A Reaserch For Individual Pedicle Screw Placement In C3～C6 Assisted By CT Imaging

Objective: Making certain the relationship between manual measurement and CT measurement by making statistic analysis of both values, learning about the accuracy of projecting points of pedicle on lateral mass determined by CT imaging and angle of vertebral pedicle—inferior facet(AOPF), so as to provide theory reference for individual pedicle screw placement in C3～C6.Method: 8 human adult cadaver cervical specimens containing C3 to C6 vertebrae were measured by two methods, one was manual measuring using caliper and the other was computed tomography scaning. Parameters measured included pedical width (PW), pedical height (PH). These specimens were scanned by CT scanner both perpendicularly and parallelly to the pedicle axis. Measured respective distance of projecting point to superior articular process bottom and to inferior articular process inferior border by lateral CT scanning (defining X line), obtained the distance from projecting point to ourest border of lateral mass by transverse CT scanning (defining Y line). Located two lines in specimen lateral mass on the basis of X line value and Y line value measured from CT imagings. Projecting point of vertebral pedicle (PPOP) on lateral mass was crossing point (point O) of the two lines. Used open device to check the projecting point determined by above method under dicrct vision. Gained value of total pedicle length and AOPF of C3～C6 through CT mearement and manual measurement respectively.Result: There was no statistic difference between the data of pedicle width and height of 8 cadaver speimens obtained from manual and CT measuments individually, with a more value of height than width. Via the entrypoint determined by CT imagings, all of 64 pedicles could be passed through successfully by open device utill into vertebral body without breaking pedicle walls. Polyaxial 3.0mm screws were used to simulate inserting into all 64 pedicles under direct vision, and 53 screws(82.8%) were well contained inside the pedicles while 11 screws with various degrees of pedicle breaches. The average total length of pedicle was 3.16cm at C3, 3.28cm at C4, 3.35cm at C5, and 3.48cm at C6 respectively. Angle of vertebral pedicle—inferior facet(AOPF)was about 23°at C3-C4,35°at C5, 45°at C6 respectively. There was no significant difference between parameters of left and right for each level.Conclusion: CT measurement can exactly reflect the real anatomical pamameters of cervical spine specimens and provide reliable data reference for cervical pedical screw placement. The projecting point of vertebral pedicle (PPOP) on lateral mass determined by CT imaging is in accord with real one. Sucess of pedicle screws placement is closely related to accurate location of entry points and angles, as well as appropriate screw diameter and length. Angle of vertebal pedicle—inferior facet(AOPF)varys from segment to segment of a unity, increasing gradually from C3 to C6.