Biomechanical Evaluation Of Different Atlantoaxial Posterior Fixation Techniques

Objective: To compare the biomechanics of the different posterior instrumentations for atlantoaxial instability and to provide the biomechanical basis for the clinical use of the instrumentation choosing.Methods: In this experiment, six specimens of the atlantoaxial complex (C0-C3) are used. And the models of the normal complex and instability (type II odontoid fracture) are established. On the mechanics experimental machine, the parameters including the strength and rigidity of anti-rotation, change and strength of stress, the stability are quantified of the normal complex (group N), atlantoaxial instability (group I), Brooks wire instrumentation ( group A), Magerl+Brooks wire (group B), unilateral trans facet joint screw plus Gallie's wire ( with the bilateral articular processes intact) (group C), unilateral trans facet joint screw plus Brooks wire ( with the bilateral articular processes intact) (group D), unilateral trans facet joint screw plus Brooks wire ( with the contralateral articular process damaged) (group E).Result:Analysis of the strength:By statistics, the atlantoaxial strength of group B is the greatest under flexion, extension, lateral bending. And it is significantly different with that of the group N with P<0.05.The strength of group A is less than that of group B, group C and group D with significant difference (P <0.01) at the position of flexion, extension and lateral bending (right). Compared with that of group A, the strength of group E is greater at the position of flexion and extension but without statistical difference (P>0.05). The lateral bending strength of group A is greater than that of group E with statistical difference (P<0.05) .At the position of flexion and extension, the strength of group C is less than that of group D with apparent statistical difference (P <0.01) . But, at the position of lateral bending, the strength of group C has no difference with group D (P>0.05) .Meanwhile, the strength of group C has statistical difference with that of group E at the position of flexion, extension and lateral bending (P <0.01)The strength of group D has statistical difference with that of group E at the position of flexion, extension and lateral bending (P <0.01)Analysis of the rigidity:Statistics show significant difference between the rigidity of the control group and that of the instrumentation groups at flexion, extension and lateral bending. And the difference is the greatest with that of group B (bilateral trans articular process screw plus Brooks instrumentation).At flexion and extension, the axial rigidity of group A has not statistical difference with that of group C, group D and group E. But it has significant difference with that of group B (P <0.01) with the latter having greater axial rigidity. At flexion, the horizontal shear rigidity of group A has significant difference with that of group B, group C and group D (P <0.01) and no difference with that of group E. At extension, the horizontal shear rigidity of group A has significant difference with that of group B, group C and group D (P <0.01) and difference with that of group E (P <0.05) . At lateral bending, the axial and horizontal shear rigidity of group A has significant difference with that of group B, group C, group D and group E (P <0.01)At flexion and extension, the axial rigidity of group B has significant statistical difference with that of group C, group D and group E (P <0.01) . At flexion, the shear rigidity of group B has no difference with that of group C and group D and significant difference with that of group E (P <0.01) . At extension, the shear rigidity of group B has significant difference with that of group C, group D and group E (P <0.01). At lateral bending, the axial rigidity of group B has significant difference with that of group C and group E(P <0.01 )and difference with that of group D (P <0.05 ). At lateral bending, the shear rigidity of group B has significant difference with that of group C, group D and group E (P<0.01) .At flexion and extension, the ax...