Preoperative Computer Simulation Using a 3-D Template

Summary

In total hip arthroplasty, a two-dimensional (2-D) template on plain X-ray is usually used for preoperative planning, but deformity and contracture can cause malpositioning and measurement error. To reduce those problems, a 3-D preoperative simulation system was developed. Two methods were compared in this study: one is to create very accurate AP and ML images that can be used for a standard 2-D template, and the other is a fully 3-D preoperative template system. Because helical scanning CT is an excellent method to extract 3-D geometry of the bone, our system provides 3-D geometries using helical scanning CT. Accurate AP and ML surface- cutting 3-D images of the femur were created. Ordinary 2-D templates were compared to the surface-cutting 3-D image, and preoperative measurement was done. For the full 3-D simulation, axial images were converted to the 3-D geometry data using the STL (stereolithography) format. The extracted 3-D geometry was displayed on a personal computer using “magics” (STL data visualization software; Belgium Materialise), and 3-D geometry of the stem was then superimposed upon it. The full 3-D simulation system made it possible to observe the bone and stem geometry from any direction and by any section view. This 3-D template system was very useful for very accurate preoperative measurement and better selection of the prosthesis.