OBJECTIVETo explore the best entry point and trajectory of anterior cervical screw in the cervical screw by radiological studies, and provide reference for clincal application.

METHODSFrom January 2008 to December 2010,50 patients were scanned by cervical CT and confirmed no obvious defect of lower cervical spine. Of them, 27 cases were males and 23 were females, ranged the age from 38 to 83 years ( mean 58.5 years). On horizontal axis, the camber angle of C3-C7 anterior lower cervical pedicle of vertebral arch axis (alpha) and distance between (axial length, AL) of anterior cervical pedicle axial line was measured from C3 to C7. Vertebral were divided into four areas, and from measured side of pedicle of vertebral began to record, orderly 1 to 4, the area of pedicle vertebral arch intersert into vertebral were recorded. On sagittal view, the head or tail angle (beta) and length (sagittal length, SL) of anterior cervical pedicle axial line was also measured from C3 to C7. Vertebral were divided into four areas, and from measured side of pedicle of vertebral began to record, orderly 1 to 4, the area of pedicle vertebral arch arch intersert into vertebral were recorded. The above data were statistically analyzed to find the best entry point and trajectory of anterior cervical screw in the cervical screw and insert pedicle screw.

RESULTSThe lateral angle of lower cervical spine was 38 degrees to 45 degrees on transverse plane, C3 to C5 increasing gradually, C5 to C7 decreasing. On sagittal view, C3,C4 pedicle were head tulting, C5 were basic level, C6,C7 were tail. C3 to C5 decreasing gradually, C5 to C7 increasing gradually. C3 to C7 in AL and SL increased gradually. On horizontal axis, the intersection of C3,C4 and C5 were in the second area, the number of C6 in the second and third area were the same, but C7 were in the third area. The intersection in the first and forth area were less. On sagittal view,the intersection of C3,C4 and C5 were in the first area,the number of C6 in third and forth area were less. Six pedicle screws of 3 cases were insert into lower cervical spine, and obtained good effects, no complications occurred.

CONCLUSIONThe best entry point of C3,C4 and C5 were located in the center line and slightly to opposite vertebral body side and upper 1/4 area; C7 were located the vertebral body side and upper 2/4 area; C6 were located between them. The best insertion point were extraversion 38 degrees to 45 degrees, C3 to C5 increased graduallly, C5 to C7 decreased on horizontal axis; On sagittal view, C3,C4 for head 5 degrees to 10 degrees, C5 were basic level, C6,C7 for tail 5 degrees to 10 degrees. The anterior cervical pedicle screw for lower cervial spine is a good and feasible internal fixation.