Background Different approaches to the obturator nerve have been described. However, few have focused on the injection point inferior the iliopubic ramus, specifically at the exit of the obturator canal. This study aims to anatomically evaluate the ultrasound-guided obturator nerve block at the exit of the obturator canal, detailing anatomical landmarks and solution distribution.

Methods This anatomical study was conducted using 10 cadavers to generate 20 hemipelvis samples. Ultrasound references were utilized to identify the obturator canal, iliopubic ramus, pectineus and external obturator muscles, and the obturator membrane. An ultrasound-guided obturator nerve block was performed using a low-frequency convex probe for initial identification and a high-frequency linear transducer for the injection of a methylene blue solution. Subsequent dissections were performed to evaluate the distribution of the dye within the obturator nerve.

Results The injection of methylene blue consistently stained the common trunk and anterior branch of the obturator nerve in 100% of the cases and the posterior branch in 80% of the samples. Intrapelvic staining was observed in 65% of the specimens, indicating effective diffusion of the dye. Key anatomical landmarks, such as the iliopubic ramus and the obturator membrane, were crucial for accurate identification and injection.

Conclusion In conclusion, sagittal approaches using the iliopubic ramus as an anatomical reference achieve the most complete obturator nerve block. Our anatomical study details the structures of the obturator canal and access to the obturator nerve at its exit. Future studies are needed to confirm its safety and efficacy.