RESUMO
Objective:To analyze the ideal entry parameters and entry points for C 7 pedicle screws based on three-dimensional CT reconstruction model. Methods:A retrospective case series study was used to analyze the cervical spine CT image data of 50 adult volunteers collected from April 2021 to March 2022 at Taizhou People′s Hospital Affiliated to Nanjing Medical University, including 25 males and 25 females; aged 20-67 years [(43.8±13.5)years]. No significant structural abnormalities were seen in the cervicothorax of all volunteers. First, the 50 CT images were imported into the medical engineering software Mimics 17.0 to reconstruct the three-dimensional C 7 model, and the C 7 pedicle screw diameter (PSD), pedicle screw length (PSL), sagittal angle (SA) and lateral angle (LA) were measured. Then, the anatomical markers, namely the lateral notch and the midpoint of the inferior edge of the C 6 articular process, were used to measure the horizontal distance between the midpoint of the inferior edge of the C 6 articular process and the ideal entry point (line segment A), and the horizontal and vertical distances between the lateral notch and the ideal entry point (line segments B and C). Finally, the lateral notch and the midpoint of the inferior edge of the C 6 articular process were used as markers to observe the distribution of entry points. The values of the above measured parameters were recorded and compared with each other to analyze the differences between different sides and genders. Intra-group correlation coefficients (ICC) were also used to assess intra- and inter-observer agreement. Results:All 100 pedicles from 50 C 7 models were accessed, with the PSD being (6.5±0.7)mm, PSL being (31.8±4.5)mm, SA being (89.8±8.8)°, LA being (31.0±6.7)°, line segment A being 0.9(-0.4, 2.1) mm, line segment B being (5.8±1.7)mm, and line segment C being (3.6±1.5)mm. All ideal entry points were located medial above the lateral notch; moreover, with the midpoint of the inferior edge of the C 6 articular process as a reference, 71 (71%) of the entry points were located laterally and 29 (29%) were located medially. The 12 mm area around the midpoint of the inferior edge of the C 6 articular process was divided into 6 sections, with 47% of the entry points being located within 2 mm lateral to the midpoint, 25% within 2 mm medial to the midpoint, 19% within 2-4 mm lateral to the midpoint, and only 9% within 50% lateral to the midpoint. The measured parameters were not significantly different between the left and right sides (all P>0.05). The PSD, SA, and line segment B in males were (6.8±0.7)mm, (92.0±8.2)°, and (6.3±1.6)mm, which were significantly greater than those in females [(6.2±0.6)mm, (87.5±8.0)°, and (5.3±1.6)mm] (all P<0.01). The remaining parameters were similar between two genders (all P>0.05). All measured parameters had high intra- and inter-observer agreement (ICC: 0.84-0.91), except for line segment A that had moderate intra- and inter-observer agreement (ICC: 0.46-0.63). Conclusions:For C 7 pedicle screw implantation, when the surface of the lateral mass is used as the reference plane, SA is approximately 90°; with reference to the lateral notch, all the ideal entry points are located medially above it; with reference to the midpoint of the inferior edge of the C 6 articular process, approximately 70% of the entry points are located laterally. There are no significant differences in the parameters between the different sides of screw implantation on pedicles. The measured parameters show high intra- and inter-observer agreement, except for line segment A.