Sacrococcygeal Joint as a Landmark in Sacral Neuromodulation: A Cadaveric Study

Understanding sacrococcygeal anatomic variation aids in successful execution of office percutaneous nerve evaluation (PNE) without fluoroscopy and sacral neuromodulation (SNM).

In office PNE, the S3 foramen is approximated using an established average distance from the tip of the coccyx to the S3 foramen (approximately 9 cm). Given potential variations in coccyx length, the purpose of this study was to evaluate the reliability of the distance from the sacrococcygeal joint to the S3 foramen as an additional landmark that improves identification of the S3 foramen when performing SNM.

Ten fresh-frozen female cadavers were available for sacral dissection. Numerous bony measurements were obtained: length/width of the coccyx, tip of the coccyx to bilateral S3/S4 foramina, sacrococcygeal joint to bilateral S3/S4 foramina, and interforaminal distance. Median distances were obtained for all measurements. Relationships between measurements were calculated using Pearson product-moment correlation.

Pertinent median cadaveric measurements included coccyx length 34.7 mm, distance from the tip of the coccyx to S3 foramen was 92.2 mm (left) and 94.0 mm (right), distance from sacrococcygeal joint to S3 foramen was 61.8 mm (left, IQR, 59.8 to 67.4 mm) and 63.2 mm (right, IQR, 59.9 to 66.4 mm). A significant correlation was found between change in coccyx length and the tip of the coccyx to the S3 and S4 foramina.

Our study demonstrates reliable median distances from the sacrococcygeal joint to the bilateral S3 foramen. A distance of 6 cm superior to the sacrococcygeal joint is an additional landmark useful for locating the S3 foramen in sacral neuromodulation.