Lateral Lumbar Interbody Fusion with Prone Robotic Pedicle Screw Placement: A Ct-based Assessment of Accuracy

Introduction: Lateral lumbar interbody fusion (LLIF) has conventionally relied on pedicle screw placement (PSP) for construct stabilization. Single-position surgery with lumbar interbody fusion in the lateral decubitus with concomitant PSP has been associated with increased operative efficiency, but decreased accuracy of robot-assisted PSP. We assessed the accuracy of robot-assisted pedicle screws in the prone position after LLIF.

Methods: We identified all consecutive patients treated with LLIF and robot-assisted PSP in the prone position by a single surgeon between September 2020 and June 2024. All screws were analyzed using CTs to determine appropriate positioning according to the Gertzbein-Robbins classification.

Results: Fourteen consecutive patients (84 screws) were included, average BMI 32.8±6.4kg/m2, average age 67.3±7.8 years; 3 one-level LLIF, 8 two-level LLIF, and 3 three-level LLIF. In 9/14 cases an intra-op O-arm spin was performed after the LLIF and used for the robotic plan; in 5/14 cases the pre-operative (pre-LLIF) CT was used for planning. 76 screws (90.5%) were Gertzbein-Robbins grade A; 5 screws (6%) grade C, 3 (3.5%) were grade D. In 9/14 cases an intra-op O-arm spin was performed to verify screw accuracy, and 4 screws were repositioned intraoperatively, bringing the Gertzbein-Robbins grade A to 95.2% (80/84). One patient that underwent a three-level LLIF, developed postoperative knee extension weakness (4/5), and postoperative CT showed 2 grade D screws, and 1 grade C screw, intraoperative O-arm spin was not performed to verify screw accuracy. The patient was taken back to the OR for screw revision with navigation, with subsequent improvement of the weakness. No statistically significant difference in BMI was observed between patients with or without mispositioned screws, though BMI was greater than 30kg/m2 in all patients with mispositioned screws.

Conclusion : The present data suggest pedicle screws placed with robotic assistance in the prone position after LLIF have lower accuracy than robot-assisted PSP after posterior lumbar interbody fusion. This study highlights the importance of performing an intraoperative O-arm spin to check screw accuracy when placing robot-assisted screws in the prone position after LLIF.