Computed tomographic analysis of cervical spine pedicles in the adult Indian population.

BACKGROUND: Cervical pedicle screw insertion is a technically demanding procedure that carries the risk of catastrophic damage to surrounding neurovascular structures. Here, we analyzed computed tomography (CT)-based three-dimensional cervical spine pedicle geometry to determine the level and sex-specific morphologic differences in the adult Indian population.
METHODS: The CT scans of 200 patients (2400 pedicles) without significant cervical spine pathology were collected. The mean pedicle width (PW), pedicle height (PH), pedicle axial length (PAL), and pedicle transverse angle (PTA) from C2 to C7 were measured.
RESULTS: The smallest mean PW was at C3 in both males (4.85 ± 0.73 mm) and females (4.31 ± 0.43 mm); 7.08% of all pedicles were found to have mean PW of <4 mm. The smallest mean PH was at C5 in both males (6.25 ± 0.67mm) and females (5.54 ± 0.52 mm). The smallest mean PAL was at C2 in both males (27.46 ± 1.69mm) and females (25.90 ± 1.88 mm). The mean PW, PH, and PAL were significantly greater in males than females at all levels (P < 0.05). The smallest mean PTA was at C3 in males (41.79 ± 2.53°) and at C7 in females (42.40 ± 2.27°).
CONCLUSION: In the adult Indian population, the PW, PH and PAL were smaller than in the typical western population. Females had even smaller PW, PH and PAL as compared to males. We recommend that a small inventory of 3.5mm screws between 20mm to 30mm length be used in most cases where cervical pedicle screws are being used in the Indian population. However, individual vertebrae should be screened preoperatively with CT scans to exclude gross anatomical variations, especially in females and at the C3 and C4 levels. Copyright:

INTRODUCTION

Cervical spine fixation is needed in various conditions affecting spine, but there is considerable variability in cervical spine pedicle dimensions at each level.[1,2] Here, we have provided a three-dimensional (3D) computed tomography (CT)-based understanding of cervical pedicle morphology at different spinal levels to minimize the risk of neurovascular injury and improve outcomes for instrumented cervical pedicle screw fixations.

MATERIALS AND METHODS

With Institutional Review Board approval, we performed this prospective, observational, and single center study (2015–2017). Utilizing 3D-CT scans (using C2-C7 with 0.6mm cuts), we measured 2400 cervical spine pedicles from 200 patients. The study included 148 males and 52 females averaging 31.32 years of age (range 18-45 years). There were multiple exclusion criteria [Table 1].

Table 1:

Inclusion and exclusion criteria of the study.

3D-CT images (read by one Orthopedician and one Radiologist) were utilized to measure pedicle width (PW), pedicle height (PH), pedicle axial length (PAL), and pedicle transverse angle (PTA) [Figures 1-4 and Table 2].[7-10]

Figure 1:

Pedicle width (PW) was defined as the narrowest part of pedicle in the axial cut section between medial border of transverse foramen and medial border of pedicle on either side. Measurement was done in mid-pedicle axial CT section of cervical vertebra.

Figure 4:

Pedicle height was defined as the narrowest part of pedicle in sagittal plane between upper and lower pedicle surface on either side. Measurement was done in sagittal CT section of cervical vertebra.

Table 2:

Overall mean of PW, PH, PAL, and PTA of cervical spine pedicles from C2-C7 vertebral level.

Pedicle axial length was defined as the distance from anterior vertebral body wall to posterior margin of lateral mass along the long axis of pedicle. Measurement was done in midpedicle axial CT section of cervical vertebra.

Pedicle transverse angle was defined as the angle formed between mid-sagittal line and pedicle axis. Measurement was done in mid-pedicle axial CT section of cervical vertebra.

Statistical analysis

Descriptive statistics (mean, standard deviation) were determined. Intra-class Correlation Coefficient (ICC) was calculated to find inter-observer agreement and to analyze intra-observer agreement paired t-test (95% confidence level) was performed. To identify difference between males and females, right and left side, an independent sample t-test and paired t-test, respectively, with 95% confidence level were performed.

RESULTS

In our observations, we found that there was no significant difference between two measurements that were taken by same observer and also inter-observer agreement was very good for measurement of PW (ICC 0.95), PH (ICC 0.91), PAL (ICC 0.94), and PTA (ICC 0.92), at all cervical vertebral levels.

PW

The smallest mean PW was at C3 and largest mean PW was at C7 in both males and females while the mean PW for males was statistically significantly greater than females at all level from C2 to C7. Furthermore, noted that the mean PW for right side was greater than left side at all level from C2 to C7 (statistically significant at C3- C6) [Table 3]. About 7.08% of all pedicles were found to have mean PW of <4 mm [Table 4].

Table 3:

The mean pedicle width in males and females, also at right and left side from C2 to C7 vertebral level.

Table 4:

Distribution of pedicles at each vertebral level from C2-C7 that have pedicle width <3 mm, <4 mm, and <5 mm.

PH

The smallest mean PH was at C5 and largest at C2 in both males and females. At all levels PH was greater than PW. The mean PH for males was statistically significantly greater than females at all level from C2 to C7 [Table 5].

Table 5:

The mean pedicle height in males and females, also at right and left side from C2 to C7 vertebral level.

PAL

The smallest mean PAL was at C2 in both males (27.46 ± 1.69 mm) and females (25.90 ± 1.88 mm), while the largest mean PAL was at C7 in males (32.94 ± 1.87 mm) and C6 in females (30.35 ± 1.66 mm) [Table 6].

Table 6:

The mean pedicle axial length (PAL) in males and females, also at right and left side from C2 to C7 vertebral level.

PTA

The smallest mean PTA was at C3 in males (41.79 ± 2.53°) and at C7 in females (42.40 ± 2.27°), while the largest mean PTA was at C2 in males (44.74 ± 3.15º) and at C5 in females (45.29 ± 2.75°) [Table 7].

Table 7:

The mean pedicle transverse angle in males and females, also at right and left side from C2 to C7 vertebral level.

DISCUSSION

Cervical pedicle screw fixation is technically demanding procedure as it has risk of injury to the surrounding neurovascular structures. Munusamy et al.[5] found significant sex and ethnic variability in cervical pedicle sizes and recommended that preoperative CT scans and image-guided screw placement be utilized to ensure safety and accuracy for cervical pedicle screw placement. Here, we determined that the mean PW was smallest at C3 and largest at C7 in adult Indian male and female patients, this is similar to findings in previous studies [Tables 8 and 9].[2,4,5,8,9]

Table 8:

Comparison of PW, PH, PAL, and PTA in males of present and previous studies at C2-C7 vertebral level.

Table 9:

Comparison of PW, PH, PAL, and PTA in females of present and previous studies at C2-C7 vertebral level.

We also found that PW progressively increased for both males and females from C3 to C7, a finding also echoed to prior Indian studies.[3,6] In our study, the mean PH of males was greater than females at all levels from C2 to C7 which is similar to previous reports [Tables 8 and 9].[2,4,5,8,9] Further, we also noted that in Indian adult females, 23.07% at C3 and 15.38% at C4 had mean PW <4 mm.

Based on our finding regarding 3D-CT confirmation of pedicle size in Indian adults, we would recommend that 3.5 mm screws be utilized from the C2 to C7 levels, although 7.08% of pedicles would likely not suitable for such 3.5/4 mm screws.

Further, since we observed, the mean PAL for Indian patients fell within a narrow range of 25.90mm to 32.94 mm from C2 to C7 which is smaller than American population (range from 28.9 mm to 34.3 mm) and similar to Chinese population (range from 27.9mm to 32.5mm), a small inventory of screw lengths ranging from 20 mm to 30 mm should be kept on hand [Tables 8 and 9].

The mean PTA in our study was within a narrow range of 41.79° to 45.29°. Therefore, a rough guideline for angle could be around 40-45° from midline.

CONCLUSION

Having performed a 3D CT analysis of cervical pedicle morphometry (including PW, PH, PAL, and PTA) in the adult Indian population, we determined that 3.5 mm screws between 20 mm to 30 mm length would usually be sufficient in most cases requiring posterior cervical instrumented fusion.