Feasibility of biomechanical strength in upper cervical fixation and analysis of these screw strength

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We evaluated the pullout strength of posterior arch screw(PAS) that was our original invention to achieve safe and effective upper-cervical fixation surgery. Posterior arch screws had sufficient screw pullout strength. Compared to C1 lateral mass screw inserted via posterior arch technique(Tan), there was no statistical significance, however, PAS was statistically stronger than C1 lateral mass screw inserted directly technique(uni-Harms). The pullout strength of Tan was nearly equal to summation of PAS and uni-Harms.We analyzed clinical results of atlanto-axial fixation using C1 lateral mass screws, especially focused comparing two different techniques between Tan and uni-Harms. Overall results was satisfactory ; high union rate, low complication rate, etc. However, C2 nerve irritation was highly seen following uni-Harms.We also reported the incidence of Ponticulus Posticus in Japanese using plain computed tomography and plain X-ray films.