Biomechanical Evaluation of Composite Bone Following Removal of Proximal Femoral Fixation Hardware

Abstract

Few studies in literature have investigated the performance of bone following the removal of hardware (ROH) in proximal femoral fracture fixations and in particular, the material properties recovered in bone following insertion of bone cement into the holes created by ROH. Cadaveric bones suffer from high inter- and intra-specimen variability; consequently, this investigation utilized composite femurs with a standardized geometry and material properties that approximate healthy human bone. To assess the mechanical response, orthopaedic implants were inserted and removed from the composite bones. Twenty-one femurs were tested in axial compression. Three femurs served as controls (no augmentation) and the remaining eighteen were divided into three treatment groups: cannulated screws, a dynamic hip screw system, and an intramedullary hip screw system. Biomechanical testing of the femurs identified the linear relationship between load/deflection as well as overall load and deflection values at fracture. In addition, strain gages and optical elastography were employed to determine quantitative and qualitative localized strain. Computational modeling led to the development of a preliminary, simplified finite element (FE) model of the femur, which was correlated to experimental data. Overall deflection, stress, and strain were determined, as well as localized strain. Further development and validation of the FE model would allow for investigations into ROH implications for those with varying degrees of osteoporosis.