Optical Topographic Imaging for Spinal Intra-Operative Three-Dimensional Navigation in Mini-Open Approaches: A Prospective Cohort Study of Initial Pre-Clinical and Clinical Feasibility.

PURPOSE: Computer-assisted three-dimensional navigation often guides spinal instrumentation. Optical topographic imaging (OTI) offers comparable accuracy and significantly faster registration relative to current navigation systems in open posterior thoracolumbar exposures. Here, we validate the utility and accuracy of OTI in minimally-invasive (MIS) spinal approaches.

METHODS: Mini-open midline posterior exposures were performed in four human cadavers. Square exposures of size 25, 30, 35, and 40mm were registered to preoperative CT imaging. Screw tracts were fashioned using a tracked awl and probe with instrumentation placed. Navigation data were compared to screw positions on postoperative CT imaging and absolute translational and angular deviations were computed. In-vivo validation was performed in eight patients, with mini-open thoracolumbar exposures and percutaneous placement of navigated instrumentation. Navigated instrumentation was performed in the previously described manner.

RESULTS: For 37 cadaveric screws, absolute translational errors were (1.79±1.43mm) and (1.81±1.51mm) in the axial and sagittal planes, respectively. Absolute angular deviations were (3.81±2.91°) and (3.45±2.82°), respectively (mean±SD). The number of surface points registered by the navigation system, but not exposure size, correlated positively with the likelihood of successful registration (OR=1.02, 95%-CI 1.009-1.024, p<0.001). 55 in-vivo thoracolumbar pedicle screws were analyzed. Overall (mean±SD) axial and sagittal translational errors were (1.79±1.41 mm) and (2.68±2.26 mm), respectively. Axial and sagittal angular errors were (3.63±2.92°) and (4.65±3.36°), respectively. There were no radiographic breaches >2mm or any neurovascular complications.

CONCLUSIONS: OTI is a novel navigation technique previously validated for open posterior exposures and in this study has comparable accuracy for mini-open MIS exposures. The likelihood of successful registration is affected more by the geometry of the exposure than its size.