Analytical Model For Lumbar Pedicle Screw Based On Three-dimensional Reconstruction Of CT Image

Introductionpedicle screw fixation system now has been one of the most frequently used onein spine surgery for it's excellent biomechanical feature.But the operation is hard anddangerous due to the complicated and vital anatomy structure adjacent topedicle,malposition of screw evokes the descent of stiffness and even operationfailure.It's the key point to this operation that the path of planting screw must accordwith the macroaxis of pedicle as far as possible.So,research on how to identify theplanting path is recognized as the decisive aspect.Former research focus on thegeneral character of large samples,But individual index is the most urgent whenoperating on a specific patient.The pupose of this study is to solve this problem andmaking individualization be an ordinary technology for ordinary surgeons evenwithout the help of expensive device such as computer assistant navigationsystem.In this study,The author combine the accurate display of CT image and thedirect-viewing of three-dimensional reconstruction to form the analytical model forlambar pedicle screw.furtheremore, 60(male 30,female 30) cases of CT image oflumar spine were measure and analysis by using this model,Including transversesection angle(TSA), sagital section angle(SSA),Optimal screw path length and theposition of optimal entrance point etc.Compareed with other resemble researchs,thestudy is more thoroughly and more practical.hoping make some benefit to the clinical operation and fundamental research as well.PartⅠThe technology about the Analytical modelObjectiveTtry to shed some light on the scientific research and clinic usage of pediclescrew fixation,the author designed a kind of standard procedure for the Analyticalmodel for lumbar pedicle screw based on three-dimensional reconstruction of CTimagine by using three-dimensional reconstruction and vector analytical software,Methods1.1 Material One integrated lumbar spine CT image that scaned by 64 detectorrow helical.CT in zhujiang hospital radiology department.Scan setting:thickness oflmm,interval of 0.5mm..Patient date: male,30 year old, without vertebral structuredamage, serious anisotrophy and operation history. Computer setting: CPU1.5GHz;RAM 512MB;Operating system: Windows XP Professional SP21.2 Methods:1.2.1 Import lumbar spine CT image into Mimics8.1Use Philips Mxliteview version 1.22 to identify the consisting CT images ofeach segment and import them into Mimics8.1 separately1.2.2 Identify the core of pedicle of vertebralFinding the narrowest fraction of pedicle in all cross sections, Identifying andmark the centre point of it as the core of pedicle that all screw traverse this point.1.2.3 Create the prior screw, definite the length and diameterBy using the 3-D modeling function of Mimics8.1,Create a cylinder representthe prior screw, make sure it traverse the core of pedicle of vertebral and collineationwith the axis of pedicle as far as possible..the length of it is determined by thelocation of the tip point which is 6 mm far from the inner margin of the cortex at thehorizontal plane.The diameter of the prior screw is determined by the transversediameter of cancellous bone of the core plane of the pedicle,both left and right sidetake the equal diameter. 1.2.4 Create the inside, outside, ento-upper and ecto-upper screw models,Measure the diatance between the core of pedicle and the tip point of the priorscrew, as the radius of the sphere model that created in Mimics8.1 with the core ofpedicle as center to locating other points.In the tip of the porior screw's horizontalplane that parallel to the terminal plate, In this plane, the intersection point of spheremodel with the outer wall of vertebral body make the tip of exterior screw, theintersection point of both sphere model make the tip of interior screw,.the includedangle between the exterior and interior screw represent the safety range whileplanting screw in this direction.In the plane of upper terminal plate, the intersectionpoint of sphere model with the outer wall of vertebral body make the tip of ecto-upperscrew, the intersection point of both sphere model make the tip of ento-upper screw,.If the screw break the cortex of pedicle, regulate it manually to the adjacent degree isrequisite.1.2.5 Create the inferior screw modelBisectioning the included angle between exterior and interior screw and theincluded angle between ecto-upper and ento-upper screw in AutoCAD2006 software,Create a plane traverse the two bisection points and the core of the pedicle. Theintersection point of the plane and the sphere model in the inferior terminal platemake the tip of inferior screw, regulation manually is needed sometime. The includedangle between inferior screw and bisection point of ecto-upper and ento-upper screwrepresent the safety range while planting screw in this direction.1.2.6 Create the optimal screwBisectioning the included angle between inferior screw and bisection point ofecto-upper and ento-upper screw, from the bisection point to the core of pedicle,createthe optimal screw, the intersection point of the optimal screw with the vertebral archmake the optimal entrance point, the intersection point of the optimal screw with thevertebral body make the optimal vent point, the distance from the optimal entrancepoint to the intersection point of the optimal screw with the sphere model make the length of experimental screw, the distance from the optimal entrance point to theoptimal vent point make the length of optimal screw path1.2.7 three-dimensional reconstruction for observation and regulationBy using the three-dimensional reconstruction function(shaded surface displaySSD) of Mimics,setting the lower threshold as 226HU to make the manual regulationmore direct-viewing and easily when screws break the cortex of pedicle,make thethreshold even lower to display the entire structure of vertebral arc for anobservation of entrance points.ResultsThe establishment of the Analytical model for lumbar pedicle screw is successed,all operation process are not difficult, the prior screw accord with the optimal one indirection. Break the cortex mostly occur at interior wall and inferior wall, especiallyin the below part of lumbar spine,while break seldom occur at other wall.thecondition imply that the anatomy character of vertebra body and pedicle havedifferent influence about planting pedicle screw at different directionConclusion64 detector row helical.CT with the help of three-dimensional reconstructionsoftware can display the minute change of vertebra, finding the optimal screw pathillustrate the purpose of the experiment accomplished. It"s the Shortage of the testthat to lack the influence of biomechanics factor PartⅡAnalytic results of 60 cases by using the Analytical modelObjectiveTo assessment the available of the analytical model and measure correlated datafor clinic.Methods1.1 Material 60 integrated lumbar spine CT images that scaned by 64 detectorrow helical.CT in zhujiang hospital radiology department.Scan setting:thickness oflmm,interval of 0.5mm..Patient date: male,30 cases, age distribution from 29 to 75year old, average45.33±14.50, female,30 cases, age distribution from 21 to 63 yearold, average43.13±13.23,without vertebral structure damage, serious anisotrophyand operation history.1.2 Method1.2.1 Create screws and measure necessary data of pedicle screw at each caseaccording to the analytical model.for better illustration, make some definition below:Entry core distance(ECD): The distance from the optimal entrance point tothe core ofpedicleExterior interior angle(EIA): The included angle between the exterior andinterior screwUpper inferior angle(UIA): The included angle between the upper andinferior screwExterior interior curve (EIC): The length of the curve of EIA, as the radiusequal to ECD.Upper inferior curve(UIC): The length of the curve of UIA, as the radiusequal to ECDExperimental screw length(ESL): the distance from the optimal entrancepoint to the intersection point of the optimal screw with the sphere model.Optimal screw path length(OSPL): The distance from the optimal entrancepoint to the optimal vent pointScrew tail distance(STD): The distance between left and right optimalentrance pointTransverse section angle(TSA): Half of the included angle between left andright optimal screw Sagital section angle(SSA): The average of angle between both side optimalscrew with the upper terminal plate1.2.2 Modify the threshold of CT value to distinguish the rear partof the lumbar, Observate the the optimal entrance point and the adjustable range.1.3: Statistical Disposal:The experiment use SPSS13.0 as the statistical software, Data of both side in avertebra Were compared by Paired t test, Data between male and female Werecompared by independented t test, Data of each segment of lumbar spine Werecompared by One-way ANOVA. the significance level isα=0.05 toth tail, Results areexpressed by means x±sD.ResultsThe age between male and female have no statistically significanceThe result of One-way ANOVA show the difference between each segmenthave statistically significance.EIA＜UIA, EIC＜UIC in both sex, EIA, UIA of female is larger thanmale;EIC, UIC, ECD, STD, ESL, OSPL, screw diameter (SD) of male is large thanfemale (P＜0.05).With the descent of segment, SD, STD, TSA increase gradually. In TSA, L5is exceed hugely than L4.OSPL peak at L2, L3. L4 is shorter than L3(P＜0.05).With the descent of segment, SSA decrease gradually, the differenceamong L3, L4, L5 have no statistically significance.The optimal entrance point mostly locate at the root of accessoryprocess which adjacent to the mamillary process from L1 to L4, Theadjustable range of entrance points of the 4 segments almost cover theaccessory process, But at L5, The optimal entrance point is much moreoutside away from the accessory process, just at the middle of thetransverse process and the adjustable range of entrance points islimited. ConclusionThe data of vertebra around L3 have significant difference,which means inoperation different methods should be pay to the upper and below segments of L3,moreover L5 is special in structure compared with other segment,especially at Screwtail distance(STD),TSA, and the optimal entrance point...