An FEA-based protocol for the pre-clinical validation of custom-made hip implants

Custom-made prostheses are successfully used to treat particular pathologies such as congenital hip dysplasia. The new EC rules on medical devices require a complete technical dossier for each produced custom-made device counter signed by the surgeon who 'prescribes' the custom-made device. Thus, a specific pre-clinical validation protocol must be developed, considering the economical and temporal constraints imposed by the device type. As a first step, in the present study a protocol based on finite element analysis (FEA) was developed and validated, to verify each custom-made hip stem in terms of mechanical strength. The study was carried out on 12 custom-made cementless hip stem designs already produced and implanted, for which the 3D solid model was available. Two of the selected designs were used for the method validation, comparing strain gauges measurements with the stresses predicted by the finite element (FE) model. Once the proposed methodology was verified, all the remaining stem designs were analysed. The developed protocol made possible a complete analysis in less than 4 h; its accuracy (7-8% on the strain gauge measurements) was considered acceptable for the specific application.