Speed effects on the mechanical properties of cortical bone. Challenges for fracture risk prediction?
Résumé
In the world, a bone fracture due to osteoporosis occurs every 3 seconds (International Osteoporosis Foundation). Thus, it is obvious that bone fracture is a major concern. In clinics the assessment of the risk of fracture is based on the measurement of the bone mineral density (i.e. bone quantity in gram per cm²). Even if this method is currently the gold standard it is not sufficiently discriminant. Indeed, 50% of the patients having a fracture were diagnosed as non-osteoporotic (Siris et al., 2004). To overcome this limitation finite element models have been proposed. Such models can accurately predict the bone strength (e.g. (Duchemin et al., 2008; van Rietbergen and Ito, 2015) but there is no clear evidence that these models can better predict the fracture risk (van Rietbergen and Ito, 2015). Currently these models consider quasi-static loadings. However among elderly bone fractures occur during a fall. In case of a fall from a standing height people will hit the floor at an average speed of 2 m/s (Tan et al., 2006) and a corresponding strain rate of 0.1/s (Földhazy et al., 2005). We made the assumption that this loading speed should be considered in the bone loading.Bone structures (e.g. the femur or the radius) are made of two materials: cortical bone and cancellous bone. It was shown that bone strength of the femur is mainly due to the cortical bone (Holzer et al., 2009).speed related to a fall. Thus, the goal of our current research is to assess the cortical bone toughness under a strain rate of 0.1/s, representing a fall, and to compare, on paired samples, cortical bone toughness under a quasi-static loading configuration (considered in a wide majority of the studies in the literature e.g. (Bonfield and Datta, 1976; Nalla et al., 2004)).Our presentation will be dedicated to the presentation of our latest results regarding speed effect on human cortical bone toughness through biomechanical experiments and 3D imaging at the nanoscale.AcknowledgmentsThis work was performed within the framework of the LABEX PRIMES (ANR-11-LABX-0063) of Université de Lyon, within the program "Investissements d'Avenir" (ANR-11-IDEX-0007) operated by the French National Research Agency (ANR). Rémy Gauthier is supported by a grant from the Région Rhône-Alpes.