Abstract:
This study was designed to create a method for assessing the suitability of a new internal stabilization implant for treating proximal tibial defects under physiological-like loading conditions. The approach combined in vitro mechanical stiffness testing with finite element (FE) analysis. Five human cadaveric tibiae with defects were stabilized with a new internal fixator (LISS, Less Invasive Stabilization System) and subjected to axial compression tests. Reflective markers were used to measure interfragmentary movement during these tests. A corresponding FE model of a tibia with a defect was created using data from the Visible Human data set. The model incorporated linear elastic, isotropic, and homogeneous material properties for the bone and a titanium alloy for the implant. The FE analysis simulated both the in vitro axial compression test for validation and a more complex physiological-like loading scenario that included all muscle and joint contact forces. The in vitro and FE results showed comparable interfragmentary movements, confirming the validity of the FE model. Under physiological loading, the FEA revealed high bending and von Mises stresses on the implant, particularly when stabilizing defects in the diaphyseal (shaft) region of the bone. A short working length (the section of the implant bridging the defect) was found to increase implant loading up to the yield strength of the material. The study concludes that the implant is appropriate for proximal metaphyseal defects of the tibia, but should be used with caution for fractures extending into the diaphyseal region due to excessive implant loading. This analytical approach, combining in vitro testing with physiological FEA, provides a valuable tool for identifying the clinical indications for new orthopedic implants.
