Design And Application Of Posterior Anatomical Plate For Acetabular Posterior Column With The Lag Screw Guide Device For Anterior Column

Objective To measure anatomical parameters of the guide device for antegrade lag screw fixation of the fractures in the anterior column of acetabulum.Methods During August 2014 to December 2015,we randomly collected and obtained 56 adult patients' images of pelvis,who took complete CT scan of pelvis in our hospital.Any patients with any bony and anatomy abnormality were excluded out of this study.All the images were saved as DICOM format,then put into Medical imaging software,Mimics 15.0 The 3-dimensonal model of pelvis was reconstructed.3D-reconstruction model of pelvis was rotated to the contralateral side by 45 degrees and was made partially transparent.An virtual cylindrical implant were placed intraosseously into the anterior column of acetabulum to stimulate an antegrade lag screw placement in anterior column of acetabulum of digital model.Adjusted the virtual cylindrical implant position to avoid penetrating the cortieal margin of anterior column or into the acetabulum and increased the diameter progressively as large as possible.Then,insert point of the screw,insert angulation of the screw,maximal diameter and length of the screw were measured.CT scanning images from one healthy adult volunteer(male 30),were transform into Materialise Mimics Innovation Suite 16.0 software,three-dimensional(3D)models of pelvic were reconstructed and stored in stereolithography format.Then the Imageware 12.0 software(EDS,USA)was used to produce the optimal and safe channel of the screw for acetabulum anterior column fixation.And three types of screw fixation were generated,i.e.(1)geometric algorithm screw channel,(2)"in-out-in" channel,(3)free screw channel.Secondly,all model data were ransformed into Ansys 12.0 software to establish the finite element model.Gravity load were defined as 600N,1200N,2400N,and,the Von Mises the parameters of peak stress and deformation were recorded.The outside of the template was extracted in accordance with posterior surface features of the posterior column of the acetabulum in UG software.The lag screw guide device was aligned with the screw nail channel,according to the anatomy parameters which was measured previously.After that,the template and the lag screw guide device were fit as a whole to make Design and application of posterior anatomical plate for the posterior column of the acetabulum with the lag screw guide device for the anterior column.The original guide device was made by 3D printing technology and the solid model of guide device and the plate was manufactured by digital milling machine.The accuracy was validated by experimental study on cadaver and drying specimens of pelvis.Results(1)The average distance from the entry point of the antegrade lag screw placement in anterior column of acetabulum to apex of greater sciatic notch is(21.11±4.19)mm,while the distance from the entry point of the antegrade lag screw placement in anterior column of acetabulum to ischial spine is(56.18±2.01)mm.The average anteversion angulation of screw is(68.51±4.52)°,while the extraversion angulation is(73.67±3.17)°.The maximum diameter and length of the lag screw is(7.31±2.42)mm and(109.75±8.22)mm respectively.(2)The hip stress of screw was slightly higher than the normal hip,and hip screw geometry algorithm by minimal stress.No matter what types of screw fixation,the pressure of hip bone trabecular is almost the same.The free channel screw has the maximum stress.There was significantly higher than that in normal hip displacement displacement screw and screw in the hip,hip screw displacement in geometric algorithm of minimum.The"in-out-in" screw has the largest stress,smallest displacement.(3)A posterior anatomical plate for the posterior column of the acetabulum with the lag screw guide device for the anterior column was successful designed and manufactured according to the anatomy parameters combined with posterior column surface features.The rate of success for placement in guide device group was 84.21%,while the rate in control group decreased down to 31.58%.The differences of the rate of success for placement between groups were of statistical significance.The posterior anatomical plate for the posterior column of the acetabulum with the lag screw guide device for the anterior column can obviously improve the success rate and accuracy of antegrade lag screw implantation.Conclusions The results of our measurement can contribute to design of posterior anatomical plate for the posterior column of the acetabulum with the lag screw guide device for the anterior column,which could improve the success rate and accuracy of the screw implantation in the anterior column of acetabulum,reduce the surgery risk,and minimize operative trauma.