A CAD-CAM methodology to produce bone-remodelled composite femurs for preclinical investigations

Femoral bone remodelling, following total hip arthroplasty. is a clinically observed phenomenon attributed to the changed stress environment of the po stoperative implanted hip. While this process cannot be avoided, there is c oncern as to its consequences on the long-term survival of hip joint replac ements. Previous methods of studying remodelling, such as clinical or anima l-based studies, or finite element analyses, have their limitations. The ai m of this study is to develop experimental specimens incorporating bone res orption features typical of clinically successful implants. This work descr ibes the use of computer aided design/manufacturing methods (CAD-CAM) to pr oduce these specimens. based on modifying commercially available composite femurs, The procedures are investigated and verified for two different desi gns of cemented prostheses (Lubinus SPII and Muller Curved). Quantitative c linical data is used to define the remodelled geometry of a CAD model of th e femur for each stem design. Composite femur specimens are machined using a three-axis milling machine, where each specimen can be accurately positio ned using a custom-designed jig and a digitizer system. The accuracy of the process is assessed by analysing the deviation of the digitized premachine d and postmachined surfaces of each specimen in relation to the CAD model. The results demonstrate that the procedure can be used for developing in vi tro specimens with bone resorption features. These specimens are proposed a s a useful tool for performing preclinical trials, such as load transfer or longevity/stability testing, with the advantage of modelling a long-term c linical situation, rather than solely analysing implanted femurs in an imme diate postoperative state.