Mechanical conditions in the internal stabilization of proximal tibial defects

Objectives. The goal was to design a method which would permit an assessment of the suitability of a newly developed implant under physiological-like loading conditions. Information obtained from such an analysis is expected to delineate more clearly the indications for a new device prior to clinical utilization. Design. In vitro mechanical stiffness testing and finite element analysis. Methods. From in vitro testing of proximal tibiae with defects, the stiffness of an internal stabilization system was determined. Using a finite element model, the loading of both the implant and bone was analyzed including all muscle forces. The variation in implant loading and interfragmentary strain for different defect locations was also investigated. Results. Conventional stiffness testing demonstrated the comparability of the experimental findings with the finite element predictions. Under physiological-like loading the implant experienced high bending and von Mises stresses if defects in the region of the shaft were stabilized. A short working length increased implant loading up to the yield strength of the material. Conclusions. The finite element analysis illustrated the appropriateness of this new device for proximal defects of the tibia, but the implant should be used hesitantly in fractures or defects extending into the diaphyseal region of the bone.