Anterior pedicle screw insertion for low cervical spine：anatomical observation

Abstract:

Objective：To observe the pathlines and angles related to lower cervical spine anterior pedicle screw（APS） fixation in adults so as to provide anatomical parameters in clinics. Methods：A total of 22 cervical spine（C3-C7） specimens of human adult cadavers were individually measured by hand and CT scan to determine the height and width of the narrowest part in pedicle，thickness of inner and outer cortexes，pedicle axis length and included angle of axes followed by statistical methods. One hundred pieces of CT images from CT database were randomly selected，then three-dimensional model reconstruction was performed by Mimics software，relative parameters of screw insertion point were measured and 95% confidence interval of screw insertion parameters was also calcu－lated. Results：No significant difference of pathlines and angles measurements of 22 specimens was found between manual work group and CT scan group. Based on the calculation of measurements of adult lower cervical spines in CT images with 95% confidence inter－val，the insertion points for C3 and C4 was 2-3 mm opposite from operated pedicle in centrum median plane and 6-7 mm from upper end-plate of centrum plane，the outside inclined angle of screw insertion was 46°- 48°. Cranially inclined angles for C3 and C4 were -11°--12° and -6°--7° respectively. The insertion point for C5 was 1-2 mm beside operated pedicle in centrum median plane and 7-8 mm from upper end-plate of centrum plane，the outside and cranially inclined angles of screw insertion were 47°- 49° and 1°-2° respectively. The insertion points for C6 and C7 were at the same side with operated pedicle，4-5 mm beside centrum median plane and 7.5-8.5 mm from upper end-plate of centrum plane. The outside inclined angles of screw insertion for C6 and C7 were 40°- 42° and 36°-38° respectively，cranially inclined angles were 6°-7° and 11°-13°. For insertion screws，the length should be 30 mm，32 mm or 34 mm and the diameter should be 3.5 mm or 4.0 mm. Conclusions：This study confirms the accuracy of CT scan in the measurement of lower cervical spine and APS fixation related parameters and makes an exploration in technical range of parameters for the first time in the country using a large sample.