Pedicle Screw Placement Using an Augmented Reality Head-Mounted Display in a Porcine Model

In this protocol, we provide a detailed guide on integrating augmented reality into your minimal invasive pedicle screw replacement workflow in a pig cadaver model. Since augmented reality is still a relatively new technology in surgery, it is valuable to provide surgeons with proper guidance on its usage during surgery. In this study setup, we use a conventional navigation setup with the addition of an augmented reality headset to provide navigation information right in the surgical field.

This prevents the need of splitting the attention between the surgical field and a separate navigation display. To begin, acquire two 2D scout view shots of the porcine cadaver specimen prepared for surgery. Using the CBCT scanner Loop-X, Identify the vertebral levels of interest by fluoroscopy.

To perform the fluoroscopy scan, use the wireless control tablet of the CBCT scanner to move the scanner to the desired position and mark the position on the skin. Move the CBCT scanner away from the surgical field. Then, wear the backpack for the head-mounted display or HMD.

Expose the spinous process and attach a radiolucent navigation reference clamp to a spinous process in the area of interest. Use the dedicated screwdriver to fasten the clamp. Now, perform an anterior, posterior and lateral scan with the Loop-X.

Use the 2D scans to define the region of interest for the 3D scan. Then, perform a CBCT scan and transfer the scan to the navigation platform. Use the spinal pointer and the reconstructed inline navigation views to verify the accuracy of the patient registration on anatomical landmarks.

To calibrate a navigated drill guide and a screwdriver to the navigation system, select the instrument in the Brainlab Spine and Trauma Instrument Setup Software. Present the real instrument to the camera of the navigation system along with a calibration device. Next, equip the surgeon with a Magic Leap headset and ensure each surgeon is fitted an HMD accurately.

To establish the communication between the HMD and the Spine and Trauma Navigation Software, scan the QR code displayed on the screen of the navigation platform. The corresponding mixed reality application will start running on the HMD and initiate data transfer to it. To perform the mixed reality alignment, look at the spine reference array through the HMD for a few seconds.

Wait for a 3D model of the spine to be accurately augmented onto the specimen in the HMD. In addition to the 3D overlay, look at the 2D navigation views and a second 3D model above the 2D navigation views. Select the Screw Planning mode in the Spine and Trauma Navigation Software.

Adjust the parameters for the length, diameter, and offset of the screw. Plan the pedicle screw paths based on the 3D registered augmented model, aligning them with the anatomy of the spine. Perform fine tuning of the screw paths on the touchscreen of the navigation platform.

Then, mark small skin incisions with the scalpel for minimally invasive pedicle access based on the superimposed 3D model visible through the HMD. After dissecting the soft tissue, position and align the navigated drill guide to the planned path. Using a power drill with 4.5 millimeter drill bit, drill the pedicle.

Perform a second CBCT to acquire reconstructions of the drilled vertebrae for the accuracy analysis. Ensure the drilled canal in the vertebrae is clearly visible before using it for subsequent accuracy analyses. The postoperative CBCT scans were used to assess the time per cannulation and the clinical and technical accuracy.

The mean insertion time per cannulation was 141 plus or minus 71 seconds. All 33 cannulations were considered clinically accurate according to the Gertzbein grading scale. For the 33 pedicle cannulations performed, the technical accuracy was 1.0 plus or minus 0.5 millimeters at the entry point.

And 0.8 plus or minus 0.1 millimeters at the bottom of the drill canal. The angular deviation was 1.5 plus or minus 0.6 degrees. In our study, using augmented reality presented on a head-mounted device provides a high clinical accuracy of drilling pedicles in this pig cadaver model.

Our study provides a step-by-step guide to facilitate the integration of augmented reality in the surgical workflow.