An intraoperative fluoroscopic method to accurately measure the post-implantation position of pedicle screws

  • Robyn Newell
  • Hooman Esfandiari
  • Carolyn Anglin
  • Renee Bernard
  • John Street
  • Antony J Hodgson
Original Article



Pedicle screw malplacement, leading to neurological symptoms, vascular injury, and premature implant loosening, is not uncommon and difficult to reliably detect intraoperatively with current techniques. We propose a new intraoperative post-placement pedicle screw position assessment system that can therefore allow surgeons to correct breaches during the procedure. Our objectives were to assess the accuracy and robustness of this proposed screw location system and to compare its performance to that of 2D planar radiography.


The proposed system uses two intraoperative X-ray shots acquired with a standard fluoroscopic C-arm and processed using 2D/3D registration methods to provide a 3D visualization of the vertebra and screw superimposed on one another. Point digitization and CT imaging of the residual screw tunnel were used to assess accuracy in five synthetic lumbar vertebral models (10 screws in total). Additionally, the accuracy was evaluated with and without correcting for image distortion and for various screw lengths, screw materials, breach directions, and vertebral levels.


The proposed method is capable of localizing the implanted screws with less than 2 mm of translational error (RMSE: 0.7 and 0.8 mm for the screw head and tip, respectively) and less than \(2.3^{\circ }\) angular error (RMSE: \(1.3^{\circ }\)), with minimal change to the errors if image distortion is not corrected. Breaches and their anatomical locations were all correctly visualized and identified for a variety of screw lengths, screw materials, breach locations, and vertebral levels, demonstrating the robustness of this approach. In contrast, one breach, one non-breach, and the anatomical location of three screws were misclassified with 2D X-ray.


We have demonstrated an accurate and low-radiation technique for localizing pedicle screws post-implantation that requires only two X-rays. This intraoperative feedback of screw location and direction may allow the surgeon to correct malplaced screws intraoperatively, thereby reducing postoperative complications and reoperation rates.


Pedicle screw Fluoroscopy 3D visualization Spinal surgery Feedback 



This project was supported by the Collaborative Health Research Projects (CHRP) program and the Engineers in Scrubs CREATE program, and funded by the Natural Sciences and Engineering Research Council of Canada (NSERC, Grant #CHRPJ 462233-2014) and the Canadian Institutes of Health Research (CIHR, Grant #MOP-134758).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

This article does not contain any studies with human participants or animals performed by any of the authors.

Informed consent

This article does not contain patient data.


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Copyright information

© CARS 2018

Authors and Affiliations

  1. 1.Biomedical EngineeringUniversity of British ColumbiaVancouverCanada
  2. 2.Department of Mechanical EngineeringUniversity of British ColumbiaVancouverCanada
  3. 3.McCaig Institute for Bone and Joint HealthUniversity of CalgaryCalgaryCanada
  4. 4.Department of Civil EngineeringUniversity of CalgaryCalgaryCanada
  5. 5.Combined Neurosurgical and Orthopaedic Spine ProgramUniversity of British ColumbiaVancouverCanada
  6. 6.International Collaboration on Repair DiscoveriesUniversity of British Columbia, Blusson Spinal Cord CenterVancouverCanada
  7. 7.Department of OrthopaedicsUniversity of British ColumbiaVancouverCanada

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