Novel Method Of Pedicle Screw Insertion For C1 Transpedicle Screw Fixation Technique

Objective This experimental study was designed to provide a safe transpedicular screw trajectory and reduce the risk of pedicle screw placement by changing the entrance points and the insertion angles of transpedicular screws.Methods 30 adult human upper cervical specimens, provided by the department of anatomy from medical colleges, were randomly divided into two groups,group A and group B.The placement of pedicle screw in group A were according to method provided by Ma Xiangyang. (The entry point of C1 pedicle screw was defined as the method of making a vertical line through the midpoint of C2 lateral mass, and the entry point was 3 mm under the cross point of the superior rim of C1 posterior arch with the vertical line. The direction of the screw is approximately 10°in a convergent and about 5°cephalad to the transverse plane). Pedicle screw insertions in group B were in accordance with the new way. (The entry point of C1 pedicle screw was 2mm lateraler than group A. The direction of the screw is approximately 20°in a convergent and 5°in caudal-to-cephalad inclination). C1 pedicle screw insertions according to the above-mentioned methods were finshed by the same person. Thin cut 0.5 mm computed tomography axial cuts were made through the pedicles after pedicle screw insertion.. Measurements of the space available for the transpedicular screw(SAS), the length of transpedicular screw trajectory(LST), outside safe clearance(OSC), inside safe clearance(ISC).|LSC-MSC| and the number of screws which perforated the atlas pedicle in each group were accounted. The datas were statistical analysised by SPSS 13.0.Results SAS in group A ranged from 6.8 to 11.7 mm. SAS in group B ranged from 7.8 to 13.0 mm.SAS-group A and SAS-group B were significantly different(P<0.01;independent samples t test). The mean length of transpedicular screw trajectory(LST) in group A is shorter compared with group B (P<0.01;independent samples t test).The mean smaller safe clearance(SSC) in group A is 2.1±0.1mm,and is 3.0±0.1 mm in group B.The mean |LSC-MSC| in group A is 1.5±0.1mm, and is 0.6±0.1mm in group B,.The number of screws,which perforated the atlas pedicle in both group, are zero.Conclusions 1,We believe that the entry point of the pedicle screw should be located 2mm lateraler from the vertical line through the central point of C2 lateral mass,and about 3mm under the superior rim of C1 posterior arch,the screw insertion angle of C1 transpedicle screw should be close to 20°in a medial inclination and 5°in a cephalad direction.2,SAS according to new method is wider,LST according to new method is longer. The relationship between anatomical landmark and atlas pedicle is constant and anatomical landmark is clear. New method can be used for reference in clinic application.3,New method can take full advantage of the space available for the transpedicular screw(SAS).