Magnesium alloy-and titanium alloy-made transoralpharyngeal atlantoaxial reduction plate systems for atlantoaxial dislocation: a three-dimensional finite element analysis

Objective To evaluate biomechanical properties of transoralpharyngeal atlantoaxial reduction plate (TARP) prepared from magnesium alloy and titanium alloy for the atlantoaxial dislocation by using three-dimensional finite element analysis and to exam the feasibility of using magnesium alloy for preparation of TARP system so as to provide a theoretical basis for clinical surgery.Methods A patient with typical atlantoaxial fracture dislocation was involved in the study,and received thin CT scan with clinically used titanium alloy TARP system for obtaining DICOM image data.Three-dimensional finite element analysis software was imported to simulate magnesium alloy and titanium alloy TARP systems for reduction and fixation.Then,stress changes of the atlas,axis,internal fixators and C2/3 zygapophysial joints were determined with three-dimensional finite element analysis and analyzed statistically.Results ( 1 ) The finite element model of atlantoaxial dislocation reduction and fixation had lifelike outline and good geometric similarity.There were 53 586 nodes and 180 784 units.(2) During the simulation of head in neutral position,the stress concentration region was C2/3 zygapophysial joints followed by the anterior arch,posterior arch and lateral mass of atlas respectively,and C2 vertebral arch again.( 3 )Magnesium alloy and titanium alloy TARP systems showed significant difference in stress distribution (P ＜0.05).Conclusions (1)The atlantoaxial model established according to its structure information on CT can be used for biomechanical experiments.(2) For the treatment of atlantoaxial dislocation using the existing titanium TARP system,maintaining the integrity of anterior and posterior arch of atlas and confirming the bone fusion in lateral mass can better keep the stability of the atlantoaxis.After atlantoaxial fusion,the increased stress of the zygapophysial joints of the adjacent segments accelerates structural degeneration,which should be closely followed up.( 3 ) Magnesium alloy TARP system for fixation and reduction shows the fall in peak value of the stress concentration region,and improvement of the uniformity of stress distribution as compared with titanium alloy TARP. Key words: Spinal injuries; Atlas; Axial dislocation; Finite element analysis; Alloys