Rapid Re-Registration of Spinal Scans in the Event of Segmental Movement Using a Novel Augmented Reality System: Assessment of Precision

Introduction: Segmental spinal movement or movement of a spinal array frequently require rescanning the spine in navigated or robotic procedures. We assessed the reproducibility of a rapid 1 min reregistration technique using an Augmented Reality (AR) spine system.

Methods: A lumbar spine phantom was scanned using a 3D scanner (GE OEC 3D). An AR system (OnPoint Surgical) was used to register the scan in a coordinate system, using a surface scan collecting 100 surface points in 3 different anatomic regions, selected based on exposure. Registration error (RE) was measured by placing a pointer on the physical bone, measuring the distance between the tracked pointer tip and the CT surface. Mean RE was measured for L3 left and right pedicles. Mean RE was measured 1.) for initial registration, 2.) after placing a shim underneath the L3 vertebral body simulating segmental movement, 3.) following reregistration. Reproducibility error of the reregistration was computed as the Root Mean Square Error (RMSE) = Sum of Errors Squared/ Error Count.

Results: Mean RE and standard deviation (SD) (in mm) were for left and right pedicles:
1.) Initial registration: Left 0.04 (SD 0.16), right 0.08 (SD 0.16)
2.) After vertebral movement with shim: Left 2.10 (SD 0.61), right 2.39 (SD 0.53)
3.) Post rapid reregistration: Left 0.08 (SD 0.14), right 0.06 (SD 0.18)
Reproducibility error of reregistration was left 0.15 and right 0.18mm.

Conclusion : In addition to directly registering intraoperative 3D scans, the AR system supports surface registration of pre- and intraoperative CT scans. In the event of segmental movement, a preoperative CT or intraoperative spin can be reregistered within 1 min with sub-millimeter precision. The rapid reregistration is precise and advantageous in the presence of segmental vertebral movement or inadvertent movement of the spinal array, obviating a re-spin with 15-20 minute OR time savings.