Study of posterolateral lumbar arthrodesis by means of a finite element model

Posterolateral lumbar arthrodesis consists in the fixation of the lumbar vertebrae pedicles by means of bars and screws. It is indicated in all those cases in which instability exists previous to the surgery, or in those other cases in which the instability has been caused by the need of bone resections that put the articulations structures in danger. The pedicle fixation of the lumbar arthrodesis is a great advance in the lumbar surgery. It contributes to achieve a stable and biologic fusion. The aim of the present research is the analysis of the contact problem that exists between the screw and the bone as one of the key points to control in order to achieve a good future stability of the arthrodesed spine. In order to achieve such aim, a Finite Elements Model (FEM) of the spine was performed. Such a model was obtained using a computer vision technique that creates 3D bodies using computed tomographies of the sacrum and vertebrae L4 and L5. Not only the bone bodies have been modeled, but also the intervertebral discs that act as the joints of the bones. In order to obtain a complete simulation of the lumbar region the titanium screws and bars have been modeled too. The study of the influence of the contact between bone and screw in the biomechanical behavior of the lumbar column has been studied applying several load conditions simulating different kinds of typical movements of the column. Finally, the stresses on the different elements of the lumbar structure and the relative movements between bone and screw as well as the conclusions of this research are also expounded.

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