Ultrasound-Guided Infraspinatus-Teres Minor Interfascial Block versus Interscalene Brachial Plexus Block for Analgesia After Arthroscopic Shoulder Surgery: A Randomized Non-Inferiority Clinical Trial.

BACKGROUND: This randomized non-inferiority trial was designed to verify whether ultrasound-guided infraspinatus-teres minor interfascial block (ITMB) could produce non-inferior postoperative analgesia in adult patients undergoing arthroscopic shoulder surgery compared with ultrasound-guided interscalene brachial plexus block (ISB), while also comparing the early respiratory safety profiles and postoperative adverse events of the two techniques. METHODS: This trial adopted a two-arm parallel-group design with blinding for participants and all outcome assessors. A total of 82 eligible patients were randomly assigned 1:1 to receive either ITMB (n=41) or ISB (n=41) with 25 mL 0.375% ropivacaine for each nerve block. Two participants in the ITMB group were excluded from the per-protocol (PP) analysis due to intraoperative conversion to open surgery and unplanned intensive care unit admission, leaving 39 ITMB patients and 41 ISB patients for primary PP analysis; intention-to-treat (ITT) analysis covering all 82 randomized patients was additionally conducted to validate robustness. The primary prespecified outcome was 24-hour postoperative total oxycodone consumption, with a predefined non-inferiority margin of -5 mg (ISB minus ITMB). Non-inferiority was established if the lower limit of the 95% confidence interval (CI) for the between-group mean difference was no less than -5 mg. Secondary endpoints comprised the maximum 11-point resting NRS pain score within 24 h, incidence of rebound pain, and rescue analgesia requirements. Safety endpoints included dyspnea, diaphragmatic paralysis, Horner's syndrome, and postoperative nausea and vomiting. RESULTS: PP analysis showed the mean 24-hour oxycodone consumption was 11.26 (SD 4.38) mg in the ISB group (95% CI 9.89 to 12.65) versus 10.92 (SD 3.48) mg in the ITMB group (95% CI 9.79 to 12.05), with a between-group mean difference of 0.34 mg (95% CI -1.42 to 2.11, P<0.001). The lower bound of the 95% CI (-1.42 mg) substantially exceeded the pre-specified non-inferiority margin of -5 mg, satisfying the non-inferiority criterion (one-sided non-inferiority P<0.001). ITT analysis yielded consistent non-inferiority results (mean difference 0.26 mg, 95% CI -1.46 to 1.99, P<0.001). For secondary pain outcomes, the median worst resting NRS score within 24 h was significantly lower in the ITMB group [3.0 (IQR 3.0-4.0)] than the ISB group [4.0 (IQR 3.0-7.0), median difference 1.0, 95% CI 0 to 1.0, P<0.001]. ITMB also brought significantly lower rebound pain rate (2.6% vs 26.8%, P=0.006) and less frequent rescue analgesia requirements (7.7% vs 29.3%, P=0.016). Safety outcomes revealed significantly lower early hemidiaphragmatic paralysis and dyspnea in the ITMB group: hemidiaphragmatic paralysis occurred in only 2.6% of ITMB patients vs 90.2% of ISB patients (P<0.001); dyspnea incidence was 2.6% (ITMB) vs 19.5% (ISB, P=0.016); Horner's syndrome was absent in the ITMB group while occurring in 29% of ISB patients (P<0.001). Postoperative nausea and vomiting rates were comparable between two groups (P=0.655). No severe block-related complications such as nerve injury, local anesthetic systemic toxicity or pneumothorax were observed in either group. CONCLUSION: Ultrasound-guided ITMB provided non-inferior 24-hour postoperative opioid analgesia compared with ISB and reduced the incidence of early hemidiaphragmatic paralysis in patients undergoing arthroscopic shoulder surgery. The comparable total 24-hour oxycodone consumption reflected distinct time-dependent analgesic profiles, with ISB providing greater analgesic benefit during the early postoperative period, whereas ITMB demonstrated more sustained analgesic effects during the later postoperative period. TRIAL REGISTRATION: This trial was registered at the Chinese Clinical Trial Registry (ChiCTR2400084716). Date of registration: May 23, 2024.