Applied Anatomy Of Iliac Anchorage For Transiliac Screws: Three-Dimensional Reconstruction And Adjacent Vessels, Nerves Study Of Pelves

Background:The traditional means of human anatomy observation have always relied on ruler, caliper,conimeter and operation instrument to study the relationship of anatomic structure.Obviously,it is strongly limited by the source,quality of specimen and the ability of researchers themselves.As results,the tissues and organs with sophisticated shapes is hardly described actually by traditional methods.Radiography is still chosen frequently to diagnose problems involving bones and joints.However,it is difficult to display spatial position and orientation of the bone sufficiently with irregular shape.In clinical practice,it is difficult to display spatial position and orientation of the pelvic structures obtained from the two-dimensional computed tomography(2D-CT)images,sectional anatomy,plain radiogram.Difficult conceptual processes are required for a doctor to image the spatial position and orientation of the pelvic structures from 2D images.The large numbers of images are cumbersome,time consuming,and expensive to display on film.Recently, three-dimensional(3D)computer-based image reconstruction and analysis technique has been developed and to be widely used in the medical field that,with advances in computer technology,can be performed using a personal computer.The 3D structures of the human body can be displayed in any direction,angle and plane and any diameters,distances and angles of the reconstructed structures could be easily measured.These advantages can provide significant benefit for abundant spatial information and simplify the doctor's conceptual processes,and also provide a 3D anatomic basis for diagnostic imaging and surgical operations.Generally speaking, the 3D-reconstruction algorithm is divided into two methods of surface fitting and direct volume rendering.Different algorithm has different advantage and disadvantage,some of which are well known.Therefore,the relative accuracy or contradiction is possible appeared while the image proceeded.In current stag,the 3D computer-based image reconstruction and analysis technique,which original data come from either 2D-CT,histological sections,magnetic resonance imaging and ultrasound,has been developed and widely used in the medical field.On the other hand,the conformity among the anatomic findings,2D-CT image and reconstruction 3D image are rarely seen in the medical literature.In 1984,the Luque-Galveston technique was introduced for lumbosacral fixation, but this technique was technically demanding,especially bending rods into the appropriate alignment.Iliac support has been shown in a number of publications to improve biomechanical strength and seems to provide acceptable clinical results.One of the advantages of iliac screws compared to the conventional Galveston technique is that they can be used in combination with sacral screws,providing more rigid fixation of the sacropelvic unit.One after another,the supra acetabular,transiliac implantion have promoted the management of spine deformity,postradical sacrectomy,revision spondylolisthesis surgery,unstable H-or U-shaped sacral fractures,and fractures and dislocations of the pelvic ring.In clinical management,repeated attempts to optimize the transiliac screw position will undoubtedly decrease the biomechanical results. Moreover,the vicinal vessels,nerves and organs will be damaged once the screw punctures the cortical table.Therefore,Familiarity with the anatomy of the ilium is of paramount importance for accurate iliac screw placement.Furthermore,it is essential to obtain more than one screw anchor for stable lumbopelvic fixation in management the severe posterior pelvic ring fracture,revision surgery with diminished bone stock at the posterior superior iliac spine(PSIS)after bone grafting,and sacroiliac joint tuberculosis or tumor,which require at least two different starting points and screw paths or use uncommon trajectory.In recent years much progress has been made in the classification,imaging,and physiopathology of pelvic traumas.Surgical techniques that result in the restoration of pelvic anatomy and early mobilization of patients have been developed and are routinely applied.The potential complications of the operation include injuries to the adjacent major vessels,nerves,and major viscera(i.e.,intestines,bladder,and urethra).The operative risks associated with placement of iliac screws are considerable because there is no visual monitor to reduce the potential danger of intrapelvic vascular injury(e.g.,to the external iliac artery when excessive drilling is done for fixation of the iliac screws or to the obturator artery when the iliac screws are incorrectly inserted).To minimize such risks,it is helpful to define the location of these intrapelvic vascular and nervous structures and measured the distance to the lateral wall of pelvic.Objectives:1.To testify the conformity among anatomic measurement,2D-CT and 3D-image.2.Making some morphologic measurements on ilium anchorage for transiliac screws of the eastern population using 2D-CT to determine the length,angle and diameter of supra sciatic transiliac implant anchor sites,to define maximum safe section of the anchor with purpose of that,the results obtained in this research could give a light on the surgical procedures and hardware manufacture.3.To observe the location of the pelvic vessels and nerves on the pelvic sides, measure the vertical distance from vessels and nerves to pelvic sides,and draw the projection of important blood vessels and nerves on the outer surface of the pelvis respectively.Consequently,the results obtained in this research could give a light on the surgical procedures.Methods:In accordance with the rules and regulations of the university,we used 18 embalmed cadaveric pelves(9 male,9 female)without any gross structural abnormalities to testify of the conformity among anatomic measurement,2D-and 3D-image.1.Anatomic measurements included the length from PSIS to anterior inferior iliac spine(AIIS)on the right side ilium of each skeleton with a calliper.At the same time,the drilling angle of the passageway in the horizontal plane was determined with a goniometer.2.The remaining studies were performed on a 64-row CT scanner.Each pelvis specimen was placed into the CT scanner in a supine position with L_psisline in bilateral ilium mentioned above oriented vertically.An almost transverse plane image was thus obtained,showing the shape and orientation of iliac columns.The digitized scans were imported into Mxliteview DICOM Viewer software.CT measurements included the length and angle of the right side of Lpsis in the horizontal plane.3.Subsequently,all specimens underwent spiral CT scanning again in the supine position.Correct stance was achieved by alignment of the anterior superior iliac spine, pubic symphysis in a coronal plane and the ischial tuberosities in a horizontal plane. The scanning range was from the top of the iliac crests to the bottom of ischial tuberosity.After the imaging data had been stored in a DICOM(Digital Imaging and Communication in Medicine)file,the digitized scans were imported into MIMICS 10.0 image analysis software.For an accurate measurement of the cortical bone geometric parameters,an edge recognition application was performed based on gray level thresholds to extract the cortical surfaces of the pelvis.In this study,a lower threshold of 84 Hounsfield units(HU)and an upper threshold of 1273 HU were used. The length and angle of L_PSISwas measured on 3D-image with the tools of"measure 3D distance and measure 3D angle"after the 3D-image was cut through L_PSIS.For statistical analysis we used two-way analysis of variance and bivariate correlations.SPSS 13.0 statistical software was used to analyse the data:P-value below 0.05 was considered to be significant.Applied anatomy of iliac anchorage for transiliac screws1.Anatomic observation included three screw trajectories on bilateral ilium of each skeleton.L_ITextended from the iliac tubercle(IT)to AIIS.L_PSISextended from PSIS to AIIS.L_PIISextended from the posterior inferior iliac spine(PUS)to AIIS.2.The remaining studies were performed on a 64-row CT scanner.Each pelvis specimen was placed into the CT scanner in a supine position with the three lines in bilateral ilium mentioned above oriented vertically.An almost transverse plane image was thus obtained,showing the shape and orientation of three iliac columns respectively.The digitized scans were imported into Mxliteview DICOM Viewer software.CT measurements included the length,smallest medullary width,and angle of three columns in the horizontal plane mentioned above.Window/Level adjustment was an essential tool to represent the boundary between cortical and cancellated bone.3.Subsequently,all specimens underwent spiral CT scanning again in the supine position.Correct stance was achieved by alignment of the anterior superior iliac spine and pubic symphysis in a coronal plane,the ischial tuberosities in a horizontal plane. The scanning range was from the top of the iliac crests to the bottom of ischial tuberosity.The digitized scans were imported into MIMICS 10.0 image analysis software. For an accurate measurement of the cortical bone geometric parameters,an edge recognition application was performed based on gray level thresholds to extract the cortical surfaces of the pelvis.In this study,a lower threshold of 84 Hounsfield units (HU)and an upper threshold of 1273 HU were used.Continually,the 3D-image was reconstructed once again with the same gray level threshold.In this stage,we deleted the iliac area where the medullary width less than 6.5 mm and the area anterior to the constriction which the smallest medullary width less than 6.5 mm on each 2D-image. With the same proceeding,the 3D-images were obtained which demonstrated the maximum safe section for transiliac screws on bilateral ilium.At last,we take anatomic measurement on the safe section for the clinical aim.Applied anatomy of the pelvic vessels and nerves1.Arterial system:we observed the patterns and locations of the iliac arterial branches,and measured the vertical distance from vessels(including external iliac artery,internal iliac artery,obturator artery and common iliac artery)to pelvic sides.2.Venous system:we observed the patterns and locations of the iliac venous branches,and measured the vertical distance from vessels(including external iliac venous,internal iliac venous and obturator venous)to pelvic sides.3.Nervous system:we observed the patterns and locations of the pelvic nerves, and measured the vertical distance from nerves(including lateral femoral cutaneous nerve,genitofemoral nerve,femoral nerve and obturator nerve)to pelvic sides.4.Subsequently,all specimens underwent sham operated in the ventral decubitus. K-wire was drilled from PSIS to AIIS and the spatial relation can be observed between the wire and the vessles and nervous.At last,the dangerous region on pevic wall can be located while the wire was drilling. 5.The projection of important blood vessels and nerves on the outer surface of the pelvis:Following intestinal evisceration,each specimen was bisected in the median plane.A K-wire was used to drill the pelvic wall along lateral femoral cutaneous nerve,genitofemoral nerve,external iliac artery,internal iliac vein,internal iliac artery,obturator artery,femoral nerve and obturator nerve.After taking photos with digital camera,we import the photos into Photoshop software to draw the projection of important blood vessels and nerves with different colors on the outer surface of the pelvis respectively.Results:1.The length and angle of L_PSIS obtained from anatomic measurement,2D-and 3D-image are shown consistently.There was no significant difference among three sort values.2.In the majority measurement of L_PIIS(5 from female and 6 from male),we found the line was below or just located the top of greater sciatic notch.As a result, the length,smallest medullary width and angle of L_PIIS were not recorded.3.All specimens had relatively straight and rectangular shaped iliac columns along L_PSIS that would allow for implant of the entire length of the column.On average,the typical female pelvis had iliac columns along L_PSIS that were 125.3 mm in length,10.8 mm in width,with the drilling angle in the horizontal plane of 25.5°laterally directed from the midsagittal plane.Generally,the typical male pelvis had iliac columns that were 135.6 mm in length,13 mm in width,with the angle of 26.3°. Considering the minimum intrailiac distances,screw lengths of 115 mm and 95 mm should always be possible for transiliac insertion into L_PSIS of male and female, respectively.Relatively,the canal length along L_IT is shorter than L_PSIS in both sexes. The typical female pelvis had iliac columns that were 117.1 mm in length,8.2 mm in width,with the drilling angle in the horizontal plane of 26.5°laterally directed from the midsagittal plane.Generally,the typical male pelvis had iliac columns that were 126.9 mm in length,10.1 mm in width,with the angle of 25.8°.Considering the minimum intrailiac distances,screw lengths of 95 mm and 90 mm should always be possible for transiliac insertion into L_IT of male and female,respectively.4.The 3D-image was reconstructed with the smallest medullary width more than 6.5 mm.Therefore,the 3D-image demonstrated the maximum safe section of the anchor for transiliac screws on bilateral ilium.Generally speaking,the safe section majority located above the greater sciatic notch without significant difference between bilateral ilium.The minimal distance above the greater sciatic notch of the safe section was approximately 31 to 42 mm.The portrait distance of anterior region between the top of the section and the superior rim of the acetabulum,just above and below the AIIS,was approximately 41 to 56 mm.Similarly,the portrait distance of posterior region from the iliac crests to the PIIS was approximately 90 to 106 mm.5.The dangerous region was located on the lateral wall of pelvic and inguinal region.The K-wire may stick into acetabulum if the drilling angle is smaller.On the other hand,the obturator artery,obturator nerve and deep iliac circumflex artery will be injured while the drilling angle is larger or the screw is longer.6.It was easily to draw the projection of important blood vessels and nerves on the outer surface of the pelvis directly and clearly.To understand the projection of the pelvis deeply may prevent vital blood vessel and nerve from accidental injury during the operation of internal fixation of pelvic fracture.Conclusions:1.There was no significant difference among anatomic measurement,2D-and 3D-image.Therefore,it implies the measurements obtained from three techniques are consistent,effective and reliable.2.All specimens had relatively straight and rectangular shaped iliac columns along L_PSISthat would allow for implant of the entire length of the column.We believe the screw lengths of 115 mm and 95 mm should always be acceptable for transiliac insertion in the eastern population of male and female,respectively.3.After 18 specimen research,we located the safe section approximately above the greater sciatic notch.Generally speaking,it could be divided into anterior and posterior parts.The anterior part was approximately same to the position previously described by other authors.The posterior part,extending from the top of iliac crests to PIIS,was mainly situated at the posterior pelvic ring.It is important in management of the severe posterior pelvic ring fracture,revision surgery after bone grafting, sacroiliac joint tuberculosis or posterior pelvic ring tumors which require at least two different starting points and screw paths or use uncommon trajectory.4.The srew can be implanted safly from PSIS to AIIS with suitable drilling ange and length.Importantly,the dangerous region was located on the lateral wall of pelvic and inguinal region.