Preoperative-to-interoperative shift in spine pose measured as change in lordosis Cobb angle and its effect on navigational accuracy

Background: Successful navigation in spine surgeries relies on accurate representation of the spine's interoperative pose. However, its position can move between preoperative imaging and instrumentation. A measure of this motion is a preoperative-to-intraoperative change in lordosis. Objective: To investigate the effect this change has on navigation accuracy and the degree to which an interoperative stereovision system (iSV) for intraoperative patient registration can account for this motion. Methods: For six live pig specimens, a preoperative CT (pCT) was obtained of the lumbar spine in supine position and an interoperative CT in the prone position. Five to six iSV images were intraoperatively acquired of the exposed levels. A fiducial-based registration was performed on a navigation system with the pCT. Separately, the pCT was deformed to match iSV surface data to generate an updated CT (uCT). Navigational accuracy of both the commercial navigation and iSV systems was determined by tracked fiducials and landmarks. Change in lordosis Cobb angle between supine and prone positions was calculated representing preoperative-to-interoperative change in spine pose. Results: The preoperative-to-interoperative change ranged from 12 to 41 degrees. Registration accuracy varied by 4.8 and 1.5 mm for the commercial system (6.2+-1.9 mm) and iSV (3.0+0.6 mm) respectively. Rank correlation shows strong association between increased registration error and positional change for the commercial system (correlation of 0.94, P=0.02) while minimal association for iSV (0.09, P=0.92). Conclusion: Change in spinal pose effects navigational accuracy of commercial systems. iSV shows promise in accounting for these changes given its accuracy is uncorrelated with pose change.