INTERFERENCE-FREE INSERTION OF A SOLID BODY INTO A CAVITY - AN ALGORITHM AND A MEDICAL APPLICATION

This article presents a novel algorithm for efficiently computing an i nterference-free insertion path of a body into a cavity and shows its practical use in the insertability analysis of custom orthopedic hip i mplants. The algorithm is designed to handle tightly fit very complex three-dimensional bodies requiring fine complex, coupled six-degree-of -freedom motions in a preferred direction. It provides a practical met hod for efficiently handling the geometric complexity of tight-fit ins ertions. The algorithm computes all insertion path consisting of small interference-free body motion steps. It formulates local, linearized configuration space constraints derived from the shapes and computes s uccessive motion steps by solving a series of linear optimization prob lems whose solution corresponds to the maximum allowed displacement in a preferred direction satisfying the constraints. It either finds a s uccessful insertion path or a stuck configuration. We demonstrate the algorithm with EXTRACT a program for analyzing the insertability of ce mentless custom orthopedic hip implants. EXTRACT computes interference -free insertion paths for tightly fit implant and canal shapes describ ed with 10,000 facets to an accuracy of 0.01 inch in 30 minutes on a w orkstation. it has been successfully rested on 30 real cases provided by a medical equipment manufacturer.