The upper sacral nerve root tunnel: an anatomic and clinical study.

Objectives: To radiographically demonstrate the upper sacral nerve root tunnel (USNRT) in both cadaveric specimens and a clinical cohort and to quantify its clinical relevance.

Setting: Level 1 trauma center and anatomy laboratory.

Patients And Participants: Eleven cadaveric pelves and 23 consecutive patients who underwent fluoroscopically assisted iliosacral screw insertions.

Interventions: Cadaveric pelves were fluoroscopically imaged using standard pelvic inlet, outlet, and true lateral sacral views. The course of the USNRT pathway was identified. Then, these tunnels were filled completely with a semisolid radio-opaque agent. The specimens were reimaged after the contrast injection. Clinically, 23 consecutive patients with unstable posterior pelvic ring disruptions were treated using fluoroscopically assisted percutaneous iliosacral screws based on these predictable radiographic landmarks. A total of 44 iliosacral screws were inserted.

Main Outcome Measurements: For the cadaveric portion, the images with contrast were used to identify the USNRTs. For the clinical study, tunnel visualization was determined on all views intraoperatively. Screw placement was documented by postoperative pelvic plain radiographs and computed tomography scan.

Results: In the cadaveric specimens, the contrast agent consistently demonstrated the USNRTs on all 3 pelvic radiographic views. In the clinical series, the USNRTs were well visualized on the pelvic outlet image in all 23 patients (100%). Using the inlet image, the USNRTs were visualized in only 5 of 23 patients (21%). On the true lateral sacral views, the USNRTs were seen in 21 of 23 patients (91%). Using these USNRT radiographic landmarks, no iliosacral screw was extraosseous.

Conclusions: The USNRTs have a consistent radiographic appearance that is best seen on the pelvic outlet and true lateral sacral views, but their course is best understood when seen on all 3 views. Awareness and understanding of the USNRT, its course, and its radiographic landmarks allow the surgeon to avoid tunnel intrusion by an iliosacral screw.