Comparison of morphometric measurements of cervical paravertebral foramen screw, pedicle screw and lateral mass screw in Chinese population / 中华骨科杂志

ABSTRACT

Objective:To measure and compare the length and angle parameters of the screw paths of paravertebral foramen screws (PVFS), pedicle screws (PS) and lateral mass screws (LMS) of subaxial cervical spine.Methods:This study included the cervical computerized tomography (CT) scans of 50 healthy volunteers (25 males and 25 females) in our hospitalfrom January 2018 to June 2018. The average age of the volunteers was 56.00±15.90 years (range, 29-89 years). After three-dimensional reconstruction of CT data, the screw starting points, length of screw paths,optimal medial angles, maximum medial angles and minimum medial angles of PVFS, PS and LMS (Magerl technique) on C 3-C 7 segments were designed and measured on the reconstructed 3D model, and the pedicle widths at various segments of cervical vertebrae were measured. All parameters were measured twice in an interval of two weeks by one orthopaedic surgeons with experience in spine surgery, and the average values of the two measurements were used. Results:In general, the optimum length and medial angle of the PVFS in Chinese population were 10.65 mm and 21.12° at C 3; 10.12 mm, 22.62° at C 4; 9.82 mm, 23.66° at C 5; 9.19 mm, 24.13° at C 6; and 9.10 mm, 27.54° at C 7. The C 3 segment had the longest general optimal length, and the C 7 segment had the shortest general optimal length of PVFS ( F=19.287, P<0.001). However, there was no significant difference in optimal length of PVFS between C 6 and C 7 vertebrae ( P=0.674). The C 7 vertebra had the largest general medial angle, meanwhile the C 3 vertebra had the smallest general medial angle ( F=19.752, P<0.001). The optimum lengths of screw path of PVFS in males at the segments of C 4, C 6 and C 7 vertebrae were longer than those in females (C 4t=2.912, C 6t=3.884, C 7t=5.468, P<0.05), and the optimal medial angle at C 4, C 6 and C 7 segments were smaller than those in females (C 4t=3.560, C 6t=4.370, C 7t=4.738, P<0.05). The optimum length and medial angle of PS in Chinese population were 30.94 mm, 33.92° at C 3; 30.50 mm, 34.95° at C 4; 31.92 mm, 33.42° at C 5; 30.50 mm, 31.94° at C 6; and 29.87 mm, 31.01° at C 7. The general pedicle widths were 5.35 mm at C 3; 5.56 mm at C 4; 5.99 mm at C 5; 6.34 mm at C 6; and 6.86 mm at C 7. The optimum lengths of LMS paths in Chinese population were C 3, 14.84 mm; C 4, 15.33 mm; C 5, 15.44 mm; C 6, 14.74 mm; and C 7, 14.06 mm. In Chinese population, the optimal length of PVFS was 9.10-10.65 mm, and the optimal medial angle was 21.12°-27.54°. The general optimal length of PVFS path were shorter than those of LMS and PS at C 3-C 7 segments ( P<0.05), and the general optimal medial angles were smaller than those of PS at C 3-C 7 segments ( P<0.05). Conclusion:Because of the length of screw path of PVFS is limited, it does not have the risk of direct vertebral artery injury. The insert angle of PVFS is steeper and safer than that of PS. In summary, cervical PVFS can be used as an effective supplement to PS and LMS.