Comparison of the median and intermediate approaches to the ultrasound-guided sacral erector spinae plane block: a cadaveric and radiologic study

Background: Erector spinae plane block (ESPB) is a well -established method for managing postoperative and chronic pain. ESPB applications for the sacral area procedures are called sacral ESPBs (SESPBs). This cadaveric study aimed to determine the distribution of local anesthesia using the median and intermediate approaches to the SESPB. Methods: Four cadavers were categorized into the median and intermediate approach groups. Ultrasound -guided SESPBs were performed using a mixture of radiopaque agents and dye. Following confirmation of the solution distribution through computed tomography (CT), the cadavers were dissected to observe the solution distribution. Results: CT images of the median group demonstrated subcutaneous pooling of the radiopaque solution between the S1 and S5 horizontal planes. Radiopaque solution also passed from the sacral foramina to the anterior sacrum via the spinal nerves between S2 and S5. In the intermediate group, the solution distribution was observed along the bilateral erector spinae muscle between the L2 and S3 horizontal planes; no anterior transition was detected. Dissection in the median group revealed blue solution distribution in subcutaneous tissue between horizontal planes S1 and S5, but no distribution in superficial fascia or muscle. In the intermediate group, red solution was detected in the erector spinae muscle between the L2 and S3 intervertebral levels. Conclusions: Radiologic and anatomic findings revealed the presence of radiopaque dye in the superficial and erector spinae compartments in both the median and intermediate groups. However, anterior transition of the radiopaque dye was detected only in the median group.