Accuracy And Safety Of Freehand Versus 3D Printed Template Guided S2AI Screw Techniques

Purpose The purpose of this study was to compare the safety and accuracy of the freehand technique versus 3D printed template guided technique(TGT)system for insertion of S2 alar iliac screws.Background In scoliosis,lower lumbar infection,lower lumbar tumors and other diseases,the posterior S2 alar-iliac(S2AI)screw placement is often used in lumbarpelvic fixation.Previous studies have detailed described the S2 AI screw technique and trajectory,but because of differences in ethnicity,the optimal S2 AI screw path of the Chinese is still unclear.Therefore,this study will clarify the parameters of the optimal S2 AI screw path of the Chinese people,and guiding the design of the freehand surgical technique.Which based on this measurement method,the patient's individualized 3D printing guide plate screwing system is designed by software.Compare the safety and accuracy of the two S2 AI nailing techniques through clinical application.Methods Sixty patients with normal pelvis from January 2016 to June 2016 were selected,aged 18-89 years,mean 51.8 years,divided by gender and age(half male and half female,?60 years old and less than 60 years old),and scans by thin slice CT.The entry point was defined as the intersection of the connection vertical line of S1 dorsal foramen and S2 dorsal foramen with S1 pedicle screw entry point perpendicular.By Multiplaner reformation(MPR)technique to get the image of iliac teardrop,along the entry point into the center of teardrop above the sciatic notch and you will get the proper trajectory.The parameters of the optimal pathway including the the cephalocaudal angles(CA),the mediolateral angles(MA),the narrowest width of the ilium along this pathway(narrowest width,NW),the maximal length of pathway(ML),the distance below the skin for the starting point(skin distance,KD),the distance of the center of teardrop to sciatic notch(sciatic notch distance,SD),the distance of the starting point to midline(midline distance MD),the distance of the starting point to inferior S1 dorsal foramen(dorsal foramen distance,DD).Guiding the design of the freehand surgical technique.Which based on this measurementmethod,the patient's individualized 3D printing guide plate screwing system is designed by software.According to a prospective study,patients with S2 AI screw technique were divided into two groups from July 2016 to June 2018.The freehand technique and 3D TGT technique were used to fix the lumbosacral pelvis respectively.Postoperative CT scan of all patients were applied to evaluate the axial trajectory of S2 AI screws.For the comparison of safety and accuracy of the two techniques.The screw is defined unqualified that was violate the inner and outer plates of the ilium are more than 3 mm.All complications associated with screw placement of two group were recorded.Results The best S2 AI screw trajectory parameters were measured apply the method mentioned above.The CA,MA,ML,NW,SD,MD,DD and KD were29.21°±6.52°,39.75°±2.40°,110.3±7.22 mm,16.60±2.51 mm,11.58±1.18 mm,26.5±1.88 mm,5.18±1.08 mm,39.25±11.98 mm respectively in males,and35.21°±6.86°,40.38°±3.58°,102.64±14.28 mm,13.86±2.65 mm,10.83±1.48 mm,25.95±1.28 mm,4.60±0.83 mm,44.31±9.20 mm respectively in females.which showed significant sex-related difference with respect to these indexes of CA,ML,NW,SD and DD(P<0.05).But,there is no significant age-related difference to all indexes in our study.For the comparison of safety and accuracy of freehand versus 3D TGT.Bilateral S2 AI screws were placed in all 48 patients,ninety-six S2 AI screws were placed in this study,half of the total 96 screws were conducted by freehand,the left half by 3D TGT technique.Postoperative CT scan was applied to evaluate the axial trajectory of S2 AI screws,which showed that 6 of the screws were placed with moderate to severe penetrated iliac cortex in freehand group(12.5%,6/48),but no screw were placed with moderate to severe in 3D TGT group(P<0.05).Which showed the significant difference of the accuracy of the two techniques was existence.There were no complications associated with screw placement in either group.Conclusion Both the freehand technology and the 3D TGT technology are safe in the S2 AI screw placement.However,the 3D TGT technique is more accurate than the freehand.