Anatomical And Biomechanical Analysis Of Retropharyngeal Reduction Plate For Treating Atlantoaxial Dislocation

Purposes: Atlantoaxial dislocation can be classified two types: reducible and irreducible dislocation.Combination of anterior and posterior approach was more common for treating irreducible dislocation.However,this modality has some disadvantages such as more surgical time,more bleeding and injury.In this study,a anterior reduction plate was designed by only anterior approach.For verifying feasibility of anatomical application and biomechanics,finite element analysis was employed and differences of two surgical methods were compared.Methods: The reduction plate of anterior retropharyngeal approach was designed.Retropharyngeal plate was placed on cadaveric specimen and local specimen was harvested for CT reconstruction scan(0.5mm).Dicom data of two fixation methods were collected and 3D models were established using MIMICS software.Finite element analysis was done employing Hyperworks.Under the same loads,the stress and stress extreme value were analyzed for four different conditions including flexion,extension,left and right bending.Data of two internal fixation methods(Retropharyngeal reduction plate and posterior atlantoaxial pedicle screw)were obtained.The stress data and stress-strain indexes of two internal fixation methods were analyzed by SPSS software.Results: There was no significant difference of stress extreme between anterior reduction plate and posterior atlantoaxial pedicle screw fixation system for treating atlantoaxial dislocation under state(P > 0.05).Under the states of posterior extension,left flexion and right flexion,the stress extreme of the reduction plate system was significantly lower than that of the posterior atlantoaxial pedicle screw fixation system,and there was a statistical difference(P < 0.05).Both are far lower than the titanium alloys maximum yield strength(795-827MPa)and ultimate strength(860-896MPa).Conclusions:The results of biomechanical analysis show that the retropharyngeal plate is an effective modality for treating irreducible atlantoaxial dislocation.It is feasible to place reduction plate using retropharyngeal approach,which provides a new choice for treating atlantoaxial dislocation.