Accuracy of intraoperative image-free and tracker-free mixed reality-guided pedicle screw placement across the entire spine: a cadaveric study

To evaluate the accuracy of intraoperative image-free and tracker-free mixed reality (MR)-guided pedicle screw (PS) placement across the entire spine using human cadavers. Eight human cadaveric specimens were used in this study. Three-dimensional holograms of the cadavers were automatically generated from preoperative CT data uploaded to the Holoeyes MD service (Holoeyes Inc., Tokyo, Japan). Using a Magic Leap One® headset (Magic Leap Inc., Plantation, FL, USA), the hologram with predetermined PS trajectory lines was superimposed onto the cadaveric spine, and PSs were inserted following the trajectory lines from C2 to L5. Accuracy was evaluated using the Gertzbein–Robbins classification: Grade A (screw within the pedicle), B (breach < 2 mm), C (2–4 mm), D (4–6 mm), and E (>6 mm). Grades A and B were considered clinically acceptable. Of the 261 PSs placed (93 cervical, 118 thoracic, and 50 lumbar), 166 (63.6%) were classified as Grade A, 88 (33.7%) as Grade B, 5 (1.9%) as Grade C, 2 (0.8%) as Grade D, and none as Grade E, resulting in an overall clinically acceptable placement rate of 97.3%. The clinically acceptable placement rate differed significantly among spinal regions (p = 0.030), with the lowest rate observed in the cervical spine (93.5%), compared with the thoracic (99.2%) and lumbar (100%) spine. This cadaveric study demonstrated that image-free and tracker-free MR-guided PS placement achieved a high rate of clinically acceptable screw placement. These findings suggest that this simplified image-free and tracker-free MR navigation technique may offer a feasible approach for guiding spinal instrumentation. However, the high accuracy achieved by a single experienced surgeon may represent a best-case scenario, and its generalizability to less experienced surgeons remains uncertain.