下颈椎椎板和侧块作为椎弓根置钉角度参考标志的可靠性

Reliability of subaxial vertebral lamina and lateral mass for the orientation of pedicle screw insertion

目的：探讨下颈椎椎板和侧块作为椎弓根置钉角度参考标志的可靠性。方法：完整成人颈椎骨性标本10具，男、女各5具，模拟施行下颈椎椎弓根置钉手术；术前对C3～C7进行螺旋CT扫描多平面重建，确定椎弓根进钉轴，并以椎板和侧块作为椎弓根内倾角和上倾角的参考标志，测量椎弓根进钉轴与同侧椎板的夹角（PL角）及与侧块后表面的夹角（PLM角），术中以相同参考标志和置钉角度置入 椎弓根螺钉。术后复查CT并评估椎弓根螺钉置钉的7停确率：0级，螺钉完全位于椎弓根内：1级，穿破柞弓根的部分〈螺钉直径的25％；2级，螺钉直径的25％．50％穿破椎弓根：3级，螺钉直径〉50％穿破椎弓根；2级和3级螺钉为误置。对颈椎标本各节段椎弓根螺钉位置的分级与椎弓根的宽度与高度进行相关性分析。2011年10月～2012年12月，用同样方法对6例患者进行下颈椎椎弓根螺钉置钉手术，评估置钉准确率和并发症情况。结果：10具颈椎标本的下颈椎椎弓根的PL角，C3、C4〉C5、C6〉C7：PLM角，C3、C4〈C5〈C6〈C7。10具颈椎标本C3～C7共置入椎弓根螺钥‘100枚，术后CT判断螺钉位置，0级65枚，1级26枚，2级6枚，3级3枚，误置率为9％。误置节段分布：C34枚，C43枚，C51枚．C61枚。椎弓根螺钉位置的分级与椎弓根的宽度呈负相关（r=-0．356，P=0．000），与椎弓根的高度无显著相关性（r=-0．187，P=O．058）。6例下颈椎椎弓根置钉患者共置入椎弓根螺钉34枚，其中0级21枚，1级9枚，2级3枚，3级1枚，椎弓根螺钉误置率11．7％。术后随访14～19个月（平均16．5个月），无椎动脉损伤、内固定松动等并发症．仅1例患者术后遗留上肢神经根性疼痛。结论：下颈椎椎板、侧块可以作为相应椎弓根螺钉置入角度的可靠参考标志：下颈椎椎弓根的置钉角度并不都垂直于同侧柞板和侧块，不同节段椎弓根的置钉角度不同．

ObjectiveS： To explore reliability of subaxial vertebral lamina and lateral mass as anatomic land- mark for the orientation of pedicle screw insertion. Methods： Pedicle screws were inserted into C3-C7 pedi- cles on 10 adult cervical vertebral specimens（5 males and 5 females）. Vertebral lamina and lateral mass was regarded as anatomic landmark defined as transverse and sagittal angle of pedicle screw insertion respectively. Pediele-lamina angle（PL angle, the transverse angle） between the central axis of each pediele and vertebral lamina, and pediele-lateral mass angle （PLM angle, the sagittal angle） between the central axis and lateral mass were measured preoperatively on eomputed tomography（CT） images. On the postoperative CT, the grade of pediele perforation was analyzed（Grade 0 was defined when the entire screw was placed within the cortical bone of the pedicle, grade 1 was defined as less than 25% of the screw diameter violation, grade 2 was de- fined as 25% to 50% of the screw diameter violation, and grade 3 was defined as more than 50% of the screw diameter violation）. Grade 0 and 1 were considered to be the correct position, whereas grade 2 and 3 were considered to be wrong positions. Correlative analysis between the grade of each pediele screw position and the pedicle width or height was performed. From October 2011 to December 2012, 6 patients underwent pedicle screw insertion on subaxial cervical vertebra. Complications and accuracy of pedicle screw placement were evaluated. Results： Among 10 cervical spine specimens, PL angles of C3-C7 pedicles on axial CT im- ages were C3, C4〉C5, C6〉C7. PLM angles of C3-C7 pedicles on sagittal CT images were C3, C4〈C5〈C6〈 C7. 100 cortical screws were inserted into C3-C7 pedicles of 10 human specimens. Postoperative CT scan was performed for the evaluation of pedicle screw position, 65 screws were in grade 0, 26 screws were in grade 1, 6 screws were in grade 2, and 3 screws were in grade 3. The rate of the screw misplacement was 9%. Among 9 screws misplaced, there were 4 screws in C3, 3 screws in C4, 1 screw in C5, 1 screw in C6. Negative correlation was found between the grade of pedicle screw position and pedicle width （r=-0.356, P= 0.000）. There was no significant correlation between the grade and the pedicle height（r=-0.187, P=0.058）. 34 pedicle screws were inserted into C3-C7 pedicles of 6 patients. 21 screws were in grade 0, 9 screws in grade 1, 3 screws in grade 2 and 1 screw in grade 3. The rate of pedicle screw misplacement was 11.7%（4 of 34 screws）. All patients were followed up for an average of 16.5 months （ranged from 14 to 19 months）. Complications such as screw loosening and vertebral artery injury were not found. Radicular pain on one up- per limb was found in 1 patient. Conclusions： Subaxial vertebral lamina and lateral mass is a reliable anatomic landmark for orientation of pedicle screw insertion. The direction of screw insertion is not always vertical to the ipsilateral lamina or lateral mass. The PL and PLM angle of the pedicle screw placement varies from different levels.