Biomechanical Study On The Selection Of Internal Fixation Materials For Zygomaticomaxillary Complex Fractures

Objective:The purpose of this study is to assess the stability of different internal fixation materials for zygomaticomaxillary fractures by biomechanical numerical analysis and provide a new research method and objective numerical basis for selecting suitable internal fixation material,and to help clinicians choose repair materials more accurately.Methods:The data of patients with zygomaticomaxillary complex fractures(ZMCF)who recovered well and were fixed with bioresorbable materials in The Second Hospital of Dalian Medical University from January 2018 to June 2018 were collected.Three different types of ZMCF were selected,one in each.The preoperative orbital CT images and data were obtained.Based on the preoperative CT images of the patients,the anatomical reduction model of the craniofacial bone of the fractured side was reconstructed by means of mirroring the non-fractured side in Mimics software.The three-dimensional design software Solid Works was used to segment the fracture according to the actual fracture position,and the fixation sites were marked on the model,then the three-dimensional models of bioresorbable material repair and titanium repair were established on the surgical fixation sites.Finally,the masticatory force was applied to the models and boundary conditions were set to establish finite element models in Abaqus.The stress and displacement of internal fixation materials and fracture ends were analyzed and the rotation angle of zygoma was calculated to compare the fixation stability of different repair materials.Results:1.The modeling method of this study has been validated.The finite element models of 6 cases of ZMCF repaired with bioresorbable materials and titanium have good geometric similarity,the quality of the mesh has been checked,and the number of meshes is reasonable.2.For the ZMCF with zygomatic frontal suture(ZFS)and inferior orbital rim(IOR)fracture and dislocation,finite element models of bioresorbable materials and titanium metal fixation were established:FEM/ZFS+IOR~b,FEM/ZFS+IOR~t.The analysis showed that the maximum stress of the internal fixation plates was 11 MPa and211 MPa,the maximum displacement was 0.05 mm and 0.04 mm,respectively.The maximum displacement of the fractured ends was 0.08 mm and 0.07 mm,and the rotation angle of zygoma was 0.09°and 0.07°,respectively.3.For the ZMCF with ZFS,IOR and zygomatic arch(ZA)fracture and dislocation,finite element models of bioresorbable material,titanium fixed ZFS and IOR were established:FEM/ZFS+IOR+ZA~b,FEM/ZFS+IOR+ZA~t.Results showed that the maximum stress of the internal fixation plates was 8 MPa and 169 MPa,the maximum displacement was 0.06 mm and 0.05 mm,respectively.The maximum displacement of the fractured ends was 0.16 mm and 0.16 mm,and the rotation angle of zygoma was0.11°and 0.08°,respectively.In the above two cases of ZMCF,the maximum stress of bioresorbable materials were lower than the ultimate strength of the material 57 MPa and of titanium plates were lower than the yield strength 483 MPa.The differences of the maximum displacement of internal fixation plates between the two types of materials were≤0.01 mm,of the fracture ends were≤0.01 mm,and the differences of the rotation angle of zygoma were≤0.03°.Therefore,the stability of the internal fixation of the two types of materials was similar in the above two cases of ZMCF.4.For the ZMCF with zygomatic complex completely fractured and displaced(zygomatic frontal suture,zygomatic sphenoid suture,infraorbital rim,zygomatic maxillary suture and zygomatic arch were all fractured),finite element models of bioresorbable material,titanium fixed ZFS and IOR were established:FEM/Zygomatic Complex~b,FEM/Zygomatic Complex~t.The analysis showed that the maximum stress of the internal fixation plates was 23 MPa and 265 MPa,the maximum displacement was0.12 mm and 0.04 mm,respectively.The maximum displacement of the fractured ends was 0.28 mm and 0.06 mm,and the rotation angle of zygoma was 0.15°and 0.09°,respectively.For this case of complete isolated ZMCF,the maximum stresses of bioresorbable materials and titanium plates were lower than the ultimate strength 57MPa and yield strength 483 MPa.The difference of the maximum displacement of internal fixation plates between the two types of materials was 0.08 mm,of the fracture ends was 0.22 mm,and the difference of the rotation angle of zygoma was 0.06°.Therefore,for this type of ZMCF fixed by bioresorbable materials was not as stable as titanium.Conclusion:The biomechanical numerical analysis method can make the stability of ZMCF after repairment measurable,visible and knowable.It can not only provide digital analysis and evaluation of the internal fixation stability of different repair materials and provide preoperative estimate,but also provide a new research method and objective numerical basis for the selection of suitable repair materials for ZMCF.