Abstract】Objective: To study the anatomical parameters of the pivot lamina in patients with craniocervical junctional deformity and to investigate the feasibility of posterior pivot lamina screw fixation in patients with craniocervical junctional deformity. Methods: Forty patients with craniocervical junctional deformity were scanned by spiral CT and a three-dimensional model of the atlantoaxial spine was constructed. The anatomical data related to the pivot plate screw approach technique were measured by selective display, cutting and multi-angle rotation of the three-dimensional model. medial and lateral cortical bone thickness. Results:The average thickness of the upper vertebral plate was (4.12 mm)The average thickness of the middle vertebral plate was (5.87 mm)The average thickness of the lower vertebral plate was (5.16 mm)The average height of the vertebral plate was (11.74 mm)The average distance from the entry point to the medial wall of the foramen of the vertebral artery was (30.62 mm)The average distance from the entry point to the midpoint of the lateral mass was (26.75)The average angle of the vertebral plate axis in the sagittal plane was ( 44) Conclusion: The atlantoaxial spine of patients with craniocervical junctional deformity undergoes different degrees and modes of deformity fusion based on different degrees of developmental incompleteness, and individual differences are large. Although the anatomical morphology of the atlantoaxial spine of patients with craniocervical junctional deformity differs greatly from the normal structure, the application of posterior pedicle screw fixation of the pivot is feasible in most cases and is applicable to 85% of patients. Posterior pedicle screw fixation is less likely to damage the vertebral artery than pivotal pedicle fixation, but the mechanical properties of the two need to be further compared. Screw fixation systems are increasingly used in posterior cervical fixation, both in the upper and lower cervical spine, and can provide strong fixation; however, patients with craniocervical junctional deformities often face many problems with posterior transcentral pedicle fixation in the upper cervical spine, i.e., deformities in the development of the pivotal pedicle, deformities in the development of the vertebral plate, loss of normal anatomic landmarks when performing pedicle fixation, difficulty in determining the entry point, abnormalities in the travel of the vertebral artery in some patients, and abnormalities in the transverse process. In some patients, the vertebral artery travels abnormally, and the transverse foramen forms a large sinus cavity in the lateral fastenings of the cardinal vertebrae, making it easy to damage the vertebral artery when performing pedicle fixation. Recently, the trans-pivotal plate cross screw fixation technique introduced by WRIGHT can avoid the above deficiencies, and the trans-pivotal plate screw fixation technique is becoming more and more accepted in China, but no one has studied the anatomical relationship between the pedicle screw and the pivotal plate, and whether this technique is suitable for the anatomical structure of patients with craniocervical junction deformity? Anatomical measurements were analyzed. Materials and methods: 1.1 Materials and tools: cervical spine imaging data of 30 patients with craniocervical junctional deformity, regardless of gender. three-dimensional reconstruction of the pivot spine by CT (measurement of linear anatomical indices and angles) 1.2 Method of nail entry: according to the entry point in the left and right side of the spinous process midline and the position of the upper and lower vertebral plates called right upper screws, left lower screws. Upper plate nail in the projection of the upper edge of the contralateral vertebral plate bone ridge continuation line intersects with the midline of the middle of the vertebral plate on that side as the entry point to the midpoint of the contralateral inferior articular eminence, and the lower plate nail in the upper edge of the contralateral vertebral plate bone ridge continuation line intersects with the midline of the lower part of the vertebral plate on that side as the entry point to the midpoint of the contralateral inferior articular eminence. The upper and lower cross fixation was formed 1.3 Measurement indexes Anatomical structure measurement indexes: thickness of the upper vertebral plate W1 thickness of the middle vertebral plate W2 thickness of the lower vertebral plate W3 height of the vertebral plate H. Screw fixation measurement indexes: distance from the entry point to the contralateral inferior articular eminence L1, distance from the entry point to the medial wall of the contralateral vertebral artery foramen L2, angle between the axis of the vertebral plate and the sagittal plane a 1.4 Data statistics SPASS10.0 statistical software was used to The data from the left and right sides were processed to find out the mean value of each measurement parameter, and the paired t-test was performed on the data from the left and right sides, and the P value was set at 0.05 2. Results See Tables 1 and 2. The P values for each index measured on the left and right sides of the central vertebral spine were greater than 0.05 when comparing the left and right sides, and there was no statistical difference, so the data from both sides were combined to calculate the mean value of the upper thickness of the vertebral plate, and the mean thickness of the central vertebral plate was 5.87 mm. The average thickness of the lower vertebral plate was less than 5 mm in 4 cases and less than 3.5 mm in 1 case, and the average thickness of the lower vertebral plate was less than 5 mm in 6 cases. There was no statistical difference in the length of the screws fixed on the left and right sides and the angle of nail entry, and the average value was taken bilaterally after the combination. The mean length of the screws was 26.75, and the mean angle with the sagittal plane was 44. 3, Discussion 3.1 Significance of pedicle screw fixation for patients with craniocervical junctional deformity The basic pathological process of craniocervical junctional deformity is deformity, dislocation and compression, and the principle of surgical treatment is to release the compression and rebuild the stability of the path junctional area. Internal fixation of the junctional zone is mostly performed posteriorly and is divided into cable and screw techniques according to the different fixation tools used, with the screw technique having a significantly superior biomechanical effect. However, anatomical studies on the application of screw-based internal fixation techniques to congenital pathway junction deformities are not available in the literature. The risk of injury to the vertebral artery during fixation of the pontine pedicle isthmus due to the variability of the pontine pedicle isthmus was shown by WRIGHT et al. to be certain in 2.4% of common patients with reapplication of pedicle screw fixation and suspected in 1.7% of patients. Patients with craniocervical junction deformity have a higher rate of anatomical variation such as the pedicle, so the risk of applying pedicle screws is significantly increased. Using pivot lamellar screws instead of pedicle screws for posterior cervical fusion, the chase plate structures are exposed in the field again during screw implantation, which can significantly reduce the risk of surgery. Some patients whose pivotal isthmus width is too small to safely implant pedicle screws can also be fixed with pedicle screws. 3.2 Feasibility of pedicle screw fixation The unique anatomy of the pivotal spine, with the largest spinous process and pedicle in the cervical spine, offers the possibility of pedicle screw fixation. The measurements in this study showed that the average height of the pedicle in patients with craniocervical junction deformity measured was 11.7 mm, which is fully permissible for the placement of two screws with a diameter of 3.5 mm in the upper and lower parts, left and right crosses. Measurements of the thickness of the vertebral plate showed that the thickness of the upper part of the plate was small, averaging 4.12 mm, the thickness of the lower part of the plate averaged 5.16 mm, and the thickness of the middle part of the plate averaged 5.87 mm, suggesting that cross fixation of 3.5 mm screws in the middle and lower parts of the plate is feasible. The bilateral screw entry points should be located at the point where the projection of the continuation line of the upper edge of the vertebral plate intersects with the midline of the middle of the vertebral plate and the midline of the lower part of the vertebral plate to the midpoint of the contralateral inferior articular eminence, respectively. The middle thickness of the vertebral plate was less than 5.0 mm in 4 cases 10%, and the lower thickness of the vertebral plate was less than 5 mm in 6 cases 15%. The mean distance from the entry point to the medial wall of the foramen of the vertebral artery was 30.6 mm and the mean distance to the midpoint of the lateral mass was 26.75, suggesting that the use of 26 mm pedicle screws would not injure the vertebral artery. the use of 4+30 mm universal screws for the fixation of the pontine plate mentioned by WRIHGT may be related to anatomical differences between Westerners and Chinese. The screws enter through the projection of the bony ridge continuation line at the upper edge of the vertebral plate where it intersects with the midline of the middle and lower midline of the vertebral plate, allowing travel over a relatively wide portion of the anatomical structure of the vertebral plate, which prevents the screws from breaking through the inner wall of the vertebral plate and entering the spinal canal, and there is no risk of injury to the vertebral artery. The average angle between the axis of the vertebral plate and the sagittal plane measured in this experiment is 44, so the direction of screw travel should be consistent with the direction of the vertebral plate, and the travel direction should be equal to or slightly greater than 44 to avoid the screw entering the spinal canal.