Morphological analysis for subaxial cervical pedicle screw insertion in developmental and non-developmental canal stenosis

Abstract

Background: This study aimed to evaluate the safety and feasibility of subaxial cervical pedicle screw (CPS) insertion by comparing the morphological parameters between developmental canal stenosis (DCS) and non-developmental canal stenosis (NDCS) patients.

Methods: A total of 120 Chinese patients who had undergone cervical spinal multiplanar CT imaging from September 2010 to December 2014 were included in this study. According to the Pavlov ratio (PR), participants were classified into a DCS group (PR < 0.82) and an NDCS group (PR ≥0.82). CT reconstruction images of the cervical pedicles from C3 to C7 were selected for further analysis, and detailed morphological parameters for subaxial CPS insertion including pedicle outer width (POW), tiny cervical pedicle (TCP), pedicle transverse angle (PTA), and range of safe angle (RSA) were measured and compared in these two groups.

Results: A total of 600 images (1200 pedicles) from these 120 patients were measured. The POW in the DCS group was wider than that in the NDCS group at each level, while the number of TCPs in the DCS group was significantly less than that in the NDCS group at the C3, C4, and C5 vertebrae. There was no significant difference in PTA at any level between the two groups, however the RSA in the DCS group was greater than that in the NDCS group from C4 to C7.

Conclusions: Subaxial CPS for DCS patients may be safer and more feasible than that for NDCS patients. However, as the subaxial cervical pedicle is relatively small, CPS insertion is difficult and preoperative CT evaluation is recommended for both DCS and NDCS patients.

Keywords: Computed tomography; Developmental canal stenosis; Parameter; Pedicle morphology; Pedicle screw; Subaxial cervical spine.

Fig. 1

Measurement of the Pavlov ratio on lateral radiography. VD indicated the vertebral diameters, namely, the cervical sagittal diameter of the vertebral body at the midpoint; CD, the canal diameter, namely, the sagittal diameter of the spinal canal from the posterior surface of the vertebral body to the nearest point of the corresponding spinal laminar line. The Pavlov ratio was determined with the formula CD/VD in every level [18]

Fig. 2

Measurement of pedicle outer width (POW) on transverse reconstruction images of computed tomography. POW indicated the mediolateral diameter of the pedicle isthmus, perpendicular to the pedicle axis

Fig. 3

Measurement of pedicle transverse angle (PTA). PTA indicated the angle between the pedicle axis and the midline of the vertebral body

Fig. 4

Measurement of range of safe angle (RSA). RSA indicated the difference of the Max TA and the Min TA, namely, the intersection angle between EI and EO. EI was the line crossing the entry point (E) and the inner cortex in the pedicle isthmus. EO was the line crossing the point E and the outer cortex in the pedicle isthmus. The point E was the crossing point of the pedicle axis and the surface cortex of the pedicle. The Max TA was the angle between the line EI and the midline of the vertebral body. The Min TA was the angle between the line EO and the midline of the vertebral body (The diameter of pedicle screw was neglected)

Fig. 5

POW in the DCS and NDCS groups. POW indicated pedicle outer width; DCS, developmental canal stenosis; NDCS, non-developmental canal stenosis

Fig. 6

TCP in the DCS and NDCS groups. TCP indicated tiny cervical pedicle of POW less than 4 mm

Fig. 7

PTA in the DCS and NDCS groups. PTA indicated pedicle transverse angle

Fig. 8

RSA in the DCS and NDCS groups. RSA indicated range of safe angle