Développement de guides chirurgicaux personnalisés, par prototypage, pour l’installation de vis pédiculaires

Abstract

Spinal instrumentation surgeries frequently use pedicle screws to fix a corrective rod on the spine. Misplacement of a screw can lead to intra- and postoperative complications. The goal of this study is to develop personalized templates, using prototyping, to ensure accurate placement of the screw in a pedicle. From a CT-scan of a L3 non pathologic vertebra, a 3D model is reconstructed with a CAD software (Catia). Drilling direction and limit angles are computed from an inverse projection of the limits of the pedicle on transverse and sagittal planes. The first template design uses a surface-to-surface registration method and was constructed by subtracting the vertebra from a rectangular prism and a cylinder with the proper orientation. This template and the vertebra were built using rapid prototyping. The second design uses a point-to-surface (6 points) registration method and has an adjustable orientation support device. A mechanism was designed to hold it in place on the spinal process. A virtual prototype was build with Catia software, and a kinematic analysis was done to ensure that the guide does not interfere with the upper and lower vertebrae. During the operation, the surgeon put the template on patient’s vertebra until a perfect match is obtained before drilling. The second design seems better than the first one because it can be reused on different patients and is less sensitive to registration errors. The next step is to build the second design and make experimental and simulations tests to evaluate the benefits of this template during a real operation.