C1-C2 pedicle screw fixation with rigid cantilever beam construct: case report and technical note

OBJECTIVE AND IMPORTANCE: Transarticular screw fixation of the C1-C2 complex provides immediate rigid fixation of the unstable spine. The technique is not feasible in a certain proportion of patients because of the position of the vertebral artery or the patient's body habitus. CLINICAL PRESENTATION: The authors describe a rigid screw technique for the surgical treatment of a woman who was excluded as a candidate for C1-C2 transarticular screw fixation. TECHNIQUE: C1-C2 pedicle screw fixation was achieved using a fixed moment arm cantilever beam system. This system provided immediate rigid fixation of the C1-C2 complex in a patient who was not a candidate for transarticular screw fixation. CONCLUSION: This technique is technically more forgiving than posterior transarticular screw fixation and may be applied to a broader spectrum of patients.     

Percutaneous atlantoaxial anterior transarticular screw fixation combined with mini-open posterior C1/2 wire fusion for patients with a high-riding vertebral artery

Context/objective: To describe the technique and clinical results of percutaneous atlantoaxial anterior transarticular fixation combined with limited exposure posterior C1/2 arthrodesis in patients with a high-riding vertebral artery.

Design setting: Zhejiang Spine Center, China.

Participants: Five patients with a high-riding vertebral artery and an upper cervical fracture.

Interventions: Percutaneous atlantoaxial anterior transarticular screw fixation combined with limited exposure posterior C1/2 wire fusion.

Outcome measures: Computed tomography scans were used to assess the high-riding vertebral artery and feasibility of anterior transarticular screw fixation preoperatively. A Philadelphia collar was used to immobilize the neck postoperatively. Anteroposterior (open-mouth) and lateral views were obtained at pre/postoperation and at the follow-up.

Results: The operation was performed successfully on all of the patients, and no intraoperative operation-related complications such as nerve injury, vertebral artery, and soft tissue complications occurred. The mean follow-up period was 33.8 months (range: 24 to 58 months). No screw breakage, loosening, pullout, or cutout was observed. Bone union was achieved in all patients at the last follow-up.

Conclusions: Our small case series results suggested that percutaneous anterior transarticular screw fixation combined with mini-open posterior C1/2 wire fusion is a technically minimally invasive, safe, feasible, and useful method to treat patients with a high-riding vertebral artery.     

Computer-assisted Magerl's transarticular screw fixation for atlantoaxial subluxation

We report two patients with rheumatoid arthritis in whom posterior atlantoaxial fixation was carried out using transarticular screws with computer assistance. Two bilateral transarticular screws were inserted in one patient; however, in the other patient, only a unilateral screw was used, because computerized images showed that the vertebral artery at the other side was placed too medially to allow insertion of the screw. Neither of these patients had any neurovascular complications after surgery. Computer-assisted surgery is useful for avoiding neurovascular complications with transarticular screw fixation of C1-2. Received: January 26, 2001 / Accepted: August 13, 2001     

前路经寰枢关节螺钉内固定术治疗寰枢椎不稳定的生物力学及临床研究

目的 探讨前路经寰枢关节螺钉内固定术的生物力学稳定性及疗效.方法 8具新鲜颈椎标本,对每一标本先后行正常状态、齿状突Ⅱ型骨折、前路经寰枢关节螺钉内固定术、后路Magerl螺钉内固定术4种状态三维运动范围的测定.并对20例创伤性寰枢椎不稳定患者施行前路经寰枢关节螺钉内固定术,在齿状突与寰椎前结节后方置入颗粒状松质骨.结果 前路经寰枢关节螺钉内固定术与后路Magerl螺钉内固定术均明显减少寰枢关节各方向运动范围,经统计学检验差异无统计学意义.20例患者中,1例颈脊髓完全损伤患者,术后1个月死于肺部感染.其余19例病例获得随访,时间7个月～3年,平均18个月,无椎动脉及脊髓损伤,所有病例获得骨性融合.结论 前路经寰枢关节螺钉内固定术,操作简便,固定可靠,损伤脊髓或椎动脉的风险较小.     

后路经关节螺钉固定颗粒状植骨融合治疗寰枢关节不稳定

目的:探讨后路经C1、C2侧块关节螺钉固定、颗粒状松质骨植骨行寰枢关节融合治疗寰枢关节不稳的效果。方法:自1999年12月~2003年4月对58例因齿状突不连、寰椎横韧带断裂或松弛导致寰枢关节不稳定的病例施行了后路经C1、C2侧块关节的螺钉固定术,然后在C1、C2后弓间植入颗粒状松质骨。术中不用钛缆固定寰椎后弓与枢椎棘突。术后不需任何外固定。结果:无手术中损伤脊髓和椎动脉的病例。49例获得随访,时间6个月～3年10个月,平均20个月,全部获得了骨性融合。结论:当寰枢关节不稳定时用两枚螺钉由后路经C1、C2侧块关节固定即可起到足够的稳定作用;在C1、C2后弓间植入颗粒状松质骨可获得很高的融合率。     

前路经寰枢关节螺钉内固定术治疗寰枢关节不稳定的解剖学及临床研究

目的 为前路经寰枢关节螺钉内固定术提供临床解剖学依据.方法 在100对中国成人干燥寰、枢椎配对标本上,对与临床前路经寰枢关节螺钉内固定术相关的数据进行解剖学测量.并对11例创伤性寰枢椎不稳定患者施行了前路经寰枢关节螺钉内固定术,在齿状突与寰椎前结节后方置入颗粒状松质骨.结果 前路经寰枢关节螺钉内固定术冠状面上螺钉植入最小外偏角(5.5±2.0)度,最大外偏角(23.6±2.1)度,矢状面上螺钉植入最小后倾角(14.9±2.6)度,最大后倾角(25.6 ±2.5)度,内侧钉道距离(16.58±1.49)mm,外侧钉道距离(26.44±1.75)mln.11例患者中,1例颈脊髓完全损伤患者,术后1个月死于肺部感染.其余10例病例获得随访,时间7个月～3年,平均17个月,无椎动脉及脊髓损伤,所有病例获得骨性融合.结论 前路经寰枢关节螺钉内固定术,操作简便,损伤脊髓或椎动脉的风险较小,为寰枢椎不稳定患者提供了一种新的内固定治疗方法.     

Safety of atlantoaxial fusion using laminar and transarticular screws combined with an atlas hook in a patient with unilateral vertebral artery occlusion (case report)

Objective and importance  A disadvantage of transarticular and C2 pedicle screws is vertebral artery (VA) injury as a result of screw misplacement. If unilateral occlusion of the VA is present, VA injury of the dominant side will cause fatal complications as a result of collateral flow insufficiency. Several authors have recently reported the usefulness of C2 laminar screws because of their safety on VA injury. We used transarticular and C2 laminar screws combined with the atlas hook in a patient with C1-2 instability and unilateral VA occlusion, in order to reduce the risk of further VA injury. Clinical presentation  A 64-year-old woman with rheumatoid atlantoaxial subluxation complained of cervical myelopathy and neck pain. Preoperative MR angiography showed a left side VA occlusion. Technique  The patient underwent atlantoaxial, posterior fusion using a transarticular screw on the side of the occlusion and a C2 laminar screw on the dominant side combined with a bilateral atlas hook. The transarticular screw was inserted using a navigation system and image intensifier, and the laminar screw was inserted free hand. Bone grafting from the iliac crest was performed. Conclusion  Transarticular and C2 laminar screws fixation combined with the atlas hook in a patient with unilateral VA occlusion is a useful technique, in order to reduce the risk of further VA injury.     

A biomechanical study of unilateral posterior atlantoaxial transarticular screw fixation

The purpose of this study was to investigate the fixation of C1-C2 instability with the use of a unilateral screw. Transarticular screw placement across C1-C2 may be contra-indicated in up to 20% of specimens on at least one side because of anatomic variations or other pathological processes. Hence the current study looks into unilateral screw fixation of C1- C2 instability. Eight cervical spine specimens, C1 through C5, were harvested from fresh human cadavers (4 male and 4 female) of average age 67 years (54-80). C1 and C2-C5 vertebrae were potted to allow motion only at the C1-C2 articulation. Cutting the transverse ligament on both sides of the odontoid and the tectorial membrane destabilized the specimens. Transarticular screw fixation of C1-C2 was performed in a manner similar to the technique described by Magerl. The stability was tested after fixation with one transarticular screw together with a posterior graft and wire. Placement of the screw was randomized, resulting in half the specimens receiving screws on the right side and the remaining half on the left side. The stiffness of the C1-C2 articulation was tested in rotation, lateral bending, flexion, and anterior translation in random order. The rotational stiffness was 1.44 +/- 0.44 N-m/deg, while lateral bending stiffness values were 2.33 +/- 1.14 N-m/mm (right bending) and 2.81 +/- 1.36 N-m/mm (left bending). The stiffness value in flexion was 0.813 +/- 0.189 N-m/mm and in translation 67.1 +/- 25.1 N/m. It was found that stability after unilateral transarticular screw fixation was less than that previously reported after bilateral transarticular screw fixation, but similar to that found with modified Brooks posterior wiring, which has been shown to provide better stability than other posterior wiring methods, and fusion rates of 96% have been reported. We concluded that C1-C2 unilateral posterior transarticular screw fixation with supplemental posterior graft and wiring would confer adequate stability in cases where bilateral screw placement is contraindicated.     

C1-C2 transarticular screw fixation: technical aspects.

OBJECTIVE: I review posterior atlantoaxial fusion with transarticular screw fixation, including indications, complications, and operative technique, emphasizing my experience. METHODS: The indications for C1-C2 transarticular screw fixation include traumatic injuries to the atlantoaxial complex, instability resulting from inflammatory disease (rheumatoid arthritis), and congenital abnormalities (os odontoideum). All patients underwent stabilization using cannulated C1-C2 transfacetal screws by the method described by Magerl. Supplemental interspinous fusion with bicortical autologous iliac crest graft and titanium cable was used to restore the posterior tension band by use of the method described by Sonntag's group. Preoperatively, all patients underwent imaging with plain radiographs, magnetic resonance imaging, and axial computed tomography. Patients were maintained in a rigid cervical orthosis postoperatively. RESULTS: Measures used to improve safety and efficacy include patient positioning, fluoroscopic guidance, preoperative magnetic resonance imaging, axial computed tomography, and open reduction of C1-C2 subluxation before screw passage. In this series of 75 patients, fusion was obtained in 72 patients (96%). There were no instances of vertebral artery injury, errant screw placement, instrumentation failure, dural laceration, spinal cord injury, or hypoglossal nerve injury. CONCLUSION: C1-C2 transarticular screw fixation with a posterior tension band construct provides excellent fusion rates with few perioperative complications. Preoperative imaging and meticulous surgical technique improve outcomes.     

Anterior retropharyngeal fixation C1-2 for stabilization of atlantoaxial instabilities: study of feasibility, technical description and preliminary results

Posterior transarticular screw fixation C1-2 with the Magerl technique is a challenging procedure for stabilization of atlantoaxial instabilities. Although its high primary stability favoured it to sublaminar wire-based techniques, the close merging of the vertebral artery (VA) and its violation during screw passage inside the axis emphasizes its potential risk. Also, posterior approach to the upper cervical spine produces extensive, as well as traumatic soft-tissue stripping. In comparison, anterior transarticular screw fixation C1-2 is an atraumatic technique, but has been neglected in the literature, even though promising results are published and lectured to date. In 2004, anterior screw fixation C1-2 was introduced in our department for the treatment of atlantoaxial instabilities. As it showed convincing results, its general anatomic feasibility was worked up. The distance between mid-sagittal line of C2 and medial border of the VA groove resembles the most important anatomic landmark in anterior transarticular screw fixation C1-2. Therefore, CT based measurements on 42 healthy specimens without pathology of the cervical spine were performed. Our data are compiled in an extended collection of anatomic landmarks relevant for anterior transarticular screw fixation C1-2. Based on anatomic findings, the technique and its feasibility in daily clinical work is depicted and discussed on our preliminary results in seven patients.     

颈椎后路“组合式”内固定治疗寰枢关节不稳或脱位的临床疗效

目的:评价颈椎后路“组合式”内固定治疗寰枢关节不稳或脱位的临床效果。方法:回顾分析因颅椎区骨发育畸形、血管变异或者常规固定方式失败而实施寰枢椎后路“组合式”内固定术患者共58例,其中男性24例,女性34例;年龄7~75岁,平均47.8±14.7岁。术前诊断寰枢关节不稳33例,寰枢关节脱位25例。合并颈脊髓功能损害者32例(JOA 8~16分,平均13.2±1.8分)。采用的内固定方式包括寰枢椎弓根螺钉、经寰枢侧块关节螺钉(Magerl技术)、枢椎椎板螺钉、下颈椎侧块螺钉及下颈椎棘突螺钉。58例“组合式固定”患者中,45例应用2种内固定方式组合,9例应用3种方式组合,4例应用4种方式组合。使用“组合式固定”的原因包括:枢椎段椎动脉高跨、枢椎椎弓根细小或椎体发育不良、颈椎椎弓根变薄(颈椎融合畸形患者)、枢椎椎弓根骨质疏松明显以及医源性枢椎椎弓骨折等。观察手术融合率及并发症,并比较手术前后的脊髓功能。结果:全部病例术中均未出现脊髓及血管损伤。随访时间24~72个月,平均36.8±10.5个月。57例(98.3%)未出现内固定松动或断裂并获得骨性融合,1例发生内固定松动造成未融合。术前合并颈脊髓功能损害者32例,术后脊髓功能均获得不同程度改善(术后JOA 11~17分,平均15.2±1.5分)。6例患者出现了并发症,包括伤口感染延迟愈合、脑脊液漏以及内固定松动。结论:针对合并颅椎区骨发育畸形、血管变异或者常规固定方式失败的寰枢椎不稳或脱位患者,合理选择“组合式”内固定治疗是安全、有效的。     

Value of intraoperative true lateral radiograph of C2 pedicle for C1-2 transarticular screw insertion.

BACKGROUND CONTEXT: Transarticular C1-2 screws are widely used in posterior cervical spine instrumentation. Injury to the vertebral artery during insertion of transarticular Cl-2 screw remains a serious complication. Use of a computer-assisted surgery system decreases this complication considerably. However, this system encounters problems in ensuring complete accuracy because of positional variations during preoperative and intraoperative imaging generation. Therefore, intraoperative fluoroscopy still is one of the commonly used methods to guide insertion of transarticular Cl-2 screw. Evaluation of a true lateral radiographic view of the C2 pedicle for screw trajectory during C1-2 transarticular screw insertion may help to minimize this potential complication. PURPOSE: To evaluate the value of intraoperative true lateral radiograph of the C2 pedicle for screw trajectory during C1-2 transarticular screw insertion. STUDY DESIGN: To compare the height of the C2 pedicle area allowing instrumentation on true lateral view radiograph of the C2 pedicle and computed tomographic (CT) scan with multiplanar reconstruction. METHODS: Twenty embalmed human cadaveric cervical spine specimens were used to insert a total of 40 C1-2 transarticular screws using Magerl and Seemann technique. One side of the C2 transverse foramen was filled with radiopaque material (lead oxide) to simulate the artery and to demarcate the danger zone for better visualization on radiography. Measurements and calculation of the mean and standard deviation of the height of the area allowing instrumentation of the C2 pedicle were done on true lateral view radiograph of the C2 pedicle, the sagittal and 30 degrees sagittal views relative to the frontal plane passing exactly through the center of the C2 pedicle of CT scans. Student t test was applied to calculate the statistical significance of measured values. Statistical significance was defined as por=.36. Using sagittal CT scan views, the height of pedicles was 7.71+/-0.7 mm (right) and 7.58+/-1.01 mm (left), p>or=.23. On 30 degrees sagittal CT scan views, the height of pedicles was 7.84+/-1.00 mm (right) and 7.76+/-1.02 mm (left), p>or=.27. The p value was >or=.78, >or=.56, and >or=.49 for true lateral radiographic view and sagittal CT scan view, true lateral radiographic view and 30 degrees sagittal CT scan view, and sagittal CT scan view and 30 degrees sagittal CT scan views, respectively. On lateral view of cervical spine, the decline angle of the transarticular screw was 51.3+/-0.50 degrees (right) and 50.68+/-0.41 degrees (left), p>or=.17. Mean decline angle was 51+/-0.43 degrees . On the anteroposterior (AP) view, radiograph median angle was 6.87+/-0.53 degrees (right) and 6.0+/-0.59 degrees (left), p>or=.25. Mean median angle was 6.44+/-0.62 degrees. CONCLUSIONS: True lateral radiographic views of the pedicles provide useful information for defining screw trajectory intraoperatively. Using this view along with AP and lateral view of cervical spine and preoperative three-dimensional CT scan may narrow the margin of error in this delicate area.     

Atlantoaxial transarticular screw fixation and posterior fusion using ultra-high-molecular-weight polyethylene cable

This article attempts to evaluate the effectiveness of the ultra-high-molecular-weight polyethylene (UHMW-PE) cable system in atlantoaxial transarticular screw fixation and posterior fusion through the clinical results of 10 postoperative patients with atlantoaxial subluxation secondary to rheumatoid arthritis. Among them, one patient with only one screw placed owing to an anomalous vertebral artery had the correction loss of the 3-mm atlas-dens interval after surgery. Another patient had a second operation to remove the screw and cable after 2 years 11 months because a unilateral transarticular screw had come to protrude through the lateral mass of the atlas ventrally. All patients had achieved C1-C2 osseous fusion without any complications associated with this cable system. The UHMW-PE cable is a very useful material as sublaminar wiring in atlantoaxial transarticular screw fixation and posterior fusion.     

Misdiagnosis and management of iatrogenic pseudoaneurysm of vertebral artery after Harms technique of C1-C2 fixation

Harms technique of C₁-C₂ fixation for atlantoaxial complex becomes more popular due to good fusion rate and low vertebral artery injury (VAI) rate. But considering the unique and variable anatomy of atlanto-axial complex, iatrogenic VAI will result in catastrophic consequences and provides particular surgical challenges for surgeons. To our knowledge, comparing with iatrogenic VAI in the screw hole, iatrogenic VAI in the “open space” is much rarer during the Harms technique of C₁-C₂ fixation. In this article, we present a case of iatrogenic vertebral artery pseudoaneurysm after Harms technique of posterior C₁-C₂ fixation. This case of iatrogenic VAI effectively treated by endovascular coil occlusion and external local compression was initially misdiagnosed as VAI by pedicle screw perforation. It can be concluded that intraoperative or postoperative computed angiography is very helpful to diagnose the exact site of VAI and the combination of endovascular coil occlusion as well as external local compression can further prevent bleeding and abnormal vertebral artery flow in the pseudoaneurysm. However, patients treated require further follow-up to confirm that there is no recurrence of the pseudoaneurysm.     

寰枢椎后路经关节螺钉内固定治疗寰枢椎不稳定的生物力学及临床研究

目的评价寰枢椎后路经关节螺钉内固定术两种不同钉道的生物力学稳定性及疗效。方法在8例新鲜尸体标本依次轮流测试正常、Ⅱ型齿状突骨折行AO进钉点与改良进钉点两种后路钉道螺钉固定术模型三维运动范围，并在16例寰枢椎不稳定患者，采用枢椎下关节突下缘正中点为进钉点的方法行经关节螺钉固定及自体颗粒样松质骨植骨术。结果两种入钉方法均能明显减少寰枢关节的各向运动角度（P〈0．01），但两者间差异无统计学意义（P〉0．05）。经5～48个月随访，16例患者寰枢关节稳定性均获得恢复与骨融合，无并发症。结论新入钉点解剖标志明确。钉道长，能提供牢固地固定，并发症发生率低。     

C1-2 transarticular screw fixation in high-riding vertebral artery: suggestion of new trajectory

A significant drawback of atlantoaxial transarticular screw fixation is a potential risk of vertebral artery injury, especially with a high-riding type. The authors propose a relatively safe trajectory in cases of high-riding vertebral artery by using the 3-dimensional computerized tomography image reconstruction programs. Twelve consecutive patients with a pathologic condition in atlantoaxial complex were prospectively analyzed. Five other patients, whose high-riding vertebral arteries were incidentally found during the 3-dimensional computerized tomography performance for other cervical pathologic conditions, were also included. The preoperative screw simulation images, convergence angle, and caudal tilting angle for each screw were obtained from each patient. Of 17 subjects, 7 had high-riding vertebral artery unilaterally and 1 had bilaterally. All 12 patients with pathologic atlantoaxial complex, including 2 unilateral and 1 bilateral high-riding vertebral artery, had atlantoaxial transarticular screw fixation. For these 3 patients, the entry point and the trajectory for screw were moved more superiorly and medially as in cases with C2 pedicle screwing. The mean convergence angle and caudal tilt angle obtained during screw simulation for patients with high-riding vertebral arteries was 17.6 and 38 degrees compared with 21 and 53.3 degrees for patients with normal course of vertebral artery. It was possible to insert transarticular screws safely in patients with high-riding vertebral artery guided by preoperative screw insertion simulation program.     

前路三钉内固定治疗寰椎-齿状突Ⅱ型骨折

背景：齿状突加寰枢椎前路经关节螺钉内固定是近来治疗寰椎-齿状突Ⅱ型骨折的一种新方法,临床报道较少。 目的：探讨颈前路三钉,即齿状突螺钉加寰枢椎前路经关节螺钉内固定治疗寰椎-齿状突Ⅱ型骨折的方法及疗效。 方法：2008年2月至2011年10月于C型臂X线机透视下行颈前路齿状突螺钉加寰枢椎经关节螺钉内固定治疗寰椎-齿状突Ⅱ型骨折5例。 结果：5例骨折患者共植入5枚齿状突螺钉,9枚经寰枢关节螺钉,1例因左侧经寰枢关节螺钉进钉点处骨折而行右侧单侧固定。全部获得随访,随访时间为10~30个月,平均18个月,螺钉位置满意,齿状突骨折均获骨性愈合,寰枢关节稳定,无一例发生螺钉松动、断钉,无一例发生脊髓、椎动脉损伤等并发症。 结论：颈前路齿状突螺钉加寰枢椎经关节螺钉内固定治疗寰椎-齿状突Ⅱ型骨折,对齿状突直接固定同时即刻稳定寰枢椎,为寰椎-齿状突Ⅱ型骨折患者提供了一种新的治疗方法。     

Morphologic considerations of C2 isthmus dimensions for the placement of transarticular screws

STUDY DESIGN: This study examines the C2 vertebrae using both direct anatomic and computed tomographic measurements. OBJECTIVE: To define the relation of the C2 vertebrae bony elements to the vertebral artery and the spinal canal, to determine individuals at risk for vertebral artery injury during C1-C2 transarticular screw placement. SUMMARY OF BACKGROUND DATA: Recent literature assessing the safety of upper cervical spine transarticular screws has concentrated on technique, including the optimal point of entry and path projection of the screw. The actual dimensions of the C2 isthmus of the pars interarticularis has not been examined in a large number of specimens. METHODS: C2 isthmus width and height measurements were made on 205 human cadaveric C2 vertebrae. Vertebrae predicted to be at risk for vertebral arterial injury were imaged by computed tomography. RESULTS: There were 102 female and 103 male specimens with mean isthmus widths of 8.2 +/- 1.5 mm and 7.2 +/- 1.3 mm, respectively. Five specimens (2.4%) had an isthmus width less than 5 mm. The mean isthmus heights were 8.6 +/- 2.0 mm and 6.9 +/- 1.5 mm for male and female specimens, respectively. In twenty-four specimens (11.7%), one or both isthmi had a height of less than 5 mm. Six of these specimens were male and 18 were female. The right C2 isthmus was generally smaller than the left. Computed tomographic measurements closely approximated those of the actual dimensions of the isthmi. CONCLUSIONS: Placing a 3.5 mm screw in a patient with narrow C2 isthmus dimensions (smaller than 5 mm in either the height or width) is technically difficult. Because of narrow C2 isthmus width and/or height, approximately 10% of patients may be at risk for a vertebral artery injury with placement of C1-C2 transarticular screws.     

Risk of vertebral artery injury: comparison between C1–C2 transarticular and C2 pedicle screws

Background contextTo our knowledge, no large series comparing the risk of vertebral artery injury by C1–C2 transarticular screw versus C2 pedicle screw have been published. In addition, no comparative studies have been performed on those with a high-riding vertebral artery and/or a narrow pedicle who are thought to be at higher risk than those with normal anatomy.PurposeTo compare the risk of vertebral artery injury by C1–C2 transarticular screw versus C2 pedicle screw in an overall patient population and subsets of patients with a high-riding vertebral artery and a narrow pedicle using computed tomography (CT) scan images and three-dimensional (3D) screw trajectory software.Study designRadiographic analysis using CT scans.Patient sampleComputed tomography scans of 269 consecutive patients, for a total of 538 potential screw insertion sites for each type of screw.Outcome measuresCortical perforation into the vertebral artery groove of C2 by a screw.MethodsWe simulated the placement of 4.0 mm transarticular and pedicle screws using 1-mm-sliced CT scans and 3D screw trajectory software. We then compared the frequency of C2 vertebral artery groove violation by the two different fixation methods. This was done in the overall patient population, in the subset of those with a high-riding vertebral artery (defined as an isthmus height ≤5 mm or internal height ≤2 mm on sagittal images) and with a narrow pedicle (defined as a pedicle width ≤4 mm on axial images).ResultsThere were 78 high-riding vertebral arteries (14.5%) and 51 narrow pedicles (9.5%). Most (82%) of the narrow pedicles had a concurrent high-riding vertebral artery, whereas only 54% of the high-riding vertebral arteries had a concurrent narrow pedicle. Overall, 9.5% of transarticular and 8.0% of pedicle screws violated the C2 vertebral artery groove without a significant difference between the two types of screws (p=.17). Among those with a high-riding vertebral artery, vertebral artery groove violation was significantly lower (p=.02) with pedicle (49%) than with transarticular (63%) screws. Among those with a narrow pedicle, vertebral artery groove violation was high in both groups (71% with transarticular and 76% with pedicle screws) but without a significant difference between the two groups (p=.55).ConclusionsOverall, neither technique has more inherent anatomic risk of vertebral artery injury. However, in the presence of a high-riding vertebral artery, placement of a pedicle screw is significantly safer than the placement of a transarticular screw. Narrow pedicles, which might be anticipated to lead to higher risk for a pedicle screw than a transarticular screw, did not result in a significant difference because most patients (82%) with narrow pedicles had a concurrent high-riding vertebral artery that also increased the risk with a transarticular screw. Except in case of a high-riding vertebral artery, our results suggest that the surgeon can opt for either technique and expect similar anatomic risks of vertebral artery injury.     

Translaminar screws of the axis—an alternative technique for rigid screw fixation in upper cervical spine instability

C2 pedicle screws or transarticular atlantoaxial screws are technically demanding and carry an increased risk of vertebral artery injury. In up to 20% of cases, pedicle and transarticular screw placement is not possible due to a high-riding vertebral artery or very small C2 pedicles in addition to other anatomical variations. Translaminar screws have been reported to rigidly capture posterior elements of C2 and therefore appear to be a suitable alternative. We present our first experiences and clinical results with this new method in two neurosurgical spine centers. Twenty-seven adult patients were treated between 2007 and 2010 in two neurosurgical spine departments with C2 translaminar screw fixation for upper cervical spine instability of various origins (e.g., trauma, tumor, dens pseudarthrosis). Eight patients were men and 19 were women. Mean age was 68.9 years. In most cases, translaminar screws were used because of contraindications for pedicle or transarticular screws as a salvage technique. All patients were clinically assessed and had CT scans postoperatively to verify correct screw placement. Follow-up was performed with reexamination on an ambulatory basis. Mean follow-up was 7.6 months for all patients. In 27 patients, 52 translaminar screws were placed. There were no intraoperative complications. Postoperatively, we identified four screw malpositions using a new accuracy grading scale. One screw had to be revised because of violation of the spinal canal >4 mm. None of the patients had additional neurological deficits postoperatively, and all showed stable cervical conditions at follow-up. Two patients died due to causes not associated with the stabilization technique. The fusion rate for patients with C1/C2 fixation is 92.9%. Translaminar screws can be used at least as an additional technique for cases of upper cervical spine instability when pedicle screw placement is contraindicated or not possible. The current data suggest comparable biomechanical stability and fusion rates of translaminar screws to other well-known posterior fixation procedures. In addition, translaminar screw placement is technically less demanding and reduces the risk of vertebral artery injury.