| ObjectivesTo study the feasibility of screw placement strategies and the technique of axis quadricortical pedicle screw,and to test anti axial pullout strength of axis quadricortical pedicle screw and axis pedicle screws,make clear whether there is statistical difference between the biomechanical strength of these two kinds of screws,the main research purposes are as follows:1.Oberseve the MRI imaging data of axis pedicle level,evaluate the space between the spinal cord and axis pedicle and the space between dura matter and axis pedicle,to explore the feasibility of screw placement strategy and the technique of axis quadricortical pedicle screw.2.To compare the biomechanics difference between axis quadricortical pedicle screw and axis pedicle screw,and provide theoretical basis for reasonable clinical choice of the posterior axis quadricortical pedicle screw.Materials and methodsPart one49 males and 43 females with normal cervical spine were selected.At the C2 pedicle level of MRI images,we marked the tangent of pedicle medial wall(TPMW)which was parallel with central axis of C2 pedicle,and measured the distance between the tangent and spinal cord(TSC)and the distance between the tangent and dura mater(TDM).The tangent of C2 spinal canal medial wall(TSCMW)which was parallel with sagittal axis of C2 was marked,and we measured the distance between the tangent and spinal cord and the distance between the tangent and dura mater.We also measured spinal cord transverse diameter(L1)and anteroposterior diameter(L2),spinal canal transverse diameter(L3)and anteroposterior diameter(L4).Both sides of the axis were measured;each data was measured 3 times by two physicians and take the average as the standard value,all parameters are measurement data.It was recorded as mean+/-SD,the data were analyzed by SPSS19.0 statistical software,comparison between male and female was conducted with independent sample t-test.The independent sample t test were conducted in comparing with bilateral parameters of male and female,P=0.05.Part two6 fresh cervical spine specimens were selected,but specimens with atlantoaxial dislocation,basilar impression,and other diseases which affect the spinal cord and spinal canal anatomy structure were excluded.Before operation,we should remove the muscle and other soft tissue attached to the bone,and expose the C2 spinous process,laminar and inferior facet process of axis clearly.According to the results of imaging measurement,on one side of the axis,standard C2 pedicle screw is inserted,and we should make the screw tip break through the anterior cortex of axis.On the other side of the axis,axis quadricortical pedicle screw is inserted;we also make the screw tip break through the anterior cortex of axis.We perform the same operation on other specimens,The strength of the axial pulling out strength of bilateral pedicle screws was tested in the biomechanics test machine,compare the axial pulling force of two kinds of screw,and make clear whether they have statistical difference.All the parameters are measurement data,It is recorded as mean+/-SD,the data were analyzed by SPSS19.0 statistical software,the bilateral data were compared by means of paired samples t-tests,P=0.05.Results Radiological measurement results:There was no significant difference in age between male and female.The spinal cord transverse diameter of male and female were 12.47 mm and 12.05 mm,the anteriorposterior diameter of the spinal cord was 8.38 mm and 7.91 mm;spinal canal transverse diameter were 26.26 mm and 24.96 mm,and the anteriorposterior diameter of the spinal canal was 17.38 mm and 16.50 mm.There were no significant differences between male and female about the above parameters.The ratio of spinal cord transverse diameter and spinal canal transverse diameter was 0.48 in male and female,the ratio of spinal cord transverse diameter and spinal canal transverse diameter was 0.49 in male,0.48 in female.There was no significant difference between male and female about above parameters mentioned(table 1).Statistical analysis showed that there was no significant difference about the parameters between the two axis sides of the same sex,so the mean value was calculated after the bilateral parameters were combined.The parameters of male and female were statistically different except the distance between TDM and TSCMW,and the distance between TDM and TPMW,but the average difference was less than 0.5 mm,the distance between TPMW and TSC was more than 5 mm about male,and that parameter about female was more than 6 mm;the distance between TPMW and TDM was more than 4 mm in 87.8% male,and this parameter of 73.3% female was more than 4 mm.The distance between TSCMW and TSC was more than 5 mm in 99% male,and this parameter of 97.7% female was more than 5 mm.The distance between TDM and TSCMW was more than 4 mm in 11.22% male,the parameter of 72.4% males was more than 3 mm,the distance between TDM and TSCMW was more than 4 mm in 8.1% male,the parameter of 67.4% males was more than 3 mm.Biomechanical test results:The pullout strength of bilateral pedicle screw is(1506.67±478.345)N(914 N~1964N),the pullout strength of quadricortical pedicle screw is(1393.33±252.350)N(1139 N~1755N).Paired samples t test showed that there was no statistical difference between the two groups(t=0.455,p=0.668).Conclusions1.At the level of the axis pedicle,there was safe space between spinal cord and TPMW,the screw placement strategy and the technique of axis quadricortical pedicle screw is feasible.Because of the larger distance between the spinal cord and TPMW,if we insert the screw close to the axis pedicle,the screw has large adjustment space,but it is difficult to control the screw angle.Because the distance between the spinal cord and the medial wall of spinal canal is relatively small,if we make the screw perpendicular to the sagittal plane of axis,it is difficult to control the screw angle,but the screw has small adjustment space,and there is greater risk of injury to the spinal cord and dura mater.At the C2 level,the space between the C2 spinal canal medial wall and dura mater was safe for C2 quadricortical pedicle screw;However,there were individual differences among patients.Therefore,different screw placement strategies should be applied based on different situations.2.C2 quadricortical pedicle screw is an alternative method of C2 pedicle screw,but it should be strict select cases before surgery to avoid serious complications of spinal cord injury. |
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