Introduction: Fracture impaction is a surgical technique used to support the fractured humerus with locking plate or intramedullary nail when treating proximal humeral fractures. However, few studies have investigated the mechanical difference between fracture impaction with locking plate and with intramedullary nail. The mechanism of fracture impaction to increase stability is still unclear. The aim of this study was to use numerical methods to compare the biomechanical effect of treating proximal humeral fracture. Methods: Six different humerus models, including intact and fractured humeri with various fixation patterns were used in this study. Fracture impaction was simulated by moving the distal fragment of the humeral shift upwards directly until touching the inferior surface of the proximal fragment. We also considered both poor- and normal-quality bone in the simulation. Results: Results confirmed that fracture impaction increases fracture stabilityand decreases peak stress in both implant and bone. Also, fracture impaction and plating with medial shift of the humeral shaft provides the highest stability. The metallic implant shared loading with the bone in the impacted models, while implants sustained all the loading alone in the nonimpacted models. Conclusions: Based on the results, the technique of fracture impaction is suggested for both nail and plate to reduce stresses on bone and implants and to increase structural stability. Furthermore, impaction with medial shift of the humeral shaft with plate is found to achieve the highest stability when treating proximal humeral fractures.
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