Obturator nerve block: a technique based on anatomical findings and MRI analysis

The block of the obturator nerve is used in pain medicine mostly for the management of acute pain after lower limb surgery or for chronic hip pain. The aim of this study was to define an injection technique based on an anatomical investigation and a magnetic resonance (MRI) analysis.

Ten cadavers were studied, four of them bilaterally. The relationship of the nerve to the relevant landmarks were measured. An MRI study was undertaken on 20 patients to identify the approach that would minimize penetration of great vessels during needle insertion.

The median (range) distance between projection of the obturator nerve to the skin on the sagittal plane and the pubic tubercle and pubic symphysis was 2.5 cm (1.0-3.8) and 5.4 cm (4.6-6.5), respectively. The nerve was located 2.0 cm (1.5-2.8) deeper to the superior ramus of the pubis. The MRI analysis revealed that a skin point of entry that is close to the 25th percentile of the distance between projection of the nerve to the skin and pubic tubercle (2.3 cm) or symphysis (5.1 cm) is associated with a very low risk of vessel puncture.

Based on the above findings, a technique of block of the obturator nerve could be defined. The method has the potential to enable an efficient and safe identification of the target nerve in clinical practice.