Imaging of the Microstructural Failure Mechanism in the Human Hip

Saulo Martelli; Egon Perilli

doi:10.3791/64947

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Method Article

Imaging of the Microstructural Failure Mechanism in the Human Hip

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DOI:

10.3791/64947

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September 29th, 2023

Saulo Martelli¹^,² , Egon Perilli²

¹School of Mechanical, Medical and Process Engineering, Queensland University of Technology, ²Medical Device Research Institute, College of Science and Engineering, Flinders University

Summary

The protocol enables the measurement of the deformation of the bone microstructure in the entire proximal human femur and its toughness by combining large-volume micro-CT scanning, a custom-made compressive stage, and advanced image processing tools.

Abstract

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe a protocol for obtaining a sequence of three-dimensional microstructural images of the entire proximal femur under progressively increasing deformation, causing clinically relevant fractures of the femoral neck. The protocol is demonstrated using four femora from female donors aged 66-80 years at the lower end of bone mineral density in the population (T-score range = −2.09 to −4.75). A radio-transparent compressive stage was designed for loading the specimens replicating a one-leg stance, while recording the applied load during micro-computed tomography (micro-CT) imaging. The field of view was 146 mm wide and 132 mm high, and the isotropic pixel size was 0.03 mm. The force increment was based on finite-element predictions of the fracture load. The compressive stage was used to apply the displacement to the specimen and enact the prescribed force increments. Sub-capital fractures due to opening and shear of the femoral neck occurred after four to five load increments. The micro-CT images and the reaction force measurements were processed to study the bone strain and energy absorption capacity. Instability of the cortex appeared at the early loading steps. The subchondral bone in the femoral head displayed large deformations reaching 16% before fracture, and a progressive increase in the support capacity up to fracture. The deformation energy linearly increased with the displacement up to fracture, while the stiffness decreased to near-zero values immediately before fracture. Three-fourths of the fracture energy was taken by the specimen during the final 25% force increment. In conclusion, the protocol developed revealed a remarkable energy absorption capacity, or damage tolerance, and a synergic interaction between the cortical and trabecular bone at an advanced donor age.

Introduction

Fractures of the femoral neck are a major burden to the aging population. Micro-computed tomography (micro-CT) imaging and concomitant mechanical testing allow for observing the bone microstructure and studying its relationship to bone strength, its age-related changes, and displacements under load¹^,². However, until recently, micro-CT studies of bone under load were limited to excised bone cores³, small animals⁴, and human spine units⁵. The present protocol can quantify the displacement of the microstructure of the entire proximal hu....