| Objective:?1?To measure the parameter A of lumbar isthmus which is the angle between the axis of the pedicle and the lateral margin of the isthmus?2?To measure the parameter D1 of lumbar isthmus which is the straight distance between the tangent line of median wall of pedicle and the lateral border of isthmus?3?To measure the Parameter D2 of lumbar isthmus which is the straight distance between the isthmus lateral tangent and the inferior border of transverse process.A derived parameter D3 is a calculated distance which equal to D2 minus 1mm.?4?According to the requirement of precise anatomy target oriented screw placement theory,pedicle screw can be inserted using the different anatomic landmarks at the different steps safely and effectively.?5?This study aims to evaluate clinical significance of Parameter A,D1,D2,D3 in the clinical application of traditional pedicle screw and cortical bone screw.Methods:Lumbar isthmus parameters were measured in normal lumbar X-ray and cadaveric specimens using computer software and manual operation.Parameter A is the angle between the axis of the pedicle and the lateral margin of the isthmus;Parameter D1 is the distance between the tangent line of median wall of pedicle and the lateral border of isthmus;Parameter D2 is the isometric distance between the isthmus lateral tangent and the inferior border of transverse process.A derived distance D3??equal to D2 minus 1mmwas calculated,and compare the measurememt result between X-ray and cadaveric specimens.Pedicle screw and cortical bone trajectory?CBT?fixations were carried out on six wet?including 3 males and 3 females?lumbar specimens based on our proposed method and measurement result(average on each level of lumbar vertebral from X-ray and cadaveric specimens.The specimens were examined by X-ray and CT to evaluate clinical significance of parameter A,D1,D2,D3 in the clinical application of pedicle screw and cortical bone screw.40 orthopedic surgeons?The rank at least to be chief physician?participated in assessing different distances and angles on questionnaire paper.Different distance of 2,4and 6mm according to our precious anatomy and imaging study on isthmus parameters?D1?D2?D3?,and assess the angles:5,10 and 20 which is the most common used angle degrees in the pedicle and cortical screw placement.Ratio of bias was calculatedYoung surgical resident who had no previous experience in spinal surgery were included in the study.The residents were instructed to place the pedicles on one side of the lumbar pedicle depending on their previous experience and knowledge of the spine surgery without information about the D1value.After they were provided with the average D1 and A value of each vertebra achieved in 25 specimens and 120 radiologic exams,and place pedicle screws on the other side.Accuracy of pedicle screw insertion was evaluated with x-rays and CT scans.Accuracy of screw placement at the sagittal plane was recorded as described by Tang et al.Accuracy of screw placement at the transverse plane was recorded as described by Xu et al.At last,in order to grasp the experience of CBT placement and cherish the limited and expensive wet lumbar specimens.We performed the Cortical bone trajectory?CBT?fixations research on four dry lumbar specimens,and then on the six wet?including 3males and 3 females?and using the new enter point and guiding system.The starting points were determined based on the isthmus tangent point of lumbar,where the x-axis was located D1 from the tangent point to the vertebral midline,and y-axis was located D3up from the x-axis position,and were evaluated for accuracy and safety of screw insertion through naked eyes observation,probe checking,X-ray and CT scans.Result:In the study,parameter A on 25 cadaver specimens is:L1:93±1.1°,L2:94.1±1.1°,L3:97.0±1.8°,L4:99.6±1.7°,L5:104.0±1.9°.In the meanwhile,A value on 120 X-ray films are:L1:92.6±1.1°,L2:93.7±1.5°,L3:97.2±1.8°,L4:99.8±2.2°,L5:103.9±1.3°.From L1to L5?P>0.05?,significant differences were found between different level of cadaveric specimens or X-ray films concerning the parameter A?P>0.05?.The differences in L1,L2and L3 between two genders were not statistically significant?P>0.05?.However,the angles were larger in women than in men in L4 and L5,and the differences were statistically significant?P<0.05?.D1 value on cadaver specimens is:L1:1.92±0.12mm,L2:2.06±0.09mm,L3:3.36±0.24mm,L4:4.38±0.15mm,L5:5.54±0.24mm.In the meanwhile,D1value on X-ray films are:L1:2.1±0.13mm,L2:2.3±0.13mm,L3:3.6±0.33mm,L4:4.4±0.36mm,L5:5.7±0.36mm.Except from L4 vertebra?P>0.05?,significant differences were found between cadaveric specimens and x-ray films concerning the D1 value?P<0.05?.D2 value on cadaver specimens is:L1:4.84±0.86mm,L2:5.98±0.77mm,L3:5.26±0.84mm,L4:3.76±0.40mm,L5:2.20±0.36mm.In the meanwhile,D2value on X-ray films are:L1:5.0±0.83mm,L2:6.19±0.84mm,L3:5.38±0.86mm,L4:3.66±0.42mm,L5:2.30±0.37mm.From L1 to L5?P>0.05?,no significant differences were found between cadaveric specimens and x-ray films concerning the D2 value?P>0.05?.D3 can be calculated based on D2,A derived distance D3?equal to D2 minus 1mm?was calculated,and is therefore a reflection of D2 on statistical analyze.Orthopedic surgeons in our hospital had a 105.5%bias concerning the angle over screw fixation.In the meanwhile,they only had 14.33%bias concerning the distance,which was significantly less than the bias of screw fixation angle.In comparison of estimated and real value,there were no significant differences while estimating the distance of 2mm?P>0.05?,but there were significant differences estimating all the other distance and angles?P<0.05?.Accuracy of screw placement at the sagittal plane was recorded as described by Tang et al.The difference in the deviation rate of screw placement before and after the learning was statistically significant only in the L5 segment.The difference in overall excellent rate was statistically significant?P<0.05?.Accuracy of screw placement at the transverse plane was recorded as described by Xu et al.The result of pedicle screw placement was significantly better after the application of value?excellent rate 86.7%?than before the D value was provided to the residents?excellent rate 37.5%?.The difference in overall excellent rate was statistically significant?P<0.05?.Cortical bone trajectory?CBT?fixations were carried out on six wet?including 3males and 3 females?and 4 dry lumbar specimens using the new system,and were evaluated for accuracy and safety of screw insertion through naked eyes observation,probe checking,X-ray and CT scans.A total of 100 CBTs were evaluated.Among them,7out of the 60 screws in the 6 wet specimens penetrated into the lateral pedicle bone,the successful rate was 88.7%?53/60?;2 out of the 40 screws in the 4 dry specimens,penetrated through the lateral or median pedicle bone,the successful rate was of95%?38/40?.Conclusion:?1?In order to reduce intraoperative radiation to the patients and surgeons,we apply lumbar ismuths parameters such A?D1?D2?D3 values in instrument insertion process,which may increase the accuracy of pedicle screw placement.According to the requirement of precise anatomy target oriented screw placement,pedicle screw can be inserted using those values at the different steps,and it is also a stable and important anatomical characteristic of lumbar spine which is not influenced by patient'operation position and vertebrae rotation.Our data show that the technique is safer,less invasive,and easier to operate and apply between two different instruments system.It would help reduce bleeding,intraoperative X-ray exposure and surgical operation time.?2?Parameter A of lumbar isthmus is the angle between the axis of the pedicle and the lateral margin of the isthmus.On X-ray image and and cadaveric specimens,we can draw a conclusion that the angle increase from L1to L5.The tendency of promoting is not clear at the L1 and L2,but from L3 is significantly evident.So we classify L1and L2 belong to upper lumbar,and L3,L4 and L5 to lower lumbar.At the upper lumbar,we can apply the degree with right angle or little bitter,but at the lower lumbar,we take the angle of100.However,the angles were larger in women than in men in L4 and L5,and the differences were statistically significant?P<0.05?.?3?Parameter D1 of lumbar isthmus is the distance between the targent line of median wall of pedicle and the lateral border of isthmus.It's apparent that D1 value increases gradually from from 2mm of L1 to 5.5mm of L5.An easy way to memorize D1value is that it's 2 millimeters at the L1 and L2,3mm at L3,4mm at L4,and 6mm at L5.According to clinical and anatomical studies,the safe D1 value is 2.5 to 6mm.The value is bigger in male patients than female patients.D1 value should not exceed 5.5mm in female patients and 6mm in male patients,in order to avoid breaking the inner wall of lumbar pedicle.?4?Parameter D2 of isthmus is the isometric distance between the isthmus lateral tangent and the inferior border of transverse process.D2 increases from L1 to L2,and then decreases from L2 to L5.At the upper lumbar of L1 leval,it is 5mm.L2:6mm,but from L3:5mm,L4:4mm,and L5:2mm,the result comparsion between L1 and L3 is similar.?5?Parameter D3 is not a data from measurement,it is calculated from D2?D2-1mm?,and is therefore a function of D2.An easy way to conclude:D3 value is that it's 4millimeters at L1,5mm at L2,4mm at L3,3mm at L4,and 1mm at L5.Compared with the traditional point,the new starting point had the same position on the vertical axis with different anatomical marker,was D3mm over the tangent point of isthmus lateral border,instead of 1mm below the baseline of the inferior border of the transverse process?traditional method?.Since the lateral border is used as reference instead of inferior border,it is more symmetrical on the left and right sides and the tangent points on both sides are basically located on a straight line,making the operation more practical,less invasive and more convenient,and meet the aesthetic requirements of doctor and patients on operation.?6?It is easy to drive the conclusion that the insertion angle of screw can be decided by doctor more accurately by relying on the distance rather than estimating degree of angle rigidly.Controlling the track of pedicle screw requires the application of a certain set of anatomic parameters at the beginning,during and at the end of screw placement process to keep the screw on its expected course accurately and safely,and unlikely to damage the nerve roots and vessels,induce operation complications.?7?Traditional pedicle screws are inserted sagittal plane according to the angle between the axis of the pedicle and the lateral margin of the isthmus,and the horizontal plane based on the parameter D1 which is the distance between the tangent line of median wall of pedicle and the lateral border of isthmus.The original angle at the insertion point should not exceed line of 1/2 D1 median to the lateral edge of pedicle;The target location for pedicle screw is at the middle line of spinous process and lateral edge of isthmus.?8?The aim of this study was to conduct a morphometric measurement of lumbar isthmus to develop the new reference system for CBT.The novel starting points of CBT were determined by parameter D1and D3 based on our proposed method,where the x-axis was located D1 from the tangent point to the vertebral midline,and Y-axis was located D3up from the X-axis position.CBT screws are inserted cephalad angle according to inferior border of spinal process,and the end of screw touch closely to the spine process controlling the outward angle from the horizontal plane.The intermediate and final target location for screw insertion is the intersection of accessory process with lateral edge of isthmus,and the the caudal end of the accessory process.When placing the screw during operation,operator should observe planes acrossing such targets mentioned above which being parallel to the lateral edge of isthmus.Thus the surgeon just like a marksman should target the head of the pedicle screw towards the different anatomy landmarks or its projection lines precisely during screw placement. |
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