Computed tomography measurement of the bone matrix of vertebral pedicle and its clinical significance

Abstract

Background: To provide the anatomic basis for the clinical application of the transpedicular screw fixation. Materials and methods: Thirty spine (C 2-L 5) specimens were used. The width of the pedicle cortex and width of the pedicle medullary cavity (WPC and WPMC), and the height of the pedicle cortex and height of the pedicle medullary cavity (HPC and HPMC) were measured at the isthmus of the pedicle using computed tomography (CT) scanning. Results: Width of the pedicle medullary cavity changed in a three-dovetailed-saddle shape with four peaks and three valleys, namely C 2 (high), C 4`5 (low), T 2 (high), T 4 (the lowest), T 12 (high), L 1 (low) and L 5 (the highest). HPMC of the cervical pedicle changed in a saddle shape, gradually increasing from C 5-L 5. WPC, WPMC, HPC and HPMC showed a regular change, respectively. In each segment, the superior border of the pedicle cortex had a nearly consistent thickness to the interior border within an identical pedicle, while the pedicle cortex thickness radio of the medial and lateral border was nearly 3:1 among the cervical pedicles, 2:1 among thoracic pedicles, and 1:1 among lumbar pedicles. Conclusions: Both HPMC and WPMC are the dominant factors for the choice of screw diameter, but HPMC should also be considered in C 2-T 1 pedicles, especially C 6 and C 7. Additionally, the screw for C 3-6 or T 4-6 pedicles should be about 3.0 mm in diameter.

Modified Tap-drilling Technique for Mid-cervical Pedicle Screw Placement

“…In studies evaluating pedicle diameters, many find the C4 pedicle diameter is wider than the C3 pedicle diameter, 14,15,18,28 and many find the C3 pedicle diameter to be larger than the C4 pedicle diameter 17,19 . However, almost all studies examining the medial pedicle angle found the C4 medial angle to be greater than the C3 medial angle 7,12,14,15,17,18,28,29 .…”

“…In studies evaluating pedicle diameters, many find the C4 pedicle diameter is wider than the C3 pedicle diameter, 14,15,18,28 and many find the C3 pedicle diameter to be larger than the C4 pedicle diameter. 17,19 However, almost all studies examining the medial pedicle angle found the C4 medial angle to be greater than the C3 medial angle. 7,12,14,15,17,18,28,29 Although the lateral devi- ation of C4 pedicle screws is higher than that of C3 screws, the lack of a difference between the medial deviations suggests that the high rate of deviation in C4 pedicle screws is due to the wide medial angle of the pedicles rather than their thinness.…”

“…[5][6][7][8][9][10][11] Several insertion techniques have been described to improve the cervical pedicle screw placement accuracy, including the notch-referred technique, 12 contralateral lamina-referred technique, 13 laminoforaminotomy technique, 2,14,15 funnel technique, 16 computer-assisted navigation techniques, 17,18 and patient-specific screw guide template technique. 19 Jeanneret, the author of one of the first 2 articles describing cervical pedicle screw fixation in 1994, also described the tap-drilling method and laminoforaminotomy used for screw placement in the same article. 2 Cervical pedicle screw placement accuracy was significantly varied in these techniques.…”