Pudendal Nerve Block Techniques for Pain Control After Hemorrhoidectomy

Context, rationale and hypothesis: Hemorrhoidectomy remains one of the most painful ambulatory surgical procedures, frequently associated with substantial postoperative opioid consumption despite multimodal analgesia. This persistent nociceptive burden has direct implications for delayed recovery, unplanned admissions, and opioid-related adverse events. Consequently, optimizing regional analgesic strategies is a priority within enhanced recovery pathways.

Pudendal nerve block (PNB), targeting sacral roots S2-S4, has emerged as an effective adjunct for postoperative analgesia in anorectal surgery. Randomized trials and meta-analyses consistently demonstrate reductions in pain scores and opioid requirements when PNB is incorporated into perioperative care. However, these studies encompass heterogeneous techniques, and critically, do not address whether the anatomical level of blockade influences clinical efficacy.

From a mechanistic perspective, the pudendal nerve divides into its terminal branches-the inferior rectal, perineal, and dorsal genital nerves-after traversing the region of the ischial spine and entering Alcock's canal. The inferior rectal nerve, which provides the principal sensory innervation to the anal canal and perianal region, typically branches proximally before the pudendal nerve courses distally within the pudendal canal. This anatomical arrangement suggests that distal approaches to PNB, such as the transperineal technique, may incompletely anesthetize the inferior rectal nerve due to injection beyond the point of branching or variable spread within the ischiorectal fossa.

In contrast, the posterior transgluteal approach targets the pudendal nerve at a more proximal location, near the ischial spine and sacrospinous ligament, where the nerve remains a single trunk. Ultrasound guidance at this level enables precise deposition of local anesthetic before division into terminal branches, theoretically ensuring a more consistent and comprehensive blockade, including the inferior rectal nerve. This distinction in injection level-proximal versus distal-represents a fundamental but underexplored determinant of block success.

Despite increasing adoption of ultrasound-guided regional anesthesia, there is a striking absence of randomized controlled trials directly comparing proximal (transgluteal) and distal (transperineal) approaches to PNB in the context of hemorrhoidectomy. Existing evidence is therefore insufficient to determine whether improved anatomical coverage translates into superior clinical analgesia or reduced opioid consumption.

Addressing this gap is clinically relevant for several reasons. First, inadequate blockade of the inferior rectal nerve may contribute to residual pain during defecation, a key determinant of patient dissatisfaction after hemorrhoidectomy. Second, identifying a more reliable and reproducible technique could standardize PNB within perioperative protocols. Third, demonstrating superiority of a proximal approach would support broader integration of ultrasound-guided regional techniques into opioid-sparing strategies.

The present trial is designed to test the hypothesis that a proximal, ultrasound-guided transgluteal PNB provides superior postoperative analgesia compared with a distal transperineal approach. By directly comparing these techniques in a randomized controlled setting, this study seeks to determine whether anatomical optimization of nerve blockade translates into meaningful clinical benefit.

Originality and innovative aspects: Hemorrhoidectomy remains associated with significant postoperative pain, often requiring substantial opioid consumption. Pudendal nerve block (PNB), targeting nerve roots from S2-S4, has demonstrated efficacy in reducing postoperative pain and opioid requirements. Anatomically, the pudendal nerve gives rise to the inferior rectal, perineal, and dorsal genital nerves. The effectiveness of PNB depends on the level of injection:

• Transgluteal (proximal) approach: blockade at the level of the ischial spine before nerve branching
• Transperineal (distal) approach: injection within or near Alcock's canal after branching The distal approach may spare the inferior rectal nerve, leading to suboptimal anorectal analgesia. In contrast, the proximal ultrasound-guided technique may provide a more complete and reliable block.

To date, no randomized controlled trial has directly compared proximal (transgluteal) and distal (transperineal) approaches to pudendal nerve block in hemorrhoidectomy, despite clear anatomical rationale suggesting differences in nerve coverage and analgesic efficacy.

Methods This study is a prospective, Randomized, Controlled, Parallel-group , Superiority trial, Assessor-blinded The protocol follows SPIRIT recommendations, and reporting will adhere to CONSORT guidelines Setting The study will be conducted at VinMec International Hospital, Can THo, Vietnam. Interventions Control Group (Standard Management): Trans perineal Group (Distal PNB) Spinal anesthesia protocol standardized; Ultrasound-guided transperineal approach ; Injection in rectoperineal/ischiorectal fossa; Bilateral; Ropivacaine 0. 5%, 8 mL per side; Oral Paracetamol 500 mg every 6 hours; Oral Celecoxib 200 mg every 12 hours ( if no contra-indication); Rescue opioids if NRS pain values >3/10 converted to MME Intervention Group: Transgluteal Group (Proximal PNB) General anesthesia protocol standardized; Ultrasound-guided posterior approach; Injection near ischial spine/sacrospinous ligament; Bilateral; Ropivacaine 0. 5%, 6 mL per side; Oral Paracetamol 500 mg every 6 hours; Oral Celecoxib 200 mg every 12 hours (if no contra-indication); Rescue opioids if NRS pain values >3/10 converted to MME

The Block Techniques:

Transperineal Approach Patient Positioning The patient is placed in the lithotomy position with slight hip abduction. Adequate exposure of the perineum is ensured under strict aseptic conditions.

Ultrasound Equipment and Probe Position A high-frequency linear transducer (10-18 MHz) is used. The probe is placed: Transversely or slightly oblique; On the perineum, lateral to the external anal sphincter; Over the ischio-rectal fossa.

Sonoanatomy Key structures to identify include: External anal sphincter (medial landmark); Ischioanal (ischiorectal) fossa (hypoechoic fat-filled space); Obturator internus muscle (lateral boundary); Internal pudendal artery (identified using color Doppler). The pudendal nerve is often not directly visualized, but lies medial to the internal pudendal artery and within or near Alcock's (pudendal) canal Needle Insertion Approach: in-plane, typically medial to lateral; Needle: 50mm echogenic needle advanced to the ischioanal fossa, adjacent to the internal pudendal artery.

Injection 8 mL of local anesthetic is injected per side. The spread should be observed within the ischioanal fossa Controlled by Color echo Doppler to prevent IV injection.

Transgluteal Approach Patient Positioning The patient is placed in the prone position (or lateral decubitus if needed). The gluteal region is exposed and prepared under sterile conditions.

Ultrasound Equipment and Probe Position A low-frequency curvilinear probe (2-5 MHz) or a high-frequency probe in lean patients may be used.

The probe is positioned transversely over the gluteal region, at the level of the ischial spine Sonoanatomy Key landmarks: Ischial spine (hyperechoic bony structure with acoustic shadow); Sacrospinous ligament; Sacrotuberous ligament; Internal pudendal artery (identified with Doppler). The pudendal nerve is located medial and posterior to the internal pudendal artery between the sacrospinous and sacrotuberous ligaments. It may appear as a small hyperechoic oval structure, although visualization is variable.

Needle Insertion Approach: in-plane, usually lateral-to-medial; Needle: 50 or 80 mm echogenic needle. The needle is advanced through the gluteal muscles, toward the ischial spine region, Into the interligamentous plane (between sacrospinous and sacrotuberous ligaments) Injection 6 mL of local anesthetic is injected per side. The spread of LA expands of the interligamentous space, circumferential spread around the pudendal artery controlled by Color echo doppler Sample Size: Assuming a mean 48h opioid consumption at 60 mg MME with a standard deviation: 30 mg and a clinically meaningful difference of 15 mg (25% reduction) with an Alpha risk : 0.05 (two-sided) and a β risk Power: 80%, the required sample is 64 patients per group. Accounting for 10% dropout the Total sample size: 140 patients (70 per group).

Analysis of the Population: Intention-to-treat (ITT) (primary analysis) and Per-protocol (sensitivity analysis) Descriptive Statistics: Continuous variables: mean ± SD or median (IQR) and Categorical variables: n (%)

Primary Outcome Analysis:

Comparison of cumulative MME at 48 h: If normally distributed → Student's t-test; If non-normal → Mann-Whitney U test Additionally: Linear regression adjusted for: Age, Sex, Surgical technique, Baseline pain Effect size: Mean difference with 95% confidence interval

Secondary Analyses :

Pain scores (repeated measures): Mixed-effects linear models ; Fixed effects: group, time, group × time interaction; Random intercept for patient

Time-to-event outcomes:

Time to first opioid: Kaplan-Meier analysis; Log-rank test; Cox proportional hazards model

Categorical outcomes:

Chi-square or Fisher's exact test; Report relative risks with 95% CI

Continuous outcomes:

t-test or Mann-Whitney depending on distribution Handling Missing Data : Multiple imputation if >5% missing; Sensitivity analyses Significance Threshold : p \< 0.05 (two-sided) Randomization Randomization and Blinding : Allocation ratio: 1:1; Computer-generated random sequence with variable block sizes; Allocation concealment via secure electronic system

Blinding:

The patients are blinded; Outcome assessors: blinded; Data analysts: blinded; Performing anesthesiologist: not blinded Data Collection Methods: Pain opiates consumption and functional outcomes will be assessed at predefined time points using scales and validated questionnaires: NRS pain score at rest and during movement, .Lickert scale for patient satisfaction, consumption of rescue analgesia opiates (MME), Brief Pain Inventory and QOR 15 form. Data will be collected during follow-up visits or via structured interviews.