| Atlantoaxial instability,easy to cause the cervical spinal cord compression and irritation,happens unrarely in the clinical.For this kind of patient,operation is often necessary to remove the compression and stabilize the atlantoaxial.,But it is very difficult and high potential risk to operate in this area,due to the complicated anatomical structure of the C1-C2.During many surgical methods used to treat atlantoaxial instability in recent years,the posterior C1-C2 transarticular screw fixation is considered as the gold standard for a good curative effect and a widespread clinical use.But during the surgical procedure,there is a risk to injury the vertebral artery,which is an important reason for some patients who cannot receive this operation.As far as we know,there is no study on the systematic anatomy about the relationship between the vertebral artery and screw trajectory related to the posterior screw fixation in the literature.In this study,basing on the relationship of the screw trajectory and vertebral artery,some related parameters were measured respectively on dry axis and atlas vertebrae of Chinese adult skeletons,atlantoaxial CT image with three-dimensional reconstruction of normal persons during the process of preoperative plan,and fresh upper cervical cadavers stimulating the posterior C1-C2 transarticular screw fixation.The aim of the study is to provid the theoretical data enhancing the security of the operation by exploring the relationship of screw trajectory,vertebral artery and individual anatomical structure of the patientsPart one The anatomical measurement about the relationship of screw trajectory and vertebral artery of posterior C1-C2 transarticular screw fixationObjective:Focusing on the relationship between vertebral artery and screw trajectory,the aim of the study is to provid Chinese morphological data for posterior C1-C2 transarticular screw fixation by proceeding measurement on the related anatomic data of posterior C1-C2 transarticular screw fixation.Method:The related anatomic parameter of posterior C1-C2 transarticular screw fixation were measured on 30 pairs of dried Chinese adult human C1 and C2 vertebraes.The insertion point of the posterior screw fixation is the center of lower edge on axis processus.First,a vernier caliper with the precision of 0.01 mm was adopt into the measurement such as the the width of the axis pedicle(on upper port of the pedicle on transverse foramen of axis),the internal hength of the axial lateral mass(the distance between the topmost point of the vertebral artery groove to superior facet of the axial), the depth of the vertebral artery groove(the distance between the inferior margin of transverse foramen of axis and the topmost point of vertebral artery groove),the distance from the topmost point of the vertebral artery groove to the internal margin of the axial superior facet,the length of the screw,the distance from vertebral artery groove of posterior arch of atlas to the median line,the distance from the internal margin of the vertebral artety of the axis to the median line,the distance from the internal margin of the vertebral artety of the atlas to the median line,and the width of the massa lateralis atlantis.Second,a conimeter with precision of 0.50 degree was used to measure the superior angle of the axis pedile(the angulation from the longitudinal axis of the pedicle to the horizontal plane),the medial angle of the axis pedile(the angulation from the longitudinal axis of the pedicle to the sagittal plane),the superior angle of the screw(the angulation from the line between the inserting and outing point to the horizontal plane),the medial angle of the screw(the angulation from the line between the inserting and outing point to the sagittal plane). All data were statistically processed with SPSS 11.5 software and were expressed as Mean±SD.Paired t-tests were employed for comparison of parameters from the left and right sides of the same vertebrae.Multitude mean comparison of several specimens were processed with One-way ANOVA and LSD analysis..The significant standard of the statistical test was atα=0.05Results:1.In 30 cases(60 sides)specimens,there were 9 sides(15%) whose pedicle width was less than 4.5mm or equal to 4.5mm,including 6 cases(left side)(10%) and 3 cases(right side)(5%).No significant difference happened between the parameters from the left and right sides(P＞0.05).of data have.the average length of the ideal screw trajectory was40(33.7-45.1)mm,the average medial angle of the screw was14.5(11-28)°;the average superiorl angle of the screw was 49(42-58)°.2.The depth of the vertebral artery groove on the inferior surface of the superior facet of the axial was(5.86±1.45)mm.Larger variation existed among the individuals in the vertebral artery groove,which extented to internal third of the superior facet in 15 sides(25%),to its middle third in 35(60%),and to its lateral third in 9 sides(15%). Corresponding to these,the medial angle of the screw trajectory were 26.4°,16.1°,15.1°respectively.Between the medial angles from the internal third and the middle,there was a significant difference(P＜0.05),but no significant difference between the angles form the middle and the lateral third.The distance from the topmost point of the vertebral artery groove to the internal margin of the axial superior facet were(6.07±1.14)mm,(7.84±0.90)mm,(9.43±0.82)mm respectively, only 2 sides in the internal group which was less than 4.5mm..In the three groups, there were significant difference in the widths of the axis pedicle and the distances from the topmost point of the vertebral artery groove to the internal margin of the axial superior facet.In the middle third group,the medial screw angle was largest than the others,but two data including the width of the axis pedicle and the distance from the topmost point of the vertebral artery groove to the internal margin of the axial superior facet were smallest than the others.Of the 9 side with the width of the axis pedicle that not larger than 4.5mm,8 sides in the internal third group and one side in the lateral third group. Conclusions:During the technique of the posterior C1-C2 transarticular screw fixation,the screw trajectory angle is decided by the location of the vertebral artery groove.,The screw trajectory is immediately close to the vertebral artery on the inferior of the superior facet of the axial,but there is a certain safety distance between them,If the vertebral artery groove extented the superior facet to its internal third in the individual,the medial angle of the screw should be increased,otherwise,the vertebral artety may be injuried by the screw.Part two The relationship analysis of vertebral artery and screw trajectory in the preoperative designof the posterior C1-C2 transarticular screw fixationObjective:Multiplanar reconstruction of spiral computed tomography was used in the normal person to find out the individual anatomy structure of the C1-C2,On the reconstructed image,individual preoperative design of posterior C1-C2 transarticular screw fixation would be tried to be imitated to realise the angle range and of the screw trajectory and the safe distance between the trajectory and the vertebral artery.The aim of the study in this part is to improve the accuracy of the posterior transarticular screw fixation and surgical safety.for every special patient.Methods:40 health persons received spiral computed tomography scans in the axial plane with 2 mm sections,1.0 mm reconstruction interval and a 2.0 pitch.The CT files including the all atlanto-axial segment were transmitted to hard disk in Voxel Q picker work station for procession..On the reconstruction CT images,the center of lower edge on axis processus was used as the insertion point of posterior transarticular C1-C2 screw fixation,the screw tip was determined on the superior border in atlas lateral mass for the largest superior slop angle of the screw,,the middle-upper 1/3 for the smallest superior slop angle,respectively.First,the screw superior angle on sagitta plane was identified,and then the largest and the smallest superior angle of the screw were located on the oblique coronal plane,where the appropriate screw medial angle,including the smallest,best,the greatest medial angle,and the distance from screw to the vertebral artery and the length of screw trajectory were measured under the various angles.The parameters,such as the isthmus width of the axial in the screw plane,the length of the screw,the maximum superior angle of the screw trajectory,the minimum superior angle of the screw trajectory and the maximum,the minimum and the best medial angle of the screw trajectory,the distance from the screw trajectory in the plane of the atlas,axial transverse foramen to the screw trajectory, were measured with digital gaugeon the reconstruction pictures.Statitical treatment was taken with SPSS13.0 software to analyse the all data which were expressed in mean±standard deviation(±s).The corresponding parameters of the left and right sides on the same specimen were processed by paired t-test statistics. The significant standard of the statistical test was atα=0.05Results:1.No significant difference was found out between the relevant parameters respectively fromthe left and right sides of the individual.,The largest superiorl angle was(52.6±4.57)°,the minimum was(47.4±5.03)°.When the superior angle was at the largest,there was the maximum range(5.8～15.5)°in the screw medial angle,the ideal medial angle was 12.0°(5.5°-19.0°).When the superior angle was at the minimum, the medial angle range was(6.8～14.9)°,the ideal medial angle was 11.5°(7.1°-19.5°);the ideal screw length was(37.5-40.7)mm.2.When the largest or ideal medial angle was decided,the more large the superior angle was,the more big the distance from the vertebral artery to screw trajectory.The distance from the vertebral artery in the axial transverse foramen to the ideal screw trajectory is about 3.0(0.3-4.7)mm,the maximum distance between it was 4.4(0.4-6.0)mm.3.There were 9 samples with not larger than 4.5mm in the pedicle width of axial. when the screw trajectory was at the maximum superior angle,the range of the medial angle was(15.4～18.5)°,the distance between the screw trajectory to and the vertebral artery was smaller than 1.00mm.When the screw trajectory was at the minimum superior angle,the rangle of the medial angle was(15.6～17.8)°,the distance between the screw trajectory to and the vertebral artery was smaller than 0.8mm.When the isthmic of the cases was smaller,the medial rangle of the screw was(15.6～17.8)°,the best medial angle was16.5°.Conclusion:Multiplanar reconstruction of helical computed tomography in the normal person,can simulate the screw trajectory,the safe angle rangle and the best angle of the posterior atlanto-axial screw fixation,to avoid the vertebral artery injury. Part three The experiment study on the anatomic relationship of vertebral artery and screw trajectory of posterior atalanto-axial transarticular screw fixationObjective.According to the data involving in the relationship between the screw and vertebral artery obtained from part one and part two,posterior C1-C2 transarticular screw fixation was taken on the fresh upper cervical vertebra cadavers,to explore further the safety of the operation and provide related experiment data for the clinic.Methods:6 fresh embalmed upper cervical vertebra cadavers were used for the experiment.The bilateral laminar and the processus of the axial were exposed.The tip of aiming device was placed on the center of lower edge on axis processus which was determined to be insertion point for screw.The guide wire with 1.0 mm diameter, aiming at the anterior tubercle of atla,should then pass through the device,and the caudal of the pin was lateral offside(10-15)°from the midline.The entire operating procedure was monitored by C-arm X-ray fluuorroscopy in order to ensure that the screw did not break through the cortical bone.A appropriate length of AO cannulated screw with 3.5 mm diameter was choosed to wrest step by step along the guide pin,the screw out from middle-superior third of the lateral mass of atlas.After the simulated operation,anteroposterior and lateral radiographs,computed tomography(CY) scan were taken on all the screwed cadavers.The imformation was measured with E-ruler software to measure the related real angles of the trajetory, screw length on the X-ray,and the distance from the screw to the vertebral artery on the horizontal plane via the transverse process at the lower edge of the axis,the plane of the inferior articular surface of the axis,the transverse foramen of atlas,the topmost point of the vertebral artery groove of the axial on the CT film. SPSS13.0 software was used for analyze the parameters,the statistical data were expressed in mean±standard deviation(±s).Results:1.In the 6 specimens(12 sides),there were 1 side whose vertebral artery groove extended to the internal third of articular surface,8 side to middle third,3 side to lateral third.The screw medial angle of imitating screw fixation on the cadavers was(12.5±0.85)°,the screw superior angle was(50.5±2.88)°.2.The distance between the vertebral artery and screw trajetory was different from the different levels.The smaller distances were on the plane of the superior and inferior margin of the transverse foramen of the axial,and the topmost point of the vertebral artery groove of the axial,but the latter was the smallest[(2.75～5.78)mm].Conclusions:there are intimate relationship between the vertebral artery and screw trajectory of posterior atalanto-axial transarticular screw fixation,but there is a safe distance between the vertebral artery and the screw,as long as preoperative plan is perfect including understanding of the anatomic structure and excluding the existence of anatomic variations of the individual and operating carefully. |
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