| BackgroundPeri-acetabular corridor screws play an important role in acetabular fracture surgery.With the study of the complex anatomical characteristics of acetabulum,some scholars have found an infra-acetabular screw corridor,which can pass through the anterior and posterior columns simultaneously.Biomechanical studies have shown that the screw can significantly increase the strength of the internal fixation device.In clinical use,patients could get good functional recovery after surgery.At present,in anatomical,biomechanical and clinical studies,the exit point of infra-acetabular screw was located at the ischial tuberosity.As a trauma center in South China,we found that when the exit point was between the ischial tuberosity and the ischial spine,it was easier to place a 3.5 mm infra-acetabular screw for some patients,which could provide an option for the placement of this screw.However,anatomical and biomechanical studies of this new infra-acetabular screw channels are lacking.ObjectiveThe first objective is to study the anatomical parameters of the two infraacetabular screw channels with different exit points(Screw Ⅰ:the ischial tuberosity,Screw Ⅱ:the ischial tuberosity and the ischial spine).The second objective is to study the fixation effect of the two different infra-acetabular screws applied to posterior column fractures by finite element analysis.Methods1.Use Mimics and Geomagic software to perform 3-D reconstruction and image processing on the left hip bone of the specimen respectively.The two different infraacetabular virtual screws were placed respectively by "axial perspective method" in Mimics.Anatomical parameters,including the diameter,length,distance between insertion point and center of the iliopubic eminence,and the angle between the corridors and space plane were measured.Then,the results were analyzed statistically.2.Six pelvic specimens were used to verify the two different infra-acetabular screws corridors.3.Acetabular posterior column fracture was designed by SolidWorks software.Four internal fixation methods were also designed by SolidWorks software:Group Ⅰ,1 posterior column screw;Group Ⅱ,2 posterior column screws;Group Ⅲ,1 posterior column screw and 1 Screw Ⅰ;Group Ⅳ,1 posterior screw and 1 Screw Ⅱ.A load was applied to the four internal fixation models in Abaqus respectively,and the displacement of the articular surface fracture line and the stress distribution were analyzed.Results1.Screw Ⅰ:In 65.31%males and 40.54%females,a Screw Ⅰ corridor with a diameter of at least 5 mm was found.The mean maximum diameter and length were 5.30±1.25mm and 94.57±6.07mm,respectively.The anterior and medial distances between the entry point and the center of IPE were 7.49±4.68mm and 12.32±3.12mm,respectively.The angles of the screw to the sagittal plane were-0.49±6.43°.2.Screw Ⅱ:In 77.55%males and 62.16%females,a screw Ⅱ corridor with a diameter of at least 5 mm was found.The mean maximum diameter and length were 5.68± 1.39mm and 80.16±4.46mm,respectively.The anterior and medial distance between the entry point and the center of IPE of Screw Ⅱ were 20.24±5.00mmand 12.41 ±3.18mm,respectively.The angles of Screw Ⅱ to the sagittal plane were1.19±6.91°.3.Both in males and females,the differences of diameter,length,anterior distance,angles to transverse and coronal planes between the Screw Ⅰ and Screw Ⅱ were of statistical significance(p<0.05),but the differences of medial distance and angles to sagittal plane between the Screw Ⅰ and Screw Ⅱ were not of statistical significance(p>0.05).4.The two different infra-acetabular screw corridors were all successfully found on the pelvic speciments.5.In the finite element analysis,the nodes displacement of articular surface fracture line of Group Ⅳ were the smallest.ConclusionFor East Asians,changing the exit point of the infra-acetabular screw can increase the scope of use of the infra-acetabular screw in the population,especially for females,and the fixation effect could be also improved. |
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