| BackgroundAtlantoaxial (C1-C2) fusion can be used for the treatment of atlantoaxial instabilitypatients. With the development of technology of cervical spine surgery， posterioratlantoaxial fusion have great progress in the improvement of clinical symptoms ofatlantoaxial instability patients and atlantoaxial stability and fusion rate. Although everyoperation method is to improve expected results in the operation and satisfaction ofpatients, some postoperative complications has greatly reduced the living quality ofpatients, such as cervical curvature straightening, kyphosis. Even some patients also havethe corresponding clinical symptoms, seriously need operation treatment. Recently thesubaxial cervical spine disalignment after C1-C2fusion has been a popular topic.Objective1. We explore the ideal atlantoaxial fusion angle by comparative analysis of dataincluding the range of motion of subaxial cervical spine, anterior longitudinal ligamenttension, von mises of intervertebral disc and facet joint capsule, through the establishmentof full three-dimensional finite element model of the cervical spine in different atlantoaxialfusion angle.2. Through the establishment of full three-dimensional finite element model of C1-C2fusion and C2C3fusion, we analysed the effects on C2C3vertebral fusion result in thelower cervical spine biomechanics, provides a theoretical basis for cervical disaligment.3. Through the simulation of different grades of disc degeneration, we buildthree-dimensional finite element models of the cervical spine of normal, moderate, severedegeneration. We calculated the range of motion of subaxial cervical spine, anteriorlongitudinal ligament tension, von mises of intervertebral disc and facet joint capsule, andanalyzed the impact of intervertebral disc degeneration on cervical biological mechanics. Our experiments provide a theoretical basis for lower cervical curvature abnormalitybecause of intervertebral disc degeneration.Methods1. We constructed three-dimensional finite element model of the skull base to C7. Inorder to verify the validity of the mode, we compared the range of motion of subaxialcervical spine with other references.2. The cervical three-dimensional finite model was loaded on the lateral mass of atlasand axis pedicle screw internal fixation system (Harms). And five kinds of cervicalthree-dimensional finite model with different C1-C2fusion angle (+10°,+5°, normalangle,-5°,-10°) were created by changing the C1angle. The range of motion and vonmises of5models were analyzed.3. We created a C1-C2fusion and the C2C3vertebral plate fusion model with normalC1-C2angle. In order to created C2C3vertebral plate fusion, the interspinal ligament,supraspinal ligament and ligamentum flavum were substituted with cortical bone based onthe cervical three-dimensional finite model. The range of motion and von mises werecalculated.4. We created three-dimensional finite element models of cervical spine by differentdegree of disc degeneration. The range of motion and von mises of this three kinds ofmodel were calculated.Results1. The three-dimensional finite element model of us contains506564elements and173655nodes. It has proved that our model is good for finite element analysis of cervicalby compare with former references.2. When C1-C2angle is±10°the models’ range of motion and von mises are greaterthan the models with C1-C2angle of normal or±5°. There are no obvious differencesbetween the models with C1-C2angle of±10°. As a whole there are no obvious differencebetween the models with C1-C2angle of±5°and normal. 3. The C2C3fusion model’ range of motion and von Mises are reduced than the C2C3no fusion model in C2C3segment. But the C2C3fusion model’ range of motion and vonMises have no difference compared with the C2C3no fusion model in C2C3, C4C5, C5C6and C6C7segments.4. As a whole the models’range of motion is intervertebral disc normal model＞intervertebral disc moderate degeneration model＞intervertebral disc severedegeneration model. The models’ disc von Mises is normal model＜moderatedegeneration model＜severe degeneration model. Generally the C1-C2fusionmodel’range of motion is decreased compared with C1-C2no fusion model. And themodel’ disc von Mises with C1-C2fusion is increased than model without C1-C2fusion.Conclutions1. In conclusion the model with C1-C2angle of±10°has serious impact on subaxialcervical spine’s alignment. According to the experimental studies, we recommend theoptimal angle of C1-C2fusion is within±5°.2. After the C2C3fusion the model’s range of motion is limited obviously. But in theother segments of subaxial cervical spine the change are not obvious. This shows that onone hand the impact of C2C3fusion on subaxial cervical spine is less than the differentangel of C1-C2fusion. On the other hand, it may be a chronic course of C2C3fusionresulting in abnormal subaxial cervical spine’s alignment.3. The degeneration of discs may exacerbate disc degeneration, so we draw aconclusion that disc degeneration is an important cause of abnormal subaxial cervicalspine’s alignment. |
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