Comparative Analysis of the Biomechanical Behavior of two different design metaphyseal-fitting short stems using digital image correlation; Finite Element Modelling and Analysis Validation

Background The progressive evolution in hip replacement research is directed to follow the principles of bone and soft tissue sparing surgery. Regarding hip implants, a renewed interest has been raised towards short uncemented femoral implants. A heterogeneous group of short stems have been designed with the aim to approximate initial, post-implantation bone strain to the preoperative levels in order to reduce the risk of stress shielding. This study aims to investigate the biomechanical properties of two distinctly designed femoral implants based on experiments and numerical simulations. Nevertheless, finite element models of implant–bone constructs should be evaluated for their validity against mechanical tests wherever it is possible. In this work, the validation was performed via a direct comparison of the FE calculated strain fields with their experimental equivalents obtained using the digital image correlation technique. Results Design differences between Trilock BPS and Minima S femoral stems conditioned different strain pattern distributions. A distally shifting load distribution pattern as a result of implant insertion and also an obvious decrease of strain in the medial proximal aspect of the femur was noted for both stems. Strain changes induced after the implantation of the Trilock BPS stem at the lateral surface were greater compared to the non-implanted femur response, as opposed to those exhibited by the Minima S stem. Linear correlation analyses of the FE model-predicted strains against corresponding experimentally-measured strains revealed a strong correlation indicating that the developed FE models can be used for the calculation of stresses and strains at the implanted femurs. Conclusion The study findings support the use of DIC technique as a preclinical evaluation tool of the biomechanical behavior induced by different implants and also identify its potential for experimental FE model validation. Furthermore, this study demonstrates that stress shielding effect cannot be avoided as proximal unloading of the femur was noted after the implantation of both short stem designs. Design specific variations in short stems were sufficient to produce dissimilar biomechanical behaviors, although their clinical implication must be investigated through comparative clinical studies.