Cadaveric morphometric analysis for atlantal lateral mass screw placement

OBJECTIVE: Atlantal lateral mass screws provide an alternative to C1/C2 transarticular screws and, in some cases, can obviate the need for extending a fusion to the occiput. For these reasons, C1 lateral mass screws are becoming increasingly popular. However, the critical local anatomy and unfamiliarity with this new technique can make C1 screw placement more challenging. METHODS: Morphometric analysis was performed on 74 cadaveric spines obtained from the Department of Anatomy at the Keck School of Medicine, University of Southern California. Critical measurements were determined for screw entry points, trajectories, and lengths for application of the technique described by Harms and Melcher. RESULTS: The mean height and width for screw entry on the posterior surface of the lateral mass were 3.9 and 7.3 mm, respectively. The maximum medialized screw trajectory ranged from 25 to 45 degrees (mean, 33 degrees). The mean maximal screw length to obtain bicortical purchase was 22.5 mm, and the mean minimum screw depth was 14.4 mm. Screw depths varied on the basis of the entry point, trajectory, and vertebral morphology. The overhang of the posterior arch averaged 11.4 mm (range, 6.9-17 mm). All specimens could accommodate 3.5-mm lateral mass screws bilaterally with proper preparation of the entry site. CONCLUSION: Significant variations in the morphology of C1 exist. However, the large size of the atlantal lateral mass makes screw placement forgiving. Preoperative computed tomographic scans and intraoperative fluoroscopy are useful in guiding proper screw placement. Close attention should be paid to preparation of the screw entry site.     

Hypoglossal nerve palsy after posterior screw placement on the C-1 lateral mass. Case report

Atlantoaxial fixation in which C1-2 screw-rod fixation is performed is a relatively new method. Because reports about this technique are rather scant, little is known about its associated complications. In this report the authors introduce hypoglossal nerve palsy as a complication of this novel posterior atlantoaxial stabilization method. A 67-year-old man underwent a C1-2 screw-rod fixation for persistent neck pain resulting from a Type 2 odontoid fracture that involved disruption of the transverse atlantal ligament. Posterior instrumentation in which a C-1 lateral mass screw and C-2 pedicle screw were placed was performed. Postoperatively, the patient suffered dysphagia with deviation of the tongue to the left side. At the 4-month follow-up examination, bone fusion was noted on plain x-ray studies of the cervical spine. His hypoglossal nerve palsy resolved completely 2 months postoperatively. To the authors' knowledge, this is the first report in the literature of hypoglossal nerve palsy following C1-2 screw-rod fixation. The hypoglossal nerve is one of the structures that can be damaged during C-1 lateral mass screw placement.     

Ideal screw entry point and projection angles for posterior lateral mass fixation of the atlas: an anatomical study

Although various posterior insertion angles for screw insertion have been proposed for C1 lateral mass, substantial conclusions have not been reached regarding ideal angles and average length of the screw yet. We aimed to re-consider the morphometry and the ideal trajections of the C1 screw. Morphometric analysis was performed on 40 Turkish dried atlas vertebrae obtained from the Department of Anatomy at the Medical School of Ankara University. The quantitative anatomy of the screw entry zone, trajectories, and the ideal lengths of the screws were calculated to evaluate the feasibility of posterior screw fixation of the lateral mass of the atlas. The entry point into the lateral mass of the atlas is the intersection of the posterior arch and the C1 lateral mass. The optimum medial angle is 13.5 ± 1.9° and maximal angle of medialization is 29.4 ± 3.0°. The ideal cephalic angle is 15.2 ± 2.6°, and the maximum cephalic angle is 29.6 ± 2.6°. The optimum screw length was found to be 19.59 ± 2.20 mm. With more than 30° of medial trajections and cephalic trajections the screw penetrates into the spinal canal and atlantooccipital joint, respectively. Strikingly, in 52% of our specimens, the height of the inferior articular process was under 3.5 mm, and in 70% was under 4 mm, which increases the importance of the preparation of the screw entry site. For accommodation of screws of 3.5-mm in diameter, the starting point should be taken as the insertion of the posterior arch at the superior end of the inferior articular process with a cephalic trajection. This study may aid many surgeons in their attempts to place C1 lateral mass screws.     

不同内倾角置入寰椎后路侧块螺钉的安全性比较

目的:将寰椎后路侧块螺钉上倾角固定在15°的情况下,比较不同内倾角度置钉相对应的寰椎侧块有效宽度和进钉深度,以确定寰椎后路侧块螺钉在横断面上的最佳内倾角度。方法:募集颈椎结构正常的健康成年国人64名,男32名,女32名;年龄32.7±7.8岁(18~60岁),进行颈椎CT平扫,通过Mimics软件对志愿者的颈椎CT数据进行测量,在寰椎后路侧块螺钉上倾角为15°的情况下,分别测量内倾角度为0°、5°、10°、15°、20°、25°、30°和理想内倾角(β角)时的寰椎侧块有效宽度和寰椎后路侧块螺钉的进钉深度;测量正中矢状面与寰椎后弓最后缘的交点与进钉点之间的距离和进钉点处的后弓下缘侧块高度;并进行统计学数据分析。结果:寰椎后路侧块螺钉的β角男性为20.01°±2.97°,女性为21.89°±3.14°。寰椎后路侧块螺钉内倾角度为0°、5°、10°、15°、20°、25°、30°和β角时的寰椎侧块有效宽度男性分别为8.95±1.18、9.51±1.14、10.00±1.17、10.42±1.20、10.39±1.29、9.41±1.25、8.04±1.21、11.02±0.96mm,女性分别为7.64±1.01、8.31±1.11、8.88±1.10、9.32±1.11、9.51±1.09、8.90±1.02、7.62±1.07、9.97±0.98mm;进钉深度男性分别为19.03±1.34、19.60±1.39、20.28±1.47、21.20±1.48、22.11±1.54、23.06±1.63、24.19±1.97、22.37±1.52mm,女性分别为17.47±1.68、17.90±1.64、18.50±1.79、19.31±1.93、20.47±2.03、21.67±2.18、22.89±2.38、21.26±1.99mm。相较于其他内倾角,β角对应的寰椎侧块有效宽度最大且差异有统计学意义(P0.01)。寰椎后路侧块螺钉内倾角为β时,寰椎后路侧块螺钉进钉点距离正中矢状面与寰椎后弓最后缘的交点距离男性为28.35±1.75mm,女性为26.70±1.60mm;进钉点处的后弓下缘侧块高度男性为4.38±0.85mm,女性为4.13±0.80mm。结论:寰椎后路侧块螺钉上倾15°时,以所对应的寰椎侧块有效宽度最大的内倾角β角进钉,理论上损伤椎动脉、脊髓等结构的几率最低。     

Transfacet screw placement for posterior fixation of C-7

OBJECT: Lateral mass screws are traditionally used to fixate the subaxial cervical spine, while pedicle screws are used in the thoracic spine. Lateral mass fixation at C-7 is challenging due to thin facets, and placing pedicle screws is difficult due to the narrow pedicles. The authors describe their clinical experience with a novel technique for transfacet screw placement for fixation at C-7. METHODS: A retrospective chart review was undertaken in all patients who underwent transfacet screw placement at C-7. The technique of screw insertion was the same for each patient. Polyaxial screws between 8- and 10-mm-long were used in each case and placed through the facet from a perpendicular orientation. Postoperative radiography and clinical follow-up were analyzed for aberrant screw placement or construct failure. RESULTS: Ten patients underwent C-7 transfacet screw placement between June 2006 and March 2007. In all but 1 patient screws were placed bilaterally, and the construct lengths ranged from C-3 to T-5. One patient with a unilateral screw had a prior facet fracture that precluded bilateral screw placement. There were no intraoperative complications or screw failures in these patients. After an average of 6 months of follow-up there were no hardware failures, and all patients showed excellent alignment. CONCLUSIONS: The authors present the first clinical demonstration of a novel technique of posterior transfacet screw placement at C-7. These results provide evidence that this technique is safe to perform and adds stability to cervicothoracic fixation.     

枢椎后路侧块螺钉固定的解剖研究

目的:通过解剖测量验证枢椎后路侧块螺钉固定技术的可行性。方法:用电子游标卡尺和量角器,对50例干燥枢椎标本测量与进钉技术相关的解剖学数据,包括枢椎椎弓根的宽度和高度以及枢椎侧块螺钉的钉道长度和螺钉的内斜角度与上斜角度。结果:枢椎椎弓根的上缘宽度平均7.56mm,全部大于5.0mm;中部平均宽度5.70mm,22%小于5.0mm,7%小于3.5mm;下缘平均宽度3.95mm,75%小于5.0mm,40%小于3.5mm。枢椎椎弓根外缘高度5.62mm,40%小于5.0mm,5%小于3.5mm;内缘高度8.80mm,均大于5.0mm。枢椎侧块螺钉的钉道平均长度为18.33mm,最短15.32mm,最长20.87mm。枢椎侧块螺钉的平均内斜角度为5.35°,上斜角度为58.62°。结论:进行枢椎后路侧块螺钉固定是可行的,适用于93%的患者,比枢椎后路椎弓根螺钉固定具有更大的适用范围。     

Aberrant posterior inferior cerebellar artery injury with C1 lateral mass screw placement: a case report and review of the literature

Background contextComplications associated with C1 lateral mass screw placement are relatively infrequent. The most commonly feared complications include neural or vascular injury. Although both vertebral artery and internal carotid artery injuries have been discussed in the literature, there have been no reports of posterior inferior cerebellar artery (PICA) injury from C1 lateral mass screw placement. We report a case of patient who had a cerebellar stroke after C1 lateral mass screw placement, secondary to injury of an aberrant PICA.PurposeTo describe the normal anatomy of the PICA, the anatomic variations previously reported in the literature, the sequela and symptoms of a patient with PICA injury, and the relevance to C1 lateral mass screw placement. No previous reports of PICA injury with a cerebellar stroke have been reported with C1 lateral mass screw instrumentation.Study designCase report and literature review.MethodsThe patient underwent an Occiput–C6 posterior instrumentation for a pathologic fracture, secondary to multiple myeloma. In the postoperative period, the patient was found to have dysarthria, imbalance, and dysdiadochokinesia. Urgent computed tomography confirmed well placed C1 lateral mass screws. Magnetic resonance imaging/Magnetic Resonance Angiography showed an infarct in the PICA distribution with an abnormal variant of the PICA coursing extracranially around C1. Neurologic monitoring did not detect the injury intraoperatively.ResultsThe patient was treated with anticoagulation and he made a reasonable recovery from his stroke.ConclusionsWe report the first case of an aberrant PICA injured during a C1 lateral mass screw placement, resulting in a cerebellar stroke. Consideration should be given to abnormal PICA variation when placing C1 lateral mass screws.     

经口咽前路寰椎侧块置钉固定治疗合并寰枕融合畸形颅底凹陷症的临床疗效

目的:探讨经口咽前路寰椎侧块置钉固定治疗合并寰枕融合畸形颅底凹陷症患者的可行性及临床疗效。方法:回顾性分析2009年3月~2011年10月我院收治的55例合并寰枕融合畸形的颅底凹陷症患者,行颅底和颈椎薄层CT扫描,冠状面和矢状面图像重建,同期我院影像数据库中55例无枕颈畸形患者上颈椎CT资料作为对照。在PACS图像系统上测量寰椎侧块的前高Ha、后高Hp、外侧高度Ho、内侧高度Hi、侧块的矢径A和横径B,观察并测量硬腭后缘投影点到寰椎侧块下缘的高度d等参数。并以寰椎侧块中下1/3的水平线与内中1/3垂线的交点作为侧块螺钉的模拟进钉点,在PACS图像工作站上寻找最合适的钉道方向,测量钉道的外倾角α和上倾角β,螺钉理论钉道长度L等。按照上述设计方案,所有患者接受了经口咽前路寰枢椎脱位松解复位,钢板内固定手术(TARP)。术后CT扫描观察钉道情况,测量螺钉的实际外倾角α2和上倾角β2,螺钉长度L2等,并与影像学测量数据对比。临床疗效采用JOA评分系统对患者术后3个月、6个月及12个月随访时脊髓功能进行评分,测量术前、术后脑干脊髓角评价脊髓压迫改善情况。结果:寰枕融合组寰椎切面的形态与对照组形状相似,测量寰椎侧块的横径为14.5±3.4mm,纵径为19.3±2.6mm,均小于对照组(P<0.05)。侧块前、后、外、内高度均小于对照组,其中后高差别尤为明显(P<0.05)。寰枕融合组的硬腭投影点明显偏下,投影点与侧块下缘的距离均值为4.7±1.7mm,明显小于对照组的17.6±2.4mm(P<0.05)。该组病例手术顺利,共置入寰椎侧块螺钉110枚,其中2枚螺钉偏外指向椎动脉孔,3枚螺钉偏内部分穿破侧块内侧缘,并呈切线进入椎管内,但未引起神经症状,其余均位于侧块内。术后患者肢体麻木、肌肉无力等症状均有明显改善,JOA评分术前8.1±1.6分,术后3个月复查时恢复至15.9±0.9分(P<0.05),末次随访时为16.0±0.8分。脑干脊髓角由术前127°±11°改善至156°±14°(P<0.05)。结论:经口咽前路侧块螺钉技术用于合并寰枕融合的颅底凹陷症是可行的,采用该技术的经口咽前路复位钢板治疗颅底凹陷症可获得良好疗效。     

下颈椎侧块安全置钉内固定的解剖学测量

目的测量成人C3～C7颈椎侧块干骨标本,选择下颈椎侧块安全、稳定、简便的进钉区间.方法成人颈椎干骨标本30套,每套均按C3～C7顺序排列,分别测量侧块的上关节面最长径(A)、前后径(B)、最长径与矢状面的夹角(α)、神经根通道与矢状面的夹角(β)、上关节面与水平面的夹角(γ)、侧块高度(H).结果C3～C7侧块上关节面最长径逐渐增大(10.7±1.0～12.0±1.2 mm);前后径为7.O±1.2～8.2±1.7 mm,其中C3～C6接近,C7最短;侧块最长径与矢状面的夹角为48.8°±4.6°～50.°±3.7°;神经根通道与矢状面的夹角为59.4°±5.5°～62.9°±4.7°;侧块上关节面与水平面的夹角C3～C6较为接近,为48.4°±8.3°～53.2°±5.9°,C7较大为62.7°～5.4°;侧块高度从C3～C7呈增大趋势.为12.3±1.8～15.7±2.0mm.C3～C7进钉点靠近侧块的中点内侧,进钉途径愈趋向于和上关节面最长径平行,螺钉在侧块内的通道愈长;从C3～C7与矢状面夹角大于10.并趋向于相应节段α之间,与水平面夹角大于15°并趋向于相应节段γ之间的进钉角度为安全、稳定的进钉角度.结论C3～C7颈椎侧块螺钉内固定存在一个安全、稳定的进钉区间.     

跟骨内外侧经皮置针安全区解剖学研究

目的 划定国人跟骨内、外侧外固定针进针位置解剖学相对安全区.方法 解剖14具正常成年人足踝部标本.于跟骨内侧取跟骨最内下后点为A点,内踝最下点为B点,足舟骨结节为C点.解剖出跟骨内侧神经、足底外侧神经最后分支、足底外侧神经、足底内侧神经、胫后动脉、足底外侧动脉和足底内侧动脉.根据各结构行经AB、AC线的位置,确定跟骨内侧的相对安全区;于跟骨外侧取跟骨最外下后点为D点,外踝最下点为E点,解剖出跟骨外侧神经、腓肠神经、小隐静脉主干,同理确定跟骨外侧的相对安全区.结果 跟骨内侧神经、足底外侧神经最后分支、足底外侧神经、足底内侧神经、胫后动脉分别行经AB线后下22%、50%、56%、64%及58%处,跟骨内侧神经、足底外侧神经最后分支、足底外侧神经、足底内侧神经、足底外侧动脉、足底内侧动脉分别行经AC线后下14%、39%、49%、63%、41%及57%处.跟骨外侧神经、腓肠神经、小隐静脉分别行经DE线后下 19%、65%及61%处.结论 在跟骨内侧,AB线后1/2、AC线后1/3所在圆形区域为经皮置针相对安全区.在跟骨外侧,经DE线中点垂线后方的跟骨为经皮穿针相对安全区.     

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.     

全椎板减压侧块螺钉内固定治疗颈椎后纵韧带骨化症的疗效分析

【摘要】 目的：探讨后路全椎板减压侧块螺钉内固定治疗颈椎后纵韧带骨化症的疗效。方法：32例颈椎后纵韧带骨化症患者,平均年龄57.5岁,分别行后路单开门椎管扩大椎板成形术（A组,17例）和全椎板减压侧块螺钉内固定术（B组,15例）治疗。随访观察并比较两组患者手术时间、术中出血量、术后神经功能恢复情况及手术并发症的发生情况,并对两组患者术后颈椎的生理曲度及颈项肩背部疼痛、僵硬等轴性症状进行评估。结果：A组患者术后均无椎板开门再闭发生,B组患者术后植骨均完全融合,无内固定脱出、断裂等并发症发生。随访12个月,J     

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.