Transiliac-transsacral screw fixation is a challenging task in clinical practice. The teleoperated robotic system-assisted surgery offers a solution to the difficulty of transiliac-transsacral screw placement. Using this technique, surgeons can perform procedures outside the operating room, thus avoiding the danger of radiation exposure.
Additionally, robot-assisted surgery has a higher position-retention capacity compared with the conventional method. This technology can be combined with 3D navigation, virtual reality, augmented reality, and mixed-reality technologies for percutaneous screw placement in the pelvic acetabulum. For efficient fixation, doctors should be skilled in placing the sacroiliac screws using freehand under fluoroscopy prior to using this technique.
To begin, fix the cadaveric pelves in the supine position using a fluoroscopic plate base by inserting two Schanz pins through the femur. In the supine position, place both the posterior superior iliac spines simultaneously on the plank, and the lumbar vertebrae parallel to the floor. Using the Med CAD module of the preoperative planning software, create a cylinder of the pelves'image and define the size of the cylinder by typing in the diameter and length.
Place the cylinder into the S1 or S2 vertebral body and adjust the orientation of the cylinder midline on the axial and coronal images. Check the relationship between the edge of the cylinder and the cortical bone in each image. Fix the pelvis in the supine position on the fluoroscopic operating table.
Then place the robot on the ipsilateral side at 45 degrees to the operating table, with the C-arm perpendicular to the operating table on the contralateral side. Next, place the workstation of the master manipulator outside the operating room. Fix the grid position maker with adhesive tape on the ipsilateral side.
Select the target area by a grid position marker on the true lateral view of the sacrum. Ensuring that the manual traction mode on the console is selected and started, drag the robotic arm to the general area of the S1 or S2 transiliac-transsacral screw entry point. Visualizing the true lateral view of the sacrum, operate the master manipulator in the master-slave operation mode, and adjust the tip of the distal sleeve to be located in the guidewire entry area.
After selecting the remote center of motion, or RCM, mode, continue the C-arm fluoroscopy for the lateral sacral view. Adjust the center of the guidewire sleeve into concentric circles to be consistent with the screw channel. Lock the robotic arm and insert a 2.5 millimeter guidewire through the contralateral ileum using an electric drill.
Then remove the robot in manual traction mode. Turn the C-arm to the inlet and outlet angles to check that the guidewire has broken through, or contacted the interior and posterior sacral cortex and the sacral nerve canal. Insert a 7.3-millimeter semi-threaded screw along the guidewire to the contralateral iliac cortex.
Assess the screw position in the pelvic inlet, outlet, and lateral view. Import the acquired CT scan data into the pre-operative planning software in the DICOM format, to obtain the screw position in coronal, sagittal, and axial images of the pelvis. Post-operative CT reconstruction images and X-rays to evaluate the screw placement showed that no screws penetrated the cortical bone, and all the screws were completely in the cancellous bone.
Sagittal CT reconstruction images of the midline site suggested that the screw is located in the S1 and did not enter the sacral canal, as seen on the reslice axial image. Also, the screw is safe, as seen on the reslice coronal CT reconstruction image. The true lateral view of the sacrum revealed that the screw is located entirely within the bone and is at a safe distance from the anterior and posterior sacral cortex and the sacral nerve canal on the inlet and outlet images.
Remote controlling of this procedure is possible. The key things in this protocol are the accuracy and stability of the master-slave operation mode and RCM mode. This method is expected to become an essential part of telemedicine in the future.
