Three-dimensional surgical simulation

Abstract

In this article, we discuss the development of methods for computer-aided jaw surgery, which allows us to incorporate the high level of precision necessary for transferring virtual plans into the operating room. We also present a complete computer-aided surgery system developed in close collaboration with surgeons. Surgery planning and simulation include construction of 3-dimensional surface models from cone-beam computed tomography, dynamic cephalometry, semiautomatic mirroring, interactive cutting of bone, and bony segment repositioning. A virtual setup can be used to manufacture positioning splints for intraoperative guidance. The system provides further intraoperative assistance with a computer display showing jaw positions and 3-dimensional positioning guides updated in real time during the surgical procedure. The computer-aided surgery system aids in dealing with complex cases with benefits for the patient, with surgical practice, and for orthodontic finishing. Advanced software tools for diagnosis and treatment planning allow preparation of detailed operative plans, osteotomy repositioning, bone reconstructions, surgical resident training, and assessing the difficulties of the surgical procedures before the surgery. Computer-aided surgery can make the elaboration of the surgical plan a more flexible process, increase the level of detail and accuracy of the plan, yield higher operative precision and control, and enhance documentation of cases.

Figure 1

(1) Cone beam CT’s are taken for each patient. (2) Segmentation involves delineation of the anatomical areas of interest. (3) Visualization of the 3D skull. (4) Diagnosis occurs in 3D. (5) Preparation of an operative plan and simulation of the actual surgery. (6) Measurements, dental splints and intra-operative guidance can then be utilized for intra-operative realization of the virtual surgical plan.

Figure 2

Cone beam CT images are imported as DICOM files into ITK Snap. In a process known as semiautomatic segmentation anatomical areas of interest are identified and delineated. Manual editing is performed to ensure accuracy of the segmentations. The images can be viewed in three dimensions and as axial, coronal, and sagittal slices of each image.

Figure 3

Cephalometry can be performed on the three dimensional skeletal model formed from the CBCT. This allows the user to define landmarks, lines, planes, and measurements.

Figure 4

Mirroring can be a valuable technique in the treatment of asymmetries. As shown below the lateral orbit (1) has been delineated on each side. (2) The left orbit was mirrored onto the right side using the CMF applications mirror function and the mid-saggital plane was defined for the image. (3) The lateral left orbit was then reincorporated back into the whole skull model with the right side recreated as a mirror of the left side.

Figure 5

Virtual surgical cuts were placed in the three dimensional skull models by placing three or more points in the desired orientation of the cuts. The newly cut segments were then painted different colors to allow better visualization of the cuts. Each of these segments can then be relocated and tracked with precise control using movements with six degrees of freedom. (X, Y, and Z in rotational and translational planes of space.)

Figure 6

Paired points registration establishes a correlation between virtual images and real anatomy. In the image below the initial cone beam images were taken with bite splints that had metallic objects built into the splints. These areas appeared on the radiographic images. A tracked pointer is then used to digitize these points on the patient during the operation. This allows transfer of the virtual surgeries to the operating room.

Figure 7

Paired points registration was used to link the virtual surgeries with the operating room. Once they are linked the software updates in real time the surgical movements on the computer. The object is to guide the hand of the surgeon while maintaining precise control in three translational and three rotational planes of space.