Abstract
PurposeCortical porosity is a key characteristic governing the structural properties and mechanical behaviour of bone, and its quantification is therefore critical for understanding and monitoring the development of various bone pathologies such as osteoporosis. Axial transmission quantitative acoustics has shown to be a promising technique for assessing bone health in a fast, non-invasive, and radiation-free manner. One major hurdle in bringing this approach to clinical application is the entanglement of the effects of individual characteristics (e.g. geometry, porosity, anisotropy etc.) on the measured wave propagation. In order to address this entanglement problem, we therefore propose a systematic bottom-up approach, in which only one bone property is varied, before addressing interaction effects. This work therefore investigated the sensitivity of low-frequency quantitative acoustics to changes in porosity as well as individual pore characteristics using specifically designed cortical bone phantoms.Materials and methods14 bone phantoms were designed with varying pore size, axial-, and radial pore number, resulting in porosities (bone volume fraction) between 0% and 15%, similar to porosity values found in human cortical bone. All phantoms were manufactured using laser sintering, measured using axial-transmission acoustics and analysed using a full-wave approach. Experimental results were compared to theoretical predictions based on a modified Timoshenko theory.ResultsA clear dependence of phase velocity on frequency and porosity produced by increasing pore size or radial pore number was demonstrated, with the velocity decreasing by between 2–5 m/s per percent of additional porosity, which corresponds to -0.5% to -1.0% of wave speed. While the change in phase velocity due to axial pore number was consistent with the results due to pore size and radial pore number, the relative uncertainties for the estimates were too high to draw any conclusions for this parameter.ConclusionsThis work has shown the capability of low-frequency quantitative acoustics to reflect changes in porosity and individual pore characteristics and demonstrated that additive manufacturing is an appropriate method that allows the influence of individual bone properties on the wave propagation to be systematically assessed. The results of this work opens perspectives for the efficient development of a multi-frequency, multi-mode approach to screen, diagnose, and monitor bone pathologies in individuals.
Highlights
Osteoporosis is a systemic bone pathology characterized by the degradation of micro- and macroscopic bone properties [1,2,3] and a corresponding increase in fracture risk
While the change in phase velocity due to axial pore number was consistent with the results due to pore size and radial pore number, the relative uncertainties for the estimates were too high to draw any conclusions for this parameter
Considerable changes occur within the trabecular bone structure due to osteoporosis [5,8], the endosteal cortex is known to be affected, where an imbalance in bone resorption over bone formation leads to an increase in cortical porosity, as well as thinning of the cortical shell, thereby increasing bone fragility [5,9,10,11,12]
Summary
Osteoporosis is a systemic bone pathology characterized by the degradation of micro- and macroscopic bone properties [1,2,3] and a corresponding increase in fracture risk. Osteoporosis is the most widespread skeletal disorder, affecting one in two women and one in five men over the age of 50 in the western world [4,5] and more than 200 million individuals worldwide [2]. The lifetime risk of suffering from an osteoporosis-related fracture in subjects over 50 years is estimated to be 53.2% in women and 20.7% in men [6], a number that will likely be exacerbated by increasing life expectancies. Any state-of-the-art approach to clinically assess bone health clearly needs to take cortical porosity into account
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