Characterization of the Poroelastic Material Properties of Skeletal Repair Tissues Using Microindentation

Nearly 10% of the approximately six million fractures that occur each year in the United States do not heal, causing lasting pain and repetitive injury [1]. Although the causes of poor healing are unknown in many cases, the sensitivity of the repair process to mechanical factors is well established. In an effort to understand how mechanical factors such as axial and shear micromotion at the fracture site affect healing, prior studies have sought to characterize the local mechanical environment using finite element (FE) analysis (e.g., [2,3]). However, a key set of inputs for the FE analyses is the distribution of material properties of the various tissues that comprise the fracture callus. Recent studies using nano- and microindentation have estimated these properties by approximating the tissues as linear elastic [4,5]. As a next step in this line of inquiry, the overall goal of this study was to estimate the linear, poroelastic material properties of callus tissues. The specific objectives were: 1) to develop an FE model for use in simulating microindentation experiments; and 2) to compare the results of the simulation to experimental microindentation data in order to derive the mechanical properties of the healing tissues.