两种长度的颈椎椎弓根螺钉与侧块螺钉拔出试验比较

目的:比较两种长度的颈椎椎弓根螺钉和侧块螺钉的抗拔出力,探讨颈椎经椎弓根短螺钉固定的可行性。方法:5具C3~C5共15节新鲜颈椎标本,用长度为28mm和20mm的皮质骨螺钉分别置入椎弓根,并用20mm的螺钉行侧块双皮质固定,螺钉进入侧块深度约14mm。行拔出试验,比较螺钉的最大轴向拔出力。结果:椎弓根长螺钉的最大拔出力为650N,椎弓根短螺钉为585N,两者比较无显著性差异(P>0.01);侧块螺钉的最大拔出力为360N,与椎弓根短螺钉比较有显著性差异(P<0.0001)。结论:颈椎椎弓根短螺钉固定可提供足够的稳定性,其安全性相对较高。     

Load sharing properties of cervical pedicle screw-rod constructs versus lateral mass screw-rod constructs

Lateral mass screws have a history of successful clinical use, but cannot always be used in the subaxial cervical spine. Despite safety concerns, cervical pedicle screws have been proposed as an alternative. Pedicle screws have been shown to be biomechanically stronger than lateral mass screws. No study, however, has investigated the load sharing properties comparing constructs using these screws. To investigate this, 12 fresh-frozen single cervical spine motion segments (C4–5 and C6–7) from six cadavers were isolated. They were randomized to receive either lateral mass or pedicle screw-rod constructs. After preloading, the segments were cyclically loaded with a uniplanar axial load from 0 to 90 N both with and without the construct in place. Pressure data at the disc space were continuously collected using a dynamic pressure sensor. The reduction in disc space pressure between the two constructs was calculated to see if pedicle screw and lateral mass screw-rod constructs differed in their load sharing properties. In both the pedicle screw and lateral mass screw-rod constructs, there was a significant reduction in the disc space pressures from the no-construct to construct conditions. The percentage decrease for the pedicle screw constructs was significantly greater than the percentage decrease for the lateral mass screw constructs for average pressure (p ≤ 0.002), peak pressure (p ≤ 0.03) and force (p ≤ 0.04). We conclude that cervical pedicle screw-rod constructs demonstrated a greater reduction in axial load transfer through the intervertebral disc than lateral mass screw-rod constructs. Though there are dangers associated with the insertion of cervical pedicle screws, their use might be advantageous in some clinical conditions when increased load sharing is necessary.     

Biomechanical comparison of the pullout strengths of C1 lateral mass screws and C1 posterior arch screws

Background contextConditions of the atlantoaxial complex requiring internal stabilization can result from trauma, malignancy, inflammatory diseases, and congenital malformation. Several techniques have been used for stabilization and fusion. Posterior wiring is biomechanically inferior to screw fixation. C1 lateral mass screws and C1 posterior arch screws are used for instrumentation of the atlas. Previous studies have shown that unicortical C1 lateral mass screws are biomechanically stable for fixation. No study has evaluated the biomechanical stability of C1 posterior arch screws or compared the two techniques.PurposeThe purpose of the study was to assess the differences in the pullout strength between C1 lateral mass screws and C1 posterior arch screws.Study designBiomechanical testing of pullout strengths of the two atlantal screw fixation techniques.MethodsThirteen fresh human cadaveric C1 vertebrae were harvested, stripped of soft tissues, evaluated with computed tomography for anomalies, and instrumented with unicortical C1 lateral mass screws on one side and unicortical C1 posterior arch screws on the other. Screw placement was confirmed with postinstrumentation fluoroscopy. Specimens were divided in the sagittal plane and potted in polymethylmethacrylate. Axial load to failure was applied with a material testing device. Load displacement curves were obtained, and the results were compared with Student t test. DePuy Spine, Inc. (Raynham, MA, USA) provided the hardware used in this study.ResultsMean pullout strength of the C1 lateral mass screws was 821 N (range 387?1,645 N±standard deviation [SD] 364). Mean pullout strength of the posterior arch screws was 1,403 N (range 483?2,200 N±SD 609 N). The difference was significant (p=.009). Five samples (38%) in the posterior arch group experienced bone failure before screw pullout.ConclusionsBoth unicortical lateral mass screws and unicortical posterior arch screws are viable options for fixation in the atlas. Unicortical posterior arch screws have superior resistance to pullout via axial load compared with unicortical lateral mass screws in the atlas.     

Biomechanical advantage of C1 pedicle screws over C1 lateral mass screws: a cadaveric study

Purpose

The established technique for posterior C1 screw placement is via the lateral mass. Use of C1 monocortical pedicle screws is an emerging technique which utilizes the bone of the posterior arch while avoiding the paravertebral venous plexus and the C2 nerve root. This study compared the relative biomechanical fixation strengths of C1 pedicle screws with C1 lateral mass screws.

Methods

Nine human C1 vertebrae were instrumented with one lateral mass screw and one pedicle screw. The specimens were subjected to sinusoidal, cyclic (0.5 Hz) fatigue loading. Peak compressive and tensile forces started from ±25 N and constantly increased by 0.05 N every cycle. Testing was stopped at 5 mm displacement. Cycles to failure, displacement, and initial and end stiffness were measured. Finally, CT scans were taken and the removal torque measured.

Results

The pedicle screw technique consistently and significantly outperformed the lateral mass technique in cycles to failure (1,083 ± 166 vs. 689 ± 240 cycles), initial stiffness (24.6 ± 3.9 vs. 19.9 ± 3.2 N/mm), end stiffness (16.6 ± 2.7 vs. 11.6 ± 3.6 N/mm) and removal torque (0.70 ± 0.78 vs. 0.13 ± 0.09 N m). Only 33 % of pedicle screws were loose after testing compared to 100 % of lateral mass screws.

Conclusions

C1 pedicle screws were able to withstand higher toggle forces than lateral mass screws while maintaining a higher stiffness throughout and after testing. From a biomechanical point of view, the clinical use of pedicle screws in C1 is a promising alternative to lateral mass screws.     

Increase of pullout strength of spinal pedicle screws with conical core: biomechanical tests and finite element analyses.

Screw loosening can threaten pedicle screw fixation of the spine. Conical screws can improve the bending strength, but studies of their pullout strength as compared with that of cylindrical screws have shown wide variation. In the present study, polyurethane foam with two different densities (0.32 and 0.16 gm/cm3) was used to compare the pullout strength and stripping torque among three kinds of pedicle screws with different degrees of core tapering. Three-dimensional finite element models were also developed to compare the structural performance of these screws and to predict their pullout strength. In the mechanical tests, pullout strength was consistently higher in the higher density foam and was closely related to screw insertion torque (r=0.87 and 0.81 for the high and low density foam, respectively) and stripping torque (r=0.92 and 0.78, respectively). Conical core screws with effective foam compaction had significantly higher pullout strength and insertion torque than cylindrical core screws (p<0.05). The results of finite element analyses were closely related to those of the mechanical tests in both situations with or without foam compaction. This study led to three conclusions: polyurethane foam bone yielded consistent experimental results; screws with a conical core could significantly increase pullout strength and insertion torque over cylindrical; and finite element models could reliably reflect the results of mechanical tests.     

中上颈椎侧块与寰椎椎弓根位置关系的解剖研究

目的研究中上颈椎侧块与寰椎椎弓根的位置关系,建立以中上颈椎侧块为解剖标志的寰椎椎弓根螺钉进钉点定位技术。方法20具尸体标本,分别测量寰椎椎弓根和中上颈椎侧块的内缘、中点、外缘与正中矢状面的垂直距离,通过分析测量值间的关系,建立寰椎椎弓根螺钉进钉定位技术。结果C2-4侧块的内缘分别在寰椎椎弓根内缘外侧0．37mm、0．27mm、0．24mm处;C2-4侧块的中点分别在寰椎椎弓根中点外侧1．18mm、1．41mm、1．74mm处;C2-4侧块的外缘分别在寰椎椎弓根外缘外侧1．96mm、2．54mm、3．24mm处。结论中上颈椎侧块与寰椎椎弓根间存在较恒定的解剖位置关系,C3和C4侧块与枢椎侧块一样,可作为术中确定寰椎后弓显露范围和判断寰椎椎弓根螺钉进钉点的解剖学标志。     

Cervical spine injuries associated with lateral mass and facet joint fractures: New classification and surgical treatment with pedicle screw fixation

To clarify the injury pattern, initial spinal instability, degree of discoligamentous injuries in cervical lateral mass and facet joint fractures, we retrospectively analyzed radiological parameters and introduced a new classification for these injuries. Surgical treatment was performed with cervical pedicle screw fixation (CPS), and overall neurological and radiological outcome was evaluated with a minimum follow-up period of 2 years. Lateral mass fractures were divided into the following four subtypes: separation, comminution, split, and traumatic spondylolysis. The sagittal and frontal alignments were evaluated at both mainly injured and adjacent spinal segments on radiographs. The initial discoligamentous injuries were investigated on magnetic resonance imaging in terms of their frequencies, subtype of injuries, and involved spinal levels. Anterior translation of fractured vertebra was demonstrated in 77% of lateral mass fractures, while 24% of anterior translation was observed, even in cephalad-adjacent vertebrae. On magnetic resonance imaging, signal changes in anterior longitudinal ligament (ALL) and intervertebral disc were demonstrated in 76% of caudal segments and 24% of cephalad segments adjacent to fractured vertebra of lateral mass fractures. The subtype analyses of lateral mass fractures demonstrated high rates of anterior translation in separation, split, and traumatic spondylolisthesis, as well as significant coronal malalignment in comminution and split types (p<0.05). Thirty-one patients underwent surgical treatments using a cervical pedicle screw fixation. The CPS provided the superior capability of deformity correction without pseudoarthrosis, as well as excellent neurological recovery. The average numbers of stabilized segments were minimized without serious complications. In separation, facet joint fracture, and fractures with mild lateral mass comminution, the single level posterior fixation can be considered. The significant unstable injuries of split and comminution type with coronal malalignment can be treated with exclusive two-level posterior stabilization with CPS. The initial evaluation of fracture subtypes helps to successfully minimize the stabilized spinal segment.     

Characteristics of pullout failure in conical and cylindrical pedicle screws after full insertion and back-out

BACKGROUND CONTEXT: Biomechanical studies show that bone-mineral density, pedicle morphology, and screw thread area affect pedicle screw pullout failure. The current literature is based on studies of cylindrical pedicle screw designs. Conical screws have been introduced that may provide better "fit and fill" of the dorsal pedicle as well as improved resistance to screw bending failure. However, there is concern about loss of fixation if conical screws must be backed out after insertion. PURPOSE: To determine that conical screws have comparable initial stiffness and fixation strength compared with standard, cylindrical screws, and to assess whether conical screw fixation deteriorates when screws are backed out from full insertion. STUDY DESIGN/SETTING: This biomechanical analysis compared pullout strength of cylindrical and conical pedicle screw designs, using porcine lumbar vertebrae in a paired testing format. METHODS: Porcine lumbar vertebrae were instrumented with conical and cylindrical pedicle screws with the same thread pitch, area and contour, and an equivalent diameter at the pedicle isthmus, 1.2 cm distal to the hub. Axial pullout was performed at 1.0 mm/minute displacement. Pullout loads, work and stiffness were recorded at 0.02-second intervals. Conical versus cylindrical screws were tested using three paired control configurations: fully inserted, backed out 180 degrees and backed out 360 degrees. Fully inserted values were compared with each set of back-out values to determine relative loss of fixation strength. Screw pullout data were analyzed using a Student's t test. RESULTS: Pullout loads in these porcine specimens were comparable to data from healthy human vertebrae. Conical screws provided a 17% increase in the pullout strength compared with cylindrical screws (P<.10) and a 50% increase in initial stiffness (P<.05) at full insertion. There was no loss in pullout strength, stiffness or work to failure when conical or cylindrical screws were backed out 180 or 360 degrees from full insertion. CONCLUSIONS: Conical screws offer improved initial fixation strength compared with cylindrical screws of the same size and thread design. Our results suggest that appropriately designed conical screws can be backed out 180 to 360 degrees for intraoperative adjustment without loss of pullout strength, stiffness or work to failure. Intraoperative adjustments of these specific conical screws less than 360 degrees should not affect initial fixation strength. These results may not hold true for screws with a smaller thread area or larger minor diameter.     

下颈椎经关节螺钉和Magerl侧块螺钉与脊神经关系的解剖学比较

目的对比下颈椎经关节螺钉和Magerl侧块螺钉固定技术神经根(前支和后支)损伤的潜在风险。方法应用经关节螺钉和Magerl侧块螺钉两种固定技术,固定C_(3-7)节段,每种技术使用2具标本和20枚螺钉。使用直径为3．5mm、长度为20mm的螺钉进行过度穿透侧块腹侧皮质固定。仔细解剖颈部的前侧方,观察螺钉与脊神经前、后支的关系。结果下颈椎经关节螺钉固定技术总体神经损伤比例(45%)明显低于Magerl侧块螺钉固定技术(90%),两者差异有显著性意义(P＜0．05)。经关节螺钉和Magerl侧块螺钉固定技术引起的神经损伤均最多见于脊神经后支,分别为25%和45%。结论经关节螺钉固定技术神经根损伤的风险低于Magerl侧块螺钉固定技术。     

下颈椎椎板和侧块作为椎弓根置钉角度参考标志的可靠性

【摘要】 目的：探讨下颈椎椎板和侧块作为椎弓根置钉角度参考标志的可靠性。方法：完整成人颈椎骨性标本10具,男、女各5具,模拟施行下颈椎椎弓根置钉手术;术前对C3~C7进行螺旋CT扫描多平面重建,确定椎弓根进钉轴,并以椎板和侧块作为椎弓根内倾角和上倾角的参考标志,测量椎弓根进钉轴与同侧椎板的夹角（PL角）及与侧块后表面的夹角（PLM角）,术中以相同参考标志和置钉角度置入椎弓根螺钉。术后复查CT并评估椎弓根螺钉置钉的准确率：0级,螺钉完全位于椎弓根内;1级,穿破椎弓根的部分<螺钉直径的25%;2级,螺钉直径的25%~50%穿破椎弓根;3级,螺钉直径>50%穿破椎弓根;2级和3级螺钉为误置。对颈椎标本各节段椎弓根螺钉位置的分级与椎弓根的宽度与高度进行相关性分析。2011年10月~2012年12月,用同样方法对6例患者进行下颈椎椎弓根螺钉置钉手术,评估置钉准确率和并发症情况。结果：10具颈椎标本的下颈椎椎弓根的PL角,C3、C4>C5、C6>C7;PLM角,C3、C4相似文献   

Cervical pedicle screw insertion using a gutter entry point at the transitional area between the lateral mass and lamina

Purpose  

The purpose of this study was to describe a free-hand pedicle screw insertion technique and to evaluate the accuracy of pedicle screw placement and validity of pedicle screw fixation in patients with subaxial cervical spine injuries.     

Perforations and angulations of 324 cervical medial cortical pedicle screws: a possible guide to avoid lateral perforations with use of pedicle screws in lower cervical spine

Background Context

More than half of the perforations reported with usage of cervical pedicle screws (CPS) are lateral perforations, endangering the vertebral artery. The medial cortical pedicle screw (MCPS) technique with partial drilling of the medial cortex shifts the trajectory of pedicle screws medially, decreasing the lateral perforations.

寰椎椎弓根螺钉技术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-2010年1月,行寰椎椎弓根螺钉固定技术32例（A组）,行寰椎侧块螺钉固定技术28例（B组）。通过术中失血量,手术时间,颈枕区疼痛缓解,JOA评分和术后植骨融合情况评定疗效。结果：两组患者在JOA评分,颈枕区疼痛缓解WAS评分）和植骨融合率方面无明显差异。A组术中失血量和手术时间明显低于B组,有统计学意义。B组中有3例术后出现颈枕区疼痛加重。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、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。     

Anatomy of subaxial cervical foramens: the safety zone for lateral mass screwing

Introduction  

The purpose of this study was to measure the structures of the ventral of lateral masses using cadaver specimens and to quantitatively compare the safety zone for the two major techniques used on each vertebral level from C3 to C6.     

下颈椎经关节螺钉与侧块钉棒固定的生物力学比较

目的 :比较下颈椎经关节螺钉与侧块钉棒系统固定的生物力学特点。方法 :采用8具新鲜尸体下颈椎标本(C5~T1),用牙托石膏粉包埋后,通过脊柱试验机对标本施加最大2.0Nm纯力偶矩,在不同测试状态下,包括完整(A组)、C5/6后方韧带复合体切除(B组)、C5~C7经关节螺钉固定(C组)、C5~C7侧块钉棒系统固定(D组),测量屈伸、侧弯及旋转方向上的三维运动范围(ROM)。在C6椎体前缘粘贴应变片,测量不同状态下椎体前柱载荷变化。结果:A组C5/6节段屈伸、侧弯和旋转方向上的ROM分别为13.6°±1.2°、6.1°±0.5°、4.2°±1.6°;B组为14.4°±1.2°,6.4°±0.6°,4.8°±0.8°,C组为2.8°±0.7°、0.7°±0.3°、0.4°±0.1°,D组为1.2°±0.3°、0.5°±0.2°、0.8°±0.3°,在屈伸方向上B组的ROM较A组明显增大(P0.05),C组和D组在各方向上均较A组和B组明显减小(P0.05);在屈伸方向上,C组与D组比较有统计学差异(P0.05),在侧弯和旋转方向上,C组和D组无统计学差异(P0.05)。A组C6/7节段屈伸、侧弯和旋转方向上的ROM分别为12.3°±1.4°、5.5°±1.2°、2.7°±0.9°;B组为12.0°±1.3°、5.6°±1.0°、2.8°±0.9°,C组为2.9°±0.9°、0.4°±0.2°、0.4°±0.1°,D组为1.2°±0.3°、0.4°±0.1°、0.7°±0.3°,A、B两组在各方向上的ROM无显著性差异(P0.05);在屈伸方向上,C组和D组的ROM有统计学差异(P0.05),在侧弯和旋转方向上,两组无统计学差异(P0.05)。C组C6椎体前柱的应变在侧弯方向上较A组明显减小(P0.05),D组在前屈、后伸、侧弯方向上较A组明显减小(P0.05),C、D组在前屈方向上比较有统计学差异(P0.05)。结论:下颈椎后方韧带复合体损伤可造成屈伸和侧弯方向上失稳,经关节螺钉固定在轴向旋转和侧弯方向上与侧块钉棒系统固定效果相似,但限制屈伸运动的能力较弱。     

Lamina-guided lateral mass screw placement in the sub-axial cervical spine

Lateral mass (LM) screws are commonly used in posterior instrumentation of the cervical spine because of their perceived safety over pedicle screws. A possible complication of cervical LM screw placement is vertebral artery injury or impingement. Several screw trajectories have been described to overcome the risks of neurovascular injury; however, each of these techniques relies on the surgeon’s visual estimation of the trajectory angle. As the reliability hereof is poorly investigated, alignment with a constant anatomical reference plane, such as the cervical lamina, may be advantageous. The aim of this investigation was to determine whether alignment of the LM screw trajectory parallel to the ipsilateral cervical lamina reliably avoids vertebral artery violation in the sub-axial cervical spine. 80 digital cervical spine CT were analysed (40 female, 40 male). Exclusion criteria were severe degeneration, malformations, tumour, vertebral body fractures and an age of less than 18 or greater than 80 years. Mean age of all subjects was 39.5 years (range 18–78); 399 subaxial cervical vertebrae (C3–C7) were included in the study. Measurements were performed on the axial CT view of C3–C7. A virtual screw trajectory with parallel alignment to the ipsilateral lamina was placed through the LM. Potential violation of the transverse foramen was assessed and the LM width available for screw purchase measured. There was no virtual violation of the vertebral artery of C3–C7 with lamina-guided LM screw placement. LM width available for screw purchase using this technique ranged from 5.2 to 7.4 mm. The sub-axial cervical lamina is a safe reference plane for LM screw placement. LM screws placed parallel to the ipsilateral lamina find sufficient LM width and are highly unlikely to injure the vertebral artery, even in bi-cortical placement. Placing LM screws parallel to the lamina appears favourable over conventional techniques.     

An analysis of the anatomic features of the cervical spine using computed tomography to select safer screw insertion techniques

Purpose

The purpose of the present study was to evaluate the anatomic features of the cervical spine using computed tomography (CT) to select safer screw insertion techniques, particularly emphasizing the location of the transverse foramen.

Methods

Fifty patients who underwent multiplanar CT reconstruction were evaluated. There were 34 males and 16 females with an average age of 67 years. The parameters included the following measurements: foramen width (the size of the transverse foramen FW), foramen height (the size of the transverse foramen FH), pedicle width (PW), foramen angle (FA the position of the transverse foramen), pedicle transverse angle (PTA) and lateral mass angle (LMA).

Results

The mean FW ranged from 6.2 to 6.3 mm (n.s). The mean FH ranged from 5.0 to 5.7 mm, with significant differences between each vertebra, except for the FH between C4 and C5 and the FH between C5 and C6. The mean PW ranged from 5.4 to 6.1 mm. There were significant differences between each vertebra, except for the PW between C3 and C4 and the PW between C3 and C5. The mean FA ranged from 18.8° to 20.5°. There were significant differences between each vertebra, except for the FA between C3 and C6 and the FA between C4 and C5. The mean PTA ranged from 37.1° to 45.4°. There were significant differences between each vertebra, except for the PTA between C3 and C5. The mean LMA ranged from 1.0° to 5.3°. There were significant differences between each vertebra, except for the LMA between C4 and C5. The FW and FH exhibited no correlations with PW, PTA or LMA. FA was found to be positively correlated with both PTA and LMA. There was also a positive correlation between PTA and LMA.

Conclusions

We suggest that in cases in which pedicle screw insertion is difficult, lateral mass screws (LMS) can be inserted safely and longer sizes can be selected. In contrast, in cases in which LMS insertion is difficult, the insertion of pedicle screws can be performed relatively easy.     

外侧块螺钉内固定术治疗颈椎骨折脱位

采用外侧块螺钉内固定术治疗颈椎骨折脱位。受伤部位:C_3损伤2例,C_4损伤6例,C_5损伤7例,C_6损伤5例,C_7损伤3例。按Frankel神经功能分类法,A级11例,B级3例,C级4例,D级3例,E级2例。随访时间7个月～4年7个月,平均2年9个月。结果23例中优良6例,显效13例,差4例,有效率82.6％,植骨融合率100％。术中无损伤神经血管、术后感染、内固定物断裂等并发症。外侧块螺钉内固定治疗颈椎骨折脱位的优点是:在进行后方减压的同时能进行坚强的内固定;适用于伴有后方结构损伤的中下颈椎骨折脱位的内固定治疗;有利于促进脊髓功能的恢复。     

Cervical pedicle screw placement: feasibility and accuracy of two new insertion techniques based on morphometric data

This morphometric and experimental study was designed to assess the dimensions and axes of the subaxial cervical pedicles and to compare the accuracy of two different techniques for subaxial cervical pedicle screw (CPS) placement using newly designed aiming devices. Transpedicular fixation is increasingly used for stabilizing the subaxial cervical spine. Development of the demanding technique is based on morphometric studies of the pedicle anatomy. Several surgical techniques have been developed and evaluated with respect to their feasibility and accuracy. The study was carried out on six conserved human cadavers (average age 85 years). Axes and dimensions of the pedicles C3-C7 (60 pedicles) were measured using multislice computed tomography (CT) images prior to surgery. Two groups consisting of 3 specimens and 30 pedicles each were established according to the screw placement technique. For surgical technique 1 (ST1) a para-articular mini-laminotomy was performed. Guidance of the drill through the pedicle with a handheld aiming device attached onto the medial aspect of the pedicle inside the spinal canal. Screw hole preparation monitored by lateral fluoroscopy. In surgical technique 2 (ST2) a more complex aiming device was used for screw holes drilling. It consists of a frame with a fully adjustable radiolucent arm for carrying the instruments necessary for placing the screws. The arm was angled according to the cervical pedicle axis as determined by the preoperative CT scans. Drilling was monitored by lateral fluoroscopy. In either technique 3.5 mm screws made of carbon fiber polyetheretherketone (CF-PEEK) were inserted. The use of the CF-PEEK screws allowed for precise postoperative CT-assessment since this material does not cause artifacts. Screw placement was qualified from ideal to unacceptable into four grades: I = screw centered in pedicle; IIa = perforation of pedicle wall less than one-fourth of the screw diameter; IIb = perforation more than one-fourth of the screw diameter without contact to neurovascular structures; III = screw more than one-fourth outside the pedicle with contact to neurovascular structures. Fifty-six pedicle screws could be evaluated according to the same CT protocol that was used preoperatively. Accuracy of pedicle screw placement did not reveal significant differences between techniques 1 and 2. A tendency towards less severe misplacements (grade III) was seen in ST2 (15% in ST2 vs. 23% in ST1) as well as a higher rate of screw positions graded IIa (62% in ST2 vs. 43% in ST1). C4 and C5 were identified to be the most critical vertebral levels with three malpositioned screws each. Because of the variability of cervical pedicles preoperative CT evaluation with multiplanar reconstructions of the pedicle anatomy is essential for transpedicular screw placement in the cervical spine. Cadaver studies remain mandatory to develop safer and technically less demanding procedures. A similar study is projected to further develop the technique of CPS fixation with regard to safety and clinical practicability.     

Anterior cervical pedicle screw and plate fixation using fluoroscope-assisted pedicle axis view imaging: a preliminary report of a new cervical reconstruction technique

Anterior procedures in the cervical spine are feasible in cases having anterior aetiologies such as anterior neural compression and/or severe kyphosis. Halo vests or anterior plates are used concurrently for cases with long segmental fixation. Halo vests are bothersome and anterior plate fixation is not adequately durable. We developed a new anterior pedicle screw (APS) and plate fixation procedure that can be used with fluoroscope-assisted pedicle axis view imaging. Six patients (3 men and 3 women; mean age, 54 years) with anterior multisegmental aetiology were included in this study. Their original diagnoses comprised cervical myelopathy and/or radiculopathy (n = 4), posterior longitudinal ligament ossification (n = 1) and post-traumatic kyphosis (n = 1). All patients underwent anterior decompression and strut grafting with APS and plate fixation. Mean operative time was 192 min and average blood loss was 73 ml. Patients were permitted to ambulate the next day with a cervical collar. Local sagittal alignment was characterised by 3.5° of kyphosis preoperatively, which improved to 6.8° of lordosis postoperatively and 5.2° of lordosis at final follow-up. Postoperative improvement and early bony union were observed in all cases. There was no serious complication except for two cases of dysphagia. Postoperative imaging demonstrated screw exposure in one screw, but no pedicle perforation. APS and plate fixation is useful in selected cases of multisegmental anterior reconstruction of cervical spine. However, the adequate familiarity and experience with both cervical pedicle screw fixation and the imaging technique used for visualising the pedicle during surgery are crucial for this procedure.