聚乙烯醇水凝胶人工髓核置入对腰椎运动影响的生物力学研究

目的：研究髓核摘除后聚乙烯醇水凝胶人工髓核置入对腰椎活动度和椎间隙高度的影响.方法：对7具新鲜成人尸体L4/5正常椎间隙、髓核摘除后和置入人工髓核后在8.0Nm扭矩下的屈伸、侧弯和旋转的活动度（ROM）、中性区（NZ）和椎间隙高度变化进行测试、比较.结果：髓核摘除后,L4/5椎间屈伸、侧弯、旋转的ROM和NZ较正常组显著增加（P＜0.05或0.01）,在0和200N的负荷下椎间隙高度较相同情况下正常组分别下降1.2mm和1.7mm;置入人工髓核后,相对于正常椎间隙,L4/5椎间屈伸、侧弯、旋转的ROM和NZ无明显差异,较髓核摘除组明显下降（P＜0.05或0.01）,在0N和200N的负荷下椎间隙高度较相同情况下髓核摘除组分别增加1.6mm和2.0mm.结论：聚乙烯醇水凝胶人工髓核置入椎间盘切除后的椎间隙可有效恢复椎间隙高度,维持腰椎节段正常的三维运动功能稳定性.     

Biomechanical stability of five stand-alone anterior lumbar interbody fusion constructs

Anterior lumbar interbody fusion (ALIF) cages are expected to reduce segmental mobility. Current ALIF cages have different designs, suggesting differences in initial stability. The objective of this study was to compare the effect of different stand-alone ALIF cage constructs and cage-related features on initial segmental stability. Human multi-segmental specimens were tested intact and with an instrumented L3/4 disc level. Five different ALIF cages (I/F, BAK, TIS, SynCage, and ScrewCage) were tested non-destructively in axial rotation, flexion/extension and lateral bending. A cage ‘pull-out’ concluded testing. Changes in neutral zone (NZ) and range of motion (ROM) were analyzed. Cage-related measurements normalized to vertebral dimensions were used to predict NZ and ROM. No cage construct managed to reduce NZ. The BAK and TIS cages had the largest NZ increase in flexion/extension and lateral bending, respectively. Cages did reduce ROM in all loading directions. The TIS cage was the least effective in reducing the ROM in lateral bending. Cages with sharp teeth had higher ‘pull-out’ forces. Antero-posterior and medio-lateral cage dimensions, cage height and wedge angle were found to influence initial stability. The performance of stand-alone ALIF cage constructs generally increased the NZ in any loading direction, suggesting potential directions of initial segmental instability that may lead to permanent deformity. Differences between cages in flexion/extension and lateral bending NZ are attributed to the severity of geometrical cage-endplate surface mismatch. Stand-alone cage constructs reduced ROM effectively, but the residual ROM present indicates the presence of micromotion at the cage-endplate interface. Received: 3 June 1999/Revised: 3 September 1999/Accepted: 8 September 1999     

The multidirectional bending properties of the human lumbar intervertebral disc.

BACKGROUND CONTEXT: While the biomechanical properties of the isolated intervertebral disc have been well studied in the three principal anatomic directions of flexion/extension, axial rotation, and lateral bending, there is little data on the properties in the more functional directions that are combinations of these principal anatomic directions. PURPOSE: To determine the bending flexibility, range of motion (ROM), and neutral zone (NZ) of the human lumbar disc in multiple directions and to determine if the values about the combined moment axes can be predicted from the values about principal moment axes. STUDY DESIGN/SETTING: Three-dimensional biomechanical analysis of the elastic bending properties of human lumbar discs about principal and combined moment axes. METHODS: Pure, unconstrained moments were applied about multiple axes. The bending properties (flexibility, ROM, and NZ) of isolated lumbar discs (n=4 for L2/L3 and n=3 for L4/L5) were determined in the six principal directions and in 20 combined directions. The experimental values were compared with those predicted from the linear combination of the six principal moment axes. RESULTS: The maximum and minimum values of the biomechanical properties were found at the principal moment axes. Among combined moment axes, ROM and NZ (but not flexibility) values were predicted from the principal moment axis values. CONCLUSIONS: The principal moment axes coincide with the primary mechanical axes of the intervertebral disc and demonstrate significant differences in direction for values of flexibility, ROM, and NZ. Not all combined moment axis values can be predicted from principal moment axis values.     

Dynamics of an Intervertebral Disc Prosthesis in Human Cadaveric Spines

Low-back pain is a common, disabling medical condition, and one of the major causes is disc degeneration. Total disc replacements are intended to treat back pain by restoring disc height and re-establishing functional motion and stability at the index level. The objective of this study was to determine the effect on range of motion (ROM) and stiffness after implantation of the ProDisc®-L device in comparison to the intact state. Twelve L5–S1 lumbar spine segments were tested in flexion/extension, lateral bending, and axial rotation with axial compressive loads of 600 N and 1,200 N. Specimens were tested in the intact state and after implantation with the ProDisc®-L device. ROM was not significantly different in the implanted spines when compared to their intact state in flexion/extension and axial rotation but increased in lateral bending. Increased compressive load did not affect ROM in flexion/extension or axial rotation but did result in decreased ROM in lateral bending and increased stiffness in both intact and implanted spine segments. The ProDisc®-L successfully restored or maintained normal spine segment motion.     

Biomechanical characterization of an annulus-sparing spinal disc prosthesis

Background contextCurrent spine arthroplasty devices require disruption of the annulus fibrosus for implantation. Preliminary studies of a unique annulus-sparing intervertebral prosthetic disc (IPD) found that preservation of the annulus resulted in load sharing of the annulus with the prosthesis.PurposeDetermine flexibility of the IPD versus fusion constructs in normal and degenerated human spines.Study design/settingBiomechanical comparison of motion segments in the intact, fusion and mechanical nucleus replacement states for normal and degenerated states.Patient settingThirty lumbar motion segments.Outcomes measuresIntervertebral height; motion segment range of motion, neutral zone, stiffness.MethodsMotion segments had multidirectional flexibility testing to 7.5 Nm for intact discs, discs reconstructed using the IPD (n=12), or after anterior/posterior fusions (n=18). Interbody height and axial compression stiffness changes were determined for the reconstructed discs by applying axial compression to 1,500 N. Analysis included stratifying results to normal mobile versus rigid degenerated intact motion segments.ResultsThe mean interbody height increase was 1.5 mm for IPD reconstructed discs versus 3.0 mm for fused segments. Axial compression stiffness was 3.0±0.9 kN/mm for intact compared with 1.2±0.4 kN/mm for IPD reconstructed segments. Reconstructed disc ROM was 9.0°±3.7° in flexion extension, 10.6°±3.4° in lateral bending, and 2.8°±1.4° in axial torsion that was similar to intact values and significantly greater than respective fusion values (p<.001). Mobile intact segments exhibited significantly greater rotation after fusion versus their more rigid counterparts (p<.05); however, intact motion was not related to motion after IPD reconstruction. The NZ and rotational stiffness followed similar trends. Differences in NZ between mobile and rigid intact specimens tended to decrease in the IPD reconstructed state.ConclusionThe annulus-sparing IPD generally reproduced the intact segment biomechanics in terms of ROM, NZ, and stiffness. Furthermore, the IPD reconstructed discs imparted stability by maintaining a small neutral zone. The IPD reconstructed discs were significantly less rigid than the fusion constructs and may be an attractive alternative for the treatment of degenerative disc disease.     

利用成年猪脊柱制作胸腰段后凸畸形模型进行脊柱三维运动实验

[目的]探讨应用成年猪脊柱制作胸腰段后凸畸形模型进行生物力学实验研究的可行性,以及胸腰段后凸畸形对腰椎三维运动的生物力学影响.[方法]收集24例成年家猪胸腰椎脊柱新鲜标本,随机分为三组,制造两个Cobb角度水平的胸腰段后凸畸形和相应的腰椎过度前凸模型,进行脊柱三维运动实验,测量L2、3和L4、5的前屈/后伸、左/右侧弯、左/右旋转的运动范围( ROM)以及所对应的中性区(NZ)的大小,对各组数值进行方差分析,用snk(q检验)法对分组变量进行多重比较.[结果]后凸的胸腰段对邻近运动节段(L2、3)矢状面上的运动(前屈/后伸)ROM以及NZ的影响更明显,P＜0.05,而左/右侧弯、左/右旋转的ROM及NZ没有统计学差异,P＞0.05;而下腰椎运动节段(L4、5)的前屈/后伸、左/右侧弯、左/右旋转的ROM及NZ均没有统计学差异,P＞0.05.[结论]利用成年猪脊柱制作胸腰段后凸畸形模型进行脊柱三维运动实验是可行、简便、有效的;腰椎前屈/后伸运动范围的过度增大,是胸腰段后凸畸形后为维持脊柱矢状面平衡的一个重要代偿改变,且ROM的增大以上腰椎的改变更为明显.     

In vitro flexibility of the cervical spine after ventral uncoforaminotomy. Laboratory investigation

OBJECT: Degenerative spine disorders are, in the majority of cases, treated with ventral discectomy followed by fusion (also known as anterior cervical discectomy and fusion). Currently, nonfusion strategies are gaining broader acceptance. The introduction of cervical disc prosthetic devices was a natural consequence of this development. Jho proposed anterior uncoforaminotomy as an alternative motion-preserving procedure at the cervical spine. The clinical results in the literature are controversial, with one focus of disagreement being the impact of the procedure on stability. The aim of this study was to address the changes in spinal stability after uncoforaminotomy. METHODS: Six spinal motion segments derived from three fresh-frozen human cervical spine specimens (C2-7) were tested. The donors were two men whose ages at death were 59 and 80 years and one woman whose age was 80 years. Bone mineral density in C-3 ranged from 155 to 175 mg/cm3. The lower part of the segment was rigidly fixed in the spine tester, whereas the upper part was fixed in gimbals with integrated stepper motors. Pure moment loads of +/- 2.5 Nm were applied in flexion/extension, axial rotation, and lateral bending. For each specimen a load-deformation curve, the range of motion (ROM), and the neutral zone (NZ) for negative and positive directions of motion were calculated. Median, maximum, and minimum values were calculated for the six segments and normalized to the intact segment. Tests were done on the intact segment, after unilateral uncoforaminotomy, and after bilateral uncoforaminotomy. RESULTS: In lateral bending a strong increase in ROM and NZ was detectable after unilateral uncoforaminotomy on the right side. Overall, the ROM during flexion/extension was less influenced after uncoforaminotomy. The ROM and NZ during axial rotation to the left increased strongly after right unilateral uncoforaminotomy. Changes after bilateral uncoforaminotomy were marked during axial rotation to both sides. CONCLUSIONS: Following unilateral uncoforaminotomy, a significant alteration in mobility of the segment is found, especially during lateral bending and axial rotation. The resulting increase in mobility is less pronounced during flexion and least evident on extension. Further investigations of the natural course of disc degeneration and the impact on mobility after uncoforaminotomy are needed.     

Graded thoracolumbar spinal injuries: development of multidirectional instability

Injuries of the thoracolumbar spine are serious, disabling, and costly to society. These injuries vary from mild ligament tears to severe bony fractures. Increased range of motion (ROM) and neutral zone (NZ) have been suggested as indicators of the resulting clinical instability. The purpose of the present study was to investigate the relative sensitivities and merits of the ROM and NZ in relation to spinal injuries of the thoracolumbar junction. A graded spinal trauma experiment was designed, in which the threshold of injury and injury progression were examined. Ten thoracolumbar human spine specimens (T11–L1) were traumatized using a high-speed incremental trauma model. The ROM and NZ, which indicate altered mechanical properties, were determined for three physiological motions: flexion/extension (FE), lateral bending (LB), and axial rotation (AR). The injury threshold was found to be 84 J (or 84 Nm) by examining both ROM and NZ for all motion types (P < 0.05), but the NZ was more sensitive. At the injury threshold, the NZ showed an overall average increase of 566% above that of the intact, while the equivalent increase in the ROM was only 94%. The NZ was also a more sensitive parameter documenting the progression of the injury beyond the injury threshold. After the maximum trauma of 137 J, the NZs for the three motions (FE, LB, and AR) increased by 700%, 1700%, and 3000% above their respective intact values. Corresponding increases in the ROM were much smaller: 115%, 184%, and 425% respectively. Direct extrapolation of the in vitro experimental findings to the clinical situation, as always, should be done with care. Our findings, however, suggest that the ROM, as measured from functional radiographs of a traumatized patient, may underestimate the true injury to the spinal column. Received: 20 October 1997 Revised: 29 January 1998 Accepted: 9 February 1998     

Biomechanical comparison of anterior cervical plating and combined anterior/lateral mass plating.

BACKGROUND CONTEXT: Previous studies showed anterior plates of older design to be inadequate for stabilizing the cervical spine in all loading directions. No studies have investigated enhancement in stability obtained by combining anterior and posterior plates. PURPOSE: To determine which modes of loading are stabilized by anterior plating after a cervical burst fracture and to determine whether adding posterior plating further significantly stabilizes the construct. STUDY DESIGN/SETTING: A repeated-measures in vitro biomechanical flexibility experiment was performed to investigate how surgical destabilization and subsequent addition of hardware components alter spinal stability. PATIENT SAMPLE: Six human cadaveric specimens were studied. OUTCOME MEASURES: Angular range of motion (ROM) and neutral zone (NZ) were quantified during flexion, extension, lateral bending, and axial rotation. METHODS: Nonconstraining, nondestructive torques were applied while recording three-dimensional motion optoelectronically. Specimens were tested intact, destabilized by simulated burst fracture with posterior distraction, plated anteriorly with a unicortical locking system, and plated with a combined anterior/posterior construct. RESULTS: The anterior plate significantly (p<.05) reduced the ROM relative to normal in all modes of loading and significantly reduced the NZ in flexion and extension. Addition of the posterior plates further significantly reduced the ROM in all modes of loading and reduced the NZ in lateral bending. CONCLUSIONS: Anterior plating systems are capable of substantially stabilizing the cervical spine in all modes of loading after a burst fracture. The combined approach adds significant stability over anterior plating alone in treating this injury but may be unnecessary clinically. Further study is needed to assess the added clinical benefits of the combined approach and associated risks.     

Fracture pattern and instability of thoracolumbar injuries

Summary Spinal fractures are common in the thoracolumbar region. Assessment of fracture instability is often made from fracture patterns seen on plain radiographs or CT scans. The purpose of this in vitro study was to correlate three-dimensional flexibility to each fracture type, i.e., endplate, wedge, and brust. Ten fresh cadaveric human spine specimens (T11-L1) were incrementally impacted in a high-speed trauma apparatus until a fracture occurred. All fractures were produced by the same mechanism (axial compression/flexion load). The occurrence of a fracture was monitored by lateral radiographs of the specimen, whose canal was lined with 1.6-mm steel balls. After each impact, the specimen was studied for its flexibilily in flexion, extension, left and right lateral bindings, and left and right axial rotations. The flexibility was determined in response to the application of maximum pure moments of 7.5 Nm. Each moment was applied individually and in three load cycles. Parameters of neutral zone (NZ) and range of motion (ROM) were computed. Average flexion-extension ROM (and NZ) for intact, endplate, wedge, and burst fracture were respectively, 12.7° (1.3°), 13.9° (1.7°), 19.2° (3.2°), 22.0° (6.0°). The average lateral bending ROM (NZ) were 12.6° (1.2°), 13.6° (1.9°), 19.1° (3.7°), 27.2° (9.8°). The average axial rotation ROM (NZ) were 4.7° (0.4°), 6.1° (0.7°), 7.1° (1.0°), 12.9° (3.1°). The highest instability (fracture/intact motion) was seen in the axial rotation NZ in all three fracture types: 3.2, 5.4, and 14.7, respectively, for the endplate, wedge, and brust fractures. The average kinetic energy and force necessary to produce endplate, wedge, and burst fractures were 57, 84, 104 Nm, and 4.8, 6.5, 6.3 kN, respectively.     

Interbody device endplate engagement effects on motion segment biomechanics

Background ContextStand-alone nonbiologic interbody fusion devices for the lumbar spine have been used for interbody fusion since the early 1990s. However, most devices lack the stability found in clinically successful circumferential fusion constructs. Stability results from cage geometry and device/vertebral endplate interface integrity. To date, there has not been a published comparative biomechanical study specifically evaluating the effects of endplate engagement of interbody devices.PurposeLumbar motion segments implanted with three different interbody devices were tested biomechanically to compare the effects of endplate engagement on motion segment rigidity. The degree of additional effect of supplemental posterior and anterior fixation was also investigated.Study Design/SettingA cadaveric study of interbody fusion devices with varying degrees of endplate interdigitation.Outcome MeasuresImplanted motion segment range of motion (ROM), neutral zone (NZ), stiffness, and disc height.MethodsEighteen human L23 and L45 motion segments were distributed into three interbody groups (n=6 each) receiving a polymeric (polyetheretherketone) interbody spacer with small ridges; a modular interbody device with endplate spikes (InFix, Abbott Spine, Austin, TX, USA); or dual tapered threaded interbody cages (LT [Lordotic tapered] cage; Medtronic, Memphis, TN, USA). Specimens were tested intact using a 7.5-Nm flexion-extension, lateral bending, and axial torsion flexibility protocol. Testing was repeated after implantation of the interbody device, anterior plate fixation, and posterior interpedicular fixation. Radiographic measurements determined changes in disc height and intervertebral lordosis. ROM and NZ were calculated and compared using analysis of variance.ResultsThe interbody cages with endplate spikes or threads provided a statistically greater increase in disc height versus the polymer spacer (p=.01). Relative to intact, all stand-alone devices significantly reduced ROM in lateral bending by a mean 37% to 61% (p≤.001). The cages with endplate spikes or threads reduced ROM by ～50% and NZ by ～60% in flexion-extension (p≤.02). Only the cage with endplate spikes provided a statistically significant reduction in axial torsion ROM compared with the intact state (50% decrease, p<.001). Posterior fixation provided a significant reduction in ROM in all directions versus the interbody device alone (p<.001). Anterior plating decreased ROM over interbody device alone in flexion-extension and torsion but did not have additional effect on lateral bending ROM.ConclusionThe cages with endplate spikes or threads provide substantial motion segment rigidity compared with intact in bending modes. Only the cages with endplate spikes were more rigid than intact in torsion. All devices experienced increased rigidity with anterior plating and even greater rigidity with posterior fixation. It appears that the endplate engagement with spikes may be beneficial in limiting torsion, which is generally difficult with other “stand-alone” devices tested in the current and prior reports.     

新型钛合金颈椎前路接骨板的三维稳定性试验

背景：目前,颈椎前路接骨板已经广泛应用于颈椎创伤、畸形、退行性变以及颈椎肿瘤的治疗。目的：应用新型钛合金研制颈椎前路多功能接骨板（multifunctional cervicalplate,MCP）,并且对其进行三维稳定性试验。方法：收集24具6个月左右宰杀的猪颈椎标本随机分为4组,每组6具标本。在连续的4种状态下,即完整状态、植骨状态、接骨板固定状态以及疲劳测试后状态,对颈椎C3-C7施加2.0Nm的纯力矩,测量标本前屈、后伸、左右侧屈、左右旋转的活动范围（rang of motion,ROM）和中性区（neutral zone,NZ）。结果：所有节段在6个方向的ROM上,MCP固定状态、MCP疲劳状态、C-mark接骨板（C-markplate,CMP）固定状态、CMP疲劳状态之间相比较,差异无统计学意义（P〉0.05）,但与完整状态、植骨状态相比较,差异均有显著统计学意义（P〈0.01）。在前屈、左右侧屈方向的ROM上,植骨状态与完整状态相比较,差异有显著统计学意义（P〈0.01）。在屈伸NZ上,MCP固定状态、MCP疲劳状态、CMP固定状态、CMP疲劳状态之间差异无统计学意义（P〉0.05）,但与完整状态、植骨状态相比较,差异均有显著统计学意义（P〈0.01）。在侧屈NZ上,除完整状态与其他状态之间有统计学意义外（P〈0.01）,其他状态之间没有差异（P〉0.05）。在旋转NZ上,所有状态之间均无统计学意义（P〉0.05）。结论：体外生物力学研究表明MCP能够给颈椎提供足够的三维稳定性,在进行扭转疲劳试验后仍然可以保持三维稳定性。     

Load-displacement properties of the normal and injured lower cervical spine in vitro

The objective of this study was to determine which discoligamentous structures of the lower cervical spine provide significant stability with regard to different loading conditions. Accordingly, the load-displacement properties of the normal and injured lower cervical spine were tested in vitro. Four artificially created stages of increasing discoligamentous instability of the segment C5/6 were compared to the normal C5/6 segment. Six fresh human cadaver spine segments C4-C7 were tested in flexion/extension, axial rotation, and lateral bending using pure moments of ± 2.5 Nm without axial preload. Five conditions were investigated consecutively: (1) the intact functional spinal unit (FSU) C5/6; (2) the FSU C5/6 with the anterior longitudinal ligament and the intertransverse ligaments sectioned; (3) the FSU C5/6 with an additional 10-mm-deep incision of the anterior half of the anulus fibrosus and the disc; (4) the FSU C5/6 with additionally sectioned ligamenta flava as well as interspinous and supraspinous ligaments; (5) the FSU C5/6 with additional capsulotomy of the facet joints. In flexion/extension, significant differences were observed concerning range of motion (ROM) and neutral zone (NZ) for all four stages of instability compared to the intact FSU. In axial rotation, only the stage 4 instability showed a significantly increased ROM and NZ compared to the intact FSU. For lateral bending, no significant differences were observed. Based on these data, we conclude that flexion/extension is the most sensitive load-direction for the tested discoligamentous instabilities. Received: 12 August 1999/Revised: 15 October 1999/Accepted: 28 October 1999     

Biomechanical evaluation of the New Zealand white rabbit lumbar spine: a physiologic characterization

Physiologic motions of the human, sheep, and calf lumbar spines have been well characterized. The size, cost, and ease of care all make the rabbit an attractive alternative choice for an animal lumbar spine model. However, comparisons of normal biomechanical characteristics of the rabbit lumbar spine have not been made to the spines of larger species. The purpose of this study was to establish baseline physiologic kinematic data for the rabbit lumbar spine. Ten skeletally mature New Zealand white rabbit osteoligamentous spines were obtained. L4-L7 spine segments were harvested and mounted. Multi-directional flexibility testing was performed by applying pure moments up to 0.27 Nm. Resulting rotations were measured using an Optotrak system. Data were analyzed for each intervertebral level in the three planes of rotation. The three levels tested had roughly similar range of motion (ROM). The mean (SD) angular ROMs in flexion for L4-L5, L5-L6, L6-L7 were 12.10° (2.59°), 12.38° (2.70°), and 15.17° (3.22°), respectively. The ROMs in extension were 5.86° (1.21°), 5.58° (1.48°), and 6.13° (2.03°). Lateral bending and axial rotation were roughly symmetric due to the symmetric nature of the spine. For right lateral bending, the ROMs were 8.25° (2.44°), 4.96° (1.70°), and 4.25° (1.20°). For left axial rotation, the ROMs were 1.23° (1.16°), 0.35° (0.61°), 0.87° (0.64°). Neutral zone (NZ) was on average 60% (29%) of ROM for the motions studied. The physiologic ROM of the New Zealand white rabbit lumbar spine was found to be similar between the rabbit and human. This relatively conserved physiologic flexibility supports the use of the rabbit as a model of the lumbar spine for kinematic studies. However, the overall NZ was found to be a greater percentage of ROM in the rabbit than the corresponding percentage in the human (60% as compared to 25%). This suggested that the rabbit lumbar spine has a greater laxity than that of the human. Received: 23 August 1999 Revised: 15 December 1999 Accepted: 26 January 2000     

双节段后路腰椎椎体间融合术单侧椎弓根钉固定的生物力学稳定性

目的 分析对模拟双节段腰椎后路椎体间融合术(PLIF)采用单侧椎弓根钉固定(单侧固定)的生物力学稳定性.方法 将6具新鲜成人尸体腰椎标本(L2～S2)分别制备成L4～S1的PLIF模型,应用MTS 858实验机模拟产生屈伸、侧弯、轴向旋转,并按初始状态、单侧不稳、单侧不稳-单侧固定、双侧不稳-单侧固定、双侧不稳-双侧固定、双侧不稳的顺序进行测试,动态摄取记录各个节段角位移运动范围(ROM)与中性区值(NZ).结果 单侧不稳-单侧固定屈伸、侧弯、轴向旋转方向ROM值依次为2.53±1.12、4.03±2.19、2.78±1.00,NZ值依次为1.14±0.70、1.96±1.13、1.28±0.71,均显著小于初始状态(P<0.05),相比双侧不稳-双侧固定,各方向ROM与NZ值分别增加60.13%与17.52%、315.46%与243.86%、8.17%与6.20%,但差异无统计学意义(P>0.05).双侧不稳-单侧固定侧弯与旋转状态ROM与NZ值较双侧不稳-双侧固定显著增加(P<0.05).结论 单侧固定对人腰椎标本模拟双节段单侧PLIF可提供与双侧固定相似的生物力学稳定性,而对于模拟双节段双侧PLIF则单侧固定在大多数三维运动方向上不能提供足够的力学稳定性.

Abstract：

Objective To analyze the biomechanical efficacy of unilateral pedicle screw fixation on human cadaveric lumbar spine model simulated by two-level posterior lumbar interbody fusion (PLIF). Methods Six fresh-frozen adult human cadaveric lumbar spine motion segments (L2-S2) were simulated to unilateral/bilateral L4-S1 PLIF constructs augmented by unilateral/bilateral pedicle screw fixation sequentially and respectively. All configurations were tested by MTS 858 in the following sequential construct order: the intact, UI (unilateral instability), UIUF1C (unilateral instability via unilateral pedicle screw fixation plus one cage) , BIUF1C (bilateral instability via unilateral pedicle screw fixation plus one cage) , BIBF1C (bilateral instability via bilateral pedicle screw fixation plus one cage) and BI (bilateral instability without pedicle screw and cage). Each specimen was nondestructively tested in flexion/extension, lateral performed between different simulated constructs with One Way of ANOVA and Post hoc LSD tests. Results BIBF1C had the lowest ROM and NZ of L4-S1 fusion segments in all loading models, which were significantly lower than those of any uninstmmented construct (the intact, UI and BI) (P < 0. 05). In flexion/extension, lateral bending, and axial rotation, the ROM of UIUF1C was respectively 2.53 ± 1. 12, 4.03 ± 2. 19, 2. 78 ±1.00 and the NZ of UIUF1C was respectively 1.14 ±0.70, 1.96 ±1. 13, 1.28 ±0.71, which were significantly lower than those of the intact (P <0. 05). Compared to BIBF1C, the ROM and NZ were respectively increased 60.13% and 17.52% in flexion/extension, 315.46% and 243.86% in lateral bending, 8. 17% and 6. 20% in axial rotation, however, there were no significant differences between these two constructs (P > 0. 05). In lateral-bending and axial rotation, the ROM and NZ of BIUF1C were significantly higher than those of BIBF1C (P < 0. 05). In flexion/extension, the ROM and NZ of BIUF1C were higher than those of BIBF1C but there were no significant differences (P >0. 05). Compared to the intact, BIUF1C had lower ROM and NZ except for higher NZ in axial rotation, and there were significant differences only in flexion/extension (P < 0. 05). Conclusions All tested two-level unilateral fixation on simulated human cadaveric model with unilateral PLIF can achieve similar initial biomechanical stability in comparison with two-level bilateral pedicle screw fixation. However in most test modes, two-level unilateral pedicle screw fixation on simulated human cadaveric model with bilateral PLIF can not achieve enough biomechanical efficacy in comparison with two-level bilateral pedicle screw fixation.     

Effect of a novel interspinous implant on lumbar spinal range of motion

Interspinous devices have been introduced to provide a minimally invasive surgical alternative for patients with lumbar spinal stenosis or foraminal stenosis. Little is known however, of the effect of interspinous devices on intersegmental range of motion (ROM). The aim of this in vivo study was to investigate the effect of a novel minimally invasive interspinous implant, InSwing^®, on sagittal plane ROM of the lumbar spine using an ovine model. Ten adolescent Merino lambs underwent a destabilization procedure at the L1–L2 level simulating a stenotic degenerative spondylolisthesis (as described in our earlier work; Spine 15:571–576, 1990). All animals were placed in a side-lying posture and lateral radiographs were taken in full flexion and extension of the trunk in a standardized manner. Radiographs were repeated following the insertion of an 8-mm InSwing^® interspinous device at L1–L2, and again with the implant secured by means of a tension band tightened to 1 N/m around the L1 and L2 spinous processes. ROM was assessed in each of the three conditions and compared using Cobb’s method. A paired t-test compared ROM for each of the experimental conditions (P < 0.05). After instrumentation with the InSwing^® interspinous implant, the mean total sagittal ROM (from full extension to full flexion) was reduced by 16% from 6.3° to 5.3 ± 2.7°. The addition of the tension band resulted in a 43% reduction in total sagittal ROM to 3.6 ± 1.9° which approached significance. When looking at flexion only, the addition of the interspinous implant without the tension band did not significantly reduce lumbar flexion, however, a statistically significant 15% reduction in lumbar flexion was observed with the addition of the tension band (P = 0.01). To our knowledge, this is the first in vivo study radiographically showing the advantage of using an interspinous device to stabilize the spine in flexion. These results are important findings particularly for patients with clinical symptoms related to instable degenerative spondylolisthesis.     

Instability in injury of the alar ligament. A biomechanical model

Fresh human cadaveric specimens of occiput (C0) to C3 were subjected to 1.5 nm of flexion, extension and bilateral bending and axial torque. The resulting physiological motions were studied in an unconstrained three-dimensional manner. The effects of sequential transections of the left and right alar ligaments on the relative motion of C0-1 and C1-2 were studied. After transection of the left alar ligament, the percentage increases in neutral zones (NZ) and ranges of motion (ROM) were documented at both the C0-1 and C1-2 joints. In the sagittal plane, the most increase was at C1-2 due to the flexion moment, e.g., 47.4% in NZ and 27.6% in ROM. In lateral bending, the left alar transsection resulted in mostly right lateral bending increases and at the C0-1 joint, 37.1% in NZ and 19.6% in ROM. In axial rotation, changes in the total motion of the C0-2 joint complex were more reliable indicators. For left alar transsection, most increases were in right axial rotation, e.g., 25.6% for right rotation versus 11.2% for left rotation in the NZ parameter. Functional loss of the alar ligaments indicates a potential for instability which, however, must be determined in conjunction with other clinical findings, such as neurological dysfunction, pain and deformity.     

Total disc arthroplasty: consequences for sagittal balance and lumbar spine movement

This in vivo biomechanical study was undertaken to analyze the consequences for sagittal balance and lumbar spine movement in three different lumbar disc prostheses. A total of 105 patients underwent total disc replacement in three different centers. The Maverick^® prosthesis was used in 46 patients, the SB Charité^® device was used in 49 patients and the Prodisc^® device was utilized in 10 patients. The analysis was computer assisted, using Spineview^® and Matlab^® softwares. The intra and inter-observer reliability and measurement uncertainty was performed. The analysis of lateral X-ray films in flexion–extension allowed to measure the prosthesis positioning, the range of motion (ROM), the localization of the mean center of rotation (MCR), the vertebral translation and the disc height, for each prosthesis device. The sagittal balance was analyzed on a full spine film. The parameters studied were described by Duval-Beaupère. The results were compared to the data found in literature, and compared to 18 asymptomatic volunteers, and 61 asymptomatic subjects, concerning the sagittal balance. The prostheses allowed an improvement of the ROM of less than 2°. The ROM of L5–S1 prostheses ranged from 11.6 to 15.6% of the total lumbar motion during flexion–extension. At L4–L5 level, the ROM decreased when there was an arthrodesis associated at the L5–S1 level. There was no difference of ROM between the three prostheses devices. The MCR was linked to the ROM, but did not depend on the prosthesis offcentering. The disc height improved for any prosthesis, and decreased in flexion or in extension, when the prosthesis was offcentered. An increase of translation indicated a minor increase of the ROM at L4–L5 level after Maverick^® or SB Charité^® implantation. The L5–S1 arthrodesis was linked with an increase of the pelvic tilt. The lumbar lordosis curvature increased between L4 and S1, even more when a prosthesis was placed at the L3–L4 level. Total disc arthroplasty is useful in the surgical management of discogenic spinal pathology. The three prostheses studied allowed to retorate the disc height, the ROM, without disrupting the sagittal balance, but induced modification of the lumbar curvature.     

Morphologic changes in the lumbar intervertebral foramen due to flexion-extension, lateral bending, and axial rotation: an in vitro anatomic and biomechanical study

STUDY DESIGN: A biomechanical and anatomic study with human cadaveric lumbar spine. OBJECTIVES: The purpose of this study is to examine the morphologic changes in the intervertebral foramen during flexion, extension, lateral bending, and axial rotation of the lumbar spine and to correlate these changes with the flexibility of the spinal motion segments. SUMMARY OF BACKGROUND DATA: Previous studies showed morphologic changes in the intervertebral foramen during flexion and extension; however, those changes during lateral bending and axial rotation were not well known. METHODS: There were 81 motion segments obtained from 39 human cadaveric lumbar spines (mean age 69 years). The motion segments were imaged with CT scanner with 1-mm thick consecutive sections. For biomechanical testing each motion segment was applied with incremental pure moments of flexion, extension, lateral bending, and axial rotation. Rotational movements of the motion segment were measured using VICON cameras. After application of the last load, the specimens were frozen under load, and then CT was performed with the same technique described above. Six parameters of the intervertebral foramen were measured, including foraminal width (maximum and minimum), foraminal height, disc bulging, thickness of ligamentum flavum, and cross-sectional area of the foramen. RESULTS: Flexion increased the foraminal width (maximum and minimum), height, and area significantly while significantly decreasing the disc bulging and thickness of ligamentum flavum (P < 0.05). However, extension decreased the foraminal width (maximum and minimum), height, and area significantly. Lateral bending significantly decreased the foraminal width (maximum and minimum), height, and area at the bending side, whereas lateral bending significantly increased the foraminal width (minimum), height, and area at the opposite side of bending. Likewise, axial rotation decreased the foraminal width (minimum) and area at the rotation side significantly while significantly increasing the foraminal height and foraminal area at the opposite side. The percent change in the foraminal area was found significantly correlated with the amount of segmental spinal motion except for the extension motion. CONCLUSIONS: This study showed that the intervertebral foramen of the lumbar spine changed significantly not only on flexion-extension but also on lateral bending and axial rotation. The percent change in cross-sectional foraminal area was correlated with the amount of segmental motion except for extension motions. Further studies are needed to assess the morphologic changes in the intervertebral foramen in vivo and to correlate clinically.     

Biomechanical characterization of the three-dimensional kinematic behaviour of the Dynesys dynamic stabilization system: an in vitro study

The Dynesys, a flexible posterior stabilization system that provides an alternative to fusion, is designed to preserve intersegmental kinematics and alleviate loading at the facet joints. Recent biomechanical evidence suggests that the overall range of motion (ROM) with the Dynesys is less than the intact spine. The purpose of this investigation was to conduct a comprehensive characterization of the three-dimensional kinematic behaviour of the Dynesys and determine if the length of the Dynesys polymer spacer contributes to differences in the kinematic behaviour at the implanted level. Ten cadaveric lumbar spine segments (L2–L5) were tested by applying a pure moment of ±7.5 Nm in flexion–extension, lateral bending, and axial rotation, with and without a follower preload of 600 N. Test conditions included: (a) intact; (b) injury; (c) injury stabilized with Dynesys at L3–L4 (standard spacer); (d) long spacer (+2 mm); and (e) short spacer (–2 mm). Intervertebral rotations were measured using an optoelectronic camera system. The intersegmental range of motion (ROM), neutral zone (NZ), and three-dimensional helical axis of motion (HAM) were calculated. Statistical significance of changes in ROM, NZ, and HAM was determined using repeated measures analysis of variance (ANOVA) and Student–Newman–Keuls post-hoc analysis with P<0.05. Implantation of the standard length Dynesys significantly reduced ROM compared to the intact and injured specimens, with the least significant changes seen in axial rotation. Injury typically increased the NZ, but implantation of the Dynesys restored the NZ to a magnitude less that that of the intact spine. The Dynesys produced a significant posterior shift in the HAM in flexion–extension and axial rotation. The spacer length had a significant effect on ROM with the long spacer resulting in the largest ROM in all loading directions without a follower preload. The largest differences were in axial rotation. A 4 mm increase in spacer length led to an average intersegmental motion increase of 30% in axial rotation, 23% in extension, 14% in flexion, and 11% in lateral bending. There were no significant changes in NZ with different spacer lengths. Typically, the short spacer caused a greater shift and a greater change in orientation of the HAM than the long spacer. The long spacer resulted in a ROM and a motion pattern, as represented by the HAM, that was closer to that seen in an intact specimen. The results of this study suggest that the length of the Dynesys spacer altered the segmental position and therefore affected kinematic behaviour.