| Objective:To obtain the point cloud data of the anterior column and quadrilateral plate by application of reverse engineering technology。To design new anatomical locking plate and its scew holes by making use of computer-aided design on the base of point cloud data.To creat finite element models of three interal fixation methods fixing the fracture of acetabular anterior column fracture involving quadrilateral plate by using computer-aided engineering technology To compare internal fixation stability of three models by analysis of strain and displacement of them.Methods:The obtainment of point cloud data of the anterior column and quadrilateral plate To obtain the point cloud data of the anterior column and quadrilateral plate,100 cases of CT scan data including 50 males and50 females were collected from the medical image database of the department of radiology of the 1st Affiliated Hospital of Chongqing Medical University,Scans with pelvic ring or acetabular injury,bone tumour or deformed sacrum were excluded.Three-dimensional reconstruction of pelvic models were performed by mimics 15.0 software.The arc lengths between the anteriormost point of sacroiliac joint(point A)and the pubic tubercle(point B) was measured in male and female,then the average value of AB were calculated in males and females, respectively.2 pelves(1male and 1 female),which the value of AB were equivalent the average of AB value,were chosen from all the specimen.Both of them were exported in Point Cloud format.2.The design of new plate for quadrilateral fracture involving The point cloud of the two chosen pelves were imported into Imageware 14.0software and Triangulation meshed.The new plate was composed of three sections:(1)The true pelvic edge section:it started from the anteriormost point of sacroiliac joint,along with the true pelvic edge and end at the pubic tubercle, the outer border is 10 mm away from the inner border.(2)The front wall of acetabulum section:the true pelvic edge section of the plate extended to the outward at the border of the anterior inferior iliac spine and the front wall of acetabulum which covered the front wall of acetabulum.(3)The quadrilateral plate section: it was composed of two flap,the anterior flap close to the anterior border of the quadrilateral plate,which length was about half of anterior border of the quadrilateral plate;The posterior flap close to the posterior border of the quadrilateral plate,which length was about half of posterior border of the quadrilateral plate.The width of both flap were 10 mm,according to the design requirement above,the undersurface of the plate was virtualized on the corresponding position of pelvis in imageware 14.0,and the undersurface of the plate was adjusted in 0.4 mm increment to make it fit the anatomical features of surface of the anterior column and the quadrilateral plate,then the undersurface was thickened to 2mm in UG 9.0,and 0.3mm rounded edge, 2mm rounded corner of the plate, bending grooves were proceeded.The screw holes were added in three section.(1) Common elliptical screw holes which long diameter was 6mm and short diameter was 4mm were added in the true pelvic edge section of the plate.(2)Round locking holes which diameter was 2.7mm were added in the the superior wall of acetabulum section.(3)Common elliptical screw holes which long diameter was 6mm and short diameter was 4mm were added in the quadrilateral plate section.all the orientations of screw holes were perpendicular to the plate.3. The finite element analysis of the plate The CT data of one pelvis without bone loss was selected and input into Mimics 15.0 sofeware,then it was three-dimensional reconstructed.a smoother pelvis was obtained by reducing the triangular surface, filtering sharp-shaped triangle surfaces and surface smoothing.The model of the pelvis was input into Geomagic Studio12,a finite element analysis model was made through a process of reducing the triangular surface,filtering sharp-shaped triangle surface and suface smoothing,then the model was input into Hypermesh12.0 to creat a acetabular anterior column with posterior column transverse fracture involving quadrilateral plate model.The pelvic fracture model,the new plate,the true pelvic edge plate,the true pelvis wall preconstruction plate and the lliopubic edge plate were input into Solid Works 2015,then the new plate,the true pelvic edge plate combined with the true pelvis wall reconstruction plate,the lliopubic edge plate combined with the true pelvis wall reconstruction plate were assembled on the appropriate position of the pelvic fracture models.These models were input into the Hypermesh12.0again to finish the mesh generation,and they were saved as Inp format.These models were imported to Abaqus6.14,the material of pelvis,plates and screws were applied.as a binding connection were set to the screw and the bone.(1)The vertical static analysis of the models:to limit the the range of motion on six direction,the acetabular fossas were constrained,then 400 N axial static load was applied on the top surface of S1 vertebrae in these models.(2)The anterio-posterior static analysis of the models:to limit the the range of motion on six direction,the back of the sacrum was constrained,then 400 N axial static load was applied on the anterior surface of pubic symphysis in these models.(2)The lateral static analysis of the models:to limit the the range of motion on six direction,the contralateral acetabular fossa was constrained,then 400 N axial static load was applied on the surface of the left iliac wing in these models.The von Mises stress and displacement distribution in these three loadings were analyzed.Results1.The average value of AB were( 117.23±6.36) mm in male and( 126.39±9.05) mm in female, there were no significant differences between genders(P<0.05),the point cloud data was obtained by saving the chosen pelves as point cloud.The point cloud of two chosen pelves were import to imageware 14.0and Triangulation meshed,the undersurface of the plate was virtualized on the corresponding position of pelvis in imageware 14.0,and the undersurface of the plate was adjusted it to make it fit the anatomical features of surface of the anterior column and the quadrilateral plate,then the undersurface was thickened to 2mm in UG 9.0,,and 0.3mm rounded edge and 2mm rounded corner of the plate were proceeded.The new plate was composed of three sections:(1)The true pelvic edge section:the length of them were 119 mm in male and 124 mm in female.it started from the anteriormost point of sacroiliac joint,along with the true pelvic edge and end at the pubic tubercle, the outer border is 10 mm away from the inner border.(2)The front wall of acetabulum section:the true pelvic edge section of the plate extended to the outward at the border of the anterior inferior iliac spine and the front wall of acetabulum which covered the front wall of acetabulum.(3)The quadrilateral plate section: it was composed of two flap,the anterior flap close to the anterior border of the quadrilateral plate,the length of anterior flap were 47 mm in male and 40 mm in female;The posterior flap close to the posterior border of the quadrilateral plate,the length of posterior flap were 50 mm in male and 45 mm in female,the width of both flap were 10 mm.The screw holes were added in three sections.(1)Common elliptical screw holes which long diameter was6 mm and short diameter was 4mm were added in the true pelvic edge section of the plate,the quantity of screw holes were 10 in male and 9 in female.(2)Round locking holes which diameter was 2.7mm were added in the the front wall of acetabulum section,the quantity of screw holes were 9in male and 7 in female.(3)Common elliptical screw holes which long diameter was 6mm and short diameter was 4mm were added in the quadrilateral plate section,the quantity of screw holes of anterior flap were 3 in both gender,and the quantity of screw holes of posterior flap were 4 in male and 3 in female.all the orientations of screw holes were perpendicular to the plate.3.The von Mises stress and displacement distribution pattern were obtained through vertical static analysis of the models of three fixation.The maximum displacement of the new plate model is 0.1 mm, the maximum stress of the pelvis is 14.8MPa, the maximum stress of the new plate is 88 MPa.;The maximum displacement of the true pelvic edge plate combined with the true pelvis wall reconstruction plate model is 0.11 mm,the maximum stress of the pelvis is 19.4MPa, and the maximum stress of the plate is 37.6MPa;the maximum displacement of the lliopubic edge plate combined with the true pelvis wall reconstruction plate model is 0.19 mm,the maximum stress of the pelvis is 11.5MPa, and the maximum stress of the plate is 98.9MPa.The von Mises stress and displacement distribution pattern were obtained through anterio-posterior static analysis of the models of three fixation. The maximum displacement of the new plate model is 0.16 mm, the maximum stress of the pelvis is 15.8MPa, the maximum stress of the new plate is 101 MPa.;The maximum displacement of the true pelvic edge plate combined with the true pelvis wall reconstruction plate model is 0.15 mm, the maximum stress of the pelvis is 28.8MPa, and the maximum stress of the plate is 93.8MPa;the maximum displacement of the lliopubic edge plate combined with the true pelvis wall reconstruction plate model is 0.23 mm, the maximum stress of the pelvis is 12.2MPa, and the maximum stress of the plate is 107 MPa.The von Mises stress and displacement distribution pattern were obtained through lateral static analysis of the models of three fixation. The maximum displacement of the new plate model is 3.3 mm, the maximum stress of the pelvis is 149.5MPa, the maximum stress of the new plate is335.7MPa.;The maximum displacement of the true pelvic edge plate combined with the true pelvis wall reconstruction plate model is 2.24 mm,the maximum stress of the pelvis is 162.4MPa, and the maximum stress of the plate is 349.3MPa;the maximum displacement of the lliopubic edge plate combined with the true pelvis wall reconstruction plate model is4.2mm, the maximum stress of the pelvis is 126.1MPa, and the maximum stress of the plate is 558.1MPa.Conclusion :1.The point cloud data of pelvis was obtained by using reverse engineering technology and computer-aided design technology,on this basis,the new plate for acetabular anterior column fracture involving quadrilateral plate was designed.2.the fix effect of new plate is better than other plate models in vertical static analysis,and lies between the other 2models in anterio-posterior and lateral static analysis.3.The quadrilateral plate is suitable for acetabular anterior column,quadrilateral plate and acetabular front wall fracture. |
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