448 Journal of Applied Biomechanics, 2012, 28, 448-456 © 2012 Human Kinetics, Inc. Alexander Tsouknidas (Corresponding Author) is with the Laboratory for Machine Tools and Manufacturing Engineering, Mechanical Engineering Department, Aristoteles University of Thessaloniki, Greece. Nikoalos Michailidis is with the Physical Metallurgy Laboratory, Mechanical Engineering Department, Aristoteles University of Thessaloniki, Greece. Savvas Savvakis is with the Laboratory of Applied Thermodynamics, Mechani- cal Engineering Department, Aristoteles University of Thes- saloniki, Greece. Kleovoulos Anagnostidis is with the Third Orthopaedic Department, “Papageorgiou” General Hospital, Aristoteles University of Thessaloniki, Greece. Konstantinos- Dionysios Bouzakis is with the Laboratory for Machine Tools and Manufacturing Engineering, Mechanical Engineering Department, Aristoteles University of Thessaloniki, Greece. Georgios Kapetanos is with the Third Orthopaedic Department, “Papageorgiou” General Hospital, Aristoteles University of Thessaloniki, Greece. A Finite Element Model Technique to Determine the Mechanical Response of a Lumbar Spine Segment Under Complex Loads Alexander Tsouknidas, Nikoalos Michailidis, Savvas Savvakis, Kleovoulos Anagnostidis, Konstantinos-Dionysios Bouzakis, and Georgios Kapetanos Aristoteles University of Thessaloniki This study presents a CT-based inite element model of the lumbar spine taking into account all function- related boundary conditions, such as anisotropy of mechanical properties, ligaments, contact elements, mesh size, etc. Through advanced mesh generation and employment of compound elements, the developed model is capable of assessing the mechanical response of the examined spine segment for complex loading conditions, thus providing valuable insight on stress development within the model and allowing the prediction of critical loading scenarios. The model was validated through a comparison of the calculated force-induced inclination/ deformation and a correlation of these data to experimental values. The mechanical response of the examined functional spine segment was evaluated, and the effect of the loading scenario determined for both vertebral bodies as well as the connecting intervertebral disc. Keywords: biomechanical response, cadaveric experiments, spine segment inclination Three-dimensional inite element models represent- ing functional parts of the spine have been repeatedly introduced over recent years to simulate the biomechani- cal response of spinal units (Little et al., 2010; Ezquerro et al., 2004; Wang et al., 2006) or to investigate trauma- related surgical treatment (Polikeit et al., 2003; Ashish & Pramod, 2009). Several methods have been employed to obtain the desired geometrical characteristics. Even though touch probe digitizers (Lee et al., 2003) and laser scanners (Heuer et al., 2008) are able to provide high accuracy measurements, thus leading to an accurate representation of the spine, nonintrusive methods such as CT (Klinder et al., 2009) or magnetic resonance imaging (MRI) (Pir- rmann et al., 2001) ease the extraction of the geometric information while comparing favorably in terms of data processing and inherent defect determination. Recent studies have used combinations of the above techniques to simulate parts of the human spine ranging from a set of vertebra (Lodygowski et al., 2005) up to several parts of the spine (Guan et al., 2006). The novelty of the introduced model is based on the anatomical speciic mesh generation and the usage of compound elements, allowing the direct implementation of the meshed model in various solver environments, reproducing similar and directly comparable results. This is not possible in the case of automated mesh gen- eration within different solvers, as the generation of a mesh independent grid and subsequent consideration of anatomical characteristics will simulate, in most cases, unlike stress distributions. This in combination with sev- eral innovative aspects of spine modeling that have been separately considered in previous studies, such as mate- rial speciic properties (unequal properties distribution among anulus ibrosus layers, directional bone anisotropy, etc.) and all connective tissue (ligamenta longitudinale anterius, ligamenta longitudinale posterius, ligamenta supraspinalia, etc.) constitute a new modeling approach that will be presented in detail in this article. All these aspects combined in a high accuracy CT-based model of a functional spine unit (FSU) facilitate the simulation of Note. In this article, the figures are in color in the online PDF. An Official Journal of ISB www.JAB-Journal.com ORIGINAL RESEARCH