This protocol facilitates the virtual treatment of patients with facial deformities and the creation of novel surgical guides and fixation plates for the operation we're planning. The advantages of this technique include full surgical control, the ability to plan osteotomies and fixation plates, a significantly reduced cost and operation duration, a superior performance and highly accurate results. This technique can be used with any surgical intervention that requires bony alterations as it allows the creation of personalized surgical guides and fixation plates.
We're currently using this protocol for research studies in rabbits using personalized scaffolds. Also these programs are very user friendly. It can take time to master the computer assisted design process.
Patients and practice will help with the learning process. As the method is based on virtual planning, observing each stage of the process can be extremely helpful. To plan the jaw repositioning, load the patient facial bone computed tomography in the appropriate imaging software.
To enter the editing mode for future editing sessions, click 3D and Edit. Use the orientation button to orient the 3D image and use the build X-ray buttons to create a panoramic image. Open Tools, Orthognathic surgical planning, start new workup and position the segments within the panoramic image.
Crop each segment to contain the area of the corresponding bone and select the appropriate osteotomy for the patient, moving the yellow circles to mark the exact location of the osteotomy lines. Then click on each location to mark the location for each landmark of interest. To perform movements of bone segments, right click and select input movements using keyboard to move the bone to the correct location.
To track the movement of key landmarks, click Treat options and select showed landmark offset in measurement tables. Then use the slide bar, the export segments and STL button to export the STL files of the pre and one in the post operative stage bone positions. To prepare patient's specific fixation plates and surgical guides, import the STL files showing the position of the upper jaw and mid face following the osteotomy and the repositioning to the final position into the appropriate 3D design software program.
Under the Planes menu, select Create plane and move the plane parallel to the bone where the plate will be placed. Use a circle shape from the sketch menu to create a circle with a size appropriate for the screws to be used and create a three millimeter diameter larger second circle around the previous circle to outline the fixation plate. Place copies of the circles over the screw positions.
Under curves, use the project sketch tool to select the circles that will be transferred from the plane to the bone. To connect the outer circles for the outer border plate design, select the split tool and define the part of the circle that will be removed to allow for connection to the adjacent circles. Using the select option, select the defined part of the circle and delete it.
Using the draw curve tool, connect the outer circles to create a continuous outer shape of the patient's specific plate. Before creating the fixation plate, right click to duplicate and select duplicate from the object list to duplicate the upper jaw. In the Detail Clay menu, select the emboss with curve tool to modify the volume of the fixation plate based on the previously projected curves.
Select the outer shape curve and place the circle shaped cursor inside on the surface of the shaped plate on the side to be embossed. Set the parameters of the function mainly the distance to control the thickness of the future fixation plate and separate the plate from the upper jaw. Right click the original upper jaw and click Boolean, Remove From an upper jaw with plate.
To create the holes for the screws, select the circles to be cut and in the Sub D surfaces menu, select the wire cut sub D tool in the circles of interest to create rods perpendicular to the plate in the size of the desired holes. Then use Boolean and remove from to select each rod to be subtracted from the plate. To create the guides, reposition the upper jaw to its original location but with the screw holes marked.
Under the Select move clay menu, select Register pieces and select upper job post movement for the source in the upper jaw and mid face prior to the movement for the target. It is essential to align the maxilla with the fixation plate holes to ensure that the surgical guide planning will be based on the correct position of the final holes. Then, based on newly positioned holes, create the surgical guides as demonstrated for the fixation plates.
In these images, the retrognathic upper jaw and prognathic lower jaw of a 23 year old female who suffered from condylar hyperplasia at a younger age exhibiting the discrepancies between the jaws are shown. In the frontal view, the severe asymmetry can be observed even more clearly. Using imaging software as demonstrated, a surgical treatment plan based on the lateral cephalometric analysis can be performed.
The 3D. STL files were imported into the 3D design software in both pre and post planned bony movement steps to allow planning of the patient specific fixation plate. The surgical guide was then planned and the plate could then be implanted via bimaxillary surgery resulting in correction of the severe jaw asymmetry and discrepancies.
This method can be applied to almost any surgical bone for both the creation of surgical guides and the creation of fixation plates after ablation surgery or fracture treatment. This technique facilitates the creation of novel surgical guides and plates. For example, we have created fracture reduction guides for use in the operation room.
