| Objective By choosing 60 adult pelvic CT scans,60 sacrum digital models were established,and sacrum related anatomical parameters were measured by Mimics software.One male and one female model were selected to match with internal fixation,and then finite element analysis was carried out by ansys software,which provided basis for surgical treatment of low transverse sacrum fractures,design and improvement of internal fixation materials in clinical work.Methods The cases were selected from 60 consecutive CT scans of adults with non-sacral diseases in the imaging department of the Second Affiliated Hospital of Inner Mongolia Medical University(male to female ratio 1:1,age 25-43 years,average 34 years).The scanning conditions were: CT scan(voltage 120 kV,current150 mA,slice thickness 1.25 mm,512 x 512 matrix).The data were imported into Mimics 17.0 software with DICOM format,and the three-dimensional model database was established.After reconstruction,the anatomical data of sacrum was measured(depth,angle,distance between upper and lower sacrum foramen,etc.)and then the internal fixation was matched with the fracture model for finite element analysis.Results 1.The anatomical parameters of each nail point measured in the experiment are detailed in Table 1-Table 4.2.Loading 500 N vertically downward to the sacrum floor to simulate normal standing stress,the stress distribution of bridging combined internal fixation of the three fixation schemes was uniform,and there was no stress concentration around the fracture line in 2 specimens.In female low sacrum transverse fracture model,the maximum stress and minimum stress of scheme A fixation were 358 MPa and 27.54 MPa respectively;the maximum stress and minimum stress of scheme B fixation were 335 MPa and 25.769 MPa respectively;and the maximum stress and minimum stress of scheme C fixation were 328 MPa and25.231 MPa respectively.In male low sacral transverse fracture model,the maximum stress and minimum stress of scheme A were 358.11 MPa and 27.548 MPa respectively,the maximum stress and minimum stress of scheme B were 336 MPa and42.012 MPa respectively,and the maximum stress and minimum stress of scheme C were 353 MPa and 27.154 MPa respectively.Conclusion 1.(1)The midpoint of the line between the inferior edge of L5 articular and the superior edge of S1 posterior foramen is allowed to be inserted;(2)The midpoint of the line connecting the lower edge and the upper edge of the sacrum posterior hole on each side,that is,the pedicle screw point described by many scholars also allows the nail to be placed;(3)There are no significant difference in each measurement index(P > 0.05).(4)The results show that the digital simulation technology is used to measure the nail points of the sacrum,and the obtained depth and angle of nail placement can be used as a reference for clinical treatment of sacral fractures.(Detailed parameters are shown in Table 1-Table 4.)2.Through finite element analysis,the fixed devices with rod diameters of 3 mm,3.5 mm and 4.5 mm in bridging combined internal fixation can provide strong mechanical stability in fixing the transverse sacrum fracture model.However,considering the special anatomy of the posterior sacrum,the internal fixator with smaller rod diameter should be selected as far as possible in practical application. |
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