Safety Study On Free Hand Placement Of Atlantoaxial Pedicle Screw Fixation

Objective:To provid reference data for the clinical use of free hand placement of atlanto-axial pedicle screw by measuring anatomy parameters of atlanto-axial in CT data of upper cervical lesions patients,and to investigate the feasibility and safety of bare-handed fixation of cervicalpedicle screws.Methods:The atlanto-axial parameters of 50 cases who was admitted from 2007 to 2014 included vertica and transverse diameter of pedicle, upward and inward angel,biggest upward angle, biggest inward angel and optimal inward angle, the maximum distance between axial transverse foramen to the vertebral artery and ideal inward angle of axis were measured by CT scanning and application of MPR and Inspace software, and to understand course and variation of the vertebral artery.The surgical technique was used by free hand atlanto-axial vertebral pedicle screw placement. The specific exposed procedures included intubation anesthesia, longitudinal incision in the middle of cervical vertebra rear, cutting the skin, subcutaneous and fascia in turn, exposing along the white line, subperiosteal dissecting the paraspinal muscles along both sides of cervical spinous process. The scope of exposure that need to protect the venous plexus, vertebral artery and cervical nerve root in atlas and axis were 20 mm outward of posterior tubercle of atlas and lateral margin of the facet of axis, respectively. The position of placement screw in atlas and axis were the horizontal intersection between the sagittal extensive line of atlas superior articular process midpoint in atlas and the centre point of axis, respectively. The suitable polyaxial pedicle screw whose length was selected according to CT data and diameter is 3.5 mm was placed,then connection reset bar, reduction and fixation, flushing, hemostatic, placed drainage tube, closing wounds s was perfomed step by step.Results: 1.Atlanto-axial pedicle CT measurement results revealed that the vertical and transverse diameters, upwar angle and inward angle and pedicle length in atlas were(4.45 ±0.56) mm and(8.76±0.73)mm,(7.77±0.62) oand(9.13±0.46) oand(27.88±1.23) mm, respectively, those parameters in axis were(5.09±0.43) mm and(6.62±0.46) mm,(40.02±1.25) o and(28.43±0.97) o and(26.64± 0.85) mm. 2.The range of inward angle of atlantal pedicle screw were(7.1-9.5)°、(7.0-9.4)°, and the maximum distances from atlantal to transverse foramen the screw were 4.6mmand 4.3mm respectively,when the screw was maximal and minimum inward angle. 3.A total of 7cases of atlas was observed vertebral artery sulcus ring variation, the incidence was 14.00%. These cases included mutation of posterior ring in 6 cases,which accounted for 85.14% of the total variation rate. Type I, II, III, IV mutation of posterior ring rates were 2.00%, 1.00%, 1.00% and 2.00%, respectively,and mutation of lateral ring rate was 1.00%. 4. According to the measurements, the atlantal pedicle screw were longest as 10o of inward angle, left and right sides were(27.46±1.75)mm and(27.45±1.78) mm, respectively. Compared with 0°,5 °, 15 °, the length of screw had no significant difference(P > 0.05). 5.The results based on the distances from entry point of different inward angle to posterior midline showed the distance from the bilateral enter point of atlantal pedicle screw to posterior midline presented an increasing trend from 0°to 15°. At the same angle,the distance had no significant diference(P > 0.05),while the distance had statistical differences at different angle(P < 0. 05). 6.The results of 1-year follow-up showed that all of patients recovered well, without screw loose and deformation, and clinical effect of 96% patients was signifcannt, and the accuracy rate of placement screw was 97.5%.Conclusion:The preoperative observation and measurement of CT imaging can provide the necessary reference and guidance for accurate placement of atlanto-axial pedicle screws, which can ultimately improve the safety and effectiveness of free hand placement of atlanto-axial pedicle screw. The satisfactory curative effect can be achieved in surgical treatmen of upper cervical lesions patients. This technique was worth to extensive application and promotion.