152 Introduction Up to now, the mechanical properties of bones are deter- mined by means of simple tension or compression tests 1,2 on unique material specimens with pre-formed dimensions as described in numerous publications. In order to enable the determination of the elastic–plastic deformation behaviour of the various materials included in the structure of a lumbar spine vertebrae, such as of the cor- tical shell and the cancellous bone by means of compression tests directly on entire vertebra, an experimental-analytical procedure based on Finite Elements Method (FEM) simula- tions of the test and the specimens was developed. The detected bulk material properties in the case of can- cellous bone have to be considered as apparent ones, due to the fact that they do not correspond to individual structural components as, for example, to trabecular bone struts. Aiming to determine trabecular bone struts stress–strain curves, nanoindentation techniques were applied 3-5 . The obtained data were taken into account in the FEM simula- tion of a cancellous bone structure by means of an appropri- ate network of beam elements. In this way a compression test diagram, indicating the load versus the vertebra deformation, can be accurately described with the aid of FEM–calculations using as a simu- J Musculoskel Neuron Interact 2004; 4(2):152-158 Loading simulation of lumbar spine vertebrae during a compression test using the finite elements method and trabecular bone strength properties, determined by means of nanoindentations K.-D. Bouzakis 1 , S. Mitsi 1 , N. Michailidis 1 , I. Mirisidis 1 , G. Mesomeris 1 , G. Maliaris 1 , A. Korlos 1 , G. Kapetanos 2 , P. Antonarakos 2 , K. Anagnostidis 2 1 Laboratory for Machine Tools and Manufacturing Engineering, Mechanical Engineering Department, Aristoteles University of Thessaloniki, Greece, 2 3 rd Orthopaedic Department, Papageorgiou General Hospital, Medical School, Aristoteles University of Thessaloniki, Greece Abstract The mechanical strength properties of lumbar spine vertebrae are of great importance in a wide range of applications. Herein, through nanoindentations and appropriate evaluation of the corresponding results, trabecular bone struts stress–strain characteristics can be determined. In the frame of the present paper, an L2 fresh cadaveric vertebra, from which posterior ele- ments were removed, was subjected to compression. With the aid of developed finite elements method based algorithms, the cortical shell and the cancellous core bulk elasticity moduli and stresses were determined, whereas the tested vertebra geomet- rical model used in these algorithms was considered as having a compound structure, consisting of the cancellous bone sur- rounded by the cortical shell. Moreover nanoindentations were conducted and an appropriate evaluation method of the obtained results was applied to extract stress-strain curves of individual lumbar spine vertebra trabecular bone struts. These data were used in the mathematical description of the vertebrae compression test. The vertebral cancellous bone structure was sim- ulated by a beam elements network, possessing an equivalent porosity and different stiffnesses in vertical and horizontal direc- tion. Thus, the measured course of the compression load versus the occurring specimen deformation was verified. Keywords: Vertebrae Compression Test, Nanoindentation, Stress-strain Curves, Apparent Strength, Trabecular Bone Struts, Mechanical Properties Original Article Hylonome The authors have no conflict of interest. Corresponding ·uthor: K.-D. Bouzakis, Laboratory for Machine Tools and Manufacturing Engineering, Aristoteles University of Thessaloniki, GR 54124 Thessaloniki, Greece E-mail: bouzakis@eng.auth.gr Accepted 28 May