Injectate volumes needed to reach specific landmarks in s1 transforaminal epidural injections.

Objectives:   We identify the contrast volumes needed to reach specific landmarks during S1 transforaminal epidural injections (S1-TFEIs).

Design:   Prospective, nonrandomized, observational human study. Setting.  Academic/private pain management practice. Subjects.  Forty-two patients undergoing S1-TFEIs were investigated. Thirty-seven patients were included in this study. Interventions.  S1-TFEIs were performed using contrast-enhanced fluoroscopic visualization.

Main Outcome Measurements:   After confirming appropriate spinal needle position, up to 5 mL of nonionic contrast was slowly injected. Under biplanar fluoroscopic guidance, contrast volumes were recorded as flow reached specific anatomic landmarks: the ipsilateral S1 pedicle, the superior aspect of the L5-S1 disc space, and across the midline of the spinous process.

Results:   After injecting 2 mL of contrast, 100% of S1-TFEIs spread to the medial aspect of the ipsilateral superior pedicle of S1. After injecting 3.0 mL of contrast, 92% of S1-TFEIs spread to the superior aspect of the L5-S1 intervertebral disc. After injecting 4 mL of contrast, 27% of S1-TFEIs spread beyond the midline of the spinous process, but by only a few millimeters.

Conclusions:   This study demonstrates injectate volumes needed to reach specific anatomic landmarks in S1-TFEIs. A volume of 3.0 mL of contrast reaches the superior aspect of the L5-S1 intervertebral disc 92% of the time.