A large proportion of the expense incurred due to hip fractures arises due to secondary factors such as duration of hospital stay and additional theatre time due to surgical complications. Studies have shown that the use of intramedullary (IM) nail fixation presents a statistically higher risk of re-fracture than plating, which has been attributed to the stress riser at the end of the nail. It is not clear, however, if this situation also applies to unstable fractures, for which plating has a higher fixation failure rate. Moreover, biomechanical studies to date have not considered newer designs of IM nails which have been specifically designed to better distribute weight-bearing loads. This aim of this experimental study was to evaluate the re-fracture risk produced by a newer type of nailing system compared to an equivalent plate. Experimental testing was conducted using fourth generation Sawbones composite femurs and X-Bolt IM hip nail (n=4) and fracture plate (n=4) implants. An unstable pertrochanteric fracture pattern was used (AO classification: 31-A1 / 31-A2). Loading was applied along the peak loading vector experienced during walking, up to a maximum load of 500N. The risk of re-fracture was evaluated from equivalent strains measured using four rosette strain gauges on the surface of the bone at known stress riser locations.Background
Methods
Numerical modelling using Finite Element (FE) Analysis has become ubiquitous in orthopaedic biomechanics, with both commercial and freely available packages widely used. Three FE packages in particular have gained popularity: Abaqus (Simulia); Ansys (ANSYS, Inc.) and FEBio (University of Utah). Although FEBio is now well established, its developers advise that comparisons should be made against more extensively tested software before trusting its results for specific problems. The aim of the study to conduct a comparison of mesh convergence and to provide validated open-source models of the femur for use all three FE packages. Three-dimensional FE models of the femur were created in Abaqus. To ensure that all aspects of the models were identical, custom scripts were developed to import the models into other packages. Mesh convergence studies were conducted for each solver using seven mesh densities for linear tetrahedral elements (up to 2 million). Experimental validation used fourth generation Sawbones composite femurs (n=8) with surface strains measured at four locations. The loading applied at the hip was the averaged peak joint reaction force during walking (Bergman et al); experimentally, this loading vector was used for a reduced load of 500N.Background
Methods
