| Objective: Observation and measurement were done on the atlantaloaxial joint to get the parameters of posterior transarticular screw fixation.It can be helped to give scientific evidence of clinical treatment,and reduce the relative complications. Method:50 matched normal adult and dry atlantoaxial bone speciments of Chinese were elected firstly. It were used to observe the upper articular surface and the transverse foramina of the axes, and were used to determine the screw insertion point in completely anatomic reduction. Direct measurement were taken to the width and the height of the pedicle and the upper articular surface of the axes ,and the corresponding screw path length and all kinds of the angles of screw insertion. The sagittal dimention and the coronary dimention on the superior surface and the inferior surface of the transverse foramina of the axes also were measured. All of the parameters can be used to understand the factors which can effect the correctly placement of the screw insertion. Results: 1 It is the feature of the upper articular surface of the axis that is relatively symmetry to both sides , looks slightly apophysis, appers slant towards external side. It makes an angle of 110-120° with sagittal plane. It also in parallel with horizontal plane. 2 The shapes of the axis transverse foramina were variable. The impress of the road of spinal artery makes it looks like hang in the air. 3 When the joint surface completly anatomic reduction,it can be found out that it was suitable for elect the position consider as the screw insertion point which is upper 3 milimeter to posterior edge of the inferior joint surface,and which was outward 3 milimeter to external edge of the lateral joint. 4 The upper width,medium width ,down width and height of the pedical of C2 was(6.73±1.42)mm,(6.68±1.21)mm, (4.35±1.03)mm, (7.93±1.15)mm.The width of the one third posterior to the upper joint surface,the sagittal dimention of the upper joint surface and the angle of slant towards external of the upper joint surface was(14.86±1.15)mm, (17.22±1.24)mm,(28.31±3.30)°.The maximum angle of the screw insertion,the optimum angle ,the lower limit angle, the minimum angle,the angle of the slant towards internal and the length of the screw path was(54.45±3.15)°,(44.67±2.66)°,(33.18±4.25)°,(26.80±3.98)°,(10.10±0.44)°, (36.86±2.74)mm. The sagittal dimention and the coronary dimention on the superior surface was(6.85±1.09)mm, (6.35±0.97)mm. The sagittal dimention and the coronary dimention on the inferior surface was (6.73±0.94)mm, (6.13±0.86)mm。 Conclusion: According to the view of the clinical anatomy, transarticular screw fixation in Chinese population is close related to the anatomic structure. 1 All of the patients who are suitable to the operation must get to completely anatomic reduction of the atlantoaxis in order to guarantee the properly screw position and can get rid of vertebral artery injury. 2 It was suitable to elect the marked point for screw insertion which is upper 3 milimeter to posterior edge of the inferior joint surface,and which is outward 3 milimeter to external edge of the lateral joint. 3 The angle for screw insertion has a range which can be adjusted. In view of the down width of the pedicle of the axes are relatively thinner than medium width and upper width,it shoud be selected that the optimum angle(average 45°)and the angle of the slant towards internal(average 10°)ought to be considered as the reference criteria. 4 The length of the screw shoud be concluded by the heli computer tomography before orperation and by the conclusion of the C-arm in orperation. 5 Because of the variation of the transverse foramina are bigger,it mentioned that blind operation must be prohibited in order to avoid vertebral artery injury. 6 Individual diversity,sex diversity and both sides diversity must be considered before operation, and the date of imagine must be carefurly analysized in order to master the variation of the pedical of the axes, the transverse foramina, the vertebral arter... |
