Magnesium alloy hollow screw for type ⅡA odontoid fracture: a finite element analysis

English Keywords:Odontoid fracture  Magnesium alloy  Hollow screws  Finite element

English Abstract:

  【Abstract】 Objectives: To establish a finite element model of type ⅡA odontoid fracture fixed by screw and analyze the stability of magnesium alloy screw fixation. Methods: Spatial structure information acquisition axis by CT scanning a normal male volunteer′s cervical vertebra, the 3D data were imported to software Mimics 10.01, Solidworks 2010 to establish the three-dimensional finite element model of normal axis and odontoid process fracture of ⅡA type fixed by hollow screw. The finite element software Ansys 13.0 was used to analyze hollow screw axis, the normal model of odontoid fractures of type ⅡA(magnesium alloy, titanium alloy screws fixed screw), respectively, and the simulation of cervical extension, flexion when subjected to horizontal load of 50N, 100N, 150N, 200N force and cervical rotation by 50N·mm, 100N·mm, 150N·mm, 300N·mm torque were added to meassure the maximum displacement of odontoid process, the maximum stress of odontoid process, the maximum stress of C2 vertebral body and the maximum stress of screw. The screw elastic modulus of titanium alloy was 108000MPa, with a yield strength of 930MPa; the elastic modulus of magnesium alloy was 45000MPa, with a yield strength of 193MPa. Results: The normal axis and hollow screw fixation after establishment of the finite element model was realistic and geometric similarity. At three kinds of state of flexion, extension and rotation, the maximum stress of magnesium alloy screw under different load was less than the titanium alloy screw, the stresses of both alloys were less than the yield strength; the maximum stress of odontoid process and the maximum stress of C2 vertebral body of the model of odontoid process fracture of ⅡA type fixed by two kinds of materials respectively was less than the cortical bone stress threshold(200Mpa), the maximum displacement of odontoid process was 5-8 timesthe to maximum displacement normal axis, both were less than 1mm(the size of grid finite element model was 1mm). Conclusions: The filite element model established by CT-scan and axial space structure can be used for biomechanical test, magnesium alloy hollow screw fixation of type ⅡA odontoid process fracture is enough to ensure stability.