dc.description.abstracteng | The aim of this study was to analyze methods and results of in vitro experiments examining kinematical behavior of the spine, which are presented in literature. Instead of simply describing range of motion, a rotational/scew axis is of high interest, because it is the only parameter that delivers information about the three-dimensional behavior of the spine. First, physiological basics were explained, which shall be used for examining the studies found in literature. A systematic review of studies examining in vitro spine kinematical behavior was conducted using PUBMED and WEB OF SCIENCE. Known kinematical and biomechanical keywords were used as search terms. Concerning the applied methods, all studies showed severe simplifications of actual in vivo behavior of the spine. Often a preload was applied to simulate muscle forces and body weight. These procedures enabled a high reproducibility and controllability, but were not consistent with physiological circumstances. They rather showed artefact moments and shear forces. The different ways of torque application also rarely resulted in an independent movement of the test objects in six degrees of freedom. Concerning the used parameters (preload, torque) no standardized values were applied, which complicates comparing the different test results. Generally, consistency between the studies could rarely be found. A few authors calculated a stationary rotational axis. In other cases, a migrating screw axis was described. Nevertheless the movement was divided in only a few intervals. Only few authors could describe the movement of the screw axis continuously and describe it in a quantitative and qualitative way. In those cases in which the preload was variated in value and position, a relevant influence of those parameters was shown on the kinematical behavior of the spine. Determining position and orientation of the screw axis always delivers different values depending on the point in time of measuring. While moving of the spine, the position of the screw axis was always different compared to any other measured interval. So the authors could show a continuously migrating screw axis. Generally the authors agree that there is no two- dimensional motion of the spine. It is rather a complex three dimensional motion, which is the so called coupled motion. Nevertheless, in literature this complex movement has often been neglected because of the limits of technical possibilities and conditions. Sometimes directions of movements were not examined, because complex movement could not be recorded.
Summarizing valid measuring of kinematical motion of the spine requires capturing the movement in differential small intervals. Therefore it needs a high time dependent and spatial resolution. The applied forces and torques, generating movement of the test object, have to enable physiological movements without any counteraction between test objective and test apparatus. The test results should be reproducible and controllable. Ideally, there should be a measuring apparatus, which is able to simulate any single muscle force acting on the test object and to simulate varying body weight.
In this study, it could be shown that there is no available apparatus which fulfils all requirements. Only a few authors are able to capture kinematical behavior. | de |