A prospective randomized controlled trial comparing subpectineal and interfascial obturator nerve block techniques in preventing adductor muscle spasm during transurethral resection of bladder tumors

Obturator nerve block (ONB) is commonly used to prevent adductor muscle spasm during transurethral resection of bladder tumors (TURBT) involving lateral wall lesions. This study aimed to compare the clinical effectiveness and safety of ultrasound-guided subpectineal (proximal) and interfascial (distal) ONB techniques, utilizing an anatomically tailored dosing regimen adapted to the targeted fascial compartments. This prospective randomized controlled trial included 60 patients scheduled for elective TURBT under spinal anesthesia. Patients were randomly allocated into two equal groups: subpectineal ONB (Group I, n = 30), which received a single 10 mL bolus of 0.375% bupivacaine into the single subpectineal plane, and interfascial ONB (Group II, n = 30), which received a total of 20 mL of 0.375% bupivacaine split into two separate 10 mL injections for the two distinct interfascial planes. Intraoperative adductor muscle spasm was evaluated by a blinded surgeon using a 4-grade scale (Grades I–IV). The primary outcome was the block success rate, defined as the absence of severe spasm (Grade IV) requiring rescue general anesthesia. Baseline demographic characteristics and the number of needle insertions were similar between the groups. No vascular puncture, hematoma, or bladder perforation occurred. The descriptive block success rate was high in both groups, reaching 86.7% (95% c onfidence interval: 74.6% to 98.8%) in Group I and 93.3% (95% Confidence Interval: 84.4% to 100%) in Group II, with no statistically significant difference observed ( p = 0.671). Both ultrasound-guided ONB techniques demonstrate high descriptive clinical success rates when utilizing an anatomically tailored dosing regimen. Although the non-significant p-value must be interpreted with caution due to sample size limitations, both approaches provide viable and effective options for preventing severe adductor muscle spasm during lateral wall TURBT. ClinicalTrials.gov Identifier: NCT07481123 (retrospectively registered on 02 March 2026).