Morphometric measurements of sub-axial cervical vertebrae pedicles in relation to transpedicular screws in a Kenyan adult population

Abstract

Background: Morphometric measurements of sub-axial cervical vertebrae pedicles (C3-C7) are anatomical measurements that include pedicle width, height, chord length and angle of medial inclination. These measurements are used to define the right size of screw to use in transpedicular screw surgery. Transpedicular screws provide superior stability compared to other forms of fixation in sub-axial cervical spine surgery. For a spinal surgeon to perform transpedicular screw surgery he needs the anatomical measurements of the pedicle and the right size of screw. Different racial groups have been shown to have distinct anatomical measurements of the pedicle. Pedicle screws are currently based on anatomical measurements of European pedicles. Studies done on the Chinese and Indian populations have shown that they have smaller pedicle measurement and thus need smaller pedicle screw sizes. Because of lack of studies that define pedicle measurements in sub-Saharan Africa, this study will provide the anatomical measurements of sub-axial cervical vertebrae pedicles and define the right screw size for each pedicle to aid the Kenyan spine surgeon in transpedicular screw surgery. Objective: To describe the morphometric measurements of the adult sub-axial cervical vertebrae pedicles in relation to transpedicular screws in the Kenyan adult population. Methods: A descriptive cross-sectional anatomical study was conducted at the National Museum of Kenya in the month of August 2017. Ninety-seven dry bone specimens were selected for the study through purposive sampling. Measurements were collected using digital calipers and goniometer and recorded in data forms. The pedicle dimensions measured were width, height, chord length and angle of medial inclination. Data were analysed using STATA/ MP 13.0 and summarised using mean, standard deviation and presented in tables. Results: The mean pedicle width was 4.45±0.65mm at C3, 4.64±0.76mm at C4, 5.24±0.78mm at C5, 5.46±0.82mm at C6, and 6.06±1.07mm at C7.The mean pedicle height was 6.36±0.81mm at C3, 6.67±0.89mm at C4, 6.62±1.04mm at C5, 6.53±0.90mm at C6, and 7.25±1.06mm at C7. The mean chord length was 30.81±2.50mm at C3, 31.47±2.63mm at C4, 31.83±2.89mm at C5, 32.17±3.31mm at C6, and 32.65±2.84mm at C7. The mean angle of medial inclination was 45.19±3.44 degrees at C3, 46.80±3.79 degrees at C4, 48.12±3.84 degrees at C5, 45.56±3.51 degrees at C6, and 42.13±3.22 degrees at C7. Conclusion: Pedicle width and chord length increased caudally from C3 to C7. Pedicle height measurements were variable. The angle of medial inclination increased from C3 to C5 then decreased from C6 to C7. Recommendations: Based on morphometric measurements of sub-axial cervical vertebrae pedicles from this study, the recommended screw diameter at C3 and C4 is 2.7mm while at C5, C6 and C7 is 3.5mm. The appropriate screw lengths at C3 is 22 mm while at C4, C5, C6 is 24 mm and at C7 is 26 mm. The recommended angle to advance a screw in transpedicular sub-axial cervical surgery is 45°.