Feasibility Study Of Navigational Template For Antegrade Lag Screw Fixation Of The Fractures In The Posterior Column Of Acetabulum

BackgroundAcetabular fractures are one of the hotspots in recent years in the field of orthopedic trauma research, it occurs mainly in young adults, and more violence caused by the high-energy. With our country is in the rapid economic development,the traffic accidents are increasing gradually,which lead to large numbers of patients with acetabular fractures.How to treat and manage the patients of acetabular fracture is challenge for orthopedics doctors,because of the deep location, complex anatomy, reduction and fixation difficulties, complications and other reasons.Letournel-Judet had divided acetabular fractures into simple and complex fractures. On clinical, Complex acetabular fractures tend to be more common. Giannoudis had reported that Transverse fracture,tow column fracture, T-type fracture,and the anterior column with semi-transverse Account to the total acetabular fractures of44Percent.The manner of treatment for posterior column fractures:①Open reduction and internal fixation from posterior incision;②Reset and fixate anterior column with plate and posterior column fixated with lag screw through anterior incision;③Closed reduction and screw fixation by Percutaneous. When treatment for Transverse fractures, T-type fractures and two column fractures, the incision is often forced to use combined approach.The advantages of open reduction and internal fixation can restore the anatomical location,but it also lead to a large amount of bleeding, easy to damage the nerves and blood vessels, postoperative infection and heterotopic ossification.In the actually,we can reduce posterior column of most of these types of acetabular fractures from anterior incision,for avoiding to take a posterior incision,a plate should be used to fix the anterior column,at the same time a antegrade lag screw be used to fix posterior column.The combined use of plates and screws to fix the fractures, which would reduce the exposure of surgical incisions and muscle stripping, intraoperative blood loss,postoperative infection, and heterotopic ossification.The problem of using antegrade lag screw to fix posterior column of acetabular fractures such as:①Screws are easy to enter the hip joint.②Screws pierce the bone cortex,which will injure the nerve and vessels.③ntraoperative change position of patients or the surgical field can’t exposed to the full because of soft tissue masking, the Surgeon are hard to determine the direction of the needle.④Hard to place long enough screws, leading to fixation not strong enough.⑤Still in operation repeated projection X-ray. Therefore, the key and the difficulty of the operation is: how to place lag screws for the posterior column fractures successfully!The appearance of digital orthopaedic has created a new era for the basic application research of orthopaedic and traumatology. Compared with the traditional cadaveric reseach,it has the lots of advantages,like high accuracy,good consistency, repeatability strong and saving medical resources. In this study, it measure the anatomical parameters for percutaneous sacroiliac screw fixation by the Mimics software, which provide a theoretical basis for the design of the surgical navigation templatean for the sacroiliac joint screw fixation.objective1. Using the bony markers on the pelvis, to simulate anterograde lag screw fixation of the s posterior column on the pelvis’three dimensional reconstruction, and to provide evidence of applied anatomy for the feasibility of targeting device for antegrade lag screw fixation of posterior column fractures of acetabulum.2. The models of navigational templates were designed according to the anatomic features of the acetabulums and the measured parameters.,and was manufactured by rapid prototyping, which the accuracy was validated by experimental study.To analyse of the feasibility and accuracy of the navigational template for antegrade lag screw fixation of the fractures in the posterior column of acetabulum.3. Trying to resolve the difficulty of placement of antegrade lag screw fixation for posterior column fractures of acetabulum,which would provide a New method for the treatment of acetabular fractures.Methods1. Collection of images and reconstruct the3-dimensional model of pelvisObtained40adult patien randomly, who took complete CT scan of pelvis in our hospital between April2009and April2011without any bony and anatomy abnormality.20males,20females, age ranged20-77years,80cadaveric hemipelves were collected. Scan condition:tube tension120kV, tube current200-300mA, slice increment1.25mm, matrix512x512. All the images were saved as DICOM format and imported to the personal computer.All the sequent tomoscan images of pelvis were imported into the Materialise’s Interactive Medical Image Control System (Mimics) in personal computer as DICOM format. The3-dimensonal models were reconstructed by the same calculated parameter.2. Simulating lag screws into the posterior columnThe method of lag screws placement in acetabular posterior column had adapt in this project came from the report of Zhan Da-bao,that find the most prominent bony points on the anterior superior iliac spine(ASIS), and posterior superior iliac spine (PSIS) and respectively marked as (A) and (B).And then draw a plane (y) that was perpendicular to the section AB and through the midpoint (M) of section AB.3D-reconstruction model of pelvis was rotated to homonymy by45degrees (Iliac oblique view),Virtual cylindrical implants were placed intraosseously into the Posterior column of acetabulum. The diameter of the virtual cylindrical implant was Progressively increased to6.5mm,and back and obturator oblique views of Pelvis were obtained to make sure that the virtual cylindrical implant did not Penetrate the cortieal margin of Posterior column or into the acetabulum.Review the2-dimensional images of the transverse Plane;coronal plane and sagittal Plane to avoid the virtual cylindrical implant penetrate the cortieal margin of Posterior column or into the acetabulum.3. Measuring the anatomy parameter of lag screws for posterior columnThe projection point (O) of the antegrade lag screw on the inner table was thus defined. Next a line designated OD was drawn perpendicularly from the point O to the linea terminalis at the point D. Another line, designated DQ was the point D to the anterior border of the auricular surface(G). The distances OD and DG were measured on the Mimics software straightly. The length of screw andaAngle between the cylindrical and the coronal plane, and PAngle between the cylindrical and the sagittal plane,were also measured by the fomulars as below:4. Statistics and analysisThe experimental data was analyzed by the software of SPSS13.0,including the distances OD and DG,the length of screw andaAngle between the cylindrical and the coronal plane, and(3Angle between the cylindrical and the sagittal plane.Independent-samples t test and pair-sample t test were used, and an associated probability of5%(P=0.05) was considered significant.Results The average distances of OD and DG were (13.62±2.19) mm (11.4～17.3mm), and (15.27±4.01) mm (11.4～20.9) mm, respectively. The average length of lag screw was (116.65±7.19) mm (97.0～126.4) mm, aAngle about (15.47°±4.01°) andpAngle about (6.65°±2.93°).The distances of DG, The length of screw andpAngle in male and female respectively, with a very significant sexual difference (P<0.05). The distances of OD, aAngle Was not significant difference in gender(P>0.05).Conclusions1.An adequate length of antegrade lag screw can be placed on the basis of anatomy parameter.2. Applied anatomy of the parameters of antegrade lag screw fixation are measured that provides a path on purpose of the design of the surgical navigation template for the posterior column for the injury of acetabular column fractures.3. The digital model of pelvis can not only provide a new method for the study of application basis research of antegrade lag screws fixation of posterior column, but also offer a simple, intuitive personalized preoperative ideal preoperative prepare for the the use of the technique. Methods1.Designed and manufactured of the navigation template for the antegrade lag screw of the posterior columnAccording to the anatomy parameter which was measured in the part one, and laid the nail channel and template fitting as a whole,using with UG6.0software.The inner side of the template (ie, the contact surface with the bone) in accordance with quadrilateral district and iliac fossa surface anatomical features which extracted with UG software,According to the part one, the OD distance isn’t significance difference in gender, there is a certain safety zone for placing lag screw in posterior column, therefore, its average anatomy parameter should be taken to designe the navigation template.The best direction and location of extract lag screws were defined using reverse engineering according to these three situations and navigation templates were designed according to the anatomic features of the quadrilateral district and iliac fossa surface. The exact navigational template was made by rapid prototypin.2. The accuracy was validated by experimental study on cadaverAs defined the holes on the navigation template corresponding to the holes1,2,3, we took16adults left pelvic specimen for experiment.The navigation template should be attached to the quadrilateral district,and the template longitudinal axis Parallelled and overlapped to the edge of that. Operator With his left hand to seize the template,and holding a drill in right hand to place guide pin through the holes, sounding and screwed into a corresponding length of the screw,all of the screws were6.5mm diameter. The position of the needle, the rate of Success for placement from different nail holes and the length of lag screws can place in the posterior column.3.The method for the results of the judgmentThe guide pin of the needle position in the experiment has the following three kinds:1. Near the ischial tuberosity.2. Located above of the sciatic notch.3.Out of the cortical bone or into the hip joint. Therefore, the project defined the location of outlets of the drill bits pin near the ischial tuberosity as accurate positioning of the navigation template,near the ischial tuberosity as Well positioned, out of the cortical bone or into the hip joint as lose.ResultSuccessful designed and manufactured navigational templates are more consistent with the anatomical features of the quadrilateral plane.Placement of lag screw from the first hole:18.75%(n=3) achieved accurate positioning,50%(n=8) well positioning, and31.25%(n=5)loose. From the second hole:62.50%(n=10)had accurate positioning,31.25%(n=5)well positioning, and6.25%(n=1)loose.From the third hole:37.5%(n=6) had accurate positioning,6.25%(n=1)well positioning,56.25%(n=9) loose.As the location of outlets of the drill bits the lag screw location near the ischial tuberosity,it can placement the length of (106.1±3.3) mm of screws,wihle (70.4±6.1) mm as it’s location at the above of esser sciatic notch.Conclusions1. Successful designed and manufactured navigational templates according to the anatomy parameter combine quadrilateral with iliac fossa surface anatomical features.2. The navigational template designed according to the anatomic features of acetabulum and the measured parameters can accurately assist lag screw placement.3. Using reverse engineering and rapid prototyping may provide a new method for placement of lag screws for posterior column of acetabular fractures.