A Cross-sectional Study of Third to Seventh Cervical Vertebral Bodies, Pedicles, and Its Relevance to Screw Size Used in Clinical Practice

Abstract

Introduction: To provide stability to the unstable cervical spine, the usage of transpedicular screws is very common due to their success in providing good results in terms of fixation, stability, and strength. The size of the transpedicular screw used must be in accordance with the morphology of the pedicle of the vertebra in a particular region or group of the population. This helps avoid pedicle wall damage along with nearby neurovascular structures. Aim: The aim of the present study was to measure the body and pedicle of cervical vertebrae (third to the seventh) and to understand their morphology in relation to the need for a uniform screw size. Materials and Methods: A cross-sectional study was conducted from May 2019 to March 2023, using a total sample of 102 adult human dry cervical vertebrae collected from the bone bank of the Anatomy Department at the Himalayan Institute of Medical Sciences, SRHU, Dehradun. Only cervical vertebrae from the third to the seventh were included. Digital vernier calipers were used to measure the parameters, including the Transverse Diameter (TD), Anteroposterior Diameter (APD), and Vertical Height (VH) of the vertebral body, as well as the Pedicle Width (PW), Pedicle Height (PH), and Pedicle Length (PL) of the pedicle. Statistical analysis was performed using Microsoft® Excel® 2019 MSO (Version 2209 Build 16.0.15629.20200) 64-bit software (Microsoft Office Home and Student 2019, Washington, USA). The parameters of the right and left sides of the pedicle (PW, PH, PL) were compared using the student’s t-test, and Pearson correlation test was used to find correlations among them. A p-value of 0.05 or lower was considered statistically significant. Results: For the vertebral body, the mean APD was 16.6 mm, VH was 11.6 mm, and TD was 25.6 mm. For the pedicle, the mean PW was 5.1 mm, PH was 6.5 mm, PL was 8 mm, and Axial Length (AXL) was 30.4 mm. No significant difference was found between the right and left sides of PW (p=0.7), PH (p=0.2), PL (p=0.7), and AXL (p=0.2). A weak correlation (0.31-0.40) was observed among the parameters of the vertebral body (APD, TD, VH), whereas a moderate to strong correlation (0.60-0.89) was noticed among the parameters of the cervical vertebrae pedicle (PW, PH, PL, and AXL). Conclusion: The size of the screw used for spinal fixation in one region of the Indian population may not always be compatible with other regions. This morphological study of the cervical vertebral body and pedicle suggests its clinical relevance in the use of a cervical transpedicular screw with a diameter of less than 4 mm and a length of less than 30 mm. Additionally, using a screw along the sagittal plane of the vertebral body with a length of less than 16 mm may reduce bone breach and prevent neurovascular damage.

Keywords

• pedicle screw
• spinal disease
• vertebrae