Use of an inertial measurement unit sensor in pedicle screw placement improves trajectory accuracy.

Satoshi Baba,Kazuhito Itamoto,Takeshi Watanabe,Go Kato,Mitsumasa Hayashida,Kenichi Kawaguchi,Takao Mae,Yasuharu Nakashima,Dean Chou

doi:10.1371/journal.pone.0242512

Abstract

Ascertaining the accuracy of the pedicle screw (PS) trajectories is important as PS malpositioning can cause critical complications. We aimed to determine the angle range over which estimation is unreliable; build a low-cost PS placement support system that uses an inertial measurement unit (IMU) to enable the monitoring of surgical tools and PS trajectories, and determine the situations where IMU support would be most beneficial. In PS insertion experiments, we used cadaver samples that included lumbar porcine spines. Computed tomography images obtained before and after PS insertion were viewed. Offsets between the planned and implanted PS trajectories in the freehand and IMU-assisted groups were analyzed. The PS cortical bone breaches were classified according to the Gertzbein and Robbins criteria (GRC). Added head-down tilted sample experiments were repeated wherein we expected a decreased rostro-caudal rotational accuracy of the PS according to the angle estimation ability results. Evaluation of the PS trajectory accuracy revealed no significant advantage of IMU-assisted rostro-caudal rotational accuracy versus freehand accuracy. According to the GRC, IMU assistance significantly increased the rate of clinically acceptable PS positions (RoCA) than the freehand technique. In the head-down tilted sample experiments, IMU assist provided increased accuracies with both rostro-caudal and medial rotational techniques when compared with the freehand technique. In the freehand group, RoCA was significantly decreased in samples with rostral tilting relative to that in the samples without. However, In the IMU-assisted group, no significant difference in RoCA between the samples with and without head-down tilting was observed. Even when the planned PS medial and/or rostro-caudal rotational angle was relatively large and difficult to reproduce manually, IMU-support helped maintain the PS trajectory accuracy and positioning safety. IMU assist in PS placement was more beneficial, especially for larger rostro-caudal and/or medial rotational pedicle angles.

Highlights

Since lumbar spinal immobilization using pedicle screws (PSs) was conceived by Boucher [1], the indications for PS placement have been broadly expanded to include cervical spinal fixation [2]
A previous study on estimating the theoretical accuracy requirement for PS placement demonstrated that if there was no translational error for the PS placement entry point (EP), the maximum permissible rotational error tolerance for avoiding pedicle wall perforation was
The results of inaccurate angle estimation ability described above suggested that our just noticeable angle difference was not small enough for producing accurate medial rotation of the pedicle probe or PS driver at all vertebral levels, and the inaccuracy increased as the ideal medial rotational angle for PS placement into human vertebrae increased from 0 ̊ to 30 ̊, as demonstrated in a previous paper [30]

Summary

Introduction

Since lumbar spinal immobilization using pedicle screws (PSs) was conceived by Boucher [1], the indications for PS placement have been broadly expanded to include cervical spinal fixation [2]. For safe and accurate PS placement, both the coordinates of the entry point (EP) and PS trajectory are critical, and many studies have used 3-dimensional CT-based navigation system to demonstrate improved accuracy for these parameters [9,10]. Other newly developed PS placement support tools, such as spine-mounted robot-assisted systems [11,12,13,14,15] or artificial reality spine surgical navigation system [16,17,18] have been introduced

Objectives

Results

Discussion

Conclusion