Experimental pullout testing and comparison of variables in transpedicular screw fixation. A biomechanical study

The specific objective of this investigation was to assess and compare the relative performance of four types of pedicular fixation screws currently in use. All screws were tested under similar conditions. The results obtained have permitted the authors to rank the various screws tested in terms of performance as follows: 1) the Steffee screw, 2) the AO screw, 3) the Howmedica screw, and 4) the Roy-Camille screw. While the considerable variability of the bone material is recognized, the screw performance is also influenced by the geometric variables of screw design; improvements in the pullout strength can be achieved by an increase in the major diameter of the screw; screw displacement before failure appears related to the screw pitch, where an increase in the pitch of the screw will increase the amount of displacement before failure; screw angulation was found to have little effect on the pullout strength, but may have an effect on the screw displacement and energy absorption before failure.     

Comparison of perioperative morbidity in translaminar facet versus pedicle screw fixation

This retrospective study evaluated the perioperative morbidity of patients undergoing lumbar, sacral, or lumbosacral fusion using either pedicle or translaminar facet screw fixation following interbody fusion. Hospital charts of all patients who presented to a single tertiary care institution during a 4-year period were reviewed. Findings indicated translaminar facet screw fixation was a less invasive spinal fixation method with decreased perioperative morbidity compared to pedicle screw fixation.     

三种颈椎前路固定方式的体外生物力学比较

目的 ：通过体外生物力学方法比较颈椎前路单节段椎间盘切除植骨融合术的零切迹自稳锚定式椎间融合器（Zero-pofile interbody fusion device,Zero-P）和组装式板-笼内固定系统（Skate-plate fusion device,Skate）与传统钛板固定3种不同颈椎前路固定方式的即刻稳定性。方法：24具雄性新鲜山羊颈椎标本（保留C3-4节段）,通过X线片及骨密度检查排除骨质破坏、骨质疏松,剔除椎旁肌肉,保留主要韧带、关节囊及椎间盘,对24具山羊颈椎标本进行前屈-后伸、左右侧弯、左右扭转的体外生物力学测试（轴向载荷20N,运动负荷2.5N·m）并记录活动范围（range of motion,ROM）及中性区（neutral zone,NZ）。随后将24具标本随机分为3组：钛板固定组（n=8）、Zero-P组（n=8）、Skate组（n=8）,钛板组为C3/4椎间盘置入椎间融合器,再辅助前方传统钛板固定,Zero-P组为辅助Zero-P固定,Skate组为辅助SAKTE固定,再次进行相同加载条件下的屈伸、侧弯、扭转运动,记录标本ROM及NZ。结果：影像学显示...     

椎弓根钉棒系统治疗颈椎不稳定骨折的生物力学研究

目的 研究椎弓根钉棒系统治疗颈椎不稳定骨折的生物力学作用.方法 采用新鲜C3～7段小牛颈椎,制备成椎体屈曲压缩性骨折模型5具(椎管内均有骨块占位),记录椎弓根钉棒系统固定后纵向恒速拉伸过程中各种运动状态下椎管内骨块复位位移变化,描记出纵向拉伸载荷与椎管内骨块复位位移之间的关系曲线.结果 椎管内骨块位移-复位力在起始呈线性变化,但随着位移的增大呈非线性走势;颈椎轴向撑开力为50 N、相同骨块位移值时,前屈状态的骨块回复力比后伸状态大23%(P＜0.05),轴向撑开力为150 N、前屈状态的骨块回复力反而比后伸状态小11 %(P＜0.05);随着轴向撑开力的增大,椎管内骨块回复力增大,即随着载荷的减少,骨块回复的阻力越大.结论 轴向撑开力对椎管内骨折块的复位有重要影响,后纵韧带在骨折块复位过程中起决定性作用.     

改良枢椎椎板螺钉联合寰椎侧块螺钉固定治疗齿状突骨折1例报告

枢椎经椎板螺钉固定不仅操作简单,而且固定牢固,近年来受到临床医生的广泛关注。但椎板螺钉有置入椎管的风险,而且对于椎板薄小的病例不宜使用[1~3]。枢椎具有颈椎中最为宽厚的棘突,我们以棘突基底部为螺钉钉道主要把持部分,将螺钉由棘突基底部置入,进入枢椎椎板后,由椎板中上端出钉,钉尖穿出椎板背侧皮质骨,形成枢椎棘突椎板螺钉固定（C2 spinous process laminar screw）,既达到了双层皮质骨固定,又可保证螺钉没有置入椎管的风险[4]。我们对1例枢椎椎板厚度不宜进行椎板螺钉固定的Anderson Ⅱ型齿状突骨折患者进行了枢椎棘突椎板螺钉联合寰椎侧块螺钉固定,临床疗效满意,报道如下。     

A comparison of long-term outcomes of translaminar facet screw fixation and pedicle screw fixation: a prospective study

OBJECT: In this paper, the authors compare the long-term outcomes of translaminar facet screw fixation (TFSF) and pedicle screw fixation (PSF) in the treatment of degenerative lumbosacral disease. METHODS: This prospective analytical study was performed to compare the long-term outcomes of TFSF and PSF for degenerative lumbosacral disease. Outcomes were defined as the need for reoperation for the development of a nonunion, end-fusion degeneration, or for explantation of hardware. RESULTS: A total of 77 patients were analyzed. Thirty-seven patients underwent PSF and 40 received TFSF. Twenty-three of the 77 patients required a reoperation: 13 (32.5%) of the 40 patients in the TFSF group and 10 (27%) of the 37 the patients in the PSF group. The overall mean time to reoperation (regardless of outcome) was 4.05 years. For patients in the TFSF group the mean time to reoperation was 2.94 years, whereas it was 4.35 years in the PSF group (p = 0.34). Nonunion was noted in seven of the 40 patients in the TFSF group and one of 37 in the PSF group. The mean time to surgery for nonunion for patients in the TFSF group was 3.46 years and for those in the PSF group it was 6.27 years (p = 0.04). Surgery for end-fusion degeneration was performed in two patients in the TFSF group and five in the PSF group (p = 0.43). Explantation of hardware was performed in two patients with TFSF and four patients with PSF. Multivariable analysis revealed a statistically significant difference in the time to surgery for nonunion between PSF and TFSF (p = 0.048), with a hazard ratio of 0.097 (95% confidence interval 0.01-0.98). CONCLUSIONS: Findings from the current prospective study suggest that there is an increased risk of requirement for a reoperation for nonunion among TFSF cases compared with PSF cases.     

In vitro comparative biomechanical analysis of transpedicular screw instrumentations in the lumbar region of the human spine.

An analysis of the load-displacement behavior of stabilized spines in comparison with intact spines was undertaken using fresh human cadaveric spines (T12/L1--sacrum). The three-dimensional load-displacement data of the five vertebral bodies of an intact specimen in clinically relevant loading cases were recorded using the Selspot II motion measuring system. After testing the intact specimen, an instability was created at the L4-5 level. The unstable motion segment was stabilized sequentially with three transpedicular screw instrumentations. The stabilized specimens were tested, and the data for the stabilized tests were normalized with respect to the intact data to determine the degree of stabilization achieved in various loading modes as a function of the three devices. The results showed that the three transpedicular devices included in this study were effective in imparting stability to the injured ligamentous spinal segment at a p less than 0.01 level of significance. The differences among the devices were not significant.     

Modification of Wright’s technique for C2 translaminar screw fixation: technical note

Purpose  

To describe a modification of Wright’s technique for C2 translaminar screw fixation.     

A comparative biomechanical study of spinal fixation using the combination spinal rod-plate and transpedicular screw fixation system

A biomechanical study was performed comparing the stiffness and stability of the three-level combination spinal rod-plate and transpedicular screw (CSRP-TPS) fixation system with those of three anterior stabilization constructs that spanned three vertebral levels: iliac strut grafting, polymethylmethacrylate and anterior Harrington rod instrumentation (technique of Siegal et al.), and the Kaneda anterior device. The CSRP-TPS fixation system was also compared with five posterior instrumentation systems that spanned five vertebral levels: Harrington distraction rod instrumentation, segmentally wired Luque rectangular instrumentation, Cotrel-Dubousset transpedicular instrumentation. Steffee transpedicular screws and plates, and R. Roy-Camille plates under conditions of single-level instability. The relative stability of each instrumentation system was compared by mounting the fixation systems on calf spine segments containing five motion segments destabilized by complete L3 anterior corpectomies and L2-L3 and L3-L4 anterior diskectomies to simulate the two-column instability found clinically in spine fractures. Mechanical nondestructive cyclical testing in rotation, axial compression, and flexion was performed on 12 spines. All biomechanical tests were performed on a biaxial servo-controlled MTS 858 Bionix hydraulic materials testing device with a biaxial load cell. Intervertebral displacements between L2 and L4 were continuously recorded utilizing an extensometer with the knife edges placed directly adjacent to the L3 corpectomy defect during testing. This biomechanical study showed that CSRP-TPS instrumentation spanning three vertebral levels could restore the torsional, compressive, and flexural rigidity of the destabilized calf spines to that of the intact calf spines and provided more in vitro stability than either the traditional five-level Harrington distraction rod or the segmentally wired Luque rectangular instrumentation. The greatest torsional rigidity occurred with the five-level Cotrel-Dubousset instrumentation, the five-level Steffee plate and screw system, and the three-level Kaneda anterior device. In axial compression and flexural testing, the three-level CSRP-TPS system provided fixation comparable with the five-level Cotrel-Dubousset instrumentation, the five-level Steffee transpedicular screw and plate system, the five-level R. Roy-Camille plate and screw system, and the three-level Kaneda anterior device. Satisfactory levels of rigidity can be restored by three-level CSRP-TPS instrumentation under conditions of single-level instability in unstable thoracolumbar and lumbar spine fractures.     

C1侧块C2椎板螺钉固定与C1-2关节螺钉固定的生物力学性能比较

目的 比较1侧块C2椎板螺钉固定与后路C1-2关节螺钉固定的牛物力学性能,为枢椎交叉椎板螺钉的临床应用提供参考依据.方法 收集新鲜成年人尸体颈椎标本(C0-C4)10具,男6具,女4具,平均年龄58岁(50～72岁).分别制备成C1-2完整状态的模型(M0)、C1-2失稳的模型(M1)、C1,侧块螺钉C2交义椎板螺钉固定模型(M2)及后路C1-2关节螺钉固定模型(M3),进行三维生物力学测试,记录各组模型在屈伸、轴向旋转和侧屈的运动范围(ROM)和中性区(NZ).结果 屈伸模式下M0、M1、M2、M3的ROM和NZ分别为:(20.4±9.2)°、(10.4±5.8)°;(46.3±17.2))°、(34.5±14.1)°;(4.1±0.9)°、(1.9±0.8)°;(4.3±1.0)°、(2.1±0.7)°.轴向旋转模式下 M0、M1、M2、M3的ROM和NZ分别为:(65.3±12.9)°、(40.8±11.2)°;(91.7±10.5)°、(72.3±12.6)°;(8.9±2.1)°、(4.7±1.8)°;(8.4±2.5)°、(4.4±2.3)°.侧屈模式F M0、M1、M2、M3的ROM和NZ分别为:(11.5±4.3)°、(7.2±3.2)°;(35.0±12.9)°、(21.9±11.8)°;(2.9±1.1)°、(1.4±0.8)°;(2.5±1.4)°、(1.3±1.0)°.在三维运动模式下M2和M3力学稳定性均明显优于M1和M0,然而M2和M3,的差异无统计学意义(P>0.05).结论 C1侧块C2椎板螺钉固定拥有良好的生物力学稳定性,可作为C1-2关节螺钉固定的良好替代.     

膨胀式椎弓根螺钉与骨水泥强化方法增强螺钉稳定性的比较研究

[目的]比较膨胀式椎弓根螺钉(expansive pedicle screw,EPS)与骨水泥(polymethylmethacrylate,PM-MA)强化方法在体外增强螺钉稳定性的效果,并观察各方法中的钉道界面情况.[方法]45个新鲜成年绵羊腰椎随机分为3组.CPS组:直接拧入普通椎弓根螺钉;PMMA-PS组:向钉道内注入PMMA后拧入普通椎弓根螺钉;EPS组:直接拧入EPS.24 h后,对所有标本进行轴向拔出实验、X线和micro-CT检查.[结果]EPS组和PMMA-PS组中螺钉的稳定性均显著强于CPS组(P<0.05),而EPS组和PMMA-PS组之间的差异无统计学意义(P>0.05).X线检查示各组中螺钉位置良好.CPS组中骨组织包裹螺钉,形成"螺钉-骨质"界面;PMMA-PS组中,PMMA包裹螺钉,阻碍了螺钉与骨质的接触,形成了"螺钉-PMMA-骨质"界面;EPS组中,骨小梁直接包裹螺钉,形成"螺钉-骨质"界面.螺钉的前端明显膨胀,形成一个"爪状"结构.螺钉前端胀开的两翼挤压周围骨质,使膨胀部分周围的骨质较非膨胀部分更加致密.[结论]EPS可以显著提高螺钉的稳定性,其效果与目前临床上常用的PMMA强化方法接近.同时,EPS可以有效的避免因增加螺钉直径和使用PMMA可能带来的椎弓根骨折和渗漏、压迫等风险.另外,EPS的置入并不增加手术时间和手术创伤.作为一种有效、安全和操作简便的方法,EPS在临床上的广泛应用具有巨大的潜力.     

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.     

Screw fixation of radial head fractures: Compression screw versus lag screw—A biomechanical comparison

Introduction

Secondary loss of reduction and pseudarthrosis due to unstable fixation methods remain challenging problems of surgical stabilisation of radial head fractures. The purpose of our study was to determine whether the 3.0 mm Headless Compression Screw (HCS) provides superior stability to the standard 2.0 mm cortical screw (COS).

Materials and methods

Eight pairs of fresh frozen human cadaveric proximal radii were used for this paired comparison. A standardised Mason II-Fracture was created with a fragment size of 1/3 of the radial head's articular surface that was then stabilised either with two 3.0 mm HCS (Synthes) or two 2.0 mm COS (Synthes) according to a randomisation protocol. The specimens were then loaded axially and transversely with 100 N each for 4 cycles. Cyclic loading with 1000 cycles as well as failure load tests were performed. The Wilcoxon test was used to assess statistically significant differences between the two groups.

Results

No statistical differences could be detected between the two fixation methods. Under axial loads the COS showed a displacement of 0.32 mm vs. 0.49 mm for the HCS. Under transverse loads the displacement was 0.25 mm for the COS vs. 0.58 mm for the HCS group. After 1000 cycles of axial loading there were still no significant differences. The failure load for the COS group was 291 N and 282 N for the HCS group.

Conclusion

No significant differences concerning the stability achieved by 3.0 mm HCS and the 2.0 mm COS could be detected in the experimental setup presented.     

骨水泥修复颈椎前路椎体螺钉钉道的生物力学研究

目的 评价聚甲基丙烯酸甲酯(Polymethylmethacrylate,PMMA)修复颈椎前路椎体螺钉钉道的生物力学效果。方法 防腐成人颈椎标本(C_3~7)共30个,分3组:正常骨密度组(A组)、骨质疏松组(B组),骨质疏松修复组(C组),各组10个标本,测试疲劳前后的最大轴向拔出力。A、B对照组椎体二侧钉孔均放置4 mm的椎体螺钉,随机选择一侧行即时最大拔出力实验,另一侧在疲劳实验(2 Hz,20 000次)后行最大拔出力实验。C组(实验前需进行螺钉拔松实验)注入PMMA 0.6~1.0 mL,并拧入螺钉,随机选择一侧进行即时和疲劳后最大拔出力实验。结果 A、B、C组即时拔出力明显高于疲劳后拔出力,差异具有统计学意义(P< 0.05),C组疲劳后与A组即时拔出力比较,差异无统计学意义(P >0.05),但高于B组即时拔出力,差异具有统计学意义(P< 0.05)。即时拔出力C组 >A组 >B组,差异均有统计学意义(P< 0.05)。疲劳后拔出力C组 >A组 >B组,差异均有统计学意义(P< 0.05)。PMMA注射后未发现钉道渗漏。结论 PMMA钉道修复能够明显增强椎体螺钉的即时稳定性和抗疲劳能力, 并且安全有效,适用于螺钉松动和拔出的修复固定。     

Efficacy of translaminar facet screw fixation in circumferential interbody fusions as compared to pedicle screw fixation

OBJECTIVES: Posterior lumbar fixation with translaminar facet screws is a minimally invasive technique with good success rates. Long-term follow-ups show reduced reoperation rates, a decrease in pain scores, and few complications compared with pedicle screw fixation devices. The purpose of this study was to compare the reoperation rate of translaminar facet screw fixation with that of pedicle screw fixation in 360 degrees anterior and posterior fusions for incapacitating low back pain due to lumbar disc degeneration unresponsive to at least 6 months of aggressive nonoperative treatment. METHODS: One hundred five patients underwent a combined circumferential lumbar fusion with posterior fixation for discogenic pain by one surgeon between August 1993 and February 2003. Seventeen patients were excluded from the study owing to their preoperative etiology for fusion or a prior instrumented posterior fusion. A retrospective chart review was done on all 88 remaining patients. Patients were followed in the office, by phone, or by mail to obtain functional outcome measures. Any subsequent operations by this surgeon or another were recorded. The comparison focused on the rate of reoperation on the region of posterior lumbar fixation. RESULTS: Sixty-seven patients have had at least a 2-year follow-up. Twenty-four patients had a posterior fusion with pedicle screws, and 43 had translaminar facet screw fixation. Nine patients of the pedicle screw population (37.5%) had a reoperation to remove their instrumentation. Two patients of the translaminar facet screw population (4.7%) had reoperations on their lumbar spine. There was a significant association between posterior instrumentation type and reoperation (P = 0.001). CONCLUSION: The success of translaminar facet screws in circumferential fusions is justified.