Morphometric evaluation of subaxial cervical spine using multi-detector computerized tomography (MD-CT) scan: the consideration for cervical pedicle screws fixation

Abstract

BackgroundCervical pedicle screw (CPS) insertion is a technically demanding procedure. The quantitative understanding of cervical pedicle morphology, especially the narrowest part of cervical pedicle or isthmus, would minimize the risk of catastrophic damage to surrounding neurovascular structures and improve surgical outcome. The aim of this study was to investigate morphology and quantify cortical thickness of the cervical isthmus by using Multi-detector Computerized Tomography (MD-CT) scan.MethodsThe cervical CT scans were performed in 74 patients (37 males and 37 females) with 1-mm slice thickness and then retro-reconstructed into sagittal and coronal planes to measure various cervical parameters as follows: outer pedicle width (OPW), inner pedicle width (IPW), outer pedicle height (OPH), inner pedicle height (IPH), pedicle cortical thickness, pedicle sagittal angle (PSA), and pedicle transverse angle (PTA).ResultsTotal numbers of 740 pedicles were measured in this present study. The mean OPW and IPW significantly increased from C3 to C7 while the mean OPH and IPH of those showed non-significant difference between any measured levels. The medial-lateral cortical thickness was significantly smaller than the superior-inferior one. PTA in the upper cervical spine was significantly wider than the lower ones. The PSA changed from upward inclination at upper cervical spine to the downward inclination at lower cervical spine.ConclusionsThis study has demonstrated that cervical vertebra has relatively small and narrow inner pedicle canal with thick outer pedicle cortex and also shows a variable in pedicle width and inconsistent transverse angle. To enhance the safety of CPS insertion, the entry point and trajectories should be determined individually by using preoperative MD-CT scan and the inner pedicle width should be a key parameter to determine the screw dimensions.

Morphometric Analysis of Sub-axial Cervical Vertebrae and Its Surgical Implications

“…In our present study, pedicle measurements in Indian population were comparable to that reported by Bazaldua CJJ et al,, Vergas-Mena R et al, in Mexican population and Tan SH et al, in Singaporean population [2][3][4]. Other populations: Thai (Chanplakorn P et al,), Egyptian (Eldin MMM), British (Hacker AG et al,), Turkish (Kayalioglu G et al,), (Bozbuga M et al,), (Ugur HC et al,), American (Rao RD et al,), (Ludwig SC et al,) (Ebraheim NA et al,) Stanescu S et al,) presented higher values than ours [5][6][7][8][9][10][11][12][13][14] [Table/ Fig-7]. From the surgical perspective, minute divergence in cervical pedicle dimensions is a constant feature, but in Indian population it may play a decisive role as the size of the pedicle is relatively smaller than other populations.…”

“…We found the mean pedicle transverse angle in Indians to be 44.47 0 ± 2.81. A great disparity of the PTA was noted in different populations: Eldin MMM, Tan SH et al, Chanplakorn P et al, and Ludwig SC et al, reported lower value than ours while Hacker AG et al, Bozbuga M et al, Rao et al, and Stanescu S et al, observed higher values of pedicle transverse angle [4,5,7,[9][10][11][12]14]. As there is no space for the pedicle screws to diverge, preoperative Multi-Detector Computerized Tomography (MD-CT) scans are necessary to individually evaluate, the entry point and trajectories for cervical pedicle screw insertion [5].…”

“…From the surgical perspective, minute divergence in cervical pedicle dimensions is a constant feature, but in Indian population it may play a decisive role as the size of the pedicle is relatively smaller than other populations. In cases of disparity between pedicle and screw length, the pedicle wall may be breached along with infringement of the vertebral canal space [5].…”

In vitro study of accuracy of subaxial cervical pedicle screw insertion using calipers based on the gravity line

“…The superior or inferior vertebral endplate had previously been chosen as the reference line for preoperative measurements, but it is useless during operations due to variations in the spine level, physiological curvature, and operative position[7, 10–12, 15]. The authors recommended the gravity line as a credible reference line to measure the real-time sagittal angle of the pedicle in the lateral fluoroscopic view with free hanging K-wires.…”

“…Moreover, as the entrance and orientation of the pedicle were unique at each cervical level, surgeons are advised to design and insert each CPS individually [8, 9, 12, 29]. …”