Relationships between bone morphology and bone elastic properties can be accurately quantified using high-resolution computer reconstructions

Authors

  • B. Van Rietbergen,

    1. Institute for Biomedical Engineering, University of Zürich, and Swiss Federal Institute of Technology (ETH), Zürich, Switzerland
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  • A. Odgaard,

    1. Biomechanics Laboratory, Department of Orthopaedic Surgery, Aarhus University Hospital, Aarhus, Denmark
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  • J. Kabel,

    1. Biomechanics Laboratory, Department of Orthopaedic Surgery, Aarhus University Hospital, Aarhus, Denmark
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  • R. Huiskes

    Corresponding author
    1. Orthopaedic Research Laboratory, Department of Orthopaedics, University of Nijmegen, Nijmegen, The Netherlands
    • Orthopaedic Research Laboratory. Department of Orthopaedics, University of Nijmegen. P.O. Box 910 (1. 6500)
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Abstract

It would be advantageous if the mechanical properties of trabecular bone could be directly inferred from stereomorphometric parameters. For that purpose, apparent density and mean intercept length, as measures of bone mass and directionality (fabric), are commonly correlated with the elastic characteristics of bone samples, as determined in compression tests. However, complete and accurate relationships have not yet been established in this way. This may be due not only to the occurrence of artifacts in both the stereomorphometric and the mechanical assessments but also to an inherent inadequacy of mean intercept length in characterizing the full mechanical significance of bone architecture or nonhomogeneities in trabecular tissue properties not accounted for in stereomorphometry. In this study, we introduce a computer modeling approach allowing these biases to be eliminated. With use of high-resolution three-dimensional computer reconstructions of trabecular bone specimens for stereomorphometry and for microstructural finite element models to simulate mechanical tests, unbiased comparisons become feasible. The purpose was to investigate if accurate and complete relationships can be established in this way. Four different fabric measures were considered: mean intercept length and three volume-based ones. Compliance matrices were calculated from fabric tensors, with use of the mathematical relationship proposed by Cowin for 29 vertebral whale-bone specimens. These were correlated with the compliance constants determined directly from the microstructural finite element, model simulation. The nine orthotropic elastic constants of all 29 specimens were well predicted from their stereomorphometric fabric and volume fraction values, with correlation coefficients ranging from Rmath image = 0.9934 to O. 9963. When individual compliance components were considered (1/Ei,. 1/Gij, or -vij/Ei), correlation coefficients ranged from Rmath image = 0.924 to 0.9X2. All four fabric measures performed equally well. It is concluded that volume fraction and fabric measures correlate highly with the apparent elastic properties of bone samples, provided the anisotropy and nonhomgoencity in the elastic properties of the trabecular tissue itself have negligible effects on the apparent propertie Whether this is true for bone in general remains to be seen, as only a subset was analyzed here. These methods, however, can be valuable in similar assessments of other subsets.

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