Mapping the Multi‐Directional Mechanical Properties of Bone in the Proximal Tibia

Abstract

The remodeling behavior of bone is influenced by its mechanical environment. By mapping bone's mechanical properties in detail, orthopedic implants with respect to its mechanical properties could stimulate and harness remodeling to improve patient outcomes. In this study, multiaxial apparent modulus and strength of cadaveric proximal tibial bone are mapped and predicted from computed tomography (CT) derived apparent density. Group differences are identified from testing order, subchondral depth, condyle, and sub-meniscal bone with covariates; age and gender. Axial modulus is 50% greater than the transverse modulus. Medial axial modulus is 30% greater than the lateral side. On the lateral side, axial modulus decreases by 50% from proximal to 25 mm distal. On the medial side, axial modulus remains relatively constant. Differences are quantified for density and multiaxial modulus across all subchondral depths, and different power law relationships are provided for each location. Density explains 75% of variation when grouped by subchondral depth and condyle. Yield strength is well-predicted across all test directions, with density predicting 81% of axial strength variation and no differences over subchondral depth. Quantified mapping of bone multiaxial modulus based on condyle and subchondral depth is shown for the first time in a clinically viable protocol using conventional CT.

Topology Optimisation for Compliant Hip Implant Design and Reduced Strain Shielding

“…The focus of this paper was to develop the multiple load case topology optimisation approach for hip implant design, rather than to produce a specific “best” design. Hence, simplifications were made to enable research to focus on the process rather than modelling complexity: (1) The bone was modelled with only a single property each for cortical/trabecular bone, whereas the bone was both inhomogeneous and anisotropic [ 54 ]. The process developed here could be applied to a calibrated CT scanned femoral bone model to capture regional variation in properties.…”

Total and partial knee arthroplasty implants that maintain native load transfer in the tibia

“…M4 and T4 had a graded axial modulus of 0.4 GPa to 0.7 GPa to match the stiffness gradient in the proximal tibia measured in a previous study. 30 Titanium lattice tibial components were made by filling the implant volume with a stochastic lattice structure. 24 The diameter and connectivity of the lattice struts, and the strut density, were controlled to generate the desired stiffness.…”

Lattice implants that generate homeostatic and remodeling strains in bone

“…From the 195 cubes, 5 were selected to represent the variability in density of bone in the proximal tibia. Multiaxial apparent modulus was predicted for each cube from qCT with a calibration phantom using the methods described by Munford et al 25 These data were used as a target for the apparent modulus of the titanium scaffolds.…”

“…10 For the proximal tibia, the modulus of the bone is well understood and can be predicted from quantified computed tomography (qCT) derived apparent density. [25][26][27][28] Thus, it should now be possible to create tibial orthopedic implants that generate a strain gradient to maintain or improve the quality of the bone in the proximal tibia. 1 Loading in the proximal tibia is predominantly compressive and long the anatomical axis so controlling bone axial strain is a priority.…”