Anatomic Basis And Application Of Percutaneous Screw Placement Guided With Computer-assisted Navigation In Pelvic And Acetabular Fracture

Objectives:Formal internal fixation of acetabular fractures has traditionally required large surgical exposures.These exposures can be associated with significant complications,including infection,wound healing problems,major blood vessel or nerve injury,denervation or devascularization of the abductors,and heterotopic ossification.For the most part,these complications are related to the surgical exposure itself rather than to the initial traumatic injury.It therefore seems reasonable to consider percutaneous stabilization of selected acetabular fractures to avoid exposing the trauma patient to the morbidity of an extensive surgical exposure.The anatomic basis of and application of Percutaneously Placed Lag Screw into iliosacral joint,anterior column of acetabulum guided with conventional fluoroscopy had been reported in recent years.While,the anatomic basis and application of antegrade lag screw into posterior column of cetabulum,lag screw into pubic symphysis had not been reported before.The conventional fluoroscopy can display only 2D images at one time.The surgeon has to move the C-arm in order to get more different images, which need a lot of time during the surgery.CAOS provides access to either a 3-D dataset or multiple simultaneously displayed stored fluoroscopic images(virtual fluoroscopy).For both techniques,most current image-guided surgery systems use an optical tracking system(digital camera array and digitizer) or a magnetic/radiofrequency tracker to follow both the position of the patient and special surgical instruments during the course of the procedure.The predicted position of the surgical instruments is then displayed on a computer monitor relative to the position of the stored images.This process is known as surgical navigation.Virtual fluoroscopy(fluoroscopic navigation) was refined and approved for clinical use in 1999.Before this time,the distortion inherent in analog C-arm images prevented their use in surgical navigation.Software algorithms were developed for powerful computer workstations that allowed them to rapidly warp the C-arm images to make them optically correct and allow for their use for guidance. The surgeon uses a standard C-arm unit to harvest optimal 2D or 3D images in the operating room.A camera tracks the position of the C-arm unit during image acquisition,and the images are warped,stored,and displayed on a workstation.The camera can then track special instruments(such as a drill guide or probe) and display their position relative to each of the stored images.The ability to update images after fracture manipulation has now expanded the application of computer-assisted surgery to any procedure that has traditionally relied on intraoperative C-arm use.The objectives of the present study were 1.to determine the projection of the axis of the posterior column on the inner table of the iliac wing in the supraacetabular region. 2.By simulating the intraoperation of lag screws insertion guided either with conventional fluoroscopes or with computer-assisted navigation on intact pelvises the accuracy of the computer-assisted navigation were evaluated.3.A retrospective cohort study was conducted to examine whether it was possible to reduce the iatrogenic soft tissue damage while correcting trans-symphyseal instability using percutaneous screw fixation guided with Iso-C^3D computerized navigation.Methods 1.Thirty adult dried bony hemipelves specimens and other 5 intact adult dried pelvic specimens were included in this study.The projection point of the axis of the posterior column of the acetabulum was determined on the inner table of the iliac wing of the hemipelves specimens.The perpendicular distance from the optimal entry point to the linea terminalis of pelvis was measured and recorded as the lateral distance.The same measurement along the linea terminalis from the optimal entry point to the junction between the anterior border of iliosacral articulation and the linea terminalis of pelvis was made and recorded as the posterior distance.The depth of the anchor path and the corresponding average retroversion angulation and extraversion angulation were also measured.According to the results acquired from this study,a series of 6.5mm lag screws guided either with conventional fluoroscopes or with computer-assisted navigation were inserted into the posterior column of each side of the other 5 intact specimens respectively to evaluate the position of the screws.The data were expressed as Mean±Standard Deviation and analyzed by using the descriptive methods with SPSS 10.0. 2.Two iliosacral lag screws,one posterior column antegrade lag screw,one anterior column antegrade lag screw and one pubic symphysis lag screw were placed bilaterally(9 screws) in each of 6 intact adult dried pelvic specimens using standard fluoroscopy,computer-assisted fluoroscopic image guidance and Iso-C3D image guidance.Screw positions were analyzed by computerized tomography after instrumentation and assigned a score based on deviation from ideal screw position. The data were expressed as Mean±Standard Deviation and All data were given as mean value±SD.Differences between the trial groups were evaluated by a standard ttest.3.A prospective cohort study was conducted.Eight patients with pubic symphyseal diastasis were treated with percutaneous lag screw under a fluoroscopy-based Iso-C3D computer navigation system in the period from October 2005 to June 2007.The technique was used in patients with pelvic instability duo to symphysis pubis trauma.All patients but 2 were male with a mean age of 34 years. Most of the patients had multiple injuries.According to the Association for Osteosynthesis—Orthopaedic Trauma Association(AO—OTA) classification,there were 4 B1 injuries,2 B2 injuries,1 C1 injuries and 1 C2 injuries.The procedure was performed within 24 hours of injury in 5 patients,by the 3 days post injury in 2 patients,and at lweek post injury in the one remaining patient.All patients were followed up for more than 1 year.Results:1.The average length of lag screw was 104.8±4.2 mm.The average lateral distance was 16.8±2.1 mm.The average posterior distance was 23.5±3.4 mm.The corresponding average retroversion angulation and extraversion angulation were 57°36′±4°28′and 119°18′±2°32′respectively.The insertion of the single 6.5mm lag screw of adequate length guided either with conventional fluoroscopes or with computer-assisted navigation,was possible in the posterior column along its anchor path and no accidental extraosseous or intraarticular screw placement had occurred.2.The StealthStation^? with ISO-C^3D(Medtronic Surgical Navigation Technologies) appeared to provide the highest accuracy of all guidance techniques. This result was more accurate than standard fluoroscopy.3.Total blood loss during the time of the percutanous screw insertion was less than 10ml.The mean operation time used in the percutanous screw insertion for treatment of traumatic pubic symphysis diastasis was 57min(range 30-80min) from the use of fluoroscopy to wound closure and the mean total fluoroscopy time was 118s(range 90-167s).Both clinical evaluations and serial radiographs,including postoperative computed tomographic scans,were available for all the patients postoperatively.All screws were completely contained between the pubic cortical tables according to the computed tomographic scans.The initial pelvic closed reductions were maintained until last time of follow-up.No deep screw track infection had developed.Conclutions:1.The present study describes a safe anchor path of antegrade lag screw fixation in the posterior column.Insertion of the lag screws of adequate length is possible in the posterior column along its functional axis.2.Computer-assisted fluoroscopy based image navigation appears to be more accurate than standard fluoroscopy in placing these screws.However,the surgeon has to learn and be familiar with the software and hardware of the CAOS that are much more complex than conventional C-arm fluoroscopy.3.Once anatomic reduction is achieved by the close manipulative method in pubic symphysis diastasis,percutaneous screw fixation could be applied rapidly using Iso-C3D computer navigation to direct accurate screw insertion and be a reliable and safe method of stabilization of traumatic trans-symphyseal instability.