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。     

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。     

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.     

The original hole-in-one guide for atlantoaxial transarticular screw fixation

Atlantoaxial fusion by transarticular screw fixation provides firm fixation, and good results have been reported. However, there are also problems, such as injury of the vertebral artery at the time of screw insertion. For accurate facet fusion, we developed a new hole-in-one guide for screw fixation and obtained good results with its use. In 60 adult subjects, we measured the antero-posterior and transverse axes and determined the center of the atlantoaxial surface and the insertion point of the screw in three dimensions on computed tomography scans. Based on these values, we measured the optimum screw insertion angle on sagittal and coronal planes, and the distance between the center and the posterior margin of the joint surface; our new hole-in-one guide was produced with these data. When the guide tip is determined to be located at the center posterior margin of the axial joint surface, and the guidewire insertion point is determined to be located at the center of the axial inferior facet immediately above the C2/3 joint, the guidewire is passed through the axial pedicle and the center of the atlantoaxial joint. Since April 1997, we have used this hole-in-one guide technique in eight patients with atlantoaxial instability. The screws passed the pars interarticularis and the center of the atlantoaxial joint in all patients with safety and accuracy. No complications associated with this technique occurred. Received: December 24, 1999 / Accepted: August 25, 2000     

Transarticular screws in the management of C1-C2 instability in children

C1-C2 instability is a challenging problem in the pediatric population. Small patient size and poor healing potential in the at-risk groups, such as patients with Down syndrome and os odontoideum, make fixation difficult. Instability in patients with Down syndrome is a common problem, and traditional methods of fixation have a high complication rate and are a challenge given the frequent anatomic abnormalities such as an incomplete or hypoplastic arch, os odontoideum, and incomplete passive reduction. The purpose of this study was to review our experience of transarticular screw use in pediatric patients and to define the potential applications of this technique in pediatric C1-C2 instability. Twelve patients, with C1-C2 instability managed with transarticular screws at the authors' institution, were reviewed. The youngest patient treated was 5 years old with a mean age for the group of 11.5 years. The group consisted of 3 patients with Down syndrome and 9 patients with os odontoideum. Three of the patients with os odontoideum failed previous posterior wiring. Two patients presented with an acute spinal cord injury in the setting of chronic instability. Preoperative computed tomography or magnetic resonance imaging was used in all patients to define the vascular and bony anatomy. No further surgery has been required at a mean follow-up of 5.1 years in all patients. Although vertebral size and congenital anomalies may make screw positioning challenging, the technique allows fixation in the absence of a complete posterior arch of C1 and eliminates the need for instrumentation in the canal. This technique also provides a high fusion rate in a complicated patient population.     

Atlantoaxial stabilization with the use of C1-3 lateral mass screw fixation. Technical note

Atlantoaxial stabilization has evolved from simple posterior wiring to transarticular screw fixation. In some patients, however, the course of the vertebral artery (VA) through the axis varies, and therefore transarticular screw placement is not always feasible. For these patients, the authors have developed a novel method of atlantoaxial stabilization that does not require axial screws. In this paper, they describe the use of this technique in the first 10 cases. Ten consecutive patients underwent the combined C1-3 lateral mass-sublaminar axis cable fixation technique. The mean age of the patients was 62.6 years (range 23-84 years). There were six men and four women. Eight patients were treated after traumatic atlantoaxial instability developed (four had remote trauma and previous nonunion), whereas in the other two atlantoaxial instability was caused by arthritic degeneration. All had VA anatomy unsuitable to traditional transarticular screw fixation. There were no intraoperative complications in any of the patients. Postoperative computed tomography studies demonstrated excellent screw positioning in each patient. Nine patients were treated postoperatively with the aid of a rigid cervical orthosis. The remaining patient was treated using a halo fixation device. One patient died of respiratory failure 2 months after surgery. Follow-up data (mean follow-up duration 13.1 months) were available for seven of the remaining nine patients and demonstrated a stable construct with fusion in each patient. The authors present an effective alternative method in which C1-3 lateral mass screw fixation is used to treat patients with unfavorable anatomy for atlantoaxial transarticular screw fixation. In this series of 10 patients, the method was a safe and effective way to provide stabilization in these anatomically difficult patients.     

Transarticular atlanto-axial screw fixation for treatment of C1-C2 instability

Posterior transarticular screw fixation of the C1-C2 complex has become an accepted method of arthrodesis for patients requiring posterior C1-C2 fusion. Since 2000, four patients (2 males and 2 females) were treated with this surgical approach for management of atlantoaxial instability, including odontoid fracture with unilateral C1-C2 luxation, odontoid pseudarthrosis, complex congenital malformation of the craniovertebral junction and rheumatoid arthritis. All patients underwent stabilization with 2 transarticular C1-C2 screws, without any posterior interspinous graft. Patients were maintained in a rigid cervical orthesis 3 months postoperatively. Results were good, without any complication, after a short mean follow-up (8 months). Technical aspects of the technique are reported, The risk of screw malpositioning and vertebral artery or neural injury is minimal and can be lowered by using preoperative CT scan and MRI, and by using intraoperative fluoroscopy. Transarticular C1-C2 screw fixation proves to be a major surgical approach for treatment of atlantoaxial instability.     

Acute combination fracture of atlas and axis: "triple" anterior screw fixation in a 92-year-old man: technical note

BACKGROUND: The combination of odontoid and bilateral transarticular C1-C2 anterior screw fixation is a recent addition in treating C1-type II odontoid fractures. When feasible, it ensures early maximal stability, even if it slightly reduces the mobility of C1-C2 complex. We report a case of combination atlas-type II odontoid fracture that occurred in a 92-year-old man. The instability was treated with odontoid screw fixation and anterior bilateral C1-C2 transarticular screw fixation in a single stage. The aim of the article is to describe the feasibility of "triple" anterior screw fixation in the presence of C1-type II odontoid fracture. METHODS: The diagnosis, treatment, and outcome of a 92-year-old patient with mild tetraparesis caused by C1-type II odontoid fracture were assessed. RESULTS: Cervical x-rays, computed tomographic scan, and magnetic resonance imaging demonstrated a fracture of posterior arch of C1, associated with type II odontoid fracture and with presumable damage of C1 transverse ligament. Magnetic resonance imaging also showed a high cervical centromedullary area slightly hyperintense in T1-weighted images. Treatment consisted of odontoid and bilateral C1-C2 transarticular screw fixation with single anterior approach. The admission neurologic conditions improved and the patient was early mobilized. CONCLUSIONS: The authors suggest that in presence of C1-type II odontoid fracture, the triple anterior screw fixation has to be taken into account as salvage procedure, especially if other methods of stabilization failed or cannot be safely performed. This technique seems to be safety feasible also in old patients, as our report and the experience of others confirm.     

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.     

前路经寰枢关节螺钉内固定植骨融合治疗寰枢关节不稳

目的探讨前路经寰枢关节螺钉内固定植骨融合治疗寰枢关节不稳的手术方法及临床疗效。方法对23例寰枢关节不稳患者行前路寰枢关节螺钉内固定植骨融合治疗。结果所有患者术后无脊髓、椎动脉和食道损伤等并发症发生。23例获4～45个月随访(平均18.4个月),随访期间所有患者寰枢关节稳定性良好,21例寰枢关节螺钉位置满意,17例获得植骨融合。结论前路经寰枢关节螺钉内固定植骨融合术是治疗寰枢关节不稳的有效方法,能使寰枢关节即刻稳定性获得良好恢复,同时达到植骨融合的目的。     

Bilateral atlas laminar hook combined with transarticular screw fixation for an unstable bursting atlantal fracture

Introduction  The unstable atlas burst fracture (“Jefferson fracture”) is a fracture of the anterior and posterior atlantal arch with rupture of the transverse atlantal ligament and an incongruence of the atlanto-occipital and the atlanto-axial joint facets. The posterior atlantoaxial fusion is frequently used to reconstruct the stability of atlantoaxial joint. Conventional posterior atlantoaxial fixations are associated with high rates of pseudoarthrosis and chronic atlantoaxial instability. As a modified three-point fixation the bilateral C1-2 transarticular screws combined with C1 laminar hook and bone grafts can provide best biomechanical stability, but no standard protocol has been reported for the use of this fusion technique. A retrospective review of clinical series should be conducted to evaluate the clinical outcome of bilateral atlas laminar hook combined with transarticular screw fixation for unstable bursting atlantal fracture. Materials and methods  From March 2002 to March 2006, there were total 12 cases of unstable atlantal bursting fractures, 10 males and 2 females, age ranging 18–54, with mean of 36 years old. All patients were operated on posterior atlantoaxial fusion using bilateral atlas laminar hook combined with transarticular screw fixation after atlantoaxial joint were reduced and followed up for 12–24 months. The medical records and radiographs of the 12 patients were reviewed. Each patient underwent a complete cervical radiograph series including lateral flexion-extension view and a computed topographic scan. The Frankel grades and ASIA scores were applied to assess the neurologic status. Results  In all patients, a good bony fusion of the atlanto-axial segment was achieved. All patients showed significant improvement of the neurologic defect and no instability on their follow-up plain radiographs and computerized tomography in follow-up interval. Conclusions  For the patients who suffer from the unstable bursting atlantal fracture, the nonoperative methods could carry some clinical complications including infection, nerve injury, etc. and is frequently failure, Posterior atlantoaxial fusion using bilateral atlas laminar hook combined with transarticular screw fixation is an effective treatment. Xiang Guo and Bin Ni contributed equally to the article.     

Modified Gallie technique versus transarticular screw fixation in C1-C2 fusion

The effectiveness of a modified Gallie technique versus Magerl and Seeman transarticular screw fixation was compared in the management of 27 patients with symptomatic atlantoaxial instability. Twelve patients were treated using a modified Gallie technique and postoperative halo vest immobilization. Atlantoaxial arthrodesis occurred in seven (58%) patients, stable fibrous union occurred in one patient, and pseudarthrosis with recurrent instability developed in four (33%) patients. Average followup was 6.9 years. All 15 patients treated using Magerl and Seeman transarticular screw fixation and postoperative soft collar immobilization had atlantoaxial arthrodesis develop. Average duration of followup was 4 years. One patient sustained vertebral artery injury during preparation for screw placement. Magerl and Seeman transarticular screw fixation provides stability and more reliably produces atlantoaxial arthrodesis than the Gallie technique provides in patients with atlantoaxial instability without the need for rigid postoperative bracing. Potential for vertebral artery exists despite apparent accurate screw placement. To ensure that safe transarticular screw placement is possible, preoperative fine cut axial computed tomography with reconstructions is required to assess vertebral artery position and C2 isthmus anatomy. A proportion of patients have anatomy unsuitable for screw placement. Traditional wiring techniques are indicated in these patients.     

Dorsal atlanto-axial screw fixation. A stability test in vitro and in vivo

Clinical and biomechanical testing of the stability of atlantoaxial fusions was studied. For biomechanical testing, four different techniques for posterior atlantoaxial fusion were tested: (1) wire fixation with one median graft; (2) wire fixation with two bilateral grafts; (3) transarticular screw fixation and two bilateral posterior clamps. Ten fresh human cadaveric specimens were tested. The loads applied were 6 pure moments. The motion of C1 relative to C2 in the intact, injured and mechanically fixed spine were measured and compared. In flexion/extension the difference between Brooks, Magerl and Halifax were not significant, but each was significantly less than the Gallie-system. For the anterioposterior translation the stabilization of all fixation techniques was about equal. In axial rotation measuring the translations between C1 and C2, the screw-fixation technique proved to be the most stable. For lateral bending, there was no significant difference between the different techniques, except for Galliefixation, but the screw-fixation technique allowed the least motion. In additional in vivo tests ten patients with posterior atlantoaxial fusion by the transarticular screw-fixation technique underwent bending X-rays of the upper cervical spine as well as computertomograms. Solid fusion was achieved in all patients. Both investigations proved the reliability of the multidirectional stability of the atlantoaxial screw fixation technique.     

C1-C2 transarticular screw fixation for atlantoaxial instability: a 6-year experience.

OBJECTIVE: We review a 6-year, single-center experience using the technique of C1-C2 transarticular screw fixation for atlantoaxial instability in 75 consecutive operations. METHODS: The study group was composed of 43 men and 32 women, with a mean age of 44 years (range, 8-76 yr). Each patient had documented atlantoaxial instability. In 28 patients (37%), atlantoaxial instability was a result of trauma; in 22 patients, (29%), it was a result of rheumatoid arthritis; in 16 patients (21%), it was a result of prior surgery; and in 9 patients (12%), it was a result of congenital abnormalities. All patients underwent stabilization with C1-C2 transfacetal screws and a posterior interspinous construct. Nine patients had unilateral screws placed. Postoperatively, the patients were maintained in a rigid cervical orthosis for a mean of 11 weeks (range, 8-15 wk); five patients were immobilized with halo fixation for a mean of 13 weeks (range, 10-16 wk). The mean follow-up period was 2.4 years (range, 1-5.5 yr). RESULTS: Osseous fusion was documented in 72 patients (96%). There were no hardware failures; however, three patients developed pseudarthrosis. Two superficial wound infections (one at the graft site and one at the cervical incision site) required antibiotic therapy. Four patients had transient suboccipital hypesthesia. No instances of an errant screw, dural laceration, or injury to the vertebral artery, spinal cord, or hypoglossal nerve were noted. CONCLUSION: C1-C2 transarticular screw fixation supplemented with an interspinous construct yielded a 96% fusion rate, with a low incidence of complications. We attribute our successful outcomes to careful preoperative assessment and meticulous surgical technique.     

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.     

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.     

寰枢椎不稳的后路内固定治疗

目的　介绍寰枢椎不稳的后路内固定治疗的新方法。方法　 18例寰枢椎不稳患者经后路治疗 ,其中Apofix9例 ,Apofix +C1,2 经关节螺钉 9例。结果　共放置经关节螺钉 17枚 ,1例因放置过程中引起大出血 ,仅进行了单侧放置。术后并发感染 2例 ,经清创后愈合 ,无内固定失败和椎动脉及脊髓损伤等并发症。随访 5～ 16月 ,植骨全部融合。结论　Apofix和C1,2 经关节螺钉技术是治疗寰枢椎不稳的有效方法 ,可提供有效的固定和提高植骨融合率。     

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。     

Traumatic atlantoaxial rotatory dislocation with odontoid fracture: case report and review

STUDY DESIGN: A case of traumatic rotatory dislocation associated with odontoid fracture is reported. OBJECTIVES: To report a rare case of traumatic rotatory dislocation associated with odontoid fracture, and to discuss the mechanism underlying spinal instability and management. SUMMARY OF BACKGROUND DATA: This case is a cross between traumatic rotatory fixation and atlantoaxial rotatory dislocation. Classification of rotatory subluxation change after osteosynthesis of the odontoid process was undertaken. METHODS: A 24-year-old man sustained head and cervical injury after jumping. A Type 2 odontoid fracture without displacement was noted. RESULTS: Without further traumatic event, 1 month after injury, computed tomography scan showed posterior displacement of the odontoid fracture and Type 4 or B atlantoaxial rotatory luxation. After surgical fixation and reduction of the odontoid fracture, the rotatory subluxation classification changed and became Type 1 or A. Posterior C1-C2 arthrodesis was performed. The patient wore a Philadelphia cervical collar for 3 months and underwent physiotherapy. CONCLUSIONS: As the pivot of rotatory subluxation changed after odontoid process osteosynthesis, posterior C1-C2 arthrodesis was performed. The patient probably could have been treated in a single-stage procedure using posterior C1-C2 transarticular fixation with bicortical interspinous graft.     

Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note

Rigid screw fixation of the axis, for either atlantoaxial fixation or for incorporation of C2 into subaxial cervical constructs, provides significant stability and excellent long-term fusion results but remains technically demanding due to the danger of injury to the vertebral artery. Anatomic variability of the foramen transversarium in the body of the axis can preclude safe transarticular C1-C2 screw placement in up to 20% of patients. Although more recent methods of C2 screw fixation with pedicle screws allow safer fixation in a higher number of patients, there remains a significant risk to the vertebral artery with C2 pedicle screw placement. The author describes a novel technique of C2 rigid screw fixation using bilateral, crossing C2 laminar screws, not previously reported in the literature, which does not place the vertebral artery at risk during C2 fixation. This technique has been successfully used by the author in cases of craniocervical and atlantoaxial fixation as well as for incorporation of C2 into subaxial fixations. The technique is illustrated, and the author's initial experience in treating 10 patients with crossing, bilateral C2 aminar screws for indications of trauma, neoplasm, pseudarthrosis, and degenerative disease is reviewed. The possible advantages of C2 fixation with C2 laminar screws are discussed.