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Title: [Feasibility of screw placement on posterior occipital condyle assisted by occipital tangent angulation].
Author: Lou ZQ, Xu DL, Wang Y, Ma WH, Li GQ, Ruan CY, Zhao HG.
Journal: Zhonghua Yi Xue Za Zhi; 2018 Jun 19; 98(23):1863-1868. PubMed ID: 29925171.
Abstract:
Objective: To investigate the practicability of occipital tangent angle in assisting posterior occipital condylar screw placement and to verify the safety and accuracy of self-made screw placement device for auxiliary screw. Methods: Occipito-cervical region specimens of 12 adult corpses were selected and scanned by thin-cut CT examination.The three-dimensional reconstruction of occipital and atlas was simulated for each specimen, and 3-matic software was used to measure the setting parameters, including occipital tangent angle, head obliquity, internal inclination angle, length of the screw and the distance from the inferior margin of hypoglossal canal to the screw axis.Using the self-designed occipital condylar screw placement device, combined with occipital tangent angle, internal inclination angle and insertion point, the posterior occipital condylar screw specimen was inserted with nails with assisting tool.The occipito-cervical region was reconstructed and scanned by thin-cut CT examination again after the operation to measuring the parameters of screw placement after actual screwing.The paired t test was used to compare the parameters of screw placement before and after operation. Results: Pre-operative three dimensional reconstruction of occipital condyle screw showed that the head obliquity was 5.3°±0.9°, the tangent angle was 14.9°±3.7°, the internal inclination angle was 28.1°±5.9°, and the length of screw insertion was (21.4±1.7) mm respectively; the distance from the inferior margin of hypoglossal canal to the screw axis was (4.74±0.36) mm.There was no significant difference in the parameters of analogue nailing between the left and right occipital condyles before the operation (t=-1.32, -0.48, 0.10, 0.23, 0.09, all P>0.05). The occipital condylar screw was safely implanted with screw placement device.The screw was located in the ideal nail insertion channel after operation by CT scan evaluation, without any injury to the hypoglossal canal, the atlanto-occipital articular surface and other structure.After the operation, the actual nailing parameters were measured: the head inclination angle was 5.2°±0.7°, the tangent angle was 15.1°±3.2°, the internal inclination angle was 28.2°±4.2°, the length of screw insertion was (21.5±1.7) mm, the distance from the inferior margin of hypoglossal canal to the screw axis was (4.54±0.29) mm.There was no significant difference between the left and right side in the actual screw placement parameters (t=-0.77, 0.82, 0.56, 0.22, 0.21, all P>0.05). It was found that there was no significant differences in the head obliquity, the occipital tangent angle, the internal inclination angle, length of screw entry, and the distance from the inferior margin of hypoglossal canal to the screw axis before and after the operation (t=0.56, -0.47, -0.18, -0.70, 1.89, all P>0.05). Conclusion: The occipital tangent angle can be measured directly in the process of posterior occipital condyle screw insertion to guide occipital condylar screw insertion, and the self-made occipital condylar screw placement device can effectively combine the three parameters: occipital tangent angle, head inclination angle and insertion point, which can improve the safety of posterior occipital condylar screw insertion. 目的： 探讨枕骨切线角在协助后路枕骨髁螺钉置钉中的可行性，验证自制置钉器辅助置钉的安全性和准确性。 方法： 选取12具成人尸体枕颈部标本，行薄层CT扫描，将数据以Dicom格式导入mimics 19.0软件，对每具标本行枕骨及寰椎的三维重建模拟置钉，并通过3－matic软件测量置钉参数枕骨切线角、头倾角、内倾角、进钉长度及舌下神经管下缘至螺钉中轴线距离。利用自行设计的枕骨髁螺钉置钉器，结合枕骨切线角、内倾角及进钉点行工具辅助下后路枕骨髁螺钉标本置钉，术后再次对枕颈部行薄层CT扫描并行重建，测量实际置钉后相应置钉参数。手术前后对应置钉参数比较采用配对t检验。 结果： 术前三维重建下枕骨髁螺钉模拟置钉测得最佳钉道参数头倾角5.3°±0.9°，切线角14.9°±3.7°，内倾角28.1°±5.9°，进钉长度(21.4±1.7) mm，舌下神经管下缘至螺钉中轴线距离(4.74±0.36) mm，术前左右侧枕骨髁上述模拟置钉参数对比差异无统计学意义(t＝－1.32、－0.48、0.10、0.23、0.09，均P>0.05)。应用置钉器协助枕骨髁螺钉安全置入，术后CT评估螺钉均位于理想置钉通道，未对舌下神经管、寰枕关节面等结构产生损伤，术后测得实际置钉参数头倾角5.2°±0.7°，切线角15.1°±3.2°，内倾角28.2°±4.2°，进钉长度(21.5±1.7) mm，舌下神经管下缘至螺钉中轴线距离(4.54±0.29) mm，术后实际置钉参数左右侧对比差异均无统计学意义(t＝－0.77、0.82、0.56、0.22、0.21，均P>0.05)。术前及术后测量参数对比，头倾角、切线角、内倾角、进钉长度和舌下神经管下缘至螺钉中轴线距离差异均无统计学意义(t＝0.56、－0.47、－0.18、－0.70、1.89，均P>0.05)。 结论： 枕骨切线角可在后路枕骨髁螺钉置钉过程中直接测量，协助指导枕骨髁螺钉置钉；自制枕骨髁螺钉置钉工具可有效结合枕骨切线角、头倾角及进钉点辅助螺钉的准确置入，提高后路枕骨髁螺钉置钉的安全性。.

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