The optimal transarticular c1-2 screw length and the location of the hypoglossal nerve

BACKGROUND: Injury to the hypoglossal nerve is a complication associated with transarticular C1-2 screw placement. This complication can be caused by a misdirected or too long screw. Little is known about the optimal screw length and its relationship to the hypoglossal nerve. METHODS: Twenty cervical spine specimens were used to study the optimal length of the transarticular C1-2 screw. Using the Magerl technique, a 3.0 mm drill bit was inserted into the C2 lateral mass, passing through the C1-2 facet joint and penetrating the upper portion of the ventral cortex of the lateral mass of the atlas. After drilling, the hole length was measured between the dorsal cortex of the C2 inferior articular process and the ventral cortex of the C1 lateral mass. In addition, six sagittal-sectioned cadavers were carefully dissected to observe the location of the hypoglossal nerve in the anterior aspect of the atlantoaxial region. RESULTS: The results of the measurements showed that the mean optimal screw path length for all specimens was 38.1 +/- 2.2 mm with a range of 34-43 mm. There was no significant difference between sexes in the screw path length (p 0.05). The hypoglossal nerve lies vertically in front of the lateral portion of the C1 lateral mass and the C1-2 facet joint. The area where the hypoglossal nerve lies is approximately 2-3 mm lateral to the middle of the anterior aspect of the C1 lateral mass. CONCLUSIONS :This study suggests that the mean optimal transarticular C1-2 screw length may be 38 mm; however, the determination of the accurate optimal C1-2 screw length should be made on an individual basis. Risk to the hypoglossal nerve can be eliminated if Magerl's technique is performed exactly.     

Biomechanical and morphometric evaluation of occipital condyle for occipitocervical segmental fixation

Two recent novel techniques of occipital fixation are the occipitoatlantal (C0-C1) transarticular screw technique and the direct occipital condyle screw technique. The present study evaluated and compared the biomechanical stability of the direct occipital condyle screw and C0-C1 transarticular screw with the established method for craniocervical spine fixation using the midline occipital keel screw and C1 lateral mass screw. Morphometric evaluation of the occipital condyle and the hypoglossal canal was performed to avoid hypoglossal nerve injury during the screw placement. Thirteen recently frozen cadaveric specimens were used. The occipital condyle anatomy and the hypoglossal canal dimension were measured using reconstructed computed tomography images. Insertion torque and pullout strength were evaluated to compare the midline occipital keel screw, C0-C1 transarticular screw, C1 lateral mass screw, and direct occipital condyle screw. The dimensions of the occipital condyle allow use of a 3.5 or 4.0-mm diameter screw. Mean pullout strength was 1619.6 N for the midline occipital keel screw, 870.7 N for the C0-C1 transarticular screw, 707.0 N for the C1 lateral mass screw, and 431.7 N for the direct occipital condyle screw. Mean insertion torque was 0.55 Nm for the midline occipital keel screw, 0.32 Nm for the C0-C1 transarticular screw, 0.14 Nm for the C1 lateral mass screw, and 0.11 Nm for the direct occipital condyle screw. The condylar anatomy allows direct insertion of the occipital condyle screw and C0-C1 transarticular screw. These techniques are suitable options for the treatment of craniovertebral junction instabilities in selected patients.     

Lateral mass screw–rod fixation of the cervical spine: a prospective clinical series with 1-year follow-up

BACKGROUND CONTEXT: Lateral mass plating has become the technique of choice for posterior cervical fixation. Although these systems are safe and reliable, they can be difficult to use in patients with abnormal cervical anatomy; screw placement can be compromised by the fixed hole spacing of the plate; screw back-out and other forms of implant failure can occur; and extension across the cervicothoracic junction can be problematic. PURPOSE: To report a series of patients undergoing posterior cervical stabilization with a polyaxial screw-rod construct and to investigate whether this new system offers any advantages over existing methods of fixation. STUDY DESIGN: A prospective study evaluating clinical and radiographic parameters in a consecutive series of patients treated with this technique. PATIENT SAMPLE: There were 21 patients in the study group. The surgical indication was cervical spondylosis in 14, trauma in 2, postsurgical kyphosis in 2 and 1 case each of congenital cervicothoracic stenosis, C7-T1 pseudarthrosis and basilar invagination with brainstem compression. OUTCOME MEASURES: Clinical indicators included age, gender, neurologic status, surgical indication and number of levels stabilized. Note was made of whether laminectomy and concomitant anterior reconstructive surgery were performed. Radiographic indicators included early postoperative computed tomography (CT) scan to check for screw placement and plain radiographs at subsequent visits. METHODS: The participants in this study underwent posterior cervical stabilization using lateral mass screw-rod fixation. Clinical and radiographic assessment was carried out immediately after surgery, and 3, 6 and 12 months after surgery. One-year follow-up was obtained in all cases. RESULTS: A total of 212 screws were implanted in 21 patients. Fixation was carried out over an average of 5.5 spinal segments (range, 2 to 11). The system was successfully implanted in all patients despite the presence of coronal and sagittal plane deformities and/or lateral mass abnormalities in the majority of cases. This system allowed for screw placement in the occiput, C1 lateral mass, C2 pars, C3-C7 lateral masses and upper thoracic pedicles. Early postoperative CT scanning confirmed satisfactory screw placement in all cases. Three patients experienced transient single-level radiculopathy, for an incidence of 1.4% per screw placed. Two patients developed wound seromas requiring evacuation. There were no infections or other wound healing problems. There were no examples of cord or vertebral artery injury, cerebrospinal fluid leak, screw malposition or back-out, loss of alignment or implant failure. When compared with plating techniques, screw-rod fixation appeared to offer several advantages. First, unlike plates, rods proved to be amenable to multiplanar contouring, which is often needed for deformities associated with cervical spondylosis. Second, lateral mass screw placement was more precise because it was not constrained by the hole spacing of the plate. Third, screw back-out and other types of implant failure were not seen. Fourth, the screw-rod system was more easily extended to the occiput and across the cervicothoracic junction. Fifth, the screw-rod system permitted the application of compression, distraction and reduction forces within the construct, to a greater extent than plate systems. The incidence of postoperative radiculopathy was similar to that seen with plate systems. CONCLUSIONS: These data indicate that posterior cervical stabilization with polyaxial screw-rod fixation is a safe, straightforward technique that appears to offer some advantages over existing methods of fixation. Results appear to be durable at 1-year follow-up. Benefits are more significant with longer constructs, especially those extending to the occiput or crossing the cervicothoracic junction.     

寰枢椎脱位后路螺钉固定方法的临床选择

目的 探讨寰枢椎脱位后路钉棒固定术中寰椎螺钉和枢椎螺钉固定方法 的临床选择.方法 对2002 年11 月至2011 年12 月广州军区广州总医院收治的228 例可复性和23 例难复性寰枢椎脱位患者,术前进行置钉可行性和复位可能性评估,针对性地选择寰椎和枢椎的后路螺钉固定方法,进行寰枢椎后路钉棒固定治疗.结果 251 例患者均行钉棒固定并获得满意复位.寰椎螺钉固定采用椎弓根螺钉403 枚、部分经椎弓根螺钉77 枚、侧块螺钉22 枚;枢椎螺钉固定采用椎弓根螺钉437 枚、椎板螺钉56 枚、侧块螺钉9 枚.术中未发生椎动脉、脊髓损伤.237 例患者获得随访,随访时间4～38 个月,平均随访时间13 个月.230 例患者获骨性融合;6例为纤维愈合,动力位片（均随访2 年以上）未见复发脱位;另1 例为假关节未融合并双侧枢椎椎弓根螺钉松动,行后路翻修手术治愈.结论 根据寰枢椎脱位的复位难易程度和个体解剖特点灵活选择寰椎和枢椎不同的后路螺钉固定方法,扩大了寰枢椎后路钉棒固定技术的适用范围,提高了手术安全性和成功率.     

多种寰枢椎后路钉棒固定技术的临床组合应用

目的评价3种寰椎后路螺钉固定方法和2种枢椎后路螺钉固定方法构成的钉棒组合治疗上颈椎不稳的可行性和临床效果。方法在气管插管全麻下对132例患者施行了寰枢椎后路钉棒固定技术,寰椎进行椎弓根螺钉、部分经椎弓根螺钉或侧块螺钉固定;枢椎进行椎弓根螺钉或交叉椎板螺钉固定。结果全组病例获钉棒固定,其中寰椎螺钉固定采用椎弓根螺钉224枚,部分经椎弓根螺钉36枚,侧块螺钉4枚;枢椎螺钉固定采用椎弓根螺钉240枚,椎板螺钉24枚。术中未发生椎动脉、脊髓损伤。120例患者术后获得随访3～22个月,平均8个月,临床症状得到不同程度的改善;X线片、CT复查螺钉位置良好,无松动、断钉,植骨3～6个月后均达到满意融合。结论寰椎和枢椎螺钉可进行多重组合,为上颈椎后路提供灵活多变的短节段固定,增加了钉棒固定技术的临床适用范围。     

Biomechanical analysis of a novel hook-screw technique for C1-2 stabilization

The Food and Drug Administration has not cleared the following medical devices for the use described in this study. The following medical devices are being discussed for an off-label use: cervical lateral mass screws. Object As an alternative for cases in which the anatomy and spatial relationship between C-2 and a vertebral artery precludes insertion of C-2 pedicle/pars or C1-2 transarticular screws, a technique that includes opposing laminar hooks (claw) at C-2 combined with C-1 lateral mass screws may be used. The biomechanical stability of this alternate technique was compared with that of a standard screw-rod technique in vitro. Methods Flexibility tests were performed in 7 specimens (occiput to C-3) in the following 6 different conditions: 1) intact; 2) after creating instability and attaching a posterior cable/graft at C1-2; 3) after removing the graft and attaching a construct comprising C-1 lateral mass screws and C-2 laminar claws; 4) after reattaching the posterior cable-graft at C1-2 (posterior hardware still in place); 5) after removing the posterior cable-graft and laminar hooks and placing C-2 pedicle screws interconnected to C-1 lateral mass screws via rod; and 6) after reattaching the posterior cable-graft at C1-2 (screw-rod construct still in place). Results All types of stabilization significantly reduced the range of motion, lax zone, and stiff zone compared with the intact condition. There was no significant biomechanical difference in terms of range of motion or lax zone between the screw-rod construct and the screw-claw-rod construct in any direction of loading. Conclusions The screw-claw-rod technique restricts motion much like the standard Harms technique, making it an acceptable alternative technique when aberrant arterial anatomy precludes the placement of C-2 pars/pedicle screws or C1-2 transarticular screws.     

后路钉棒固定治疗创伤不稳定性Ⅱ型齿状突骨折

目的 探讨颈后路椎弓根钉或侧块螺钉-棒复位固定治疗创伤不稳定性Ⅱ型齿状突骨折临床效果.方法 对20例创伤不稳定性Ⅱ型齿状突骨折患者行后路椎弓根钉或侧块螺钉-棒复位固定,椎板或小关节间植骨.结果 患者术后颈部症状完全消失,受损颈髓神经功能明显改善,未发生并发症.20例均获随访,时间3～55（11±3.1）个月.颈椎复位良好,序列稳定;无内固定松动、断裂、植骨块移位;骨折愈合好,植骨渐进融合.结论 创伤不稳定性Ⅱ型齿状突骨折采用经后路椎弓根钉或侧块螺钉-棒复位固定治疗能够达到良好的稳定效果.     

Biomechanical comparison of transfacet screws to lateral mass screw-rod constructs in the lower cervical spine

Purpose

Transfacet screws have been used as an alternative posterior fixation in the cervical spine. There is lack of spinal stability of the transfacet screws either as stand-along constructs or combined with anterior plate. This study was designed to evaluate spinal stability of transfacet screws following posterior ligamentous injury and combined with anterior plate, respectively, and compare transfacet screws to lateral mass screw-rod constructs.

Methods

Flexibility tests were conducted on eight cadaveric specimens in an intact and injury, and instrumented with the transfacet screw fixation and lateral mass screw-rod construct at C5–C7 levels either after section of the posterior ligamentous complex or combined with an anterior plate and a mesh cage for C6 corpectomy reconstruction. A pure moment of ±2.0 Nm was applied to the specimen in flexion–extension, lateral bending, and axial rotation. Ranges of motion (ROM) were calculated for the C5–C7 segment.

Results

ROM with the transfacet screws was 22 % of intact in flexion–extension, 9 % in lateral bending and 11 % in axial rotation, while ROM with the lateral mass screw-rod construct was 9 % in flexion–extension, 8 % in lateral bending and 22 % in axial rotation. The only significant difference between two constructs was seen in flexion–extension (5.8 ± 4.2° vs. 2.4 ± 1.2°, P = 0.002). When combined with an anterior plate and mesh cage, the transfacet screw fixation reduced ROM to 3.0° in flexion–extension, 1.2° in lateral bending, and 1.1° in axial rotation, which was similar to the lateral mass screw-rod construct.

Conclusions

This study identified the transfacet screw fixation, as stand-alone posterior fixation, was equivalent to the lateral mass screw-rod constructs in axial rotation and lateral bending except in flexion–extension. When combined with an anterior plate, the transfacet screw fixation was similar to the lateral mass screw-rod construct in motion constraint. The results suggested the transfacet screw fixation a biomechanically effective way as supplementation of anterior fixation.

     

颈椎侧块及椎弓根钉棒治疗颈椎骨折脱位

目的探讨颈椎侧块及椎弓根钉棒固定、减压治疗颈椎骨折脱位伴多节段颈髓损伤的疗效。方法 2007年1月至2010年12月我科采用改良A nderson方法固定颈椎侧块,结合C2、C7椎弓根螺钉的联合应用,治疗颈椎骨折脱位伴多节段脊髓损伤34例,其中男26例,女8例;年龄18~64岁,平均41岁。按F ranke l分级标准评价,A级5例,B级20例,C级9例,入院时JOA评分平均6.8分,评价术后效果。结果术后随访6~24个月,平均15个月。术后颈椎完全复位33例,复位不完全1例。依据术前、术后JOA评分结果,术后改善率平均为62%;术后F ranke l分级平均提高1级以上。结论颈椎侧块联合椎弓根钉棒内固定可使受损颈椎获得即刻稳定,有利于脊髓功能恢复。     

The cervical end of an occipitocervical fusion: a biomechanical evaluation of 3 constructs. Laboratory investigation

OBJECT: Stabilization with rigid screw/rod fixation is the treatment of choice for craniocervical disorders requiring operative stabilization. The authors compare the relative immediate stiffness for occipital plate fixation in concordance with transarticular screw fixation (TASF), C-1 lateral mass and C-2 pars screw (C1L-C2P), and C-1 lateral mass and C-2 laminar screw (C1L-C2L) constructs, with and without a cross-link. METHODS: Ten intact human cadaveric spines (Oc-C4) were prepared and mounted in a 7-axis spine simulator. Each specimen was precycled and then tested in the intact state for flexion/extension, lateral bending, and axial rotation. Motion was tracked using the OptoTRAK 3D tracking system. The specimens were then destabilized and instrumented with an occipital plate and TASF. The spine was tested with and without the addition of a cross-link. The C1L-C2P and C1L-C2L constructs were similarly tested. RESULTS: All constructs demonstrated a significant increase in stiffness after instrumentation. The C1L-C2P construct was equivalent to the TASF in all moments. The C1L-C2L was significantly weaker than the C1L-C2P construct in all moments and significantly weaker than the TASF in lateral bending. The addition of a cross-link made no difference in the stiffness of any construct. CONCLUSIONS: All constructs provide significant immediate stability in the destabilized occipitocervical junction. Although the C1L-C2P construct performed best overall, the TASF was similar, and either one can be recommended. Decreased stiffness of the C1L-C2L construct might affect the success of clinical fusion. This construct should be reserved for cases in which anatomy precludes the use of the other two.     

C1 lateral mass screw-induced occipital neuralgia: a report of two cases

C1–2 polyaxial screw-rod fixation is a relatively new technique. While recognizing the potential for inadvertent vertebral artery injury, there have been few reports in the literature outlining all the possible complications. Aim of this study is to review all cases of C1 lateral mass screws insertion with emphasis on the evaluation of potential structures at risk during the procedure. We retrospectively reviewed all patients in our unit who had C1 lateral mass screw insertion over a 2-year period. The C1 lateral mass screw was inserted as part of an atlantoaxial stabilization or incorporated into a modular occiput/subaxial construct. Outcome measures included clinical and radiological parameters. Clinical indicators included age, gender, neurologic status, surgical indication and the number of levels stabilized. Intraoperative complications including blood loss, vertebral artery injury or dural tears were recorded. Postoperative pain distribution and neurological deficit were recorded. Radiological indicators included postoperative plain radiographs to assess sagittal alignment and to check for screw malposition or construct failure. A total of 18 lateral mass screws were implanted in 9 patients. There were three male and six female patients who had C1 lateral mass screw insertion in this unit. Two patients had atlantoaxial stabilization for C2 fracture. There were four patients with rheumatoid arthritis whose C1 lateral mass screws were inserted as part of an occipitocervical or subaxial cervical stabilization. There was no vertebral artery injury, no cerebrospinal fluid leak and minimal blood loss in all patients. Three patients developed postoperative occipital neuralgia. This neuralgia was transient, in one of the patients having settled at 6-week follow-up. In the other two patients the neuralgia was unresolved at time of latest follow-up but was adequately controlled with appropriate pain management. Postoperatively no patient had radiographic evidence of construct failure and all demonstrated excellent sagittal alignment. It has been reported that the absence of threads on the upper portion of the long shank screw may protect against neural irritation. However, insertion of the C1 lateral mass screw necessitates careful caudal retraction of the C2 dorsal root ganglion. The insertion point for the C1 lateral mass screw is at the junction of the C1 posterior arch and the midpoint of the posterior inferior part of the C1 lateral mass. Two patients in our series suffered occipital neuralgia post-insertion of C1 lateral mass screws. This highlights the potential for damage to the C2 nerve root during C1 lateral mass screw placement.     

C1 lateral mass screw insertion caudally from C2 nerve root – An alternate method for insertion of C1 screws: A technical note and preliminary clinical results

Background

C1 lateral mass screw was widely used for fixation of the upper cervical spine. However, massive bleeding from the C1–2 venous plexus is sometimes encountered. In this study, we proposed an alternate method for C1 lateral mass screw insertion, which involves insertion of the screws caudally from the C2 nerve root to reduce bleeding from C1–2 venous plexus.

创伤性颈椎不稳后路钉棒固定重建稳定

目的探讨颈后路椎弓根钉或侧块螺钉-棒内固定治疗颈椎创伤性不稳临床效果。方法对30例创伤性颈椎不稳患者行后路椎弓根钉或侧块螺钉-棒内固定,椎板或小关节间植骨。结果术后颈部症状完全消失,受损颈髓神经功能明显改善。30例均获随访,时间3～52(10±3.2)个月,未发生并发症。颈椎复位良好,序列稳定;无内固定松动、断裂、植骨块移位;骨折愈合好,植骨渐进融合。颈椎伸屈角度105°±10.5°,侧屈角度80°±7.2°,轴向旋转功能96°±9.3°。结论颈椎创伤性不稳采用经后路椎弓根钉或侧块螺钉-棒内固定治疗能够达到良好的稳定效果。     

寰椎椎弓根螺钉和侧块螺钉技术的临床疗效比较

 目的 探讨寰椎椎弓根螺钉和侧块螺钉固定技术的临床疗效。方法 2006年 1月至 2010年 1月, 对 60例寰枢椎失稳患者随机分为两组, 椎弓根螺钉组(32例)均采用寰椎椎弓根螺钉固 定技术, 侧块螺钉组(28例)均采用寰椎侧块螺钉固定技术。通过术中失血量、手术时间、颈枕区疼痛缓 解[采用疼痛视觉模拟评分法(visual analog scale, VAS)评估]、颈椎日本骨科协会评分(Japanese Or thopaedic Association Scores,JOA)和术后植骨融合情况评定疗效。结果 所有患者均获得随访, 随访时 间 12~60个月, 平均 466个月。术后 6个月均获得骨性融合, 未发现螺钉松动、移位, 螺钉断裂, 寰枢椎 再移位及失稳现象。椎弓根螺钉组术前 JOA评分为(7.1±2.8)分, VAS评分(3.0±1.2)分, 末次随访时分 别改善至(13.3±2.1)分和(1.8±0.9)分;侧块螺钉组术前 JOA评分为(7.3±2.4)分, VAS评分(3.2±1.0)分, 末次随访时分别改善至(13.0±2.6)分和(1.9±1.0)分;两组患者在 JOA评分、颈枕区疼痛缓解方面的差异 无统计学意义。 椎弓根螺钉组术中失血量和手术时间明显低于侧块螺钉组, 差异有统计学意义。椎弓根 螺钉组中 2例出现寰椎后弓骨折。侧块螺钉组中有 3例术后出现颈枕区疼痛加重, 且伴有麻木。 结论 寰椎椎弓根螺钉固定技术显露范围小, 简化了操作程序, 减少了术中和术后的并发症。 在设计手术方案时, 应优先考虑椎弓根螺钉技术, 而侧块螺钉技术可以作为一种补充。     

Hypoglossal nerve palsy secondary to cervical spine involvement in rheumatoid arthritis: Clinical and radiological features

Isolated hypoglossal nerve (HN) palsy has been reported in a variety of disorders involving the cervical spine and/or skull base, however, unilateral HN palsy caused by rheumatoid arthritis (RA) has rarely been reported. We report herein an uncommon case of isolated HN palsy secondary to RA cervical spine involvement: pannus formation at the C1–C2 articulation, atlanto-axial subluxation, as well as, erosion of the right occipital condyle, lateral mass and anterior arch of C1. Pulse therapy with methylprednisolone followed by maintenance therapy with prednisone resulted in dramatic improvement. We also present the variety of diagnostic modalities helpful for the diagnosis and follow-up.     

Biomechanical comparison of unicortical versus bicortical C1 lateral mass screw fixation

STUDY DESIGN: Biomechanical study of pullout strength of unicortical versus bicortical C1 lateral mass screws using a cadaveric cervical spine model. OBJECTIVE: To compare pullout strength of unicortical versus bicortical C1 lateral mass screws. SUMMARY OF BACKGROUND DATA: The internal carotid artery and hypoglossal nerve lie over the anterior aspect of the lateral mass of the atlas and are at risk from bicortical C1 lateral mass screws. Unicortical screws would reduce the risk of injury to these neurovascular structures; however, no data are available on the relative strength of unicortical versus bicortical C1 lateral mass screws. METHODS: Fifteen cadaveric cervical spine specimens underwent axial pullout testing of C1 lateral mass screws. A unicortical C1 lateral mass screw was placed on 1 side with a contralateral bicortical screw. RESULTS: The mean pullout strengths of the unicortical screws and bicortical screws were 588 N (range, 212 to 1234 N) and 807 N (range, 163 to 1460 N), respectively (P=0.008). CONCLUSIONS: Bicortical C1 lateral mass screws were significantly stronger than unicortical screws; however, the mean pullout strength of both the unicortical and bicortical C1 screws were greater than previously reported values for subaxial lateral mass screws. On the basis of these data, the clinical necessity for using bicortical screw fixation in all patients must be questioned. If similar strength can be achieved using unicortical C1 lateral mass screw to that currently accepted in the subaxial spine, bicortical screws might not be justified for the C1 lateral mass. However, the ability to extrapolate C1-C2 data to subaxial spine data is uncertain because of the difference in normal physiologic loading at these levels.     

Posterior C1-2 Fixation with cancellous screw and rod system for retro-odontoid pseudotumor associated with chronic atlantoaxial subluxation. Technical note

Posterior C1-2 fixation with individual screw placement in C-1 and C-2 was performed in three patients presenting with progressive myelopathy caused by retro-odontoid pseudotumor associated with chronic atlantoaxial subluxation. Postoperatively, all patients demonstrated neurological recovery with gradually diminishing pseudotumor. Posterior C1-2 fixation with the cancellous screw and rod system is a safe and reliable method, and can be used to treat retro-odontoid pseudotumor associated with chronic atlantoaxial subluxation.     

In vitro biomechanical comparison of transpedicular versus translaminar C-2 screw fixation in C2-3 instrumentation

OBJECT: In instrumentation of the upper cervical spine, placement of pedicle screws into C-2 is generally safe, although there is the potential for injury to the vertebral arteries. Owing to this risk, translaminar screws into C-2 have been used. The aim of this study was to compare the stability of the in vitro cadaveric spine using C-2 laminar compared with C-2 pedicle screws in C2-3 instrumentation. METHODS: Eight fresh frozen human cadaveric cervical spines (C1-6) were potted at C1-2 and C5-6. Pure moments in increments of 0.3 Nm to a maximum of 1.5 Nm were applied in flexion, extension, right and left lateral bending, and right and left axial rotation. Each specimen was tested sequentially in three modes: 1) intact; 2) C2 pedicle screw-C3 lateral mass fixation; and 3) C2 laminar screw-C3 lateral mass fixation. The sequence of fixation testing was randomized. Motion was tracked with reflective markers attached to C-2 and C-3. RESULTS: Spinal levels with instrumentation showed significantly less motion than the intact spine in all directions and with all loads greater than 0.3 Nm (p < 0.05). Although there was no significant difference between C2 pedicle screw-C3 lateral mass fixation and C2 laminar screw-C3 lateral mass fixation, generally the former type of fixation was associated with less motion than the latter. CONCLUSIONS: When pedicle screws in C-2 are contraindicated or inappropriate, laminar screws in C-2 offer a safe and acceptable option for posterior instrumentation.     

颈后路内固定治疗不稳定型Hangman骨折

目的探讨颈后路椎弓根与侧块螺钉系统治疗不稳定型Hangman骨折的临床效果。方法对17例不稳定型Hangman骨折患者进行回顾性研究,按Levine-Edwards分型:Ⅱ型7例,Ⅱa型8例,Ⅲ型2例。术前常规行颅骨牵引,复位后行后路C2~3椎弓根侧块螺钉内固定术。术后颈托保护6周。结果术后均未出现脊髓神经损伤及椎动脉损伤。17例均获随访,时间12~44个月。骨折愈合时间3~6个月。颈部疼痛、肢体麻木等症状消失,但颈部活动度较正常略有下降;无内固定失败及感染等并发症发生。结论颈后路椎弓根侧块螺钉系统治疗Hangman骨折疗效较满意。     

C2 Nerve Dysfunction Associated with C1 Lateral Mass Screw Fixation

The C₁ lateral mass screw technique is widely used for atlantoaxial fixation. However, C₂ nerve dysfunction may occur as a complication of this procedure, compromising the quality of life of affected patients. This is a review of the topic of C₂ nerve dysfunction associated with C₁ lateral mass screw fixation and related research developments. The C₂ nerve root is located in the space bordered superiorly by the posterior arch of C₁, inferiorly by the C₂ lamina, anteriorly by the lateral atlantoaxial joint capsule, and posteriorly by the anterior edge of the ligamentum flavum. Some surgeons suggest cutting the C₂ nerve root during C₁ lateral mass screw placement, whereas others prefer to preserve it. The incidence, clinical manifestations, causes, management, and prevention of C₂ nerve dysfunction associated with C¹ lateral mass screw fixation are reviewed. Sacrifice of the C₂ nerve root carries a high risk of postoperative numbness, whereas postoperative nerve dysfunction can occur when it has been preserved. Many surgeons have been working hard on minimizing the risk of postoperative C₂ nerve dysfunction associated with C₁ lateral mass screw fixation.