Mapping anisotropy improves QCT-based finite element estimation of hip strength in pooled stance and side-fall load configurations. (September 2018)

• Record Type: Journal Article
• Authors: Panyasantisuk, J.; Dall'Ara, E.; Pretterklieber, M.; Pahr, D.H.; Zysset, P.K.
• Is Part Of: Medical engineering & physics. Volume 59(2018)
• Page Start: 36
• Page End: 42
• Publication Date: 2018-09
• Subjects: Anisotropy -- Fabric -- Finite element analysis -- Proximal femur -- Quantitative computed tomography -- Bone strength; Biomedical engineering -- Periodicals; Biomedical Engineering -- Periodicals; Physics -- Periodicals; Génie biomédical -- Périodiques; Biomedical engineering; Electronic journals; Periodicals; 610.28
• DOI: 10.1016/j.medengphy.2018.06.004
• Languages: English
• ISSNs: 1350-4533

Abstract

Highlights: QCT-based FE models of the proximal femur were enriched with femur-specific or mean fabric. Stiffness and strength of 71 femurs were computed in side-fall and stance load cases. Results of isotropic and femur-specific/mean anisotropic models were compared to experiments. Fabric was only relevant for strength predictions when combining both load cases. Femur-specific and mean fabric were statistically not distinguishable. Abstract: Hip fractures are one of the most severe consequences of osteoporosis. Compared to the clinical standard of DXA-based aBMD at the femoral neck, QCT-based FEA delivers a better surrogate of femoral strength and gains acceptance for the calculation of hip fracture risk when a CT reconstruction is available. Isotropic, homogenised voxel-based, finite element (hvFE) models are widely used to estimate femoral strength in cross-sectional and longitudinal clinical studies. However, fabric anisotropy is a classical feature of the architecture of the proximal femur and the second determinant of the homogenised mechanical properties of trabecular bone. Due to the limited resolution, fabric anisotropy cannot be derived from clinical CT reconstructions. Alternatively, fabric anisotropy can be extracted from HR-pQCT images of cadaveric femora. In this study, fabric anisotropy from HR-pQCT images was mapped onto QCT-based hvFE models of 71 human proximal femora for which both HR-pQCT and QCT images were available. Stiffness and ultimate load computed from anisotropic hvFE models were compared with previous biomechanical tests in both stance and side-fall configurations. The influence of using the femur-specific versus a mean fabric distribution on the hvFE predictions was assessed. Femur-specific and mean fabric enhance the prediction of experimental ultimate force for the pooled, i.e. stance and side-fall, (isotropic: r 2 = 0.81, femur-specific fabric: r 2 = 0.88, mean fabric: r 2 = 0.86, p < 0.001 ) but not for the individual configurations. Fabric anisotropy significantly improves bone strength prediction for the pooled configurations, and mapped fabric provides a comparable prediction to true fabric. The mapping of fabric anisotropy is therefore expected to help generate more accurate QCT-based hvFE models of the proximal femur for personalised or multiple load configurations.