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。     

下颈椎关节突关节的解剖学测量与经关节螺钉固定的关系

目的:测量下颈椎关节突关节的相关数据,探讨其与经关节螺钉固定的关系。方法:41具成人颈椎干燥标本,测量其颈椎关节突关节的上、下关节面的高度、宽度和冠状面角度以及下关节面在侧块后方投影的高度,并对侧块进行形态学评定;根据Dalcanto技术对30具颈椎标本行经关节突关节螺钉固定,以侧块中心点下2mm为进钉点,在矢状面上尾倾40°、在冠状面上外倾20°置入螺钉,测量螺钉的长度,观察螺钉位置。结果:C3～C7下关节面在侧块后方投影的高度为7.4～9.0mm,侧块的中心点约在下关节面后方投影的上界下方2mm。C6和C7上、下关节面的倾斜角度相对更大,侧块厚度相对较薄。采用Dalcanto技术经关节突关节螺钉固定,螺钉长度从C3/4向C7/T1呈下降趋势,由16.9mm降至15.7mm,其中在C7/T1水平螺钉最短。螺钉由头侧向尾侧经关节突关节复合体,大体上从关节面的中心点穿过;在矢状面上几乎与关节面垂直;无一例损伤到横突孔,螺钉从下位椎体的上关节突基底部的侧前方穿出,钉道指向侧前下方。结论:下颈椎关节突关节复合体可为经此关节螺钉固定提供足够的皮质骨。Dalcanto技术经关节突关节螺钉不仅具有可行性,而且可以避开横突孔,钉道方向几乎与横突沟平行,安全空间较大。由于C6、C7侧块的厚度较薄,在C6/7和C7/T1行经关节固定时不宜使用16mm以上长度的螺钉。     

下颈椎经关节螺钉研究进展

近年来下颈椎经关节螺钉相关基础与临床应用研究逐渐受到重视.下颈椎经关节螺钉植入的进钉点为侧块中点下2mm,方向向尾侧倾斜40°,向外侧倾斜20°.生物力学测试证明下颈椎经关节螺钉通过四层皮质的固定获得了较侧块螺钉更强的抗拔出力,可作为锚定螺钉运用于钉板或钉棒系统,亦可单独运用于下颈椎后路固定.临床应用及随访证实下颈椎经关节螺钉植入安全,可获得满意融合.随着三维影像导航技术的出现,完全有可能采用微创方法经皮植入下颈椎经关节螺钉,这样将会对传统下颈椎后路内固定技术的发展起一定促进作用.下颈椎经关节螺钉研究尚处于基础探索阶段,需要开展大量严密细致的解剖学研究、影像学评价、安全性评估及临床中长期随访.     

颈椎侧块钢板螺钉固定术治疗颈椎失稳

为治疗颈椎失稳症,采用颈椎侧块钢板螺钉固定术治疗颈椎失稳症９例,通过６～２６个月随访,均固定牢靠,融合良好,结果见颈椎侧块钢板螺钉固定对颈椎侧块肯牢固固定作用,同时对滑脱有良好的复位作用,认为后路颈椎侧块钢板螺丝固定加植骨是治疗颈椎失稳症的可靠方法。     

胸椎关节突关节解剖学测量与经关节螺钉固定的关系

目的测量胸椎关节突关节的相关数据,并探讨与经关节螺钉固定的关系。方法选取20具福尔马林液体浸泡保存的成人尸体胸椎标本,去除所有肌肉、韧带等软组织,对胸椎每个节段从椎间盘和关节间隙进行游离,清楚暴露出各个关节面。测量胸椎关节突关节上、下关节面的高度、宽度和厚度,分析与经关节螺钉固定的关系。结果胸椎关节突关节的关节面高度、宽度和厚度的左右侧数据稍有不同,但无明显统计学意义(P0.05)。胸椎上关节面的高度9.10～11.21mm,宽度8.45～11.07mm,厚度3.87～5.71mm;胸椎下关节面的高度10.65～12.59mm,宽度9.80～12.60mm,厚度4.20～6.01mm。结论胸椎关节突关节复合体有着足够的皮质骨供螺钉行跨关节固定,胸椎经关节固定也许可以作为椎弓根螺钉应用的一种补充方法。     

下颈椎经关节突关节椎弓根螺钉固定的可行性

目的:探讨下颈椎后路经关节突关节椎弓根螺钉固定的可行性和技术参数,为临床应用提供参考。方法:取20具颈椎标本,仔细解剖颈部的后侧和前侧方,清楚显露颈椎侧块和椎弓根。以侧块外下象限的中心点为进钉点,从C3/4～C6/7直视下经关节突关节置入椎弓根螺钉,通过CT重建,测量经关节突关节椎弓根螺钉内固定进钉角度和钉道长度。结果:经关节突关节椎弓根螺钉均成功置入,螺钉固定方向在矢状面呈尾倾,冠状面呈内倾,理想角度为在矢状面尾倾50.3°±4.9°,在冠状面内倾42.8°±4.0°。螺钉钉道长度为(34.1±1.4)mm,各固定节段间略有不同,但差异无统计学意义(P>0.05)。结论:下颈椎后路经关节突关节椎弓根螺钉固定是可行的,但置钉时要求较高的准确性,可以作为颈椎侧块螺钉和椎弓根螺钉固定的一种补充方法。     

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。     

下颈椎经关节螺钉固定临床应用的最新进展

1972年由Roy-camille第一次报道了在下颈椎成功运用经关节螺钉固定,尽管存在明显的优点,但未能得到广泛的应用。2003年Takayasu等[1]对25例患者中此项技术应用治疗各种原因引起的颈椎不稳,取得良好的临床疗效。1脊柱其他部位经关节螺钉Magerl等[2]首次提出经关节螺钉固定治疗寰     

后路侧块螺钉系统内固定治疗下颈椎骨折脱位

[目的]探讨颈椎侧块螺钉固定术在下颈椎骨折脱位的临床应用。[方法]2005～2009年应用侧块螺钉系统内固定治疗下颈椎骨折脱位16例。[结果]随访时间为4个月～3年,平均13个月,除FrankelA级1例无恢复外,其余脊髓功能均得到不同程度恢复。全部68枚螺钉位置正常,无螺钉松动、钢板折断等,椎体序列整齐,植骨均融合,无复位丢失。无神经、血管、脊髓损伤情况发生。[结论]颈椎侧块螺钉固定术具有操作简单、安全、固定较牢固等优点,是颈后路固定的一种有效、可靠的方法。     

Anatomic comparison of transarticular screws with lateral mass screws in cervical vertebrae

Objective:To compare the potential incidence of nerve root (ventral and dorsal ramus) injury caused by cervical transarticular screws and Roy-Camille lateral mass screws. Methods:Insertion techniques with Klekamp transarticular screws and Roy-Camille lateral mass screws were respectively performed in this study. Each technique involved four specimens and 40 screws, which were inserted from C3 to C7. And 20-mm-long screws were used to overpenetrate the ventral cortex. The anterolateral aspect of the cervical spine was carefully dissected to allow observation of the screw-ramus relationship. Results : The overall percentage of nerve invasion was significantly lower with Klekamp (45 %) technique than with Roy-Camille (85%) technique (P<0.05). The largest percentage of nerve invasion for Klekamp transarticular screws was found at the dorsal ramus (25%), followed by the ventral ramus (15%) and the bifurcation of the ventral dorsal ramus (5 %). The largest percentage of nerve invasion for Roy-Camille lateral mass screws was found at the ventral ramus (80 %). Conclusion : The potential risk of nerve root invasion is lower with Klekamp transarticular screws than with Roy-Camille lateral mass screws.     

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.     

Cervical pedicle screws vs. lateral mass screws: uniplanar fatigue analysis and residual pullout strengths

BACKGROUND CONTEXT: Although successful clinical use of cervical pedicle screws has been reported, anatomical studies have shown the possibility for serious iatrogenic injury. However, there are only a limited number of reports on the biomechanical properties of these screws which evaluate the potential benefits of their application. PURPOSE: To investigate if the pull-out strengths after cyclic uniplanar loading of cervical pedicle screws are superior to lateral mass screws. STUDY DESIGN: An in vitro biomechanical study. METHODS: Twenty fresh-frozen disarticulated human vertebrae (C3-C7) were randomized to receive both a 3.5 mm cervical pedicle screw and lateral mass screw. The screws were cyclically loaded 200 times in the sagittal plane. The amount of displacement was recorded every 50 cycles. After cyclical loading, the screws were pulled and tensile load to failure was recorded. Bone density was measured in each specimen and maximum screw insertion torque was recorded for each screw. RESULTS: During loading the two screw types showed similar stability initially, however the lateral mass screws rapidly loosened compared to the pedicle screws. The rate of loosening in the lateral mass screws was widely variable, while the performance of the pedicle screws was very consistent. The pullout strengths were significantly higher for the cervical pedicle screws (1214 N vs. 332 N) and 40% failed by fracture of the pedicle rather than screw pullout. Pedicle screw pullout strengths correlated with both screw insertion torque and specimen bone density. CONCLUSIONS: Cervical pedicle screws demonstrated a significantly lower rate of loosening at the bone-screw interface, as well as higher strength after fatigue testing. These biomechanical strengths may justify their use in certain limited clinical applications.     

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.     

Freehand determination of the trajectory angle for cervical lateral mass screws: how accurate is it?

Different methods of lateral mass screw placement in the cervical spine have been described with separate trajectories for each technique in the sagittal and parasagittal planes. In the latter, plane 30° has been recommended in the modified Magerl’s technique as the optimum angle to avoid injury to the vertebral artery and nerve root. The estimation of this angle remains arbitrary and very much operator dependant. The aim of this study was to assess how accurately the lateral trajectory angle of 30° is achieved by visual estimation amongst experienced surgeons in a tertiary spinal unit and to determine the likelihood of neurovascular injury during the procedure. We chose an anatomical ‘sawbone’ model of the cervical spine with simulated lordosis. The senior author marked the entry points. Five spinal consultants and five senior spinal fellows were asked to insert 1.6-mm K wires into the lateral masses of C3 to C6 bilaterally at 30° to the midsagittal plane using the marked entry points. The lateral angulation in the transverse plane was measured using a custom protractor and documented for each surgeon at each level and side. The mean and standard deviation (SD) of the data were obtained to determine the inter observer variability. Utilising this data, measurements were then made on a normal axial computerised tomography (CT) scan of the cervical spine of an anonymous patient to determine if there would have been any neurovascular compromise. Among the 10 surgeons, a total of 80 insertion angles were measured from C3 to C6 on either side. The overall mean angle of insertion was 25.15 (range 20.4–34.8). The overall SD was 4.78. Amongst the 80 measurements between the ten surgeons, two episodes of theoretical vertebral artery violation were observed when the angles were simulated on the CT scan. A moderate but notable variability in trajectory placement exists between surgeons during insertion of cervical lateral mass screws. Freehand estimation of 30° is not consistently achieved between surgeons and levels. In patients with gross degenerative or deformed cervical spine anatomy, this may increase the risk of neurovascular injury. The use of the ipsilateral lamina as an anatomical reference plane is supported.     

Radiographic and clinical assessment of a freehand lateral mass screw fixation technique: is it always safe in subaxial cervical spine?

Background contextMany spine surgeons use the freehand technique for lateral mass (LM) screw fixation. However, issues about its safety still exist.PurposeTo examine the safety of the freehand technique after LM screw insertion.Study designRetrospective case series.Patient sampleA total of 26 patients (21 men and five women) who underwent LM screw fixation via the freehand technique were included.Outcome measuresPostoperative computed tomography images and medical records were analyzed.MethodsDuring surgery, the lateral trajectory of screws was set using the adjacent spinous process (SP) after the cranial trajectory was set by palpating the joint surface. Computed tomography analyses were performed for the measurement of screw angles, and axial images were evaluated to determine the SP length that would be long enough to not involve the transverse foramen. The medical records were evaluated for the investigation of surgery-related complications.ResultsEach axial and sagittal angle of the screws showed a significant difference. A total of 18 screws (13.5%) involved the transverse foramen, and the mean axial angle of the screws was significantly smaller than the group not involving the foramen (p=.0078). A total of eight screws (6.0%) violated the facet, and the mean sagittal angle was significantly smaller than the group not violating the facet. The average difference in angles between the screw and the actual joint surface was largest at C6 (p=.0472). The mean maximum length of the SP, long enough to not involve the transverse foramen was significantly short at C3 and C6 (p=.0015). The actual SP length in one patient was longer than the maximum SP length determined through analysis in the case of C6. If the SP of C7 was used in C6, the SP length would not be safe in six patients.ConclusionsExcellent outcomes were observed with the use of the freehand technique for the insertion of LM screw at the subaxial C spine. However, this technique using the SP may pose a relative risk at C6.     

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。