Research On Human Cervical Finite Element Modeling And Bionic Cervical Fusion Cage

Currently, the cervical diseases show a high incidence, professionally andyounger with the changing of people’s lifestyle; and the popularity of the vehicle alsomakes neck injury becoming a frequent injury pattern among the vehicle accidentdamage. The cervical spine biomechanical study contributes to a better understandingof the pathogenesis of cervical spine injuries, and provides a theoretical basis for theprevention and treatment of cervical spine injuries. Among of them, finite element(FE) method is optimal because of its advantages including repeatability, convenienceto perform parametric study, and cost reduction, and are increasingly applied in thehuman cervical spine biomechanics, such as cervical disease and injury mechanism,cervical surgery and internal fixation ways, the artificial prosthesis design. Becausecervical interbody fusion has the advantages of achieving immediate postoperativestability, maintaining and distracting disc height, and promoting fusion, etc., it hasbeen developed rapidly during anterior cervical surgery. But with the widespread useof it, the related complications are increasingly attracted people’s attention, such assubsidence, shift and non-fusion.In this paper, biomechanical tests of human head and neck kinematic, medicalimages of head and neck, and reverse engineering techniques were applied to studythe human cervical spine kinematic modeling. Also the bionic structure and surfacemorphology of cervical interbody fusion cage were designed, and the dual-coupledbionic cervical interbody fusion cage coupled the optimal structure and surfacemorphology was designed.Seven reflective Markers located on the human head and cervical spine weredesigned based on sports biomechanics testing methods. The motion analysis system was applied to measure5motion patterns of subject ’s head and neck under normalphysiological states including flexion, left/right lateral bending, and left/rightrotation.A three-dimensional FE model of normal human head and neck was established,containing skull,7cervical vertebrae, the first thoracic vertebra,6intervertebral disc,and13ligaments. The model was validated using the head and neck kinematic dataobtained by motion analysis device based on the same subject. Based on the rootmean square error and relative root mean square error analysis method, the predictionaccuracy of the FE head and neck model was quantified, and the material sensitivitywas also conducted to investigate the effect of material properties, including corticalbones, cancellous bones, posterior structures, fibrous annulus and ligaments underflexion, unilateral (left) lateral bending and axial rotation. Results showed that forlateral bending, there was nearly no change in model prediction results; In flexionmotion, the Young’s modulus variations of cortical bones and posterior structures alsohave nearly negligible effect on the cervical kinematics simulation results; In axialrotation, the Young’s modulus variations of cortical bones and posterior structuresalso have great impact on the cervical kinematics simulation results.In order to avoid subsidence, and improve the fusion rate, the indicators used toevaluate the interbody fusion cage performance were determined. Different shapes ofinterbody fusion cage were designed, implanted into the FE model of C5-C6segments,and simulated under several loading conditions, including axial compression, flexion,extension, lateral bending and axial rotation. Those indicators were obtained,including Von-Mises stress of the endplates, cage, adjacent vertebrae, and bone graft.The effects of different loading patterns and cage shapes on the interbody fusion cageperformances were researched by the analysis of the indicators. In the scope of thestudy, the cage of12-leaf shape has been demonstrated as the optimal one.Based on the structural characteristics of human cervical intervertebral disc, thecervical intervertebral fusion with bionic structure has been designed. Three structuralsized factors were determined, which were the distance between the center of groovestructure and the center of cage, the width of the groove structure, and the depth of the groove structure, respectively. The quadratic general spinning design was used tooptimize the bionic structural size. The regression equations between those threestructural sizes and the indicators of subsidence resistance (the stresses of endplateand cancellous bones of fifth and the sixth cervical spine) were obtained through thequadratic regression analysis method and the optimization size parameters wereobtained, respectively. The results showed that the optimized parameters for the stressof endplate and cancellous bone of fifth cervical spine were the same, also they weredifferent from which for the stress of cancellous bone of sixth cervical spine. Incontrast, the former was better.Inspired by the mechanical properties of the third metacarpal nourish of horse leg,the bionic concave surface morphology was designed and placed on the side or bothon the top and bottom of cage. Three concave size factors were determined andoptimized through the orthogonal experiment design. When the pits distributed on thecage side, the size factors was determined, which were the distance between the planepits located and the center of cage(a), the radius of pits(r), and the ratio of pit-depth topit-radius(p), respectively. For optimal subsidence resistance, the optimumcombination was the a=-2mm(+/-represented the pits located above/below the thecenter of cage), r=0.1mm，p=1; for optimal fusion rate performance, the optimumcombination was a=+2mm，r=0.3mm，p=1.5. When the pits distributed on both the topand bottom surfaces of the cage, the size factors were determined, which were thenumber of pits, the radius of pits, and the ratio of pit-depth to pit-radius, respectively.For optimal subsidence resistance and fusion rate performance of the cage, theoptimum combination was the pits’ number of12, radius of0.5mm, and ratio ofpit-depth to pit-radius of1.5.With the single-factor bionic results of cervical fusion cage, based on thecoupling bionic theory, the dual-coupled bionic cervical interbody fusion cage wasdesigned. The results showed, the subsidence resistance and fusion rate performanceof the coupling bionic fusion cage have been improved when the pits distributed onthe cage side. While, the subsidence resistance and fusion rate performance of thecoupling bionic fusion cage have been decreased when the pits distributed on both thetop and bottom of the cage.