Lumbar Spine Deformation Between Prone and Supine CTs

Introduction: 3D navigation has become increasingly popular among spine surgeons. Currently, these platforms utilize supine preoperative images to register (i.e., align) a patient’s intraoperative position. However, for many spinal procedures, patients are often in the prone position. Given how a patient’s spinal anatomy can change between the prone and supine positions, these imaging protocols may not be the most appropriate to guide surgeons during procedures that require sub-millimeter accuracy. Therefore, this study aims to analyze the deformation of the lumbar spine between the prone and supine positions to determine if imaging protocols for 3D navigation platforms should be reconsidered.

Methods: Eighty-five patients from the National CT Colonography Trial (ACRIN 6664) were included in this study. L1 slope, L1-L5 Cobb angle, pelvic tilt, pelvic incidence, and lumbar lordosis were determined from the radiological scans of each included patient in the prone and supine position. Paired two-tailed t-tests were used to determine statistical significance (p < 0.05) for each endpoint.

Results: L1 slope was greater in the prone (16.95°) than the supine (13.79°) position (p = 0.001). Pelvic tilt was also greater in the prone (22.01°) than the supine (17.74°) position (p = 0.00. However, L1-L5 Cobb angle, pelvic incidence, and lumbar lordosis were not significantly different between the prone and supine position.

Conclusion : While L1-L5 Cobb angle, pelvic incidence, and lumbar lordosis do not differ significantly between the prone and supine positions for the patients analyzed in this study, L1 slope and pelvic tilt do significantly change. These differences in spinal anatomy between the preoperative (supine) and intraoperative (prone) position highlight how imaging protocols for 3D navigation platforms should more rigorously account for these deformations. Future work may consider requiring a prone preoperative scan or accounting for non-rigid deformations in the registration process.