title: Finite element analyses of human vertebral bodies embedded in polymethylmethalcrylate or loaded via the hyperelastic intervertebral disc models provide equivalent predictions of experimental strength.
abstract: Quantitative computer tomography (QCT)-based finite element (FE) models of vertebral body provide better prediction of vertebral strength than dual energy X-ray absorptiometry. However, most models were validated against compression of vertebral bodies with endplates embedded in polymethylmethalcrylate (PMMA). Yet, loading being as important as bone density, the absence of intervertebral disc (IVD) affects the strength. Accordingly, the aim was to assess the strength predictions of the classic FE models (vertebral body embedded) against the in vitro and in silico strengths of vertebral bodies loaded via IVDs. High resolution peripheral QCT (HR-pQCT) were performed on 13 segments (T11/T12/L1). T11 and L1 were augmented with PMMA and the samples were tested under a 4° wedge compression until failure of T12. Specimen-specific model was generated for each T12 from the HR-pQCT data. Two FE sets were created: FE-PMMA refers to the classical vertebral body embedded model under axial compression; FE-IVD to their loading via hyperelastic IVD model under the wedge compression as conducted experimentally. Results showed that FE-PMMA models overestimated the experimental strength and their strength prediction was satisfactory considering the different experimental set-up. On the other hand, the FE-IVD models did not prove significantly better (Exp/FE-PMMA: R²=0.68; Exp/FE-IVD: R²=0.71, p=0.84). In conclusion, FE-PMMA correlates well with in vitro strength of human vertebral bodies loaded via real IVDs and FE-IVD with hyperelastic IVDs do not significantly improve this correlation. Therefore, it seems not worth adding the IVDs to vertebral body models until fully validated patient-specific IVD models become available.
authors.affiliation: Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany. Electronic address: yongtao.lu@tuhh.de.
authors.forename: Yongtao
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Institute of Surgical Technology & Biomechanics, University of Bern, Bern, Switzerland.
authors.forename: Ghislain
authors.initials: G
authors.lastname: Maquer
authors.affiliation: Institute of Medical Physics, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Oleg
authors.initials: O
authors.lastname: Museyko
authors.affiliation: Department of Legal Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.affiliation: Institute of Medical Physics, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Engelke
authors.affiliation: Institute of Surgical Technology & Biomechanics, University of Bern, Bern, Switzerland.
authors.forename: Philippe
authors.initials: P
authors.lastname: Zysset
authors.affiliation: Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Morlock
authors.affiliation: Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Huber
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D000368:Aged; D000465:Algorithms; D001696:Biomechanical Phenomena; D015519:Bone Density; D019245:Compressive Strength; D004548:Elasticity; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging*; D008159:Lumbar Vertebrae / Q000473:pathology; D008875:Middle Aged; D008954:Models, Biological; D015233:Models, Statistical; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D013131:Spine / Q000000981:diagnostic imaging; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000473:pathology; D014057:Tomography, X-Ray Computed
chemical_list: D019904:Polymethyl Methacrylate
keywords: Failure strength; Finite element prediction; Human vertebra; Intervertebral disc; Mechanical testing