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Abstract
The following is Part B of a two-part study. Part A evaluated, biomechanically, intramedullary (IM) nails versus locking plates for fixation of an extra-articular, metaphyseal wedge fracture in synthetic osteoporotic bone. Part B of this study introduces deterministic finite element (FE) models of each construct type in synthetic osteoporotic bone and investigates the probability of periprosthetic fracture of the locking plate compared with the retrograde IM nail using Monte Carlo simulation. Deterministic FE models of the fractured femur implanted with IM nail and locking plate, respectively, were developed and validated using experimental data presented in Part A of this study. The models were validated by comparing the load–displacement curve of the experimental data with the load–displacement curve of the FE simulation with a root-mean square error of less than 3 mm. The validated FE models were then modified by defining the cortical and cancellous bone modulus of elasticity as uncertain variables that could be assumed to vary randomly. Monte Carlo simulation was used to evaluate the probability of fracture (POF) of each fixation. The POF represents the cumulative probability that the predicted shear stresses in the cortical bone will exceed the expected shear strength of the cortical bone. This investigation provides information regarding the significance of post-operative damage accumulation on the POF of the implanted bones when the two fixations are used. The probabilistic analysis found the locking plate fixation to have a higher POF than the IM nail fixation under the applied loading conditions (locking plate 21.8% versus IM nail 0.019%).
Acknowledgements
This study was supported, in part, by an institutional grant from the Stryker Foundation to the University of New Mexico, Orthopaedics Department. The partial financial support to the first author by National Science Foundation (NSF) IGERT Program to the University of New Mexico is greatly appreciated. The study sponsors had no involvement in the study design, collection, analysis and interpretation of data, writing of manuscript, and in the decision to submit the manuscript for publication.
Notes
4. Available on the Internet through the Bel Repository managed by the Instituti Ortopedici Rizzoli, Bologna, Italy.
5. The reduced modulus of elasticity is used to represent the damage induced in the cortical bone due to post-operative motion. This damage was experimentally evaluated in Part A of this study.
6. No published data were found to date listing the maximum shear strength of the cortical region of the fourth generation composite femurs used in this study.
