Guide to CT Fluoro Workflow in Robotic Spine Surgery

In spinal surgeries, precision is paramount. CT-Fluoro workflow is a powerful combination of preoperative CT scans and real-time fluoroscopy.

In this post, we will break down the CT-Fluoro workflow, step by step, to give you a clear understanding of how this technology works and how it can improve the outcomes of spinal surgeries.

Pre-requisites

The journey begins with preoperative CT scans, which are used to plan the screw placement. Once the CT scan is obtained, fluoroscopy is employed intraoperatively to register the vertebrae and guide screw trajectories.

Key Points to Remember:

• Preoperative CT Specifications: Ensure the CT scan follows specific guidelines. If the scan doesn't meet these criteria, the robot will not proceed to the planning stage.

• CT Importation and Segmentation: The CT scan is uploaded onto the robotic system. Once uploaded, the region of interest is marked, and the software automatically segments the vertebrae.

• Labeling Vertebrae: The system labels each segment using known vertebral anatomy, typically referencing the sacrum for accurate labeling.

Addressing 3D Deformities in Vertebral Segments

Once the vertebrae are segmented, it’s time to plan the screws at each individual vertebral level. However, if a 3D deformity is present, it can distort the appearance of the vertebral segments, making screw placement more challenging.

Solution:

• Restoring Alignment: Before proceeding with screw planning, the system adjusts the axes to restore normal alignment, ensuring the screws are placed

  accurately.

Visualization of Pedicles

In some cases, the pedicle—the bony structure through which screws are inserted—might not be clearly visible. To overcome this challenge, the system allows visualization of adjacent vertebral segments.

Critical Anatomy Considerations for Safe Screw Placement

It’s essential to ensure that critical anatomical features are adequately visualized during the planning process to avoid complications.

What to Check:

• Medial, Superior, and Inferior Borders: Make sure these critical anatomy components are visible in every segment where screws will be placed.

• Pedicle Wall Violations: Review the axial and sagittal views to detect any potential breaches of the pedicle walls. This is especially crucial at the L5 level, where the trefoil-shaped canal can lead to medial pedicle breaches.

• Alignment of Tulips: Confirm the proper alignment of tulips (the top portion of screws) on both the anteroposterior and lateral views. Misalignment can make rod placement difficult.

Choosing the Right Image Intensifier

The robotic system is compatible with 9-inch and 12-inch image intensifier C-arms that have either BNC or Ethernet output.

Important Note: Currently, there is no adapter available in India for flat-panel C-arms.

C-arm Adapter

The C-arm adapter plays a crucial role in helping the robotic system determine cranial, caudal, and right-left directions during surgery. It must be securely fastened to the image intensifier.

Tip:

• Ensure the adapter is uniformly placed flush with the drum; otherwise, the system might not detect it correctly.

C-arm Setup: Verifying Orientation

To accurately orient the C-arm, the "Iron Man" marker is used, ensuring correct craniocaudal and right-left orientation. Once the orientation is confirmed, no further software adjustments can be made.

But, if something goes wrong...

• If the C-arm is rotated accidentally, the robotic software allows for reorientation to restore the proper alignment.

Region of Interest - CT-Fluoro Procedure

The region of interest is where the robotic system will focus. The robotic arm is fitted with an extender to help position the target vertebrae so they are clearly visible.

Spine Line:

• A "spine line" is drawn by selecting a head point, foot point, and labeling a vertebra in between. If the line is too short or too long, it will need to be redrawn to ensure accurate placement.

Registration: Verifying Vertebrae Positioning

At this stage, radiographs (AP and oblique views) of the target vertebrae, along with the fiducial array, are taken after fine-tuning the robotic arm’s position.

• Verification: After the images are acquired, the system checks their adequacy before proceeding to the next step.

Acquiring the Oblique Image

Once the system verifies the AP images, the fiducial array and extender are removed, and the robotic arm is repositioned to acquire the oblique image at a 65-degree lateral angle.

Vertebrae Registration

The system offers three methods for verifying vertebrae positions: automatic, semiautomatic, and manual.

Automatic Method

• A red dot marks the posteroinferior border of the pedicle on the oblique image. If labeled correctly, the system automatically detects adjacent vertebrae and segments them. If labeled incorrectly, an error message appears.

Semiautomatic Method

The semiautomatic method involves drawing a rectangle around 3/4ths of the vertebra on the oblique image to aid in segmentation. Proper alignment on the anteroposterior view is crucial for success.

 

Manual Method

If the other methods fail, the manual method can be used. While this method is available, it’s less reliable and may result in mismatching between the fluoroscopic and CT images.

CT-Fluoro Image Matching

The next step is to match the CT scan with the fluoroscopic images. The system uses a color-coded system to indicate how well the images align:

• Green: The alignment is perfect.

• Yellow: Minor issues, but the procedure can continue.

• Red: The alignment is not sufficient, and the level cannot be operated upon.

Once the images are aligned, two marks are placed on both the anteroposterior and oblique composite CT-fluoro images. These marks should match using the cortical shadows of the spinous process or pedicle.

The Final Step: Pedicle Screw Placement

With all verification steps complete, it’s time to place the pedicle screws at the planned levels.

The robotic arm guides the drilling of the screw trajectories with precision, ensuring that each screw is placed exactly where it was planned to optimize the surgical outcome.