Pre-clinical validation of a new proximal epiphyseal replacement: design revision and optimisation by means of finite element models

Pre-clinical validation of a new proximal epiphyseal replacement: design revision and optimisation by means of finite element models
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  See discussions, stats, and author profiles for this publication at: Pre-clinical validation of a new proximalepiphyseal replacement: Design revision andoptimisation by means of finite... Conference Paper  · July 2008 CITATIONS 7 READS 9 5 authors , including: Some of the authors of this publication are also working on these related projects: Synchrotron-based modelling of the deformation and fracture mechanism in normal and osteoporoticfemurs under multiaxial loading cycles   View projectSaulo MartelliFlinders University 44   PUBLICATIONS   634   CITATIONS   SEE PROFILE Fulvia TaddeiIstituto Ortopedico Rizzoli 125   PUBLICATIONS   2,852   CITATIONS   SEE PROFILE Luca CristofoliniUniversity of Bologna 217   PUBLICATIONS   5,808   CITATIONS   SEE PROFILE Marco VicecontiThe University of Sheffield 439   PUBLICATIONS   8,095   CITATIONS   SEE PROFILE All content following this page was uploaded by Saulo Martelli on 04 December 2016. The user has requested enhancement of the downloaded file.  S34  Presentation O-31  Hip Implant Modelling − I PRE-CLINICAL VALIDATION OF A NEW PROXIMAL EPIPHYSEAL REPLACEMENT: DESIGN REVISION AND OPTIMISATION BY MEANS OF FINITE ELEMENT MODELS Saulo Martelli (1), Fulvia Taddei (1), Marie Moindreau (3), Luca Cristofolini (1,2) and Marco Viceconti (1) 1. Laboratorio di Tecnologia Medica, Istituti Ortopedici Rizzoli, Bologna, Italy; 2. Engineering Faculty, University of Bologna, Italy; 3. Stryker Orthopaedics, Benoist Girard, Caen, France. Introduction   The finite element (FE) method is a powerful tool to investigate the mechanical behaviour of structural components. The recent development of accurate modelling strategies for the prediction of strain levels in bone from Computed Tomography data [Schileo, 2007a] makes it possible to apply these techniques to the pre-clinical validation of new devices. The aim of the present work was to optimise the design of a proximal epiphyseal replacement with a high degree of safety to the most common failure scenario for this kind of devices, under a large range of physiological operating conditions. Materials and Methods   The goal of the optimisation was to produce an implant geometry that would ensure very low risks of (1) femoral neck fracture, (2) prosthesis mechanical fracture, (3) aseptic loosening owing to  production of fretting debris, cement mantle mechanical damage and adverse bone remodelling. To this aim, three CT dataset of human femurs of normal anatomy and bone mineral density, spanning the patients size range were used. An experienced surgeon defined the optimal position of the device using pre-operative planning software (HipOp v1.4, B3C, Italy). The FE models of the intact and implanted femurs were generated using a well-established validated procedure [Taddei, 2006]. Aseptic loosening was studied by computing the risk of cement fretting, the lack of bone in-growth, and adverse bone remodelling. The risk of fatigue fracture was computed for prosthesis and cement. Last, the risk of femoral neck fracture was assessed using a recently proposed method [Schileo, 2007b]. The effect of osteoporosis, bone-cement interdigitation, surgical mal-positioning of the implant and different loading conditions [Bergmann, 2001] were investigated. Results were analysed and regions with high a risk of failure were identified. The device underwent a two step loop for design revision before all studied bio-mechanical parameters reached a safe value.  Figure 1: A section of the finite element model of the implanted femur. The non-homogeneous distribution of the Young modulus in bone is shown. Results   The peak bone strains were always registered in the supero-lateral aspect of the implanted femoral neck  but remained comparable to the ones predicted in the intact femur, suggesting that the risk of femoral neck fracture is not influenced by the presence of the revised implant. The cement stresses (< 10 MPa) were well below the fatigue limits, making the risk of cement cracking during cyclic loading very unlikely. The predicted micromotions at the frictional large sliding interface, were always below 35 m, showing no significant risk of fretting nor fibrous tissue formation. Finally, changes in strain energy density due to stem presence, were below the threshold commonly considered for the activation of adverse bone remodelling processes [Huiskes, 1987]. Discussion   The proposed numerical method allowed the successful optimisation of the stem design, that reached minimal risk of failure within a broad range of physiological conditions. Osteoporosis seems to  be the more critical factor for this device. Further studies are needed to investigate the mutual interaction of the different factors. The device started post market surveillance. References Taddei et al  , J Biomech 39:2457-2467, 2006. Bergmann et al  , J Biomech 34:869-871, 2001. Schileo et al  , J Biomech 2007b, Epub. Schileo et al  , J Biomech 40:2982-2989, 2007a. Huiskes et al  , J Biomech 20:1135-1150, 1987. Journal of Biomechanics  41(S1) 16th ESB Congress, Oral Presentations, Monday 7 July 2008
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