Three-dimensional assessment of robot-assisted pedicle screw placement accuracy and instrumentation reliability based on a preplanned trajectory

J Neurosurg Spine 33:519–528, 2020

Robotic spine surgery systems are increasingly used in the US market. As this technology gains traction, however, it is necessary to identify mechanisms that assess its effectiveness and allow for its continued improvement. One such mechanism is the development of a new 3D grading system that can serve as the foundation for error-based learning in robot systems. Herein the authors attempted 1) to define a system of providing accuracy data along all three pedicle screw placement axes, that is, cephalocaudal, mediolateral, and screw long axes; and 2) to use the grading system to evaluate the mean accuracy of thoracolumbar pedicle screws placed using a single commercially available robotic system.

METHODS The authors retrospectively reviewed a prospectively maintained, IRB-approved database of patients at a single tertiary care center who had undergone instrumented fusion of the thoracic or lumbosacral spine using robotic assistance. Patients with preoperatively planned screw trajectories and postoperative CT studies were included in the final analysis. Screw accuracy was measured as the net deviation of the planned trajectory from the actual screw trajectory in the mediolateral, cephalocaudal, and screw long axes.

RESULTS The authors identified 47 patients, 51% male, whose pedicles had been instrumented with a total of 254 screws (63 thoracic, 191 lumbosacral). The patients had a mean age of 61.1 years and a mean BMI of 30.0 kg/m2. The mean screw tip accuracies were 1.3 ± 1.3 mm, 1.2 ± 1.1 mm, and 2.6 ± 2.2 mm in the mediolateral, cephalocaudal, and screw long axes, respectively, for a net linear deviation of 3.6 ± 2.3 mm and net angular deviation of 3.6° ± 2.8°. According to the Gertzbein-Robbins grading system, 184 screws (72%) were classified as grade A and 70 screws (28%) as grade B. Placement of 100% of the screws was clinically acceptable.

CONCLUSIONS The accuracy of the discussed robotic spine system is similar to that described for other surgical systems. Additionally, the authors outline a new method of grading screw placement accuracy that measures deviation in all three relevant axes. This grading system could provide the error signal necessary for unsupervised machine learning by robotic systems, which would in turn support continued improvement in instrumentation placement accuracy.


Spine Navigation Based on 3-Dimensional Robotic Fluoroscopy for Accurate Percutaneous Pedicle Screw Placement

World Neurosurg. (2017) 108:76-83.

Minimally invasive spine surgery is associated with obstructed visibility of anatomic landmarks and increased radiation exposure, leading to higher incidence of pedicle screw mispositioning. To address these drawbacks, intraoperative 3-dimensional fluoroscopy (io3DF) and navigation are being increasingly used. We aimed to present our dedicated multifunctional hybrid operating room (HyOR) setup and evaluate the accuracy and safety of io3DF image-guided spinal navigation in transforaminal lumbar interbody fusion with percutaneous pedicle screw (PPS) placement.

METHODS: The HyOR includes a fixed 3D multiaxis robotic fluoroscopy arm that moves automatically to the preprogrammed position when needed. An initial io3DF assessment is performed to collect intraoperative images, which are automatically transferred into the navigation system. These data are used to calibrate the PPSs and insert them under computer-assisted navigation. A second io3DF is performed for verifying PPS position.

RESULTS: Between January 2014 and December 2016, 66 consecutive patients (age, 58.6  14.1 years) were treated for refractory lumbar degenerative pain. Seventy-three spinal levels were treated, and 276 screws were placed, with 4.2 ± 0.76 screws per patient. There was no measurable radiation to the HyOR staff, whereas the mean radiation dose per patient was 378.3  uGym2. The overall accuracy rate of PPS placement was 99.6%. There were no significant procedure-related complications.

CONCLUSIONS: Spine navigation based on io3DF images enabled us to avoid radiation exposure to the operating room team while delivering minimal but sufficient radiation doses to our patients. This approach achieved an accuracy rate of 99.6% for PPS placement in the safe zone, without significant complications.

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