Design and manufacture of anatomical hip joint endoprostheses using CAD/CAM systems

This paper contains a methodology for the design and manufacture of implants in cases when the medical indications favour the application of an anatomic custom design implant. Methods of interpretation and identification of the anatomic shapes of the human bone system (marrow cavity, trochanter, etc.) are discussed on the basis of computer tomography (CT) data. Methods for the process of modelling implants using CAD systems are then presented. The advantages of the parametric modelling for typical CAD/CAM systems are discussed. A new possibility allowing surgeons to make the final decision as to the selection of a prosthesis from the standard set is explained, based on geometric modelling preceded by a CT-based process of identification. Methods of metallic prostheses manufacturing using numerically controlled machine tools are proposed. Specific difficulties arising in the integration process of CAD and CAM modules are presented and methods for improvement are proposed. Requirements for up-to-date CAM systems pertaining to driving the tool across the complex shape surfaces are summarised and the demand for additional software to bridge the gap between the CAD/CAM and the given CNC machine tool controllers is determined (postprocessing). Attention is paid to NC programs verification techniques using substitute materials for the machining process and rapid prototyping. Limitations of the proposed method due to its relatively low productivity and the shape problems are defined, and ways of overcoming them are suggested. The results of practical experiments leading to prototype manufacture are described. The areas of problems caused by the specific kinematics of the applied CNC machine tools, as well as problems of handling large amounts of data flowing into machine control units are mentioned.