Production of customized hip stem prostheses - a comparison between conventional machining and electron beam melting (EBM)

Purpose - The purpose of this paper is to study the use of the additive manufacturing (AM) method, electron beam melting (EBM), for manufacturing of customized hip stems. The aim is to investigate EBM's feasibility and commercial potential in comparison with conventional machining, and to map out advantages and drawbacks of using EBM in this application. One part of the study concerns the influence on the fatigue properties of the material, when using the raw surface directly from the EBM machine, in parts of the implant. Design/methodology/approach - The research is based on a case study of manufacturing a batch of seven individually adapted hip stems. The stems were manufactured both with conventional machining and with EBM technology and the methods were compared according to the costs of materials, time for file preparation and manufacturing. In order to enhance bone ingrowths in the medial part of the stem, the raw surface from EBM manufacturing is used in that area and initial fatigue studies were performed, to get indications on how this surface influences the fatigue properties. Findings - The cost reduction due to using EBM in this study was 35 per cent. Fatigue tests comparing milled test bars with raw surfaced bars indicate a reduction of the fatigue limit by using the coarse surface. Originality/value - The paper presents a detailed comparison of EBM and conventional machining, not seen in earlier research. The fatigue tests of raw EBM-surfaces are interesting since the raw surface has shown to enhance bone ingrowths and therefore is suitable to use in some medical applications.