| ObjectiveAtlantoaxial specialposteriorscrewswere designed and the stress was analyzedby the way of three-dimensionalfinite element method,the size of the specific tension of the screw during the atlantoaxial reduction and the three-dimensional biomechanical stabilitywas investigated on the fresh cadaver specimens,preliminaryclinical application was carried out at the same time.Methods1.One healthy adult volunteer was selected for the upper cervical CT scan to obtain the original data of dicom format.Mimics 10.0 was used to extract the occipital and atlantoaxial bone,Geomagic Studio 2013 was applied for image optimization.Soliworks 2012was used to design the atlantoaxial posterior special screw and reconstruct cartilage andligament tissue,place the atlantoaxial posterior screw and connecting rodat the same time,and then establish a new type of atlanto-pedicle screw fixation system CAD model,Abaqus6.14-1 was applied to build atlantoaxial posterior special vertebral three-dimensional finite element analysis model of pedicle screw fixation andbiomechanical analysis;2.6 model of fresh human cervical spine were made,the atlantoaxial joint capsule and atlantoaxial ligament were resected to establish the model of atlantoaxial instability.The atlantoaxial posterior cervical screw fixations was divided into three groups:group A1:axial single pivot fulcrum screw;group A2:axial multi-pivot fulcrum screw;group B:cervical posterior fixation universal screw,the flexible ultra-thin film pressure sensor wasinserted into the atlanto-dental interval,the resistance value was measured by the universal meter after tightening the nut,,and the pressure value was converted into the pressure value by the formula,comparison was carried out among groups.3.6 models of fresh human cervical spine weremade,the atlantoaxial joint capsules and the atlantoaxial ligaments were resected to establish the model of atlantoaxial instability.The atlantoaxial posterior fixations were divided into four groups:C1:normal specimen model,C2:instability model not fixed,D1:cervical posterior screw pedicle fixation,D2:atlantoaxial posterior special screw pediclefixation.The models of atlantoaxial fixationson were put on three-dimensional exercise machine for three-dimensional stability measurement in orders,three-dimensional stability analysis and comparison were performed between groups.4.6 cases of atlantoaxial dislocation of atlantoaxial wereperformed with posterior atlantoaxial special screw fixation and follow-up.ResultsUnder the application of 42N gravity and 1500N torsional load,there was no obvious stress concentration in the internal fixation of the atlantoaxial special screw.The stress of the screw and connecting rod was relatively small under all loads.The maximum stress was generated around the root of the screw into the bone,with a maximum stress of 49.97 Mpa under the load of rotation.Among the pull force during atlantoaxial dislocation reset,group Al>group A2>group B,andwere statistically significant(F =251.603,P =0.000)among groups.Group A1>group A2,and were statistically significant(P=0.000)between groups.Group Al>group B,and were statistically significant(P =0.000)between groups.Group A2>group B,and were statistically significant(P =0.000)between groups.In the three-dimensional biomechanical stability,in the flexion direction,group D2>group D1>group C1>group C2,and were statistically significant(F=353.221,P=0.000)among groups,there were no significant difference between group D1 and group D2(P=0.529),group D2?group D1 and group C1 were all better than group C2(P =0.000);In the extension direction,group D2>group D1>group C1>group C2,and were statistically significant(F=222.108,P=0.000)among groups,there were no significant difference between group D1 and group D2(P=0.587),group D2?group D1 and group C1 were all better than group C2(P =0.000);In the left bending direction,group D2>group D1>group C1>group C2,and were statistically significant(F=446.437,P=0.000)among groups,there were no significantdifference between group D1 and group D2(P=0.586),group D2?group D1 and group C1 were all better than group C2(P =0.000);In the right bendingdirection,group D2>group D1>group C1>group C2,and were statistically significant(P=349.404,P=0.000)among groups,there were no significant difference between group D1 and group D2(P=0.616),group D2?group D1 and group C1 were all better than group C2(P=0 000);In the left rotation direction,group D2>group D1>group C1>group C2,and were statistically significant(F=1792.799,P=0.000)among groups,there were no significant difference between group D1 and group D2(P=0.678),group D2?group D1 and group C1 were all better than group C2(P =0.000);In the right rotation direction,group D2>group D1>group C1>group C2,and were statistically significant(F=917.181,P=0.000)among groups,there were no significant difference between group D1 and group D2(P=0.736),group D2?group D1 and group C1 were all better than group C2(P =0.000);The reduction of 6 cases with atlantoaxial dislocation was satisfied,and more convenient duiring operation,postoperative follow-up clinical results wereexcellent.ConclusionsThere was no obvious stress concentration in the internal fixation of the posterior atlantoaxial posterior screw.The reduction ability was enhanced,the biomechanical three-dimensional stability was excellent and operation was safe and convenient,and the clinical effect was satisfactory. |
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