Mixed Reality Guided Pedicle Screw Placement in Upper Thoracic and Scoliotic Cadaveric Spines

Introduction: Mixed reality (MR) holds potential for improving the accuracy of placing pedicle screws in spinal deformity and technically challenging regions of the spine. The goal of this study is to evaluate the safety of MR guided pedicle screw placement in upper thoracic and scoliotic cadaveric spines.

Methods: Pedicle screws were placed in cadaveric specimens spanning T1 to S1 using a MR headset integrated with SurgicalAR guidance software (Medivis, NY). Registration for navigation was conducted using a point-to-point method with four metal fiducial pins. CT scans were performed after screw cannulation to assess screw accuracy. Screw accuracy was evaluated using both the Gertzbein-Robbins and Heary classification systems. Heary scores I-II were deemed clinically acceptable. Analysis was conducted to assess the distribution of screw accuracy from T1-T5 and T6-S1 and in cadavers with and without scoliosis, focusing on the proportion of each grade within both classification systems.

Results: In total, 192 pedicle screws from T1-S1 (110 right-sided, 82 left-sided) were placed. The majority of screws were placed with sufficient clinical accuracy: 171 (89.1%) screws were Heary Grade I-II. Screws placed at T1-T5 had similar Gertzbein grade distribution compared to screws at T6-S1 (p=0.14). However, there was a higher proportion of T6-S1 screws placed with clinically acceptable accuracy, compared to T1-T5 (Heary Grades I-II: 93% vs. 76%, p=0.012). There was no difference in the Gertzbein (p=0.17) or Heary (p=0.49) distributions for screws that were placed in scoliotic spines, compared to those placed in non-scoliotic spines.

Conclusion : MR-guided pedicle screw placement in spinal deformity cadavers demonstrated high clinical accuracy. Pedicle screw placement was similar between the scoliotic and non-scoliotic cadaveric spines; however, screw placement in the upper thoracic spine (T1-T5) was clinically inferior to screws placed below T6. This demonstrates the utility of MR-guided pedicle screws in complex spinal deformity, suggesting potential to integrate MR-guided navigation into clinical practice in the near future.