寰椎后弓螺钉交叉固定的解剖学研究

 目的 研究寰椎后弓交叉螺钉固定的解剖学可行性, 以提供可供选择的寰椎固定方法 。 方法 对 10具寰椎标本进行实体测量和 CT测量。测量指标包括后结节高度、后弓的宽度、从理想入钉点到椎动脉沟内缘的距离、入钉点到后结节的距离及理想的钉道角度, 比较两种方法测量结果的统计 学差异。再对 100张寰椎三维 CT片进行测量, 测量指标有后结节(后弓中点矢状面垂直距离)高度、后弓的宽度(水平面后弓与椎动脉沟移行处内侧)、从理想入钉点到椎动脉沟内缘(螺钉完全位于髓腔内) 的距离、理想入钉点到后结节的距离及理想钉道的角度(理想钉道与水平线夹角), 分析寰椎的解剖学 特点。计算后结节高度跃7 mm, 后弓宽度跃3.5 mm及无法对侧置钉的比例。结果 寰椎标本的实体测量 和 CT测量的结果 差异无统计学意义。 100张寰椎三维 CT经测量, 椎板后弓的宽度: 左侧为(4.7±0.9) mm, 右侧为(4.6±0.8) mm;93.5%(187/200)宽度跃3.5 mm。从理想的入钉点到椎动脉沟内侧缘的髓腔距 离(理想螺钉长度): 左侧为(15.9±3.0) mm, 右侧为(15.9±3.0) mm, 提示螺钉的长度可超过 15 mm。后结 节的高度值为(7.8±1.2) mm, 91%(91/100)高度跃7 mm。理想钉道的角度: 左侧为 26.8°±6.8°(8°~44°), 右 侧为 26.8°±6.3°(13°~44°),11%(22/200)无法交叉置钉。结论 解剖学和影像学研究提示寰椎后弓交叉 螺钉技术是安全有效的固定方法 , 为寰椎后路固定提供选择。     

寰椎后弓-横突髓腔钉道的影像解剖学参数及其临床意义

目的通过影像归档和通信系统(PACS)测量成人寰椎后弓-横突髓腔钉道的解剖学参数,并结合临床病例探讨其临床意义。方法选择2016年1月—2017年6月本院PACS中18~70岁患者的颈椎三维CT数据,共200例,男女各100例,年龄(54.95±11.93)岁。选取寰椎后弓-横突髓腔最长轴切面为测量截面,利用PACS测量软件手工测量该截面入钉点与后结节距离、入钉角度与矢状面夹角、入钉角度与横截面夹角、钉道长度、椎动脉沟狭窄处髓腔高度和入钉点髓腔最大高度等解剖学参数,所得数据纳入统计学分析。结合临床病例探讨其可行性。结果入钉点与后结节距离为(7.45±1.75)mm,入钉角度与矢状面夹角为54.26°±6.06°,入钉角度与横截面夹角为9.15°±3.40°、钉道长度为(18.55±3.75)mm,椎动脉沟狭窄处髓腔高度为(2.09±0.81)mm,入钉点髓腔最大高度为(4.93±0.37)mm。男性寰椎后弓-横突髓腔钉道在入钉点与后结节距离、钉道长度、椎动脉沟狭窄处髓腔高度和入钉点髓腔最大高度均大于女性,差异有统计学意义(P0.05),不同性别之间入钉角度与矢状面夹角和入钉角度与横截面夹角差异无统计学意义(P0.05)。经有限病例初步证实该置钉方式具有可行性。结论寰椎后弓-横突髓腔的解剖学特点能够满足置钉要求,在常规寰椎椎弓根螺钉进钉点狭小无法置钉或钉道破裂置钉失败时,可以当做替代置钉钉道方案。     

寰椎后弓环抱钩棒设计的解剖学研究

目的 为研制寰椎后弓环抱钩棒提供形态学参数.方法 采用48个正常成年人干燥寰椎标本,测量各相关距离和角度参数,并进行统计学分析,以决定寰椎后弓环抱钩棒的形态学参数范围.结果 置钩中心点选择定位于后弓内环距椎动脉沟后缘5 mm处,置钩中心点高度(6.0±1.3)mm,前后径(5.0±1.3)mm,两侧置钩中心点外环间距(26.0±5.1)mm.结论 寰椎后弓环抱钩棒的设计在形态学上具有可行性,置钩中心点的位置选取合适,为了置放牢固、操作方便、避免副损伤,各部件参数有一定的选取范围.     

寰椎后弓变异患者寰椎椎弓根螺钉的置钉策略

目的:探讨寰椎后弓变异患者寰椎椎弓根螺钉的置钉方法及其安全性.方法:回顾性分析2005年1月～2011年1月寰椎后弓变异行寰椎椎弓根螺钉固定的28例患者,其中男11例,女17例;年龄6～75岁,平均36.2±15.5岁.根据CT重建图像将寰椎椎弓根划分为后弓表面、椎动脉沟底和椎弓根侧块交界区3个切面,并将每个切面再分为内侧、外侧2个部分.对各部位相应切面的后弓高度进行测量,根据所测结果,将变异寰椎后弓分为3种类型,并采用相应的椎弓根螺钉置钉方法:Ⅰ型(寰椎后弓表面高度＜3.5mm,椎动脉沟底椎弓根高度＞3.5mm),采取后弓下置钉;Ⅱ型(后弓表面高度及椎动脉沟底椎弓根高度均＜3.5mm),采取椎弓根侧块交界点处置钉;Ⅲ型(后弓表面高度＞3.5mm,椎动脉沟底椎弓根高度＜3.5mm),采取in-out-in技术置钉.术后采用CT片评价置钉准确性,并观察并发症发生情况.结果:56个寰椎后弓变异的椎弓根中,Ⅰ型34个,Ⅱ型18个,Ⅲ型4个.术中成功置钉54枚,成功率96.4％;2个Ⅱ型变异后弓椎弓根(2例一侧)因椎弓根过小无法置钉而改用椎板钩固定.术后CT显示理想和可接受置钉52枚(96.3％);不可接受置钉2枚(3.7％),均表现为螺钉穿入椎管.2例患者术后出现枕大神经刺激症状,1例经对症处理、1例拆除内固定后症状缓解.术中与术后均未发生大出血,无椎动脉、神经根及脊髓损伤,无寰椎后弓骨折等其他并发症.结论:寰椎后弓变异患者仍可采用寰椎椎弓根螺钉固定,在实施时应根据不同分型采用相应的置钉策略.     

成人寰椎后弓解剖学研究及内固定钉板系统设计

目的探究国人寰椎后弓内固定钉板系统的解剖可行性并给出初步设计,以提供可供选择的后路寰椎内固定方法。方法对60例成人(男30例,女30例)寰椎三维CT及40具(性别及年龄不详)干燥寰椎标本进行测量,测量指标有后结节中央及距中央5mm、10mm、15mm处的高度(矢状面垂直距离)及厚度(轴位垂直距离)、后弓水平面夹角、后弓内侧面外侧螺钉半距(后结节中央到外侧螺钉外缘)、后弓交叉螺钉最大长度(螺钉完全位于髓腔内且不触及外侧螺钉),比较CT测量数据与标本测量数据有无差异,分析寰椎后弓的解剖学特点并设计后弓钉板系统。结果经CT测量,后弓结节中央高度(9.48±0.95)mm,厚度(7.80±1.60)mm,后弓水平面夹角(130.70±12.31)°,后弓交叉螺钉最大长度为(13.67±0.53)mm,内侧面外侧螺钉半距为(10.51±0.95)mm;经标本测量,后弓结节中央高度为(9.97±2.18)mm,厚度为(7.44±1.32)mm,后弓夹角为(135.07±9.59)°,后弓交叉螺钉最大长度为(14.17±0.54)mm,内侧面外侧螺钉半距为(11.03±1.07)mm。左右两侧测得数据差异均无统计学意义,CT测量所得后弓交叉螺钉最大长度及内侧面外侧螺钉半距小于标本测量所得数据,差异有统计学意义。结论 CT影像资料可为临床实践提供有力参考,但可能无法完全真实的反映所有解剖特征。寰椎后弓解剖学研究提示后弓钉板系统在解剖上是可行的,为寰枢椎后路固定提供新的选择。     

变异型寰椎椎弓根的影像解剖及后路置钉策略

目的:探讨变异型寰椎椎弓根螺钉的置钉策略及其安全性.方法:2005年1月～2011年1月共收治上颈椎不稳且存在寰椎椎弓根变异者28例,男11例,女17例;年龄18～75岁.术前测量寰椎后弓表面、椎动脉沟底及椎弓根近侧块根部三个切面的内、外侧区域高度,将变异型寰椎椎弓根分为3型.Ⅰ型(寰椎后弓表面高度＜3.5mm,椎动脉沟底高度＞3.5mm)采取后弓下置钉,Ⅱ型(后弓表面高度及椎动脉沟底高度均＜3.5mm)采取椎弓根侧块交界点处置钉,Ⅲ型(后弓表面高度＞3.5mm,椎动脉沟底高度＜3.5mm)采取in-out-in的技术置钉.术后评价置钉准确性及并发症情况.结果:56个变异型寰椎椎弓根中Ⅰ型34个,Ⅱ型18个,Ⅲ型4个.寰椎近侧块面的椎弓根高度均＞5.0mm,内、外侧区域无显著性差异;椎动脉沟底的高度外侧区域显著高于内侧区域(t=13.07,P＜0.01),其中60％外侧区域高度＞3.5mm;后弓表面高度绝大多数＜3.0mm,且内、外侧区域无显著性差异.根据相应置钉策略,术中成功置钉54枚,成功率96.4％.术后CT显示理想和可接受置钉52枚占96.3％,不可接受置钉2枚占3.7％;术中与术后均未发生大出血以及椎动脉、神经根、脊髓损伤、寰椎后弓骨折等并发症,2例患者术后出现枕大神经刺激症状.结论:变异型寰椎椎弓根应根据不同分型采用相应的置钉策略,椎弓根外侧区域置钉更加安全可靠.     

后路寰椎有限内固定治疗寰椎不稳定性骨折

目的:探讨后路寰椎钉棒系统有限内固定治疗寰椎不稳定性骨折的疗效。方法:2008年4月~2010年10月采用后路寰椎钉棒系统内固定治疗寰椎不稳定性骨折10例,男7例,女3例;年龄20~60岁,平均37.5岁。患者均有不同程度的枕颈部疼痛、僵硬和颈部活动受限,均无神经损伤表现。双侧寰椎后弓并单侧寰椎前弓骨折(后3/4 Jefferson骨折,LandellsⅡ型)6例,单侧寰椎前后弓骨折(半环Jefferson骨折,LandellsⅡ型)4例;横韧带完整7例,横韧带附着处骨折和撕脱(DickmanⅡ型)3例。术前均行颅骨牵引稳定骨折块。结果:共置入螺钉20枚,其中1例在置入寰椎椎弓根螺钉时后弓破裂,1例术前进钉点处后弓破裂,直接将螺钉固定在侧块上;1例患者寰椎后弓进钉点处的高度小于4mm,无法行椎弓根螺钉固定而改为侧块螺钉固定;其余7例均行寰椎椎弓根螺钉固定。手术时间为60~90min,平均70.5min;术中出血量为100~300ml,平均150ml。术中1例患者在剥离寰椎后弓下缘时损伤静脉丛,用明胶海绵压迫止血;未发生脊髓和椎动脉损伤。术后X线片及CT示1例一侧寰椎椎弓根螺钉部分进入椎动脉孔,1例一侧螺钉偏内致椎弓根内侧皮质破裂,但均无血管神经损伤症状,未处理;其余螺钉位置良好。随访12~36个月,平均20.2个月,术后3~6个月枕颈部疼痛缓解,颈部活动范围基本接近伤前水平;术后6个月复查骨折断端达到骨性融合;随访期间颈椎序列良好,未见内固定松动、断裂,无C1-2失稳。结论:在严格选择适应证的前提下,寰椎后路钉棒系统有限内固定是治疗寰椎不稳定性骨折的较好方法,能保留枕颈部活动功能。     

寰椎椎弓根螺钉固定技术的改进研究

目的 探讨寰椎椎弓根螺钉的置钉方法. 方法 以电子游标卡尺测量48具干燥寰椎标本的相关解剖学数据;并依据寰椎椎弓根的形态对寰椎进行分类,提出了针对不同类型寰椎的各种椎弓根螺钉置钉方法. 结果 钉道处椎动脉沟底骨质厚度小于螺钉直径3.5mm的占16.7%(8/48),其中4.2%(2/48)厚度小于螺钉半径1.75mm.将寰椎分为普遍型(占83%)、轻度变异型(占13%)和重度变异型(占4%). 结论 对于寰椎后弓高度偏小的患者,可以部分经寰椎后弓或跨越寰椎后弓实现寰椎的椎弓根螺钉固定,进钉位置的确定应以术前三维CT重建和术中探查结合考虑.     

寰椎经后弓侧块螺钉固定通道的CT测量

目的:提供国人寰椎CT测量的数据,探讨寰椎经后弓侧块行螺钉置钉的可行性。方法:采用50具寰椎骨标本,对经寰椎后弓侧块的螺钉固定通道进行多个切面的CT断层扫描并测量。结果:将寰椎后结节中点旁开18～20mm的矢状面与后弓下缘上方2mm处的水平面的交线在后弓后方的投影点确定为进钉点;进钉方向保持与冠状面垂直,在矢状面上钉尖向头侧倾斜约5°,是寰椎经后弓侧块螺钉固定较理想的置钉通道。结论:寰椎具备行经后弓侧块螺钉内固定的条件。     

寰椎椎弓根钉内固定通道的三维CT影像学研究

目的利用三维影像学探讨常人寰椎椎弓根钉内固定通道的解剖学基础。方法从本院PACS系统中随机选取60例头颈部CTA枕寰枢复合体无明确异常的影像学资料,进行回顾性三维CT成像。测量相关解剖学数据,以颈椎扩孔器横截面面积(3~5 mm2)为对照,归纳出3种椎弓根类型。结果 60例头颈部CTA三维图像显示寰椎及周围结构清楚,测量出寰椎椎动脉沟底部后弓外径高度男性(4.39±1.16)mm,女性(3.84±0.84)mm,小于常规螺钉直径(3.50 mm)占27.7%;在寰椎椎弓根通道分型中,Ⅰ型68侧,占56.67%,Ⅱ型25侧,占20.83%;Ⅲ型27侧,占22.50%;皮质骨面积比例随通道面积的减小而增大,在各型椎弓根通道都在80%以上。结论寰椎椎动脉沟底部后弓外径高度是制约寰椎椎弓根钉固定的重要因素,而寰椎椎弓根骨性通道的解剖结构特点则影响置钉技术的选择;设计出适应寰椎椎动脉沟底部后弓外径高度的螺钉是非常必要的。     

Posterolateral protrusion of the vertebral artery over the posterior arch of the atlas: quantitative anatomical study using three-dimensional computed tomography angiography

OBJECT: The vertebral artery (VA) often takes a protrusive course posterolaterally over the posterior arch of the atlas. In this study, the authors attempted to quantify this posterolateral protrusion of the VA. METHODS: Three-dimensional CT angiography images obtained for various cranial or cervical diseases in 140 patients were reviewed and evaluated. Seven patients were excluded for various reasons. To quantify the protrusive course of the VA, the diameter of the VA and 4 parameters were measured in images of the C1-VA complex obtained in the remaining 133 patients. The authors also checked for anomalies and anatomical variations. RESULTS: When there was no dominant side, mean distances from the most protrusive part of the VA to the posterior arch of the atlas were 6.73 +/- 2.35 mm (right) and 6.8 +/- 2.15 mm (left). When the left side of the VA was dominant, the distance on the left side (8.46 +/- 2.00 mm) was significantly larger than that of the right side (6.64 +/- 2.0 mm). When compared by age group (< or = 30 years, 31-60 years, and > or = 61 years), there were no significant differences in the extent of the protrusion. When there was no dominant side, the mean distances from the most protrusive part of the VA to the midline were 30.73 +/- 2.51 mm (right side) and 30.79 +/- 2.47 mm (left side). When the left side of the VA was dominant, the distance on the left side (32.68 +/- 2.03 mm) was significantly larger than that on the right side (29.87 +/- 2.53 mm). The distance from the midline to the intersection of the VA and inner cortex of the posterior arch of the atlas was approximately 12 mm, irrespective of the side of VA dominance. The distance from the midline to the intersection of the VA and outer cortex of the posterior arch was approximately 20 mm on both sides. Anatomical variations and anomalies were found as follows: bony bridge formation over the groove for the VA on the posterior arch of C-1 (9.3%), an extracranial origin of the posterior inferior cerebellar artery (8.2%), and a VA passing beneath the posterior arch of the atlas (1.8%). Conclusions There may be significant variation in the location and branches of the VA that may place the vessel at risk during surgical intervention. If concern is noted about the vulnerability of the VA or its branches during surgery, preoperative evaluation by CT angiography should be considered.     

Insertion of lateral mass screw of the atlas via the posterior arch: anatomical study of screw insertion using dry bone samples of the atlas from Japanese cadavers

BACKGROUND: A new technique involving screw fixation of the atlas via the posterior arch and lateral mass has recently been reported for atlantoaxial instability. Because the posterior arch is thin, lateral mass screws risk penetrating the upper part of the posterior arch and damaging the vertebral artery running along the upper part of the posterior arch. METHODS: A total of 50 dry bone samples of the atlas from Japanese cadavers were used. We manually measured the shortest distance from the vertebral canal to the transverse foramen and the thickness at the thinnest part of the groove using calipers and investigated the frequency of dorsal ponticuli at the posterior arch. RESULTS: The area from the vertebral canal to the transverse foramen was thick enough to allow screw insertion, but the thickness of the posterior arch at the thinnest part of the groove was less than the screw diameter (3.5 mm) in 22% of vertebrae and <4 mm in 39%. A dorsal ponticuli was present in 10% of these samples. CONCLUSIONS: The size and shape of the posterior arch must be evaluated using radiography and computed tomography before inserting a lateral mass screw of the atlas via the posterior arch.     

经寰椎后弓上颈椎稳定性重建的解剖学研究

目的 通过解剖学测量,探讨经寰椎后弓螺钉固定重建上颈椎稳定性的解剖学基础.方法 测量39具干燥寰椎标本椎管内径宽度、螺钉进钉点后弓高度和宽度、寰椎椎动脉沟底后弓高度和宽度、经后弓螺钉固定钉道长度和侧块钉道长度、后弓固定与侧块固定进钉角度等解剖学数据.统计学分析所测量数据并对经寰椎后弓螺钉固定钉道长度与经侧块螺钉固定钉道长度两组数据配对student t检验,检验水准为α=0.05.结果 寰椎椎管内径宽度为(26.80±2.58)mm;进钉点寰椎后弓高度和宽度分别为(6.83±1.97)mm和(6.40±1.36)mm;椎动脉沟底后弓高度和宽度分别为(4.37±1.11)mm和(8.05±1.33)mm;经后弓螺钉固定钉道长度为(30.54±1.70)mm.进钉点置钉时钉道外倾角度为15°～20°、吻侧前倾角度为0°～5°.椎动脉沟底骨质高度小于颈椎常用螺钉直径3.5 mm的占25.6%(10具).经侧块螺钉固定钉道长度为(16.91±1.13)mm,进钉点置钉时钉道内倾角度为32.05°±6.03°、头侧前倾角度为5°.经后弓螺钉固定钉道长度与经侧块钉道长度两组数据配对student t检验统计分析结果显示差异有统计学意义(t=59.528,P＜0.001).结论 约有74.4%的人群可顺利经寰椎后弓螺钉固定完成上颈椎稳定性的重建,该技术不仅可使寰椎得到即刻、牢靠的稳定性,同时较寰椎经侧块螺钉固定技术具有较小的手术风险和操作难度,是一项具有推广价值的寰椎稳定技术.

Abstract：

Objective To investigate the anatomy of upper cervical vertebrae's stable reconstruction by poster arch of atlas screw by anatomic study. Methods To collect the anatomical data of 39 dry atlas with the average inner diameter of vessel of atlas, the average high and wide of the screw point of poster arch of atlas, the average high and wide of poster arch of atlas beneath the groove for vertebral artery, the tract length of poster arch screw, the tract length of lateral mass screw, the direction and angle of poster arch screw, and the direction and angle of lateral mass. Statistical comparison were performed with Student test between the tract length of poster arch screw and the tract length of lateral mass screw. Results The average inner diameter of vessel of atlas was (26.8±2.58) mm(21.7-31.0 mm). The screw point high and wide of poster arch of atlas were (6.83±1.97) mm and (6.40±1.36) mm respectively. The average high and wide of poster arch of atlas beneath the groove for vertebral artery were (4.37±1.11) mm and (8.05±1.33) mm respectively. The tract length of poster arch screw were (30.54±1.705) mm. The direction and angle of poster arch screw was 15°-20° incline laterally and 0°-5°incline cephalo. 25.6%(10 cases) patients with the diameter less than 3.5mm beneath the groove for vertebral artery. The direction and angle of lateral mass screw was 32.05°±6.03° incline medially and 5° incline cephalo. There were significant differences between the tract length of poster arch screw and the tract length of lateral mass screw(t=59.528, P＜0.001 ). Conclusion About 74.4% patients can reconstruct the upper cervical stable by poster arch of atlas screw. The technique can gain instant upper cervical stable, and reduce the risk of injury of blood vessel by over explore the atlas arch compare with the technique of lateral mass screw fixation of atlas. The technique is worth to promoting with its character of safe, easy perform and rigid fixation.     

Evaluation of anatomic landmarks and safe zones for screw placement in the atlas via the posterior arch

Several studies have evaluated quantitative anatomic data for direct lateral mass screw fixation. To analyze anatomic landmarks and safe zones for optimal screw placement through the posterior arc of the human atlas, morphometric parameters of 41 adult native human atlas specimens were quantitatively measured. Internal dimensions of the atlas (lateral mass, maximum and minimum intraosseous screw length), minimum height and width of the posterior arc and optimal screw insertion angles were defined on pQCT scans. By this, an optimal posterior screw insertion point (OIP) and a preferable screw direction (PSD) through the posterior arch into the lateral mass of C1 were defined. External dimensions (transverse and sagittal diameter) as well as the width of the mid-portion of C1 lateral mass were significantly higher in male specimens. The mean height of the posterior arch at the vertebral artery groove was 4.1 ± 0.8 mm in female and 4.6 ± 0.9 mm in male specimens. The optimal screw insertion point was located 21.6 ± 1.7 mm in female and 23.6 ± 2.3 mm in male lateral from the posterior tubercle of C1 (P < 0.01). The preferable screw direction was a mean medial inclination of 7.9 ± 1.9° in female and 7.3 ± 2.7° in male specimens and a mean rostral direction of 2.4 ± 1.8° in female and 3.1 ± 1.7° in male specimens. In conclusion, the presented study provides information for the use and design of upper cervical spine instrumentation techniques, such as screw placement to C1 via the posterior arch. The characterization of working areas and safe zones (OIP, PSD) might contribute to a minimization of screw malposition in this highly demanding instrumentation technique.     

寰椎后弓椎板钩联合枢椎椎弓根螺钉固定治疗Ⅱ型齿突骨折

目的评估寰椎后弓椎板钩联合枢椎椎弓根螺钉固定植骨融合治疗Ⅱ型齿突骨折的疗效。方法2004年3月-2007年3月对13例Ⅱ型齿突骨折患者以寰椎后弓椎板钩联合枢椎椎弓根螺钉固定自体髂骨植骨融合术进行治疗，其中6例伴脊髓受损症状。结果术中未发生椎动脉和脊髓损伤；平均随访时间为18个月（6—32个月）；未发生内固定物松动、断裂。所有患者寰枢椎均融合。6例脊髓受损患者术前JOA评分为10．1分（9．2～11．8分），术后2周JOA评分为15．6分（15．2～16．8分）。结论寰椎后弓椎板钩联合枢椎椎弓根螺钉固定植骨融合术治疗Ⅱ型齿突骨折是一种安全有效的方法。     

Anatomic and radiological study on posterior pedicle screw fixation in the atlantoaxial vertebrae of children

Objective： To investigate the feasibility of posterior fixation with 3.5-mm pedicle screws in the atlantoaxial vertebrae of children.
Methods： In this study, atlantoaxial vertebrae specimens were obtained from 10 cadavers of children aged 6-8 years. We measured the height and width of the C1 pedicle and the midportion of C1 lateral mass; the width of C1 posterior arch under the vertebral artery groove and the height of the external and internal one-third of this part; the external, internal height and the superior, middle, inferior width of the C2 pedicle （transverse foramen）. Furthermore, computed tomography （CT） axial scan was performed on 20 agematched volunteers to obtain relative data of their atlantoaxial vertebrae. We measured the length and width of the C1 and C2 pedicles in the atlantoaxial cross-sectional plane. On CT workstation, we also measured the angles between the longitudinal axes of the atlantoaxial pedicles and the midsagittal plane.
Results： For the cadaveric specimen group, the height and width of the C1 pedicle were （5.26±0.44） mm and （6.26±0.75） mm respectively. The height of the medial one-third of the Ct posterior arch under the vertebral artery groove was （4.07±0.24） mm. The external, internal height and superior, middle, inferior width of the C2 pedicle was （6.86±0.48） mm, （6.67±0.49） mm, （6.63 ±0.61） mm, （5.41±0.39） mm and （3.71±0.30） mm, respectively. For the volunteer group measured by CT scan, the height and width of the C1 pedicle were （5.47 ±0.34） mm and （6.63±0.54） mm respectively, while （6.59±0.51） mm and （5.13 ±0.42） mm of the C2 pedicle. The angles between the atlas, axis pedicles and the midsagittal plane were （9.60±1.32）° and （27.80±2.22）° respectively.
Conclusion： It is feasible to place a 3.5-mm pedicle screw in the C1 and C2 pedicles of children aged 6-8 years old.     

Routine insertion of the lateral mass screw via the posterior arch for C1 fixation: feasibility and related complications

Background contextTo our knowledge, there is no clinical study analyzing the feasibility and complications of the routine insertion of the lateral mass screw via the posterior arch for C1 fixation in a live surgical setting.PurposeTo evaluate the feasibility of routine insertion of the lateral mass screw via the posterior arch and related complications.Study designProspective clinical-radiological analysis.Patient sampleFifty-two consecutive patients with 102 C1 lateral mass screws inserted via the posterior arch.Outcome measuresCortical perforation, vertebral artery injuries, and visual analog scale score of occipital neuralgia recorded on a prospective database.MethodsAll consecutive patients in whom lateral mass screw placement via the posterior arch was attempted as the first choice whenever C1 posterior fixation was necessary were enrolled. Prospective database, clinical records, questionnaires regarding occipital neuralgia, pre- and postoperative computed tomography (CT) angiograms, and follow-up radiographs and CT scans were analyzed. This study was supported by a $9,000 academic research grant by the first author's hospital. The last author receives royalties for a posterior cervical fixation system, which is not the topic of this study and is not used or mentioned in this article.ResultsOne hundred two screws were attempted in 52 consecutive patients by a single surgeon. The height of 43 posterior arches (42%) was smaller than 4 mm on preoperative CT angiography. Lateral mass screws could be inserted via the posterior arch in all cases including eight with nine ponticuli posticus and seven with seven persistent first intersegmental arteries, but the posterior arch was perforated cranially by 7, caudally by 30, and craniocaudally (partially) by 3 screws and vertically split by 14 screws. Among the last 28 screws for which the authors' overdrilling technique was used, only one vertical split occurred, whereas among the first 74 screws without overdrilling, 13 vertical splits occurred. None of them led to screw loosening or nonunion. There were no vertebral artery injuries. Among the 19 patients with preoperative occipital neuralgia, 12 had complete resolution and seven had alleviation at the last follow-up. Among the 33 patients without preoperative neuralgia, seven developed new neuralgia postoperatively. Three of them underwent C2 root transection and the other four underwent C2 root dissection for intraarticular fusion of the facet joints. Of the seven, five had complete resolution and two had mild discomfort at the last follow-up.ConclusionsRoutine insertion of the lateral mass screw via the C1 posterior arch was feasible in even those with a small posterior arch, ponticulus posticus, or persistent first intersegmental artery. Although cortical perforation or vertical splitting of the posterior arch was often inevitable, it did not lead to significant weakening of the fixation or nonunion. Vertical split could be minimized by overdrilling the posterior arch. Vertebral artery injury was preventable by mobilization before screw insertion. Occipital neuralgia was not uncommon but thought to be unrelated to screw placement in most cases.     

The computed tomography angiography study of the spatial relationship between C1 transpedicular screw trajectory and V3 segment of vertebral artery

Background Context

To our knowledge, there is no study that has systematically analyzed the relationship between C1 transpedicular screw trajectory and V3 segment of vertebral artery (VA V3 segment).