Study On Safe Zone Around Acetabulum For Screw Placement In The Treatment Of Acetabular Fractures When Operated By An Anterior Approach Through Digital Technology

Objective:This study was aimed at definition of safe 、relatively safe and dangerous zone for screw placement around acetabulum. In our study, digital technology was utilized to reconstruct、optimize surface、cut and measure the pelvic CT images of either male or female adults. The result would guide the treatment of acetabular fracture with internal fixation of screws and plates in anterior approach. It could also reduce the incidence of complication of screw penetrating into the acetabular articular cavity and the usage of X ray apparatus, in addition to the providing of experimental method and imaging basis for individual therapy of acetabular fracture.Method: Pelvic computed tomography scans in DICOM format from August 2013 to March 2014 were obtained in the first Chen Zhou people′s affiliated hospital of university of south China.There are 23 male and 21 female pelvises, with no bone lesions and anatomic abnormality. Import CT images in DICOM format into Mimics 10.0 and Goemagic Studio11 to reconstruct、optimize surface and cut the pelvic CT images. Measure the screw′s safe angles of placement、appropriate length、 and the minimum distance from entry point to acetabulum in every section. Measure the safe 、relatively safe and dangerous zone for screw placement around acetabulum. The parameters measured which were imported into spss 13.0, dealed with statistics process: contrast analysis of male and female and contrast analysis of left and right.Result1 ilioinguinal approach.(1)The distances between the intersections(A、B、C、D、E) of every section and pelvic brim and the subpoint f that iliopubic eminence projects into pelvic brim were represented by: Af、Df、Ef、DE. Compared with female, male had larger Af and smaller Df, and the differences were of statistical significance(P<0.05) while Ef and DE were not(P>0.05).(2)When the screw was fixed away from acetabulum, the distance between entry point M and exit point N and the angles between the screw and coronal plane 、 sagittal plane were represented respectively by : section B:M1N1、β1cor及β2sag,section C: M2N2、β2cor及β2sag. Compared with female, male had larger M1N1、M2N2、β2cor and smaller β1sag, and the differences were of statistical significance(P<0.05) while β1cor、and β2sag were not(P>0.05).(3)When the screw was fixed towards acetabulum, the distance between entry point M3 and exit point K3 and the angles between the screw and coronal plane 、 sagittal plane were represented respectively by : M3K3、 α3cor及 α3sag 。The parameters above-mentioned were dealed with contrast analysis of male and female respectively, and there was no statistical significance.(5)When the screw was fixed away from acetabulum, the minimum distance between entry point M3 and exit point N3、the angles between the screw and coronal plane、sagittal plane were represented respectively by: minimum distance and angles: M3N-3min、β3cormin andβ3sagmin, maximum distance and angles: M3N3max、β3cormax andβ3sagmax。Compared with female, male had larger M3N3 min and smaller β3sagmax, and the differences were of statistical significance(P<0.05) while β3cormin、β3sagmin、M3N3max andβ3cormax were not(P>0.05).(6)The minimum distance between entry point of section B、section C、section D and acetabulum were respectively represented by: M1S1、M2S2 and M3S3. Compared with female, male had larger M1S1、 M2S2 and M3S3, and the differences were of statistical significance(P<0.05).2 modified stoppa approach(1) The subpoint that iliopubic eminence projects into the cutting-line was point G. Virtual screw Ii、Jj and segment JI(The connecting line of the intersections(point J and point I) between the virtual screws(Ii、Jj) and cutting-line)consisted of the dangerous zone.(2) The distance between point G and point I and point J respectively were represented by: GI and GJ. Parameters GI and GJ were dealed with contrast analysis of male and female respectively, and there was no statistical significance.(3) Virtual screw Ii、Hi and segment HI(The connecting line of the intersections(point H and point I) between the virtual screws(Ii、Hi) and cutting-line consisted of the relatively safe zone. The distance between point G and point H and point K respectively are represented by GH and GK. Parameters GH and GK were dealed with contrast analysis of male and female respectively, and there was no statistical significance.(4) Segment Ii segment Jj and was the maximum length of the screw safely used inside or outside, respectively. MS was the minimum distance between every entry point to the(5) acetabulum.Compared with female, male had larger Ii、Jj and MS, and the differences were of statistical significance(P<0.05).3 All the parameters were dealed with contrast analysis of left and right respectively, and there is no statistical difference(P>0.05)Conclusion(1) Basic study on pelvis with the assistance of technology of three dimensional reconstruction and reverse engineebrim software have advantages including: large sample size,repeatability、 high accuracy 、 economizing medical resource,in addition to the providing of experimental method and imaging basis for individual therapy ofacetabular fracture.(2) This study identifies a safe zone for screw placement in the treatment of acetabular fractures when operated by an anterior approach. For the relatively safe zone, proper angle and length should be complied with and try to place the screws away from acetabulum in ilioinguinal approach while, in the modified stoppa approach,the screws should be placed away from acetabulum or perpendicular to the plate.It was not recommended to place screws on the dangerous zone.