A New Method To Determine Volumetric Bone Mineral Density From Bi-Planar Dual Energy Radiographs Using A Finite Element Model: An Ex-Vivo Study

Finite element models (FEMs) derived from QCT-scans were developed to evaluate vertebral strength but QCT scanners limitations are restrictive for routine osteoporotic diagnosis. A new approach considers using bi-planar dual energy (BP2E) X-rays absorptiometry to build vertebral FEM. The purpose was to propose a FEM based on BP2E absorptiometry and to compare the vertebral strength predicted from this model to a QCT-based FEM. About 46 vertebrae were QCT scanned and imaged with BP2E X-rays. Subject-specific vertebral geometry and bone material properties were obtained from both medical imaging techniques to build FEM for each vertebra. Vertebral body volumetric bone mineral density (vBMD) distribution and vertebral strength prediction from the BP2E-based FEM and the QCT-based FEM were compared. A statistical error of 7[Formula: see text]mg/cm3 with a RMSE of 9.6% and a [Formula: see text] of 0.83 were found in the vBMD distribution differences between the BP2E-based and qCT-based FEM. The average vertebral strength was 3321[Formula: see text][Formula: see text] and 3768[Formula: see text][Formula: see text][Formula: see text for the qCT-based and BP2E-based FEM, respectively, with a RMSE of 641[Formula: see text]N and [Formula: see text] of 0.92. This method was developed to estimate vBMD distribution in lumbar vertebrae from a pair of 2D-BMD images and demonstrated to be accurate to personalize the mechanical properties in vitro

Vertebral strength prediction from Bi-Planar dual energy x-ray absorptiometry under anterior compressive force using a finite element model: An in vitro study

Finite element models (FEM) derived from qCT-scans were developed as a clinical tool to evaluate vertebral strength. However, the high dose, time and cost of qCT-scanner are limitations for routine osteoporotic diagnosis. A new approach considers using bi-planar dual energy (BP2E) X-rays absorptiometry to build vertebral FEM using synchronized sagittal and frontal plane radiographs. The purpose of this study was to compare the performance of the areal bone mineral density (aBMD) measured from DXA, qCT-based FEM and BP2E-based FEM in predicting experimental vertebral strength. Twenty eight vertebrae from eleven lumbar spine segments were imaged with qCT, DXA and BP2E X-rays before destructively tested in anterior compression. FEM were built based on qCT and BP2E images for each vertebra. Subject-specific FEM were built based on 1) the BP2E images using 3D reconstruction and volumetric BMD distribution estimation and 2) the qCT scans using slice by slice segmentation and voxel based calibration. Linear regression analysis was performed to find the best predictor for experimental vertebral strength (Fexpe); aBMD, modeled vertebral strength and vertebral stiffness. Areal BMD was moderately correlated with Fexpe (R2 = 0.74). FEM calculations of vertebral strength were highly to strongly correlated with Fexpe (R2 = 0.84, p < 0.001 for BP2E model and R2 = 0.95, p < 0.001 for qCT model). The results of this study suggest that aBMD accounted for only 74% of Fexpe variability while FE models accounted for at least 84%. For anterior compressive loading on isolated vertebral bodies, simplistic loading condition aimed to replicate anterior wedge fractures, both FEM were good predictors of Fexpe. Therefore FEM based on BP2E X-rays absorptiometry could be a good alternative to replace qCT-based models in the prediction of vertebral strength. However future work should investigate the performance of the BP2E-based model in vivo in discriminating patients with and without vertebral fracture in a prospective study.The authors would like to thank S. Persohn and M. Jeyasankar for contributing to mechanical testing. The authors would also thank Anabela Darbon, advanced research engineer at EOS Imaging, for EOS® dual energy acquisition and calibration. This work was supported by the Banque Publique d’Investissement through the dexEOS project part of the FUI14. The funding agencies had no role in the design and conduct of the study, in the collection, management, analysis and interpretation of the data, or in the preparation, review, or approval of the manuscript

Vertebral strength prediction under anterior compressive force using a finite element model for osteoporosis assessment

Vertebral fractures are one of the most common clinical manifestations with the major adverse consequences of osteoporosis as they usually occur under non-traumatic loading conditions. Height loss, back pain and func-tional disability are the most encountered consequences of vertebral fractures with repetitive fracture experience more likely occurring within a year after the first fracture. Early diagnosis of osteoporosis is therefore important for vertebral fracture prevention as drug treatments are more effective before perforation of the trabeculae (Mc Donnell et al. 2007). Bone mineral density (BMD) measured by dual energy X-ray absorptiometry (DXA) is the most clinically used method to diagnose osteopo-rosis. However this technique can only predict 40–70% of vertebral fractures as it only measures areal BMD which does not account for three dimensional (3D) geometry and BMD distribution (Sornay-Rendu et al. 2005). The combination of patient-specific 3D geometry and 3D BMD distribution is necessary to predict vertebral strength. Finite element models (FEM) derived from quantitative computed tomography (qCT) images are used to predict failure strength of vertebral bodies (Crawford et al. 2003; Imai et al. 2006; Buckley et al. 2007). Most of these models were validated under axial compressive forces to the vertebral body while vertebral fractures are more associated with eccentric compres-sion (Lunt et al. 2003). The purpose of this study was to compare the performance of the aBMD from DXA and qCT-based FEM in predicting experimen-tal vertebral strength. The experimental set up allowed for anterior compression testing on isolated vertebral bodies to ensure repeatable loading condition simulat-ing an anterior wedge-shape fracture

Contribution to FE modeling for intraoperative pedicle screw strength prediction

Although the use of pedicle screws is considered safe, mechanical issues still often occur. Commonly reported issues are screw loosening, screw bending and screw fracture. The aim of this study was to develop a Finite Element (FE) model for the study of pedicle screw biomechanics and for the prediction of the intraoperative pullout strength. The model includes both a parameterized screw model and a patient-specific vertebra model. Pullout experiments were performed on 30 human cadaveric vertebrae from ten donors. The experimental force-displacement data served to evaluate the FE model performance. μCT images were taken before and after screw insertion, allowing the creation of an accurate 3D-model and a precise representation of the mechanical properties of the bone. The experimental results revealed a significant positive correlation between bone mineral density (BMD) and pullout strength (Spearman ρ= 0.59, p< 0.001) as well as between BMD and pullout stiffness (Spearman ρ= 0.59, p< 0.001). A high positive correlation was also found between the pullout strength and stiffness (Spearman ρ = 0.84, p < 0.0001). The FE model was able to reproduce the linear part of the experimental force-displacement curve. Moreover, a high positive correlation was found between numerical and experimental pullout stiffness (Pearson ρ = 0.96, p< 0.005) and strength (Pearson ρ= 0.90, p< 0.05). Once fully validated, this model opens the way for a detailed study of pedicle screw biomechanics and for future adjustments of the screw design.The authors would like to thank Julie Choisne and Sylvain Persohn for their technical assistance. This study was supported by the ParisTech-BiomecAM chair program on subject-specific modeling, financed by Société Générale, Covea, Proteor and Fondation Cotrel