Specimen-specific beam models for fast and accurate prediction of human trabecular bone mechanical properties

Institute for Biomedical Engineering, University and ETH Zürich, Moussonstrasse 18, 8044 Zürich, Switzerland.
Bone (Impact Factor: 4.46). 01/2007; 39(6):1182-9. DOI: 10.1016/j.bone.2006.06.033
Source: PubMed

ABSTRACT Direct assessment of bone competence in vivo is not possible, hence, it is inevitable to predict it using appropriate simulation techniques. Although accurate estimates of bone competence can be obtained from micro-finite element models (muFE), it is at the expense of large computer efforts. In this study, we investigated the application of structural idealizations to represent individual trabeculae by single elements. The objective was to implement and validate this technique. We scanned 42 human vertebral bone samples (10 mm height, 8 mm diameter) with micro-computed tomography using a 20 microm resolution. After scanning, direct mechanical testing was performed. Topological classification and dilation-based algorithms were used to identify individual rods and plates. Two FE models were created for each specimen. In the first one, each rod-like trabecula was modeled with one thickness-matched beam; each plate-like trabecula was modeled with several beams. From a simulated compression test, assuming one isotropic tissue modulus for all elements, the apparent stiffness was calculated. After reducing the voxel size to 40 microm, a second FE model was created using a standard voxel conversion technique. Again, one tissue modulus was assumed for all elements in all models, and a compression test was simulated. Bone volume fraction ranged from 3.7% to 19.5%; Young's moduli from 43 MPa to 649 MPa. Both models predicted measured apparent moduli equally well (R2 = 0.85), and were in excellent agreement with each other (R2 = 0.97). Tissue modulus was estimated at 9.0 GPa and 10.7 GPa for the beam FE and voxel FE models, respectively. On average, the beam models were solved in 219 s, reducing CPU usage up to 1150-fold as compared to 40 microm voxel FE models. Relative to 20 microm voxel models 10,000-fold reductions can be expected. The presented beam FE model is an abstraction of the intricate real trabecular structure using simple cylindrical beam elements. Nevertheless, it enabled an accurate prediction of global mechanical properties of microstructural bone. The strong reduction in CPU time provides the means to increase throughput, to analyze multiple loading configuration and to increase sample size, without increasing computational costs. With upcoming in vivo high-resolution imaging systems, this model has the potential to become a standard for mechanical characterization of bone.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Relationship between osteoporosis and failure mechanism can be assessed through quantitative bone quality and clinical studies. Characterization and functional studies in this area is vital to identify patients at risk of bone fractures. Identification of elastic bone modulus can be done using several methods including mechanical testing and correlations between microarchitectural parameters. In this study, compressive testing was done until failure on bovine cancellous bone extracted from the neck of femur. A thorough experimental protocol was used for extraction and cleaning of cylindrical bone samples. Three cylindrical bovine cancellous bone specimens were obtained from the femoral cadaver for the experiment. The specimens have a diameter of 10 mm and a total length of 25 mm with an effective length for experiment of 15 mm. After extraction of the bone samples, the marrow was removed from the hard tissue by immersing in an ultrasound cleaner and then vacuumed. Results showed strong relationships between volume fraction and mechanical properties of cancellous bone. However, there is a weak relationship between the bulk density and the mechanical properties.
    Biomedical Engineering and Sciences (IECBES), 2010 IEEE EMBS Conference on; 01/2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Artificial bone is a suitable alternative to autografts and allografts, however their use is still limited. Though there were numerous reports on their structural properties, permeability studies of artificial bones were comparably scarce. This study focused on the development of idealised, structured models of artificial cancellous bone and compared their permeability values with bone surface area and porosity. Cancellous bones from fresh bovine femur were extracted and cleaned following an established protocol. The samples were scanned using micro-computed tomography (μCT) and three-dimensional models of the cancellous bones were reconstructed for morphology study. Seven idealised and structured cancellous bone models were then developed and fabricated via rapid prototyping technique. A test-rig was developed and permeability tests were performed on the artificial and real cancellous bones. The results showed a linear correlation between the permeability and the porosity as well as the bone surface area. The plate-like idealised structure showed a similar value of permeability to the real cancellous bones.
    Medical Engineering & Physics 12/2014; 37(1). DOI:10.1016/j.medengphy.2014.11.001 · 1.84 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This chapter focuses on the finite element method applied to spine modelling. First, the functional biomechanics of the healthy spine are presented in terms of load transfers among the different spinal structures and further related to the pathologic and treated spine. This overview naturally justifies the finite element method as a particularly convenient tool to explore the spine as an integrated organ where tissue maintenance and degeneration are strongly influenced by complex mechanical factors. The different approximations usually used in spine finite element analysis are presented and discussed in relation to the exploitability of the predictions and the computational cost. On one hand, spine models require thorough verification and improved validation protocols. On the other hand, the rapid mechanistic developments proposed are continuously increasing the reliability of both model calibration and predictions on a clinical basis, suggesting that spine finite element models will probably become highly valuable clinical tools in the near future.
    Biomaterials for Spinal Surgery, Edited by Luigi Ambrosio, K Elisabeth Tanner, 01/2012: chapter Part I: Fundamentals of Biomaterials for Spinal Surgery - Chapter 5: pages 144-232; Woodhead Publishing Ltd., ISBN: 978-1-84569-986-4

Full-text (2 Sources)

Available from
May 21, 2014