Axial Perspective To Study About The Optimal Osseous Column Of S2-Alar-Iliac Screw

Background:The posterior pelvic ring is a load-bearing ring,which plays an important role in maintaining the stability of the pelvic ring and spine.How to gain the stability of the posterior pelvic ring continues to be a difficult challenging area in trauma and spine surgery,because of the local complex anatomy,poor bone quality of the sacrum,and giant biomechanical loads.As a powerful weapon with posterior ring fixation,spinopelvic fixation shows important clinical value.The fixed end of pelvic was performed by the iliac screw technique in recent years.Recently,proposed by Sponseller and Kebaish,the second sacral alar iliac screw(S2-Alar-Iliac screw S2AI)technology shows its unique advantages:the low profile,less soft tissue irritation,screws in a linear arrangement,better operating procedure,greatly shorten the the operation time and reducing the surgical risk of infection.At the same time,because the screw penetates three layers of bone cortex,the biomechanics stability is high,the fixation is reliable,the clinical application value is high.At present,there are reports about the research of S2AI screw channel.However,they failed to find the best screw channel,and get the maximum screw diameter,screw insertion point and direction.In the present study,only little data about the diameter of the screw that can be used clearly in this channel.but failed to find the best access to the screw channel,the channel can accommodate the maximum diameter of the screw,the needle point and the needle direction.The clinical value is not high.In the present study,there is no anatomical data about the diameter of the screw that can be used tiny in this channel.Purpose:Using a novel research method-axial perspective,finding the best channel to explore and obtain S2AI bone screw related anatomic parameters,largest screw channel,amd the optimal entry point and the direction,providing reliable support for the clinical anamical application.Materials and methods:Data collection:56 cases of three-dimensional pelvic CT data were selected randomly,including 30 males and 26 females,aged from 18 to 89 years,with an average age of 47.28 + 12.4 years.Excluding operation history of pelvic area,bone deformity,anatomic variation,fracture or dysplasia.The original DICOM data of pelvis were copied to personal computer.Reconstruction model:repair the defect on the pelvis on the mimics 17.0 operating platform and then obtain a complete pelvis model through three-dimensional reconstruction.Search for the best screw channel,and measure the related anatomical parameters:translucenting pelvis three-dimensional model,and rotating pelvis model,we adjusted the perspective angle perpendicular to the S2A1 screw channel axis.A translucent region with a slightly clear boundary can be observed on the pelvis in the perspective of an approximate parallel to the axis of the screw channel.The boundary is made up of a deeper color line,which represents the overlapping cortex of the bone,and the translucent region is the osseous channel of the screw.On this axis,the three-dimensional model of the pelvis is fine tuned,and the translucent regions of different sizes and shapes can be observed,that is,the different sizes of the osseous channels are obtained.When the irregular quadrilateral translucent area obtained visually,the virtual screw is placed at a 4mm in the center of the translucent area,gradually increasing its diameter,until the virtual screw just break the darker boundary,the translucent area defined the best screw channel,record the screw diameter.Rotating pelvic model ensures that the inserted virtual screws are completely located in the bone structure without breaking through the pelvis of the bone cortex,the sacral canal and the sacral hole.By three different researchers repeat three times,the three best screw channel were obtained by selecting the largest data,measure and record the needle points and related anatomic parameters,calculate the virtual screw and three plane(transverse,coronal and sagittal)angle.Experimental results:S2AI screw channel can accommodate the maximum average average diameter of the screw was 14.68 + 1.69mm(11.24-20.04mm),the difference between men and women,or on both sides of the pelvis was no statistical significance between the average placement;maximum average screw length was 120.3 + 9.16mm(100.77-144.12mm),and the difference between left and right sides between the male and female pelvis was no statistical significance between.The best in midline needle point distance average 20.53 + 4.08mm(13.30?33.66mm),the optimal entry point on the edge of the average distance S1 13.48 + 6.00mm(4.04 + 26.27mm);the optimal entry point on the edge of the average distance S2 13.54 + 6.18mm(1.87-27.93mm),the needle points related anatomical parameters in data between the male and female,no significant the difference between both sides of the pelvis.The angles of the largest screws and the transverse,coronal and sagittal planes were 20.11°±4.82°,41.49°±5.35° and 41.31°±4.81°,respectively.There was no significant difference between men and women.The difference between the left and right sides of the pelvis was statistically significant(P<0.03)with the angle of the coronal and sagittal plane.Conclusion:All the subjects have the ideal S2AI optimal osseous channel,and the all the average maximum diameter of single screw is greater than 11.2mm.It is feasible to apply S2AI screw fixation to Chinese people,but there are differences in individual anatomical data.Preoperative screw placement and needle insertion parameters should be evaluated before clinical use.