Robot-Guided S2AI Screw Insertion

Introduction

Robotic-guided S2AI screw insertion offers precision and efficiency, requiring only minor workflow modifications compared to thoracolumbar pedicle screw placement. This guide outlines the step-by-step procedure for accurate S2AI insertion.

Workflow and Initial Setup

1. Workflow Modifications:

   • Minor changes from thoracolumbar pedicle screw workflows.

2. 3 Define Scan and Snapshot:

   

   • The robot scans the environment to define operational areas and "no-fly zones."

3. Marking Region of interest and Positioning Fiducial Array

   

   • A blunt passive planar probe is inserted into the region of interest.

   • A star marker is attached to the robotic arm for vertebra identification.

4. O-arm Scan:

   

   • The patient is covered with a plastic drape, and 3D scans are performed to ensure all beads of the star marker are visible.

5. Field of View (FOV):

   • Standard FOV: 20 cm, expandable to 40 cm.

   • S2AI Requirements: FOV of 40 cm is necessary for S2AI and iliosacral screw insertion.

     

   • Ensure bilateral iliac wings are visible during FOV acquisition.

     

6. Common Errors:

   • Narrowing the region of interest on the robot console may lead to cropped images.

Trajectory Planning

1. Planning Views:

   • Focus on axial, coronal, and sagittal sections.

2. Screw Entry Points:

   • Start Point: Midpoint between S1 and S2 foramen, lateral to the foraminal border.

   • Angles: Lateral angulation of 40-50 degrees and caudal angulation of 20-30 degrees.

   • Screw Length: Minimum 80 mm.

   • Larger entry angles increase skiving risk.

     

3. Screw Placement Technique:

   • Screws are generally placed from the contralateral side.

   • Skin incision allows bilateral S2AI screws via a midline incision.

   
   
   
   

4. Drilling Techniques:

   • Pilot Hole: Created with a feather-touch drill (30 mm long).

   • Tapping:

     • Use a 4 mm awl-tipped tap to minimize maltracking.

     • Follow with a 6.5 mm tap for full length.

   • Screw Insertion: An 8.5 mm screw is inserted under navigation guidance.

Special Considerations

1. Equipment Challenges:

   • Non-availability of a longer 3 mm high-speed drill bit.

2. Existing Instruments:

   • Adapt workflow to available tools; a sharp awl-tipped tap reduces skiving risk.

3. Planning to Execution:

   • Precise planning ensures flawless execution and enhanced precision.

Summary of the Steps

Post-Operative Assessment

1. Post-Operative CT:

   

2. Additional Planning:

   • The robot can assist in planning and placing S1 alar iliac screws for enhanced spinopelvic stability.