Intra-operative AR-supported rod bending in spinal surgery. A cadaver study

Introduction: In instrumented thoracolumbar fusion, optimal interplay of spinal alignment, screw position, and rod bending is critical to avoid mechanical overload. Augmented Reality (AR) can help to better control intraoperative alignment.
Study Objective: The purpose of the study is to compare rod selection and rod bending in AR supporting technology with conventional Freehand (FH) rod bending technique.
Methods: A cadaver study. For this in-vitro study, a human cadaver was prepared unilaterally with 6 polyaxial pedicle screws between L1-S1. Eleven spine surgeons were asked to select and bend two custom rods, one with the support of AR technology using the 3D scanning method and another one in FH technique in their usual way. All rods were scanned by an independent laboratory and 3D deviations from an “Ideal Template Rod” (ITR) were calculated.
Results: The 3D deviations were statistically significant lower at ± 2 mm (16.2% vs. 40.0%; p ≤ 0.001) and at ± 6 mm (0.0% vs. 1.3%; p ≤ 0.001) thresholds when AR technology was used. Mean total time for bending was 507s for AR and 393s for FH (p=0.126). The number of in-situ checks (p<0.001), rod length corrections (p=0.012) and x-ray controls (p<0.001) were significantly lower for AR supported technology.
Conclusion: AR technology can provide intraoperative data that support surgeons in bending rods that are more precisely adapted to the individual in situ conditions than is possible using FH techniques.