Anatomic and radiographic measurement for related parameters in term of lower cervical pedicle screw fixation

Objective:To measure the dimensions of the lower cervical pedicle so as to provide anatomic data for clinical application of cervical pedicle screw fixation.Method:20 human adult cadaver cervical specimens containing C3 to C7 vertebrae were measured by two methods,one was manual measuring using digital caliper and the other was computed tomography scaning.Parameters measured manually included pedicle width(PW),pedicle height(PH).These specimens were scanned by CT scanner both perpendicular and parallel to the pedicle axis.The outer and inner pedicle width and height,cephalocaudad angulation of the pedicles in the sagittal plane were measured using automatic digital CT measurements.Additionally,cervical pedicle width and length,transverse angle(TA) of 100 patients' CT scans of C3-C7 cervical segment were measured.Result:There was no statistic difference between the data of pedicle width and height of 20 cadaver specimens obtained from manual and CT measurements individually.At C3-C6,the average internal pedicle width(IPW) ranged from 2.5 to 2.8mm,and the average internal pedicle height(IPH) ranged from 2.9 to 3.0mm.At C7,the IPW and IPH was approximately 4.0mm.The pedicle sagittal angel(SA) was 8.6° at C3,4.6° at C4,-1.3° at C5,-4.0° at C6,and-8.2° at C7 respectively.Based on the CT measurements of 100 patients,the data of the pedicle width varied from a minimum of 3.1mm for the C3 pedicle,to a maximum of 9.3mm for the C7 pedicle,and in 92.8% cases,the pedicle width was larger than 3.5mm.Pedicle length(PL) was about 19.1 20.5mm,and total length(TL) of pedicle path was about 33.2-35.0mm.The pedicle TA was about 43.2°-45.1° at C3-C5,40.8° at C6,and 37.5° at C7 respectively.Conclusion:CT measurement can provide valuable data for cervical pedicle screw placement and lower cervical pedicle can hold screw with 3.5mm diameter.