Anatomical Analysis of the S1 Neural Foramen Using Three-Dimensional Computed Tomography Imaging: Insights for Effective S1 Nerve Root Block

OBJECTIVE: The first sacral nerve root block (S1 NRB) is used to diagnose and treat lumbosacral and radicular pain. This study aims to clarify the anatomy of the S1 neural foramen using three-dimensional (3D) computed tomography (CT) images and to establish the optimal fluoroscopic angle, localize the S1 neural foramen on fluoroscopy, and determine the safe puncture depth for S1 NRB. METHODS: In this single -center cohort study, 200 patients with lumbar degenerative disease who underwent preoperative CT were enrolled. Four distinct studies were conducted using the CT data. Study 1 examined the correlation of the sacral slope angle and the supine and prone positions. Study 2 analyzed the tunnel view angle (TVA) using 3D reconstruction. Study 3 ascertained the location of the S1 neural foramen in fluoroscopy images. Study 4 investigated the safe depth for performing S1 NRB. RESULTS: The regression analysis in Study 1 revealed a correlation of the sacral slope angle and the supine and prone positions. Study 2 determined an optimal fluoroscopic TVA of approximately 30 degrees for the S1 NRB. Study 3 found that the S1 neural foramen was located caudal to the L5 pedicle 1.7 +/- 0.2 times the distance between the L4 and L5 pedicles. Study 4 revealed that the depths of the S1 neural foramen and root were 27.0 +/- 2.1 mm and 16.5 +/- 2.0 mm, respectively. CONCLUSIONS: Our study suggests an optimal fluoroscopic angle, a simple method to locate the S1 neural foramen on fluoroscopy, and an ideal puncture depth for a safe and effective S1 NRB.