[Comparison between the Range of Movement Canine Real Cervical Spine and Numerical Simulation - Computer Model Validation].

Abstract

PURPOSE OF THE STUDY In developing new or modifying the existing surgical treatment methods of spine conditions an integral part of ex vivo experiments is the assessment of mechanical, kinematic and dynamic properties of created constructions. The aim of the study is to create an appropriately validated numerical model of canine cervical spine in order to obtain a tool for basic research to be applied in cervical spine surgeries. For this purpose, canine is a suitable model due to the occurrence of similar cervical spine conditions in some breeds of dogs and in humans. The obtained model can also be used in research and in clinical veterinary practice. MATERIAL AND METHODS In order to create a 3D spine model, the LightSpeed 16 (GE, Milwaukee, USA) multidetector computed tomography was used to scan the cervical spine of Doberman Pinscher. The data were transmitted to Mimics 12 software (Materialise HQ, Belgium), in which the individual vertebrae were segmented on CT scans by thresholding. The vertebral geometry was exported to Rhinoceros software (McNeel North America, USA) for modelling, and subsequently the specialised software Abaqus (Dassault Systemes, France) was used to analyse the response of the physiological spine model to external load by the finite element method (FEM). All the FEM based numerical simulations were considered as nonlinear contact statistic tasks. In FEM analyses, angles between individual spinal segments were monitored in dependence on ventroflexion/ /dorziflexion. The data were validated using the latero-lateral radiographs of cervical spine of large breed dogs with no evident clinical signs of cervical spine conditions. The radiographs within the cervical spine range of motion were taken at three different positions: in neutral position, in maximal ventroflexion and in maximal dorziflexion. On X-rays, vertebral inclination angles in monitored spine positions were measured and compared with the results obtain0ed from FEM analyses of the numerical model. RESULTS It is obvious from the results that the physiological spine model tested by the finite element method shows a very similar mechanical behaviour as the physiological canine spine. The biggest difference identified between the resulting values was reported in C6-C7 segment in dorsiflexion (Δφ = 5.95%), or in C4-C5 segment in ventroflexion (Δφ = -3.09%). CONCLUSIONS The comparisons between the mobility of cervical spine in ventroflexion/dorsiflexion on radiographs of the real models and the simulated numerical model by finite element method showed a high degree of results conformity with a minimal difference. Therefore, for future experiments the validated numerical model can be used as a tool of basic research on condition that the results of analyses carried out by finite element method will be affected only by an insignificant error. The computer model, on the other hand, is merely a simplified system and in comparison with the real situation cannot fully evaluate the dynamics of the action of forces in time, their variability, and also the individual effects of supportive skeletal tissues. Based on what has been said above, it is obvious that there is a need to exercise restraint in interpreting the obtained results. Key words: cervical spine, kinematics, numerical modelling, finite element method, canine.