3D printed Patient Specific Guides (PSGs) can improve the accuracy of joint-replacement. Pre-operative CT bone models are used to design a PSG that fits the patient's specific bone geometry. A key design requirement is to maximize docking robustness such that the PSG can maintain a stable position in the planned location. However, current PSG designs are typically manually defined, lack a quantitative assessment of robustness, and have an unknown consistency of docking rigidity between patients. Limited research exists on the stability and robustness of surgical guides, and no software packages are available to facilitate this analysis. Our goal was to develop such a software. In this paper, the contact between a patient's bone and the PSG is modelled using robotic grasping theory, and its docking robustness is quantified by analysis of the PSG's grasp wrench space (GWS) (i.e. the combination of contact forces and torques between the bone and PSG). To this end, a PSG design and analysis tool with a graphical user interface was developed in MATLAB. This tool allows the user to load shapes (e.g. STL bone models), select and manipulate possible contact points, and optimize the contact point locations according to the largest-minimum resisted wrench (LRW) that the grasp can resist in any direction. The LRW is a grasp quality metric equivalent to the radius of the largest (hyper)sphere contained within the convex hull of the GWS, and its value can be evaluated using frame-variant GWS calculations (i.e. centroid-dependent) or frame-invariant GWS calculations (i.e. centroid-independent).Introduction
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