Quantifying the Effects of Formalin Fixation on the Mechanical Properties of Cortical Bone Using Beam Theory and Optimization Methodology With Specimen Specific Finite Element Models

Abstract

The effects of formalin fixation on bone material properties remain debatable. In this study, we collected 36 freshfrozen cuboidshaped cortical specimens from five male bovine femurs and immersed half of the specimens into 4% formalin fixation liquid for 30 days. We then conducted threepoint bending tests and used both beam theory method and an optimization method combined with specimenspecific finite element (FE) models to identify material parameters. Through the optimization FE method, the formalinfixed bones showed a significantly lower Young's modulus (−12%) compared to the freshfrozen specimens, while no difference was observed using the beam theory method. Meanwhile, both the optimization FE and beam theory methods revealed higher effective failure strains for formalinfixed bones compared to freshfrozen ones (52% higher through the optimization FE method and 84% higher through the beam theory method). Hence, we conclude that the formalin fixation has a significant effect on bovine cortical bones at small, elastic, as well as large, plastic deformations.