Research Frontiers | Randomized Controlled Evidence That Transcutaneous Auricular Vagus Nerve Stimulation Reduces Rebound Pain After Arthroscopic Shoulder Surgery

Introduction

Pain as the Block Wears Off

Pain after arthroscopic shoulder surgery may be well controlled initially, only to intensify abruptly as the nerve block wears off. This transition from mild to severe pain is known as rebound pain. It can disrupt rest and postoperative recovery. Maintaining steady analgesia as the block subsides remains an important challenge in perioperative pain management.

On September 15, 2026, Jun Zhang and colleagues published a randomized, sham-controlled trial in Regional Anesthesia & Pain Medicine examining whether transcutaneous auricular vagus nerve stimulation (taVNS) could reduce the incidence of rebound pain after arthroscopic shoulder surgery.

The study enrolled 120 patients and compared taVNS with sham stimulation against a common anesthesia and analgesia regimen. Rebound pain occurred less often within 24 h after surgery in the taVNS group, and some measures of recovery and sleep also improved. However, the reduction in mean pain scores was small, and the between-group difference in analgesic use did not reach statistical significance.

Background

A Gap in Rebound Pain Management

A single-shot interscalene brachial plexus block (ISB) is a common regional analgesic technique for shoulder surgery. A local anesthetic acts around the nerves and can provide approximately 12–24 h of analgesia, but pain at the surgical site may emerge rapidly when its effect subsides. Rebound pain therefore warrants separate attention when evaluating analgesic strategies: a mean pain score over one day may not adequately capture such a sharp, short-lived change.

Continuous perineural catheters and adjunctive drugs can help address this problem, but they add procedural, management, or drug-related burdens. taVNS stimulates the auricular branch of the vagus nerve through skin electrodes on the ear and offers another avenue for studying adjunctive analgesia. Its mode of delivery differs from implanted vagus nerve stimulation, transcutaneous cervical stimulation, and needle-based auricular neuromodulation.

Previous studies have explored the effects of auricular nerve stimulation on postoperative pain, but evidence specific to rebound pain after a single-shot ISB remains limited. This trial specified rebound pain as its primary endpoint in advance and tested the added effect of taVNS on top of existing multimodal analgesia.

Methods

Randomized Comparison and Stimulation Protocol

This single-center trial was conducted at Deqing County People’s Hospital in Zhejiang Province, China. Of 142 people screened, 120 eligible patients scheduled for arthroscopic shoulder surgery were randomized 1:1, with 60 in each group. All completed follow-up and were included in the intention-to-treat analysis. Patients, outcome assessors, and data analysts remained blinded; the personnel administering stimulation knew the assignments.

Both groups received general anesthesia, a single-shot ultrasound-guided ISB, and standardized intravenous ibuprofen and patient-controlled sufentanil analgesia. The ISB used 15 mL of 0.5% ropivacaine. taVNS was applied to the left cymba conchae at 30 Hz with a 250 μs pulse width, alternating 30 s of stimulation with 30 s of rest. Intensity was gradually increased until the patient reported a distinct tingling sensation, then lowered to a level at which the patient confirmed that no sensation remained. The first session began in the preoperative waiting area and continued until transfer to the post-anesthesia care unit after extubation. Further 2 h sessions were given on the mornings of postoperative days 1 and 2. The sham group underwent the same electrode placement and sensory-threshold testing, but the device output was set to zero during treatment.

The primary outcome was the incidence of rebound pain within 24 h after surgery. Using a 0–10 numerical rating scale (NRS), the investigators defined rebound pain as an increase from ≤3 to ≥7 after block resolution, with a rise of at least 4 points. Resolution of the block was inferred from the change in pain rather than confirmed by serial sensory examination. Secondary outcomes included pain and cumulative sufentanil use at 6, 12, 24, and 48 h after surgery, as well as quality of recovery, sleep quality, and adverse events. The primary outcome was analyzed with a chi-square test, and repeated secondary measures with mixed-effects models. Time-point comparisons for recovery and sleep scores received Bonferroni correction. The sample size was estimated for the primary endpoint; analyses of secondary outcomes were exploratory.

Results

Primary Endpoint and Effect Size

Rebound pain occurred in 12 patients (20.0%) in the taVNS group and 26 patients (43.3%) in the sham group. The absolute risk reduction was 23.3 percentage points (95% confidence interval [CI], 7.2 to 39.5 percentage points); the relative risk was 0.46 (95% CI, 0.26 to 0.82; P = 0.006). This result supports a reduction in early rebound pain with taVNS within the analgesic regimen used in this trial.

Mean pain scores were also lower, although the magnitude of improvement was limited. In the mixed-effects model, the overall resting NRS score was 0.50 points lower in the taVNS group (95% CI, −0.63 to −0.37; P < 0.001), and the score during movement was 0.39 points lower (95% CI, −0.65 to −0.14; P = 0.003). Both differences were below the approximately 1-point threshold for a clinically important improvement cited by the authors. Statistical differences therefore should not automatically be equated with a noticeable improvement in pain experience.

For cumulative sufentanil use, the model-estimated geometric mean ratio was 0.67 (95% CI, 0.44 to 1.01; P = 0.056), showing no statistically significant between-group difference. This estimate came from an analysis after an ln(x+1) transformation of drug use and should not be described as a confirmed 33% reduction in the amount actually administered.

Scores on the 15-item Quality of Recovery questionnaire (QoR-15) were higher in the taVNS group. The between-group differences on postoperative days 1 and 2 were 7.07 and 4.81 points, respectively, with corresponding 95% CIs of 2.98 to 11.28 and 1.27 to 8.45 and P values of 0.001 and 0.008.

Scores on the Richards-Campbell Sleep Questionnaire (RCSQ) were higher by 10.86 points on the night of surgery and 7.25 points on the first postoperative night. The corresponding 95% CIs were 7.89 to 13.99 and 4.28 to 10.38; both P values were < 0.001. Higher scores indicate better status on both questionnaires, but these short-term findings do not establish an improvement in long-term functional recovery.

No stimulation-related adverse events were observed. Postoperative nausea or vomiting occurred in 8.3% of the taVNS group and 15.0% of the sham group, a difference that was not statistically significant (P = 0.255). This short-term observation in a small sample cannot rule out uncommon adverse effects.

Mechanistic Considerations

Neuromodulation and Evidentiary Limits

The investigators proposed that taVNS might influence peripheral and central sensitization through autonomic regulation, neuroimmune signaling, and cholinergic-related pathways, thereby easing pain as the block wears off. However, this trial did not measure inflammatory markers, autonomic function, or sensory thresholds. It cannot establish which pathway, if any, mediated the observed effect, nor does the clinical result verify an anti-inflammatory mechanism.

A lower incidence of rebound pain and a small reduction in mean pain scores are compatible findings. The former records whether pain jumps from mild to severe; the latter summarizes pain levels at several fixed time points. Better sleep and recovery scores may be related to fewer episodes of severe pain, but the study did not directly test that mediating relationship.

The study design also limits generalizability. Follow-up lasted only 48 h, and routine twice-daily assessments from postoperative day 1 may have missed brief episodes. The investigators did not formally test whether patients could guess their group assignment. Most enrolled patients had relatively stable general health, and conditions such as clinically significant arrhythmias requiring treatment were excluded. Use of acetaminophen and perioperative dexamethasone was not recorded as a trial variable, limiting comparisons with other analgesic regimens. The present evidence therefore supports a potential adjunctive role within a specific regimen but is insufficient to establish routine use or replacement of established analgesic measures.

Future Directions

Clinical Validation and Optimization

Future multicenter studies could enroll larger samples, extend follow-up, and use serial sensory and pain assessments around block resolution to clarify effects on the duration of rebound pain, rehabilitation activity, and long-term pain. Direct comparisons of stimulation timing, intensity, and treatment duration, along with measurement of delivered dose and assessment of blinding, could show whether the observed effect is reproducible across analgesic regimens. Studies could also measure autonomic and inflammatory markers while specifying clinically important pain improvement, analgesic requirements, and adverse events as endpoints. This would help determine whether physiological changes explain or predict patient benefit and how long any benefit persists.

Reference

Zhang, J., Lu, S., Lin, S., et al. (2026). Transcutaneous auricular vagus nerve stimulation to prevent rebound pain after interscalene block for arthroscopic shoulder surgery. Regional Anesthesia & Pain Medicine. Advance online publication, September 15. doi:10.1136/rapm-2026-108256doi:10.1136/rapm-2026-10825