A patient-specific finite element methodology to predict damage accumulation in vertebral bodies under axial compression, sagittal flexion and combined loads.
ABSTRACT Due to the inherent limitations of DXA, assessment of the biomechanical properties of vertebral bodies relies increasingly on CT-based finite element (FE) models, but these often use simplistic material behaviour and/or single loading cases. In this study, we applied a novel constitutive law for bone elasticity, plasticity and damage to FE models created from coarsened pQCT images of human vertebrae, and compared vertebral stiffness, strength and damage accumulation for axial compression, anterior flexion and a combination of these two cases. FE axial stiffness and strength correlated with experiments and were linearly related to flexion properties. In all loading modes, damage localised preferentially in the trabecular compartment. Damage for the combined loading was higher than cumulated damage produced by individual compression and flexion. In conclusion, this FE method predicts stiffness and strength of vertebral bodies from CT images with clinical resolution and provides insight into damage accumulation in various loading modes.
Article: Biomechanical effects of teriparatide in women with osteoporosis treated previously with alendronate and risedronate: results from quantitative computed tomography-based finite element analysis of the vertebral body.[show abstract] [hide abstract]
ABSTRACT: Previous antiresorptive treatment may influence the anabolic response to teriparatide. The OPTAMISE (Open-label Study to Determine How Prior Therapy with Alendronate or Risedronate in Postmenopausal Women with Osteoporosis Influences the Clinical Effectiveness of Teriparatide) study reported greater increases in biochemical markers of bone turnover and volumetric bone mineral density (BMD) when 12 months of teriparatide treatment was preceded by 2 years or more of risedronate versus alendronate treatment. The objective of this study was to use quantitative computed tomography (CT)-based nonlinear finite element modeling to evaluate how prior therapy with alendronate or risedronate in postmenopausal women with osteoporosis influences the biomechanical effectiveness of teriparatide. Finite element models of the L1 vertebra were created from quantitative CT scans, acquired before and after 12 months of therapy with teriparatide, from 171 patients from the OPTAMISE study. These models were subjected to uniaxial compression. Total BMD-derived bone volume fraction (BV/TV(d), i.e., bone volume [BV]/total volume [TV]), estimated from quantitative CT-based volumetric BMD, vertebral stiffness, and failure load (strength) were calculated for each time measurement point. The results of this study demonstrated that 12 months of treatment with teriparatide following prior treatment with either risedronate or alendronate increased BMD-derived BV/TV(d), the predicted vertebral stiffness, and failure load. However, the effects of teriparatide were more pronounced in patients treated previously with risedronate, which is consistent with the findings of the OPTAMISE study. The mean (+/-standard error) increase in stiffness was greater in the prior risedronate group than the prior alendronate group (24.6+/-3.2% versus 14.4+/-2.8%, respectively; p=0.0073). Similarly, vertebral failure load increased by 27.2+/-3.5% in the prior risedronate group versus 15.3+/-3.1% in the prior alendronate group (p=0.0042). The mechanical variables increased in greater proportion than BV/TV(d), which increased by 6.9+/-0.9% versus 4.6+/-0.8% in the prior-risedronate and prior-alendronate groups, respectively (p=0.0290). Our finding indicated that while teriparatide can be used with success on patients who have previously undergone treatment with risedronate and alendronate, it demonstrated greater anabolic effect on biomechanical properties in prior-risedronate patients in the first year of teriparatide treatment.Bone 09/2009; 46(1):41-8. · 4.02 Impact Factor
Article: QCT-based finite element models predict human vertebral strength in vitro significantly better than simulated DEXA.[show abstract] [hide abstract]
ABSTRACT: While dual energy X-ray absorptiometry (DXA) is considered the gold standard to evaluate fracture risk in vivo, in the present study, the quantitative computed tomography (QCT)-based finite element modeling has been found to provide a quantitative and significantly improved prediction of vertebral strength in vitro. This technique might be used in vivo considering however the much larger doses of radiation needed for QCT. Vertebral fracture is a common medical problem in osteoporotic individuals. Bone mineral density (BMD) is the gold standard measure to evaluate fracture risk in vivo. QCT-based finite element (FE) modeling is an engineering method to predict vertebral strength. The aim of this study was to compare the ability of FE and clinical diagnostic tools to predict vertebral strength in vitro using an improved testing protocol. Thirty-seven vertebral sections were scanned with QCT and high resolution peripheral QCT (HR-pQCT). Bone mineral content (BMC), total BMD (tBMD), areal BMD from lateral (aBMD-lat), and anterior-posterior (aBMD-ap) projections were evaluated for both resolutions. Wedge-shaped fractures were then induced in each specimen with a novel testing setup. Nonlinear homogenized FE models (hFE) and linear micro-FE (μFE) were generated from QCT and HR-pQCT images, respectively. For experiments and models, both structural properties (stiffness, ultimate load) and material properties (apparent modulus and strength) were computed and compared. Both hFE and μFE models predicted material properties better than structural ones and predicted strength significantly better than aBMD computed from QCT and HR-pQCT (hFE: R² = 0.79, μFE: R² = 0.88, aBMD-ap: R² = 0.48-0.47, aBMD-lat: R² = 0.41-0.43). Moreover, the hFE provided reasonable quantitative estimations of the experimental mechanical properties without fitting the model parameters. The QCT-based hFE method provides a quantitative and significantly improved prediction of vertebral strength in vitro when compared to simulated DXA. This superior predictive power needs to be verified for loading conditions that simulate even more the in vivo case for human vertebrae.Osteoporosis International 02/2011; 23(2):563-72. · 4.58 Impact Factor