Developing a Consistent Analysis Method for Evaluating Orthopaedic Hip Implants

This paper describes the purpose, evolution and implementation of a custom user interface for the analysis of orthopaedic [artificial] hip stem designs. The orthopaedic implant industry is regulated by the U.S. Food and Drug Administration [FDA]. Thorough testing procedures are necessary before an implant is approved for general use. Typically, this involves a variety of physical and analytical assessments including the determination of sustainable bending stresses in a particular hip stem and the corresponding peak load-carrying capacity. Ultimately, a physical prototype is fatigue tested and will be released only after passing all required tests. A combination of closed-form textbook solutions, often in spreadsheet format, has often been used for initial evaluations. The difficulties and dangers in this approach are manifold and are commonly cited: they include poorly understood and inappropriately applied formulas, as well as the limited nature of the resulting data. Despite these hazards, up-front analysis of each hip stem design is necessary to reduce the number of prototypes that are manufactured and tested. The ability to quickly complete the analysis phase of any process is critical to shorten design cycles. A customized solution was needed which would work within the context of the current finite element tools to provide reliable design information directly to the designers. This was accomplished by writing a UIDL-based “wrapper” [User Interface Design Language] for ANSYS [Canonsburg, PA] simulation software. It guides the user through a series of input screens for the selection and analysis of a variety of common hip stem evaluations. Through the use of drop-down menus, engineers are limited to evaluations that make sense for their particular product family. In a convenient and consistent way, the tool provides the means for obtaining and documenting a wealth of information, some of which was previously unavailable to designers in the absence of analyst intervention. The criticality of computational analysis in the orthopaedic industry is established. Various strategies for accomplishing the task of providing this are presented. One solution, that of codifying a set of standard physical tests into virtual form, is described. Minimally trained engineers are then able to investigate their designs more quickly, more comprehensively, and more consistently.

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