Computational steering for patient-specific implant planning in orthopedics

Fast and reliable methods for predicting and monitoring in-vivo bone strength are of great importance for hip joint replacement. To avoid adaptive remodeling with cortical thinning and increased porosity of the bone due to stress shielding, in a preoperative planning process the optimal implant design, size, and position has to be determined. This process involves interactive implant positioning within the bone as well as simulation and visualization of the stress within bone and implant due to exerting forces. In this paper, we present a prototype of such a visual analysis tool, which, to our best knowledge, provides the first computational steering environment for optimal implant selection and positioning. This prototype considers patient-specific biomechanical properties of the bone to select the optimal implant design, size, and position according to the prediction of individual load transfer from the implant to the bone. We have developed a fast and stable multigrid finite-element solver for hexahedral elements, which enables interactive simulation of the stress distribution within the bone and the implant. By utilizing a real-time GPU-method to detect elements that are covered by the moving implant, we can automatically generate computational models from patient-specific CT scans in real-time, and we can instantly feed these models into the simulation process. Hardware-accelerated volume ray-casting, which is extended by a new method to accurately visualize sub-hexahedron implant boundaries, provides a new quality of orthopedic surgery planning.