Once all plan is set, at the operation room, the navigation computer is best positioned opposite the surgeon approximately 5 feet away from the patient. The camera is located over the patient and directed downward at 45°. After surgical exposure, two 3 mm Apex pins are placed on the affected bone at least 3 cm away to the osteotomy programmed line in an area not affected for the tumor based in the preoperative planning. A navigation tracker is fixed to the pins. An image-to-patient registration to match precisely the operative anatomy and preoperative virtual CT images is performed by paired points (Fig. 8.2) and surface points (Fig. 8.3). In terms of surgical steps, 4 or at least 3 landmark points are identified in the affected bone based in the surgical exposure and anatomic visible points. Then, surface mapping of the bone is performed to reduce any mismatch between preoperative images and the patient’s anatomy, using at least 80 surface registration points in unaffected bone. After registration, the surgeon must double check with the navigation pointer if the surface of the patient`s bone in real time correlates on the virtual preoperative images. Afterwards, using the navigation pointer the osteotomies are marked in the surface of the bone (Figs. 8.4 and 8.5). The directions of the bone cuts are determined with the pointer and the osteotomies are performed with an oscillating saw or an osteotome.

Finally, another advantage that has this procedure, is the reconstruction of the bone defect, using computerized assistance. This is mainly accomplished when the reconstruction is done with bone allografts. The procedure is to reproduce the same planned cuts used during tumor resection, about the Allograft. This way can the defect can be reconstructed with more precision than the conventional way (allograft tailored by hand without any guidance), as if they were pieces of a puzzle.