Abstract
The growth plate is a thin layer of cartilage sandwiched between epiphyseal and metaphyseal bone and is the location of active bone growth during childhood. It is subjected to large compressive and shear forces while protecting its resident chondrocytes from damage. We believe that computational modeling can help us better understand how the macro-scale loads are transmitted to micro-scale stresses and strains within the growth plate cartilage. As a first step in this process we analyzed the mechanical response of compression experiments performed on bovine bone/growth plate/bone samples. We endeavored to estimate the modulus of elasticity of the growth plate itself by simulating the compression experiments of these specimens using the finite element method. It is shown that when the growth plate in the compression specimens was modeled as a flat layer, the state of stress in the cartilage was triaxial and non-uniform with the hydrostatic stress being much greater than the octahedral shear stress over most of the central region of the growth plate test samples. The computational models accounted for variations in the average cartilage thickness, the non-uniaxial, non-uniform and triaxial state of stress in the thin cartilage layer, and for the estimated extrinsic compliance resulting from compression of the variable heights of bone on either side of the growth plate cartilage. However, due to lack of information on the internal structure of each sample, the models did not account for the variations in the non-flat topography of the growth plates. The models also did not include the calcified cartilage layer. Further model development is recommendedin order to determine the degree to which accounting for the complex growth plate topography influences the predicted cartilage modulus of elasticity.
Highlights
The growth plate, a cartilage plate separating the metaphysis from the epiphysis at each end of a long bone (Figure 1A), is responsible for the longitudinal growth of bone
Different Growth Plate Topography We studied the impact of the topography of the secondary mammillary processes on the difference between EEX and EIN
Part of the reason for this discrepancy is that the triaxial state of stress present in a thin layer of soft material sandwiched between stiffer materials is usually not accounted for when the elastic modulus is calculated from uniaxial compression tests
Summary
The growth plate, a cartilage plate separating the metaphysis from the epiphysis at each end of a long bone (Figure 1A), is responsible for the longitudinal growth of bone. It consists of chondrocytes embedded in an abundant extracellular matrix (ECM) [1]. The growth plate is composed of a cartilaginous component that has three histologically distinct zones: reserve or germinal, proliferative and hypertrophic [2] (Figure 1B). From the epiphyseal side nutrients are provided by the epiphyseal blood vessels passing through the germinal zone and terminating at the proliferating layer and progress through the growth plate via diffusion [4]. On the metaphyseal side vascular loops penetrate into the spaces of dying hypertrophic chondrocytes to provide nutrients for the osteoprogenitor cells producing bone on the primary spongiosa cartilage scaffolds
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