Association placing the incidence of PN at 1 in 100,000 (Leslie et al. 2025), many healthcare professionals believe this rate to be significantly higher. Making a diagnosis of PN can be challenging, with differential diagnoses including vulvodynia, pelvic floor tension myalgia, interstitial cystitis, and neuralgias affecting other pelvic nerves such as the obturator, genitofemoral, or ilioinguinal nerves (Khoder and Hale 2014). The foundation of the diagnostic process lies in a detailed patient history followed by a thorough physical examination. In 2008, Labat et al. (Labat et al. 2008) introduced the Nantes Criteria for diagnosing PN, which has gained widespread acceptance in many clinical settings.

Pudendal nerve involves three segments and three terminal branches (Gruber et al. 2001). The initial segment originates from the third sacral root and receives contributions from the S2 and S4 nerve roots. The subsequent segments correspond to the infrapiriform canal and the pudendal canal, also known as Alcock canal. The terminal branches include the perineal nerve (PeN), dorsal clitoris nerve (DCN), and inferior anal nerves (IAN). The pudendal nerve is susceptible to entrapment at two main sites: the ischial spine due to compression from the sacrospinous and sacrotuberous ligaments, and the pudendal canal due to compression caused by the falciform process of the sacrotuberous ligament or thickening of the obturator fascia (Hibner et al. 2010).

Although procedures such as PNB have been utilized for the diagnosis and treatment of PN, the effectiveness of interventions like ultrasound‐guided or CT‐guided therapy, such as ultrasound‐guided PNB (Rofaeel et al. 2008) and CT‐guided PNB (Mamlouk et al. 2014), has shown room for improvement. Recent cases reported by Cok et al. (2011) highlight the potential benefits of transsacral S2‐4 nerve blocks for relieving vaginal pain associated with pudendal nerve. Chronic pudendal neuralgia involves continuous peripheral ectopic firing that drives central sensitization in the spinal cord (Ahmed et al. 2026; Kaur et al. 2025). Although single‐shot blocks provide transient relief, they are generally insufficient to reverse these established neuroplastic changes (Aguirre et al. 2012). In contrast, an extended 7‐day catheter blockade offers a therapeutic window to temporarily interrupt nociceptive input, which has been shown to delay mechanical allodynia and help reset central sensitization (Shankarappa et al. 2012). This minimally invasive approach serves as an ideal intermediate step before advancing to more invasive and expensive options like pulsed radiofrequency or permanent neuromodulation (Ahmed et al. 2026; Kovacevic et al. 2023). In our study, we explored the use of catheter‐based sacral nerve block with daily intermittent bolus (SNB) under CT guidance as a therapeutic approach for PN. This method is expected to provide substantial efficacy and prompt pain relief. To assess the comparative efficacy of SNB using a CT‐guided third posterior sacral foramen catheter versus CT‐guided catheter placement near the pudendal nerve for PNB in the management of PN, our research aims to offer valuable insights for selecting optimal treatment strategies.

2. Methods and Materials

This prospective double‐blinded randomized study was conducted from April 2023 to October 2024, following approval from the Institutional Ethics Committee (2022‐027) and registration in the clinical trial registry of China (ChiCTR2300068941). Patient recruitment took place at the First Medical Center of PLA General Hospital and the First Hospital of Putian City. Written informed consent was obtained from each participant upon recruitment.

2.1. Inclusion and Exclusion Criteria

Patients meeting the Nantes criteria (Labat et al. 2008) for PN were included in the study. Additional diagnostic criteria included the presence of pain in the pudendal nerve distribution area, increased pain intensity in a seated position, absence of nocturnal pain, lack of objective sensory impairment, and pain relief following diagnostic PNB. Supplementary diagnostic criteria encompassed pain associated with sexual dysfunction, the exclusion of other underlying medical conditions, chronic neuropathic pain lasting at least 6 months, failed treatments by other departments, and a minimum age of 18 years. Exclusion criteria consisted of pregnancy, coagulation disorders, pelvic infections or malignancies, inability to complete questionnaires, and pain resulting from malignant or autoimmune diseases. Severe anxiety was screened using the Hamilton Anxiety Rating Scale (HAMA), and severe depression was screened using the Hamilton Depression Rating Scale (HAMD). Patients with severe anxiety or depression, as judged by these validated scales and clinical assessment, were excluded.

2.2. Procedures

A total of 90 patients were ultimately included in the study, with detailed medical histories and examinations conducted for all participants. Patients were informed of the study procedures and treatment plan, and those who consented to participate provided written informed consent. Randomization assigned 90 patients with PN, aged 18–74 years, into two groups: the SNB group (n = 45) and the continuous PNB group (n = 45). The data collectors and patients were not privy to the group allocation. All enrolled patients were hospitalized as inpatients for the duration of the 7‐day treatment period. SNB involved sacral 2–4 nerves block once a day for 7 days through the third posterior sacral foramen under CT guidance, while PNB utilized CT‐guided catheter placement near the pudendal nerve. CT scans were acquired using a Philips Brilliance 64 CT scanner (Philips Healthcare, Best, The Netherlands). All patients received a 5 mL injection of 0.5% lidocaine (Bela‐Pharm GmbH, Vechta, Germany) via an ultrasound‐guided PNB (Figure 1B), serving as diagnostic evidence for PN before enrollment. In the treatment of patients, the following medications were administered: NSAIDs (diclofenac, indomethacin, celecoxib, etoricoxib, and parecoxib, etc., available from various manufacturers), gabapentinoids such as gabapentin (Jiangsu Hengrui Medicine Co. Ltd., Jiangsu, China) and pregabalin (Pfizer Inc., New York, USA) or serotonin‐norepinephrine reuptake inhibitors (SNRIs), including duloxetine (Eli Lilly, Indianapolis, USA) and venlafaxine (Pfizer Ireland Pharmaceuticals, Newbridge, Ireland). Dosages of medication were adjusted based on the patient's pain burden. In instances where adequate pain management was not attained, the administration of opioids was also sanctioned. Procedures were performed on the symptomatic side in patients with unilateral pain and bilaterally in patients with bilateral symptoms; bilateral pain was present in 30 patients in the SNB group and 28 patients in the PNB group.

FIGURE 1.

Exemplary illustrations depicting the CT‐guided third posterior sacral foramen and pudendal nerve catheterization procedure. (A) The schematic delineates the technique involved in puncturing the third posterior sacral foramen to facilitate targeted drug injection. It distinctly highlights the inferior hypogastric plexus (IHP) as well as the S2–S4 nerve roots, which are the focus of the blockade, as represented by the delineated black dashed circle. (B) An ultrasound‐guided pudendal nerve block is exemplified in a high‐resolution oblique ultrasound image, which vividly illustrates the pudendal nerve in close proximity to the pudendal artery (A) and vein (V). The red circle denotes the intended area for the dispersion of the local anaesthetic solution. Meanwhile, the dotted line delineates the trajectory of the puncture needle. (C, D) Axial CT images of the third posterior sacral foramen are presented, with the red circle signifying contrast diffusion around the presacral plexus within the delineated canal of the third posterior sacral foramen. White arrows indicate the position of the implanted catheter. (E, F) CT‐guided pudendal nerve catheter placement is depicted, with the yellow circle emphasizing the diffusion of contrast around the pudendal nerve following percutaneous catheter insertion. The yellow arrow designates the position of the catheter. A, pudendal artery; ISC, ischial spine; PIR, piriformis muscle; STL, sacrotuberous ligament; V, pudendal vein.

To mitigate infection risks associated with prolonged catheterization, which extensive registry data confirms is remarkably safe when managed with strict aseptic protocols (Anghelescu et al. 2012; Bomberg et al. 2018; MacDonald and Zhang 2021), all catheter placements were performed under maximum barrier precautions (surgical caps, masks, sterile gowns, gloves, and large drapes) with chlorhexidine gluconate skin preparation (Bonsignore and Nachtigall 2021). Furthermore, during the 7‐day inpatient stay, the clinical team conducted daily visual inspections of the insertion site for signs of local inflammation, erythema, or purulence prior to the administration of each bolus.

2.2.1. CT‐Guided Placement of the Third Posterior Sacral Foramen for SNB

Following the diagnostic block, patients underwent sacral 2–4 nerves block once a day for 7 days using 10 mL of 0.2% injection ropivacaine hydrochloride (AstraZeneca AB, 100 mg/vial), with 7 mg of diprospan (Schering‐Plough Labo N.V., 1 mL/vial) on the final day. The patients were positioned prone with an under‐abdominal pillow. A CT scan (1.5 mm slice thickness) was performed to locate the third posterior sacral foramen. The catheter Contiplex D (B. Braun, Meisungen, Germany) was adopted for the procedure. A CT‐guided nerve block needle was inserted into the foramen, with post‐insertion CT confirming accurate placement. The needle stylet was removed, and a catheter was advanced from the posterior sacral foramen to the anterior sacral foramen. A 2 mL iohexol (Amersham Pharmaceutical Co. Ltd., Shanghai, China) diluted to 300 mg I/mL with distilled water was injected, and a CT scan assessed the contrast distribution along the anterior sacral surface and medial piriformis muscle. The catheter was then secured with a sterile dressing (Figure 1A,C,D).

2.2.2. CT‐Guided Catheter Placement Near the Pudendal Nerve for PNB

The patient was positioned prone with an under‐abdominal pillow for support. A locator grid was affixed to the lumbosacral region, and a CT scan with a 1.5 mm slice thickness was performed to identify the sciatic spine. The puncture site was marked, and standard sterile protocols were followed, including disinfection and draping. A CT‐guided needle was advanced to the pudendal nerve, with placement confirmed via CT imaging. The needle stylet was removed, and a catheter was introduced. A total of 2 mL of contrast agent was injected, showing proper diffusion around the pudendal nerve in follow‐up CT scans. The catheter was secured with a sterile dressing. Patients received PNB on a daily basis for a duration of 7 days, during which 10 mL of 0.2% ropivacaine was administered. On the final day of the treatment regimen, the protocol was supplemented with 7 mg of diprospan (Figure 1E,F).

2.2.3. Psychophysiological Monitoring

Patients were subjected to psychophysiological monitoring at 1 week following treatment, which was conducted over a period of 10–12 h from 10 p.m. to 8 or 10 a.m. the subsequent morning. The collection of psychophysiological data (including sleep data) was facilitated by the core sensing system of the PSYCHE project, specifically the wearable monitoring platform. The system was developed by Wanmai (SF‐A22S, Wanmai, Human, China) and consists of dry textile electrodes to capture the patient's ECG, piezoresistive sensors to capture respiratory signals, and a triaxial accelerometer. The system is characterized by its ease of use, with an electrochemical equilibrium between the skin and the electrodes being established within a matter of minutes. This process yields a high‐quality and stable signal. In the context of Psyche system utilization, patients are instructed to undertake routine activities of daily living within the confines of their homes or designated hospital rooms. Concurrently, the aforementioned physiological signals are meticulously monitored and stored on a microSD card. The data received by the smartphone from the wearable system is transmitted via a Bluetooth connection, and is subsequently dispatched to a remote server for processing by algorithms. For further information regarding the Psyche project, please refer to the previous studies (Javelot et al. 2014; Valenza et al. 2014).

2.3. Outcome Measures

Pain intensity was assessed using visual analog scale (VAS) scores. A VAS score card was used for evaluation, with the score of 0 for no pain and 10 for the most intolerable pain. Patients were asked to score themselves according to the pain. Modified MacNab criteria was used to evaluate the surgical effect. Excellent indicates complete remission of symptoms and normal life. Good indicates mild symptoms with no influence on life. Poor indicates partial or no remission of symptoms with limited activity. The sitting time is defined as the maximum duration of time spent in a seated position prior to the onset of pain (Buffenoir et al. 2015). The severity of anxiety was measured using the HAMA, which comprises 14 items. An elevated score on this test indicated a more severe anxiety state, with a score of ≥ 8 being indicative of anxiety. The squared root of the mean squared differences of successive NN intervals (RMSSD) based on heart rate variability analysis were used to estimate the stress level of patients and the sleep time was obtained automatically from psychophysiological data.

The VAS scores were assessed at 4 time points: before intervention, and at 1 week, 1 month, 3 months and 6 months post‐treatment. The modified MacNab method was also evaluated 1 week, 1 month, 3 months and 6 months after treatment. The impacts of treatment on sitting time and anxiety were evaluated 6 months after the conclusion of treatment. The stress levels and sleep patterns of the subjects were evaluated on the 7th day following the conclusion of the treatment. The number of patients who had used analgesic drugs was counted 6 months after treatment postoperatively.

2.4. Follow‐Up

The subsequent methodologies are outlined below: (1) Throughout both outpatient and inpatient periods, patients were incorporated into the patient management web platform, and general information, symptoms and imaging data were meticulously documented. An electronic questionnaire was disseminated to patients on a regular basis via the web platform. The questionnaire encompassed the following domains: baseline patient data, VAS changes, and other indicators to evaluate the efficacy of treatment. (2) Patients were subjected to follow‐up at the time of enrolment and 1 week after treatment during outpatient clinics or hospitalization in order to evaluate the efficacy of the treatment. (3) Enrolled patients were contacted via telephone or WeChat at 1, 3 and 6 months after treatment to verify post‐treatment recovery. It is noteworthy that the overall response rate of the questionnaire was 90% (81/90), which can be attributed to the close doctor‐patient relationship established through outpatient return visits, the patient management web platform, and the provision of a series of systematic management measures for the patients, ranging from pre‐treatment education to post‐treatment recovery guidance.

2.5. Statistical Analysis

Sample size calculation was based on detecting clinically meaningful differences in VAS pain scores between groups across 5 longitudinal assessments. Based on the minimal clinically important differences (MCID) for VAS pain intensity, we used Cohen's d of 0.4. Statistical power was set at 80% (β = 0.20) to balance Type II error control and research feasibility. A two‐tailed alpha of 0.05 was used to control for Type I errors in longitudinal comparisons. Using meta‐analytic data on VAS stability in pain trials, which showed moderate within‐subject correlation (ρ = 0.6), we calculated a requirement of 40 patients per group. Accounting for an expected 10% follow‐up lost, the final sample size was set at 88 patients, with 44 patients per group.

Statistical analysis was carried out using the SPSS ver. 24.0 (IBM Corp., Armonk, NY, USA). The outcomes of measurement data (VAS and HAMA) were continuous variables expressed as mean ± standard deviations (SD). Categorical variables (modified MacNab and the rate of analgesic use) were presented as numbers and percentages. Continuous data that did not conform to a normal distribution (sitting time, RMSSD and sleep time) was expressed as the median and 25‐75th percentiles. Normality of data was examined using the Kolmogorov–Smirnov test.

An intention‐to‐treat analysis was performed for all randomized patients. The primary and secondary outcomes were modelled at the post‐treatment phase (primary endpoint) using mixed‐effects models with a significance level of p < 0.05. The regressors incorporated treatment group (PNB vs. SNB) and time‐point (post vs. pre‐treatment) variables, denoting months post‐treatment and means centered on 1 month (follow‐up period of 6 months), the interaction of group with time (PNB vs. SNB × post‐treatment vs. pre‐treatment), and random intercepts and slopes for each participant. we tested whether these SNB versus PNB effect sizes were significant at 6 months post‐treatment‐our longest follow‐up time point. In instances where interaction effects were found to be statistically significant, post hoc analyses were conducted using estimated marginal means to examine between‐group differences at specific time points. The simple effects of the group were tested separately at each time point, and p‐values were adjusted for multiple comparisons using Tukey's Honest Significant Difference (HSD) procedure.

3. Results

Following the screening of 114 patients (Figure 2), 24 were excluded from the study: 19 failed to meet inclusion criteria and 5 declined to participate. The remaining 90 participants were equally randomized (n = 45 per group) to receive either SNB combined with PNB or PNB alone. For the PNB cohort: The 1‐month follow‐up was completed by 43 patients (1 lost to follow‐up, 1 declined further participation). At 3 months, 42 patients completed assessment (1 lost to follow‐up). The 6‐month follow‐up was completed by 40 patients (2 lost to follow‐up). Regarding the SNB cohort: 43 patients completed the 1‐month postoperative assessment (1 lost to follow‐up, 1 withdrew citing adverse effects). Of these participants, 42 completed the 3‐month follow‐up (1 lost to follow‐up, though this individual subsequently returned for the 6‐month assessment). The final 6‐month assessment was completed by 41 patients (1 lost to follow‐up, 1 declined continued participation).

FIGURE 2.

Disposition of All Patients Screened for Study Participation. ^@one patient within the CSNB group did not attend the primary endpoint assessment at the 3‐month mark; however, this individual successfully completed the 6‐month follow‐up visit and was consequently included in the final statistical analysis.

The demographic and clinical characteristics of the two groups were well‐balanced, with no statistically significant differences observed (all p > 0.05). A comparative analysis of the two cohorts highlighted comparable gender distributions (PNB vs. SNB: 73.33% vs. 71.11% female, p = 0.81) and mean ages (PNB vs. SNB: 52.06 ± 10.51 vs. 51.12 ± 12.43 years, p = 0.71). Further examination of clinical characteristics revealed no significant disparities, as evidenced by the mean duration of symptoms (PNB vs. SNB: 8.14 ± 1.61 vs. 7.81 ± 2.15 years, p = 0.43), body mass index (BMI; PNB vs. SNB: 22.12 ± 4.07 vs. 22.90 ± 3.13 kg/m², p = 0.34), and mean baseline pain scores (assessed using VAS; PNB vs. SNB: 5.93 ± 1.36 vs. 5.91 ± 1.61, p = 0.69). Additionally, the functional parameter of sitting time (PNB vs. SNB: 26.20 ± 8.99 vs. 33.00 ± 12.14 min, p = 0.94) demonstrated comparable outcomes. Psychological and physiological assessments further corroborated baseline comparability. The two groups had an equal amount of deep sleep time (PNB vs. SNB: 1.92 ± 074 vs. 2.06 ± 0.97 h, p = 0.44). The HAMA scores (PNB vs. SNB: 11.11 ± 2.72 vs. 10.49 ± 2.88, p = 0.30), and heart rate variability (HRV) indices‐specifically, RMSSD (PNB vs. SNB: 38.19 ± 7.06 vs. 38.63 ± 5.28 ms, p = 0.74) exhibited no statistically significant differences, affirming the homogeneity of the groups prior to intervention. The pre‐treatment medication burdens were also statistically homogenous between the cohorts. Prior to the intervention, no significant differences were observed in the use of NSAIDs (PNB vs. SNB: 82.93% vs. 77.5%, p = 0.59). Similarly, the baseline reliance on gabapentinoids was comparable (PNB vs. SNB: 87.80% vs. 95.00%, p = 0.43). The use of opioids, specifically morphine, was identical between groups at baseline Table 1 (PNB vs. SNB: 29.27% vs. 40.00%, p = 0.36). Finally, anti‐anxiety medication use showed no baseline divergence (PNB vs. SNB: 51.22% vs. 65.00%, p = 0.26).

TABLE 1.

Baseline characteristics of the two groups.

Characteristics	SNB group (n = 45)	PNB group (n = 45)	p
Gender, n (%)	Female: 32 (71.11)	Female: 33 (73.33)	0.81
	Male: 13 (28.89)	Male: 12 (26.67)
Age (years), mean ± SD	51.12 ± 12.43	52.06 ± 10.51	0.71
Duration of symptoms (years), mean ± SD	7.81 ± 2.15	8.14 ± 1.61	0.43
BMI (kg/m2), mean ± SD	22.90 ± 3.13	22.12 ± 4.07	0.34
Mean pain score (VAS), mean ± SD	5.91 ± 1.61	5.93 ± 1.36	0.69
Pain character, n (%)			0.87
Stabbing pain	14 (31.11)	17 (37.78)
Burning pain	19 (42.22)	16 (35.56)
Aching pain	5 (11.11)	6 (13.33)
Throbbing pain	7 (15.56)	6 (13.33)
Painful area, n (%)			0.66
Unilateral pain	15 (33.33)	17 (37.78)
Bilateral pain	30 (66.67)	28 (62.22)
Sitting time (min), mean ± SD	33.00 ± 12.14	26.20 ± 8.99	0.94
Hamilton Anxiety Rating Scale (HAMA), mean ± SD	10.49 ± 2.88	11.11 ± 2.72	0.30
HF‐HRV
HR (bpm), mean ± SD	82.02 ± 9.27	79.74 ± 11.06	0.29
RMSSD (ms), mean ± SD	38.63 ± 5.28	38.19 ± 7.06	0.74
Stress (h), mean ± SD	5.97 ± 1.21	6.37 ± 1.99	0.25
Recovery (h), mean ± SD	3.58 ± 0.70	3.77 ± 0.54	0.15
Sleep time (h), mean ± SD	2.06 ± 0.97	1.92 ± 0.74	0.44
Substances administered during the baseline period, n (%)
Gabapentin/Pregabalin	36 (87.80)	38 (95.00)	0.43
Morphine	12 (29.27)	16 (40.00)	0.36
Anti‐anxiety drugs	21 (51.22)	26 (65.00)	0.26
Non‐steroidal drugs	34 (82.93)	31 (77.50)	0.59

SNB treatment led to significant reductions in reported pain intensity (VAS) at posttreatment relative to PNB treatment (β = 0.53 points, t[87.36] = 2.29; p = 0.002; 95% CI, 0.20 to 0.86) (Figure 3A). Albeit the absence of a difference in VAS pain score at the 1‐week assessment post‐treatment between the study groups (PNB vs. SNB: 2.89 ± 0.98 vs. 2.82 ± 1.66, p = 0.99), patients subjected to SNB exhibited notably lower VAS scores during the 1 to 6‐month evaluations relative to those treated with PNB (PNB vs. SNB, 1 month: 3.72 ± 1.08 vs. 2.98 ± 1.47, p = 0.04, Cohen's d = 0.7; 3 months: 4.17 ± 1.19 vs. 3.36 ± 1.14, p = 0.02, d = 0.69; 6 months: 4.95 ± 1.08 vs. 3.85 ± 1.04, d = 1.04, p < 0.0001), the disparity amplifying with time progression (Figure 3A,B). The difference between means of the two groups (SD) was 1.10 ± 0.24 (Figure 3B). Utilizing the modified MacNab criteria, the percentage of patients exhibiting excellent and/or good outcomes were documented at 86.66%, 74.42%, 63.40%, and 37.50% at 1 week, 1, 3 and 6 months duration in the PNB group and 91.11%, 88.39%, 83.88%, and 75.61% in the SNB group, respectively (Figure 3C). The incidence of patients exhibiting excellent and/or good outcomes post 3, and 6 months were markedly higher in the SNB cohort than the PNB group (3 months: p = 0.04; 6 months: p = 0.002). The treatment responders defined as achieving at least 50% pain relief. In the SNB cohort, 34.1% of patients qualified as responders, in stark contrast to the 15% observed in the PNB group (Figure 3D,E).

FIGURE 3.

Comparative Analysis of Pain‐Related Endpoints in Patients with PN Treated with PNB and SNB. (A) The evaluation of VAS scores at various time points demonstrates significant reductions within the SNB group at 1, 3, and 6 months post‐treatment when compared to the PNB group. (B) A detailed comparison of VAS scores between the SNB and PNB cohorts at the 6‐month post‐treatment follow‐up reveals that patients receiving SNB exhibited notably lower VAS scores than those in the PNB group; the calculated difference in means between the two groups stands at 1.10 ± 0.24. (C) The distribution of outcomes classified as excellent, good, or poor, according to the modified MacNab criteria, illustrates a statistically significant divergence between the two groups at various time points. (D,E) Individual responses to pain treatment following SNB and PNB are depicted, with each line representing the change in VAS scores at 6 months relative to baseline for patients in both groups. The dotted yellow line signifies the threshold for treatment responders, defined as achieving at least 50% pain relief. In the SNB cohort, 34.1% of patients qualified as responders, in stark contrast to the 15% observed in the PNB group. NS, no significance; PNB, continuous pudendal nerve block; SNB, continuous sacral 2–4 nerve block; VAS, visual analog scale; *p < 0.05; **p < 0.01; ****p < 0.0001.

Both groups demonstrated a significant extension in maximum sitting time at the 6‐month assessment following treatment initiation (PNB: from 26.20 ± 8.99 to 37.65 ± 16.25 min; SNB: from 33.00 ± 12.14 to 68.56 ± 21.61 min) with the SNB cohort showcasing notably prolonged maximum sitting times relative to the PNB cohort at the 6‐month evaluation (p < 0.0001, Figure 4A). Subsequently, the HAMA scores exhibited a significant decrease in both groups post 6 months of follow‐up (PNB: from 11.11 ± 2.72 to 9.95 ± 4.12; SNB: from 10.49 ± 2.88 to 6.95 ± 2.52), with patients receiving SNB observation displaying a more pronounced reduction (p = 0.0002, Figure 4B). Correspondingly, an analysis of deep sleep duration on the 7th day post‐treatment highlighted a noteworthy increase in total sleep time in the SNB group relative to the CNB cohort (PNB: from 1.92 ± 074 to 3.03 ± 1.46 h; SNB: from 2.06 ± 0.97 to 4.70 ± 1.12 h, Figure 4C). Moreover, indices measuring stress intensity, such as RMSSD, stress and recovery durations, and sleep patterns were evaluated on the 7th day post‐treatment in patients (Figure 4D–F). Notably, the RMSSD on the 7th day post‐treatment was notably lower in the PNB cohort relative to the SNB cohort (PNB vs. SNB: 34.12 ± 2.72 vs. 36.27 ± 3.33 ms, p = 0.01, Figure 4D). Furthermore, comparison of stress and recovery durations between the groups on the 7th day post‐ treatment revealed a substantially shorter stress period in the SNB group compared to the PNB group (PNB vs. SNB: 3.32 ± 0.98 vs. 2.75 ± 0.79 h, p = 0.005), with no notable variance in recovery time (PNB vs. SNB: 1.92 ± 0.71 vs. 1.94 ± 0.69 h, p = 0.92, Figure 4E).

FIGURE 4.

Comparative Analysis of Secondary Endpoints in PN Patients Treated with PNB and SNB. (A) Assessment of maximum sitting time at 6 months post‐treatment reveals a remarkable extension in the SNB group relative to the PNB group. (B) HAMA scores at the 6‐month follow‐up exhibit significant reductions in the SNB group when compared to the PNB group. (C) An analysis of sleep duration on day 7 post‐treatment highlights a substantial increase in total sleep time within the SNB group as opposed to the PNB group. (D) Monitoring of the Root Mean Square of Successive Differences (RMSSD), indicative of heart rate variability, demonstrates a notably lower RMSSD in the PNB group on day 7 post‐treatment compared to the SNB group. (E) Comparison of stress and recovery times between the SNB and PNB groups on day 7 post‐treatment indicates a significantly shorter stress duration in the SNB group, with no remarkable extension in recovery time noted. (F) An illustrative depiction displaying heart rate variability and RMSSD during sleep serves as a representative case study. (G) A visual representation of stress intensity, calculated from heart rate during sleep, is provided as an illustrative example. HAMA, Hamilton anxiety scale; PNB, catheter‐based pudendal nerve block; SNB, catheter‐based sacral 2–4 nerve block; *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001.

Furthermore, a notable reduction in the utilization of gabapentin/pregabalin, morphine, anti‐anxiety drugs, and non‐steroidal drugs were witnessed in the SNB group versus the PNB group at the conclusion of the follow‐up period (gabapentin/pregabalin: OR 0.14, 95% CI 0.04 to 0.42; morphine: OR 0.18, 95% CI 0.05 to 0.72; anti‐anxiety drugs: OR 0.41, 95% CI 0.16 to 1.03; non‐steroidal drugs: OR 0.43, 95% CI 0.15 to 1.22, Table 2).

TABLE 2.

The use of analgesic drugs in the two groups at 6 months of follow up.

	SNB group (n = 41)	PNB group (n = 40)	OR	Z	p	95% CI
Gabapentin/Pregabalin	20	35	0.136	−3.493	0.000	0.044–0.417
Morphine	3	12	0.184	−2.445	0.014	0.047–0.715
Anti‐anxiety drugs	11	19	0.405	−1.906	0.057	0.160–1.026
Non‐steroidal drugs	7	13	0.428	−1.588	0.112	0.150–1.220

4. Discussion

Therapeutic interventions for PN encompass a variety of medical protocols, including PNB with or without steroids, surgical decompression, neuromodulation with implanted pulse generators, and pulsed radiofrequency treatments targeting the pudendal nerve (Filler 2009; Kaur et al. 2025; Rhame et al. 2009; Shafik 1998). Despite the effectiveness of PNB as a diagnostic and treatment option for PN, some patients may express hesitance towards traditional techniques such as direct transvaginal or transperineal approaches to the pudendal nerve (Abdi et al. 2004). In such cases, transsacral blockade of the S2‐4 nerves can be considered as an alternative method to achieve successful pain relief in individuals with pudendal nerve injury.

This study presents a prospective randomized controlled trial investigating the use of SNB as a potential treatment for PN. The analysis revealed significant improvements in VAS scores over a 1–6 months follow‐up period with SNB compared to PNB treatment. Patients who underwent SNB experienced an extension in maximum sitting time. Although the absolute difference of 1.10 VAS points between the two active cohorts may appear numerically modest, this reduction crosses critical clinical thresholds. This aligns precisely with the validated Minimal Clinically Important Difference (MCID) of 1.0–1.1 points (or an approximately 30% relative reduction) widely established for chronic pelvic pain conditions (Farrar et al. 2001; Gerlinger et al. 2010; Wickstrom and Edelstam 2017). Furthermore, pain intensity and physical function in pudendal neuralgia do not share a strictly linear relationship. When pain intensity drops below a specific severe threshold, involuntary reflex muscle guarding in the pelvic floor (such as levator ani spasms) diminishes. This muscular relaxation drastically reduces mechanical pressure on the pudendal nerve, perfectly explaining why SNB patients experienced such a profound extension in sitting time and improved functional capacity (Kaur et al. 2025). Additionally, a higher proportion of individuals in the SNB group reported excellent and/or good outcomes at 1, 3, and 6 months post‐treatment compared to those in the PNB group. Anxiety levels among patients receiving SNB were notably reduced as evidenced by a significant decrease in HAMA scores. Moreover, the need for analgesic medications, including morphine, gabapentinoids, and anti‐anxiety drugs, was significantly decreased in SNB‐treated patients at the 6‐month follow‐up compared to those who underwent PNB.

Previous studies have highlighted the efficacy of PNB using local anaesthetics and steroids in managing persistent pain associated with PN (Antolak Jr. and Antolak 2009; Keski‐Oja 1990; Knowles and Cohen 2022). The pudendal nerve consists of fibres deriving from the S2‐4 nerves, and individual blockade of these sacral nerves can result in a blockade of the pudendal nerve at its proximal origin (Stav et al. 2009). This technique offers advantages by targeting the site closest to the nerve's origin, potentially enhancing its efficacy compared to classical methods that target more distal sites of injury (Stav et al. 2009). Lemos et al. showed that intrapelvic lumbosacral plexus entrapments can produce pudendal pain, indicating that pudendal neuralgia may arise from more than one anatomical level (Lemos et al. 2021). However, the multifactorial nature of PN, which can be triggered by mechanical injury, viral infections, or immunological processes, poses challenges in achieving optimal outcomes with traditional PNB and surgical release approaches (Finnerup et al. 2021), and our study was not designed to localize the exact entrapment site.

Pudendal neuralgia is characterized by the continuous ectopic firing of the pudendal nerve (Ahmed et al. 2026). This unyielding nociceptive input can drive maladaptive neuroplasticity within the dorsal horn, leading to central sensitization (Kaur et al. 2025). A single‐shot nerve block, even with long‐acting local anaesthetics, typically provides only 12 to 24 h of sensory blockade (Ilfeld 2017; Vorobeichik et al. 2018). Although useful for diagnostics, this transient duration is often insufficient to interrupt established central sensitization pathways (Aguirre et al. 2012). Prolonged neural blockade (approximately 1 week) has been shown in neuropathic pain models to significantly delay mechanical allodynia and decrease pathological astrocyte activation (Shankarappa et al. 2012). Clinically, 7 days represents an optimal window balancing therapeutic neuroplastic reset with safety, as prolonged catheterization up to a week carries a very low severe infection risk (0.07%) when managed correctly (Bomberg et al. 2018). Our protocol strategically administers particulate corticosteroids (compound betamethasone) solely on the final day. This safely bypasses the progressive occlusion and severe ischemic risks associated with daily particulate steroid crystallization within the catheter (Van Boxem et al. 2019), while creating a terminal anti‐inflammatory reservoir to prevent inflammatory rebound upon catheter removal (Couch et al. 2024; Li et al. 2024; Watanabe et al. 2016).

PNB has emerged as a reproducible and long‐lasting method for delivering analgesic effects in PN. PNB involves the insertion of a catheter near the target nerve or plexus, allowing for the administration of local anaesthetics to provide prolonged nerve blockade (Ilfeld 2011). Recent studies have suggested that short‐term PNB may help reduce the incidence and severity of chronic pain experienced by patients with PN. An essential parameter in assessing treatment efficacy is the improvement in sitting time before the onset of pain, a key complaint among PN patients that significantly impacts their daily activities (Cheah et al. 2014; Gemayel et al. 2015; Gharaei 2015; Tognu et al. 2012). Another crucial biomechanical factor likely contributing to SNB's superior functional efficacy and sitting time is mechanical catheter stability. The transgluteal approach for the PNB catheter places it in a highly dynamic muscular environment, making it uniquely susceptible to shearing forces and outward micro‐migration during ambulation over the 7‐day period (Capdevila et al. 2005; Ilfeld 2011; Ooi et al. 2025). Conversely, the transsacral SNB catheter is advanced directly through the rigid, osseous posterior sacral foramen. This bony canal acts as a mechanical anchor, shielding the catheter tip from superficial movement and ensuring consistent, uninterrupted perineural drug delivery. We reasonably speculate that the efficacy of the SNB is largely driven by neurolytic sympathetic blockade, which regulates visceral afferent nerves at the ganglion level (Mohamed et al. 2013). Similar to how superior hypogastric plexus blocks and presacral neurectomies effectively treat chronic pelvic pain (Kwok et al. 2001; Soysal et al. 2003), targeting the inferior hypogastric plexus (IHP)—the primary autonomic coordinating center located ventral to the S2‐4 segments—safely manages lower pelvic visceral pain (Mohamed et al. 2013). Our findings align with previous reports demonstrating the success of S2‐4 nerve blocks for severe pelvic pain (Mohamed et al. 2013). Specifically, the positive effects of our CT‐guided third posterior sacral foramen catheter over a standard pudendal nerve block can likely be attributed to an IHP block. By advancing the catheter through the sacral foramen, the anaesthetic diffuses extensively along the pre‐sacral fascia (Choi et al. 2012), achieving a synergistic dual blockade: it halts somatic nociceptive input from the sacral roots while simultaneously modulating visceral pain afferents and reducing sympathetic pelvic floor tone via the IHP (Urits et al. 2021).

In patients with distal pudendal entrapment, the benefit of SNB may also involve an indirect myofascial mechanism. Pudendal neuralgia frequently coexists with pelvic floor overactivity, myofascial tenderness, and pain‐related guarding. Persistent pudendal‐distribution pain may provoke reflex contraction of the levator ani and adjacent pelvic wall muscles, particularly the obturator internus, creating a vicious cycle in which nociceptive input increases pelvic floor tone and increased pelvic floor tone further aggravates pudendal nerve irritation during sitting (Drakonaki et al. 2022; Kadah et al. 2023; Kaur et al. 2025; Meister et al. 2018). This mechanism is anatomically plausible because pudendal entrapment may occur at the ischial spine or within Alcock's canal, where the pudendal nerve runs in close relation to the obturator internus fascia and pelvic floor structures (Drakonaki et al. 2022; Kaur et al. 2025). Broader S2–S4 blockade by SNB may interrupt pudendal and pelvic afferent input more effectively than distal PNB, thereby reducing pain‐driven pelvic floor guarding. In turn, relaxation of the levator ani and related pelvic floor musculature may secondarily reduce dynamic compression or traction on the pudendal nerve, contributing to the greater improvement in sitting tolerance observed in the SNB group. This interpretation is further supported by evidence that pelvic floor muscle down‐training and biofeedback can improve pain in levator ani syndrome, suggesting that reducing pelvic floor hypertonicity can have clinically meaningful analgesic effects (Chiarioni et al. 2010). Because pelvic floor tone was not directly measured in this study, this explanation remains hypothetical and should be tested in future studies using standardized pelvic floor examination, electromyography, ultrasound elastography, or pelvic floor manometry.

Intractable chronic pain has significant emotional consequences and a psychological component is an integral part of the pain process. Although we tried to exclude patients with severe depression using a depression scale, the emotional, psychological and social distress may be important factors of resistance to treatment in all chronic pain syndromes. Consequently, patients were permitted to administer anti‐anxiety medications as the primary treatment, and a comparison was made of the proportion of patients prescribed anxiolytics at 6 months following interventional treatments between the two groups. As expected, the number of participants used anxiolytics in the SNB group decreased compared with that in PNB group at the end of the follow‐up, although there was no significant difference (PNB vs. SNB: 19/40 vs. 11/41, p = 0.06). From a broader health economics perspective, while admitting patients for a 7‐day inpatient catheter protocol requires substantial initial logistical resources, the intervention utilizes relatively inexpensive, generic supplies (Ilfeld 2017). Because it achieves lasting desensitization for a majority of patients, this protocol functions as a highly cost‐effective intermediate therapy that has the potential to avert the need for expensive, irreversible surgical decompression or the lifelong maintenance of permanent neuromodulation implants (Gola et al. 2020; Kovacevic et al. 2023).

Our study suffers from several limitations. First, Assessment at 6 months was chosen for the end points. Previous study has reported that the interval of 12 months appears a suitable indicator of lasting success as patients having had a good result at 12 months (Robert et al. 2005). This choice (6 months follow‐up) may seem inappropriate in the evaluation of chronic pain, but has been shown here to be relevant because although it does not necessarily give the definitive result, it nevertheless reveals the efficacy of the SNB compared with PNB intervention. Second, the sample size in this study was relatively limited. Although we performed statistical calculations to determine the necessary number of participants, the low prevalence of PN necessitated that we adopt a Cohen's d value of 0.4, indicative of medium effect size, in light of the constraints imposed by the study's duration and budget. It is clear that to draw robust and definitive conclusions, an expansion of the sample size will be essential. Despite achieving an overall response rate of 90% for the questionnaire, overcoming bias in the data collection process remains a formidable challenge. This difficulty arises from the fact that the scale was assessed via WeChat or telephone, rather than through in‐person evaluations during the 1–6 month postoperative follow‐up period. Third, to confirm the diagnosis of PN prior to enrollment, we relied on a single diagnostic anaesthetic block rather than comparative dual blocks. Although comparative blocks are considered the gold standard to rule out placebo responders in certain pain conditions, we adhered strictly to the internationally validated Nantes Criteria, which mandates only a single positive diagnostic block (Labat et al. 2008). This choice was made clinically to minimize the significant patient discomfort, anxiety, and burden associated with repeating invasive transgluteal or transvaginal needle trajectories (Kale et al. 2019). Last but not least, the requirement for 7‐day hospitalization substantially limits the immediate generalizability of this protocol. In this first randomized evaluation, inpatient management was selected to standardize catheter surveillance and minimize unrecognized infection or displacement; however, future pragmatic studies should determine whether similar efficacy can be achieved with shorter protocols or ambulatory catheter pathways, and should compare this approach directly with repeated outpatient injections.

In conclusion, catheter‐based sacral nerve block with daily intermittent bolus may represent an intermediate minimally invasive option for selected patients with refractory PN in experienced centers capable of structured catheter monitoring. Because this trial was not powered to estimate rare infectious complications and required a 7‐day inpatient protocol, larger multicenter studies are needed to define safety, feasibility, cost‐effectiveness, and the potential for outpatient adaptation.

Author Contributions

Kai‐kai Guo: conceptualization, methodology, formal analysis, investigation, data curation, writing – original draft, project administration. Jing Li: methodology, investigation, data curation, validation, writing – review and editing. Ying Meng: methodology, investigation, resources, writing‐review and editing. Long Wang: revision, data verification and correction. Shu‐rong Li: investigation, resources, writing‐review and editing. Gui‐jun Lu: methodology, formal analysis, validation, visualization, writing – review and editing. Jing‐jia Sun: conceptualization, methodology, resources, supervision, funding acquisition, writing – review and editing, project administration. All authors read and approved the final manuscript.

Funding

This work was supported by National Natural Science Foundation of China (Grant No. 82271322 to Long Wang).

Ethics Statement

This experiment complies with the Helsinki principles, has been approved by the Institutional Ethics Committee (2022‐027) and registered in the Chinese Clinical Trial Registry (ChiCTR2300068941).

Consent

Patient recruitment was carried out at the First Medical Center of the PLA General Hospital and Putian First Hospital. Obtain the written informed consent of each participant at the time of recruitment.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data available on request from the corresponding author.