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Traditional 2D images provide limited use for accurate planning of spine interventions, mainly due to the complex
3D anatomy of the spine and close proximity of nerve bundles and vascular structures that must be avoided during
the procedure. Our previously developed clinician-friendly platform for spine surgery planning takes advantage
of 3D pre-operative images, to enable oblique reformatting and 3D rendering of individual or multiple vertebrae,
interactive templating, and placement of virtual pedicle implants. Here we extend the capabilities of the planning
platform and demonstrate how the virtual templating approach not only assists with the selection of the optimal
implant size and trajectory, but can also be augmented to provide surrogate estimates of the fastening strength
of the implanted pedicle screws based on implant dimension and bone mineral density of the displaced bone
substrate. According to the failure theories, each screw withstands a maximum holding power that is directly
proportional to the screw diameter (D), the length of the in-bone segm,ent of the screw (L), and the density (i.e.,
bone mineral density) of the pedicle body. In this application, voxel intensity is used as a surrogate measure of
the bone mineral density (BMD) of the pedicle body segment displaced by the screw. We conducted an initial
assessment of the developed platform using retrospective pre- and post-operative clinical 3D CT data from
four patients who underwent spine surgery, consisting of a total of 26 pedicle screws implanted in the lumbar
spine. The Fastening Strength of the planned implants was directly assessed by estimating the intensity - area
product across the pedicle volume displaced by the virtually implanted screw. For post-operative assessment,
each vertebra was registered to its homologous counterpart in the pre-operative image using an intensity-based
rigid registration followed by manual adjustment. Following registration, the Fastening Strength was computed
for each displaced bone segment. According to our preliminary clinical study, a comparison between Fastening
Strength, displaced bone volume and mean voxel intensity showed similar results (p < 0.1) between the virtually
templated plans and the post-operative outcome following the traditional clinical approach. This study has
demonstrated the feasibility of the platform in providing estimates the pedicle screw fastening strength via
virtual implantation, given the intrinsic vertebral geometry and bone mineral density, enabling the selection of
the optimal implant dimension adn trajectory for improved strength.
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