Finite Element Analysis And Clinical Application Of ROI-C Internal Fixationin The Treatment Of Hangman Fracture

Background: Hangman fracture is also called traumatic spondylolisthesis of axis(TSA),which occurs between the upper and lower articular processes under the action of violence.The fracture is often associated with peripheral ligament and disc injuries,which subsequently result in instability or dislocation of the axial vertebrae.Hangman fractures often occur in sudden accidents such as car crashes and high-altitude crashes.According to statistics,Hangman fracture accounts for about 4%~7% of cervical fracture and 23%~27% of axis fracture.In recent years,the number of Hangman fractures caused by large energy damage such as traffic accidents and falling height increases year by year.Therefore,more and more clinicians and scholars pay more attention to the treatment of Hangman fracture.The main purpose of treatment is to restore stability and normal physiological sequence of injured vertebra,so as to promote fracture healing.At present,surgical treatment has become the first choice for typeⅡ、Ⅱa and III Hangman fractures.Anterior surgery offers more direct decompression and fixation,and has less effect on cervical spine mobility for patients with unstable Hangman fractures associated with disc injury,disc herniation,and compression of the spinal cord.At present,most scholars believe that anterior cervical internal fixation for Hangman fracture is minimally invasive and relatively convenient operation.It has little effect on cervical vertebra mobility,and it’s a relatively safe and reliable method.But because of the high position of the axis and mandible block,anterior approach often results in difficult placement of titanium plate,improper location and direction of screw fixation,and affects the effect of internal fixation.Moreover,some complications are easy to occur during or after the operation,such as injury of superior laryngeal nerve;failure of internal fixation and pharyngeal discomfort.It has important clinical significance that a low notch and easy to place internal fixation device for the treatment of Hangman fractures.Double-way connection intervertebral fusion device(ROI-C)is a new type of anterior cervical fusion device developed by LDR,which is a novel self-locking,zero-notch and self-stabilizing anterior cervical fusion cage.It incorporates an integrated,self-guided,self-locking intervertebral fixation insert design.The stability is good,and it does not protrude from the leading edge of the vertebral body,and reduces the irritation to the esophagus and pharynx.ROI-C has been widely used in the treatment of lower cervical diseases.In view of the characteristics and applications of ROI-C,we treated 17 cases of Hangman fracture with ROI-C internal fixation,and achieved good clinical treatment from February 2011 to May 2016.This method can correct obvious angulation between C2 and C3 by inserting the intervertebral cage and the traction reduction of the skull.Because of zero notch design of fusion device,the utility was beneficial to be inserted into the C2 and C3 vertebral bodies and was easy to operate,and can effectively avoid the obstruction of the mandible when the insert was set.17 patients were followed up for an average of 29 months(range,8~36 months).All cases underwent bone fusion at 3 months after operation,and there was no complication of intervertebral space collapse or ROI-C shift at the last follow-up,which preliminarily confirmed that this method was feasible.But its clinical application and follow-up observation time was short,so it was necessary to further confirm its long-term efficacy.Therefore,it is necessary to study the biomechanical characteristics of Hangman fracture and ROI-C fusion device in the treatment of Hangman fracture through autopsy,cadaver experiments and finite element simulation.,which aim to verify the clinical feasibility of ROI-C fusion device in the treatment of Hangman fracture,and to promote the clinical development of Hangman fracture.In recent years,with the rapid development of computer technology,the finite element method is widely used in the field of biomechanics.The result is consistent with the result of cadaver experiment,and the finite element method has some advantages unmatched by cadaveric biomechanical experiments.It can produce many different models on the basis of the complete model.Therefore,the finite element model can effectively complement the experimental model of cadaveric specimens.In this study,thin slice spiral CT scanning technique was used to obtain the upper cervical spine(C0-C3)image information,and the information was fused with different images.At the same time,Geomagic,Studio 2014,Hypermesh13.0 and MSC.Patran/Nastran 2012 were used to analyze and process.A finite element model of the upper cervical spine,unstable model,Plate+Cagemodel,and ROI-Cmodel were established,and the above four models were calculated and analyzed under different conditions.Objectives:(1)To discuss three dimensional finite element reconstruction of upper cervical spine(C0-C3)using image fusion technique.To analyze the motion and stress distribution of finite element model(FEM)under different working conditions,which aim to provide theoretical basis for physiological activities of upper cervical spine.(2)On the basis of the established FEM of upper cervical spine,to establish.To analyze stress distribution of unstable model and two internal fixation model under various physiological loads,and to investigate and evaluate the advantages and disadvantages of the two internal fixation model.(3)To investigate the biomechanical properties and clinical feasibility of ROI-C fusion device in treatment of Hangman fracture,and to provide a new surgical approach for treatment of Hangman fracture through the application of ROI-C for treatment of 17 cases of type II and typeⅡa Hangman fractures in patients with short-term clinical follow-up,and finite element analysis experiment.Methods:(1)Establishment and validation of FEM of upper cervical spine:A healthy male volunteer was selected without skull base and cervical spine deformity,cervical spondylosis,cervical trauma,and surgical history.This volunteer was scanned with thinner slice and 0.625 mm thickness scanning from skull base(C0)to C3 vertebral segment by GE Lightspeed 64 row spiral CT,to obtain the upper cervical spine three-dimensional spiral CT data.To store CT data in an international standard DICOM format for CD.The data was extracted by Mimics16.0 software,and the upper cervical geometry model was reconstructed,and the STL format file was exported.Then,in Geomagic Studio 2014 software,patches,noise reduction and camber were exported,and STP format files were exported.Geometric model was assembled in Pro/E 5 software.The processed model was exported to the IGES format file.Then IGES file was imported into the Hypermesh 13 software for meshing and exported BDF format file.Finally,finite element mesh was processed and analyzed again in various working conditions by MSC.Patran/Nastran 2012 software.The validity of FEM was verified by comparing the results of the experiments and published literature.(2)Finite element analysis(FEA)of ROI-C internal fixation for Hangman fracture: On the basis of the validated FEM of upper cervical spine,the mesh of both isthmus of the axis was redivided,and formed a 0.5-1mm fracture line.To simulate the fracture inter tissue by weakening the elastic modulus of the layer.At the same time,the anterior and posterior longitudinal ligament and part of C2-C3 disc were removed,and the unstable mode of Hangman fracture was established.On the basis of unstable model,two groups of internal fixation models(Plate+Cage and ROI-C)were established.The same boundary conditions and loading methods were applied to the normal model,unstble model and the two groups of internal model.The lower surface of C3 was completely restrained,the axial pressure of 40 N to the skull base simulated the head gravity.and then the moment of 1.5N·m was applied to make the model produce flexion,extension,lateral flexion and rotation.Under the same load condition,the ROM and stress distribution of four models were studied and compared with the data of literature.(3)Clinical application of ROI-C internal fixation in the treatment of Hangman fracture:To retrospectively analyze 17 cases treated with ROI-C internal fixation for type II and typeⅡa Hangman fracture from February 2011 to May 2016 at Affiliated Hospital of Jining Medical University.All the patients underwent X-ray,CT scan and 3D reconstruction,and MRI examination.The preoperative neurological functions were grade E according to the American Spinal Cord Injury Association(ASIA)score.The time of operation,the amount of bleeding,the general condition after operation and the rates of intraoperative and postoperative complications were recorded.The X-ray films were reviewed at 3days,3 months,6 months and at the last follow-up.The post traumatic cervical spine clinical score,visual analogue scale(VAS),axis shift and angulation data were recorded at preoperation and the last follow-up.Results:(1)Establishment and validation of FEM of upper cervical spine:The 1.5N·m load was loaded on upper cervical spine model,and the ROM values of flexion,extension,lateral flexion and rotation were obtained by FEA.The data were in agreement with the in vitro cadaveric experiments and the finite element results in published literature.The FEM of the upper cervical spine was validated.(2)Finite element analysis(FEA)of ROI-C internal fixation for Hangman fracture: Under the same boundary condition and load,the ROM of unstable model was obviously higher than that of the intact model.The Plate+Cage and ROI-C models could effectively reduce ROM of C2-C3 segment and provide good stability for Hangman fracture.The Plate+Cage reduced 97%,98%,95% and 95.7% respectively when compared with unstable model,and the ROI-C reduced 60.3%,53.9%,37% and 53.8%.The stress peak value of Plate+Cage was equal to ROI-C under any working condition.But the former was more reasonable in structure and stress distribution.(3)Clinical application of ROI-C internal fixation in the treatment of Hangman fracture:Clinical application of ROI-C internal fixation in the treatment of Hangman fracture:The mean operative time was 58 min(45~116 min),and the amount of bleeding was 10~100 ml,with an average of 30.5 ml.There was no laryngeal nerve,hypoglossal nerve,laryngeal wall and vascular injury.No complications such as laryngeal edema,dysphagia,paralysis of tongue muscle,hematoma formation and wound infection were found.All cases were followed up for an average of 24.2 months(range,4~32 months).The fusion section and the fracture site were fused on average 3 months after operation,and all cases had no subsidence,no displacement,no intervertebral space collapse and no malunion at the last follow-up.Post traumatic cervical spine clinical score: preoperative(53.1±7.2)scores and at last follow-up(91.1±5)scores.The neck pain visual analogue scale(VAS)[[3.4±1.2]:(0.6±0.7)](Z=-5.961,P<0.05).Axis shift: preoperative(4±1.5)mm and at last follow-up(1.3±1.2)mm.The difference between the two groups of data was statistically significant(P<0.05).Axis angulation: preoperative(-0.51±0.7)and at last follow-up(1.2±2.5)degrees,there was no significant difference between the two groups(P>0.05).Conclusions: The results of the research revealed:(1)In this study,FEM of upper cervical spine with higher geometric fidelity was established,and its ROM,stress transmission and distribution under normal physiological loading and different loading conditions were analyzed.It is helpful to understand the physiological mechanism of upper cervical spine in more detail.(2)In this study,the effect of stress transmission on the unstable model and the stress distribution in Plate+Cage and ROI-C were analyzed.Two groups of internal fixation modal can effectively reduce the C2-C3 intervertebral ROM.It can be concluded that Plate+Cage fixation and ROI-C fixation in treatment for unstable Hangman fractures(type II and type IIa)can both play a good effect.The study will provide some biomechanical guidance for the clinical application of ROI-C internal fixation in the treatment of Hangman fracture.(3)Through the clinical application and short-term follow-up of 17 cases treated with ROI-C internal fixation for type II and typeⅡa Hangman fracture and FEA experiment,this study verified that anterior cervical ROI-C internal fixation in treatment of Hangman fracture had practical value and promotion significance.This study can promote surgical treatment of Hangman fractures.