gms | German Medical Science

Objective: To evaluate a method which allows preoperative definition of virtual bone resection planes in planning of spinal osteotomies. We developed a technique applying cranial navigation tools for integration of objects and navigation plans into intraoperative visualization using the image-injection of a microscope's head-up display.

Method: CT and MR image data were imported into Amira^®, a 3D visualization software. Resection planes created in a CAD-program were positioned and the resection volume for intraoperative bone removal was defined. Fused with the original CT data and converted into a DICOM image sequence, the osteotomy planes were exported to the cranial version of a Brainlab^® navigation system. A tracked surgical microscope with additional video connection allowed intraoperative in-view image overlay to visualize the preplanned planes. The microscope was positioned and rotated until the osteotomy plane on the head-up-display appeared as a single line, indicating that the axis of sight is aligned parallel to the bone dissection plane. In addition, a high speed drill was registered to the navigation system for tracking during the resection.

Results: The method was tested using a solid foam spine model, demonstrating high precision in reproducing preplanned resection angles, suggesting safe application to a clinical environment. In a next step image-injection of resection planes in the head-up-display was applied to a patient presenting with a congenital wedge-shaped hemivertebra in the thoracolumbar spine resulting in a progressive dextro-anterior scoliosis. First, dorsal stabilization with pedicle screws and rods was performed to secure the affected segment. Subsequently, the deformed vertebra was resected, guided by the visualization of the preplanned resection planes visualized by the microscope's head-up-display. By this, it was possible to perform the whole osteotomy and wedge resection through a minimal dorsal approach. After the operation a nearly physiological curvature of the spine was restored.

Conclusions: The intraoperative in-view visualization of cutting planes and resection volumes in spinal surgery was found to assist the surgeon in a way that offers the chance of further minimizing invasiveness even in complex spinal procedures.