Biomechanical And 3D Printing Manufacture Study About A New Type Of Integrated Artificial Axis(C2)

OBJECTIVE:The resection and reconstruction of the axis present one of the most challenging fields in spine surgery.Currently,there is still a lack of suitable prosthesis for reconstruction and fixation.This study,we try to use computer aided design and laser constituency molten metal 3D printing technology to develop a completely personalized design of artificial prosthesis.That it would become an ideal method of reconstruction for the axis after tumor resection.METHOD:(1)Computer aided design and 3D printing of a new integrated artificial axis reconstruction:adopting computer-aided design technology and reverse engineering software to design artificial prosthesis of vertebra,according to the position of setting nail,fix the device of upper and lower vertebrae for the prosthesis,and form an integrated prosthesis,using medical titanium alloy powder to melt-mold through laser constituency.(2)Biomechanical evaluation of a novel integrated artificial axis using three-dimensional finite element study:CT scan to obtain normal adult cervical Dicom format data,import Mimics software,three-dimensional reconstruction,separation CO-4 model,STL 3D model file format into Geomagic Studio 2013 rebuild the three-dimensional geometric solid model,STEP graphic file format into Solidworks 2012.The cervical spine model was evaluated to simulate the axial resection and the three-dimensional finite element model of the integrated artificial cervical vertebra and the modified T-shaped Harms cage was established.The ANSYS 13.0 finite element software was used to analyze and compare the mechanical properties of the two sets of internal fixation system.(3)With the same methods of(2),finite element analyses were performed for four different fixations on C3 vertebra:bilateral vertebral screw(group A),up-and-down vertebral screw(group B),unilateral anterior transpedicular screw and unilateral vertebral screw(group C),and bilateral anterior transpedicular screw(group D).The stress distribution on the C3 vertebral screw and the prosthesis displacement of all four fixtures were calculated and evaluated.(4)Biomechanical comparison of reconstruction with integrated artificial axis and modified T-shaped Harms cage:6 cases of fresh human occipital cervical vertebra were subjected to axial resection.The establishment of integrated artificial cervical reconstruction combined with posterior occipital cervical fixation model and modified T-shaped Harms cage reconstruction combined with posterior occipital and cervical fixation were performed for each specimen respectively.Comparied with the three-dimensional stability of two internal fixation methods under six conditions.RESULT:(1)A new integrated artificial axis was designed by 3D software and manufactured by selective laser melting.This system is mainly composed of atlantoaxial lateral mass screw,C3 reverse pedicle screw(or vertebral nail)and artificial axis.(2)Under various loads from four different directions,the maximum stress and displacement of the integrated artificial axis were less than those of the modified T-shaped Harms cage.Except for extension,the maximum stress of the C3 endplate of the integrated artificial axis was less than that of the modified T-shaped Harms cage.(3)The decreasing order of maximum stress on the C3 screws under flexion was group A<group D<group C<group B.The decreasing order of the maximum C2 prosthesis displacement was group D<group C<group B<group A.(4)Biomechanical analysis of fresh cadaver specimens with two sets of internal fixation system.During the test with this two internal fixation system,the maximum motion was under the loads of extension.The integrated artificial axis system fixation was significantly more stable than the modified T-shaped Harms cage group.CONCLUSION:(1)A new integrated artificial axis was designed.(2)All four fixations exhibited sufficient strength and instant stability by finite element model analysis.(3)Compared with the T-shaped Harms cage,the newly developed prosthesis showed the higher stability and the lower stress,provided a theoretical basis for clinical application.