摘要
目的
目前腰椎退行性疾病已成为骨科领域的常见病,传统手术方式为腰椎植骨融合内固定。但植骨融合内固定并不能达到理想的治疗效果。随着对脊柱生物力学研究的深入,非融合腰椎内固定由此而逐渐发展起来。目前非融合腰椎动态固定包括经椎弓根固定和棘突间固定,大多在材料组成和生物力学性能上存在局限性。本课题利用中国科学院金属研究所发明的一种超弹性低模量的新型钛合金材料来设计制作新型腰椎动态内固定系统。通过研究该装置对脊柱的稳定性和间盘载荷的影响、内部应力分布以及疲劳测试,明确该系统是否具有优良的动态固定、载荷分享效果和疲劳性能,为其临床应用提供科学依据。
材料与方法
利用中国科学院金属研究所发明的新型钛合金材料(Ti-24Nb-4Zr-7.9Sn)加工腰椎动态内固定系统(DIFS)和半硬性固定系统,SINO坚强固定系统作为对照。DIFS和半硬性系统的椎弓根螺钉均为6.0×45mm尺寸,螺钉材料弹性模量均为75GPa。DIFS系统的连接棒材料弹性模量为43GPa,直径为4mm,半硬性系统棒体材料弹性模量为43GPa,直径为4.8mm。SINO系统的螺钉尺寸为6.0×45mm,棒直径为6.0mm,装置用普通医用钛合金(Ti-6Al-4V,110GPa)制备。
稳定性和间盘压测试的实验标本采用8具平均年龄8.7个月小牛腰椎节段(L3-6),标本保持骨、间盘、韧带和关节突关节的完整性。测试前将标本的头端和尾端的半个椎体包埋制作成平行的平台,并且在各个椎体的前方、侧方以及棘突插入Marker球,用以标记节段的运动。稳定性测试的实验装置包括MTS材料试验机、滑轮组系统以及MotionAnalysis步态分析系统。加载前用MotionAnalysis步态分析系统对标本的Marker球进行识别,以标记脊柱节段的三维运动。利用MTS材料试验机、滑轮组系统对标本在前屈／后伸、侧弯和旋转方向上加载8Nm的纯力矩,预加载两个循环以减小标本粘滞性对结果的影响。MotionAnalysis系统从第三个加载循环开始记录脊柱节段的三维运动,并存储数据,以备计算节段的ROM和NZ,以及载荷位移曲线。间盘压测量的力矩加载方法与稳定性测试相同。测试前需先在邻近软骨终板的椎体中制作骨道以便插入传感器测量间盘压。测量利用KYOWA传感器系统,通过间盘终板间接测量间盘内压力。在对标本加载的同时记录间盘压变化情况以及载荷-间盘压曲线。稳定性和间盘压数据的统计采用随机区组方差分析,组内两两比较采用Bonferroni test,方法进行校正。
利用Ansys10.0软件建立DIFS系统和普通医用钛合金内固定系统的间盘切除有限元网格模型,对其进行力的加载,有限元计算分析。进行DIFS系统压缩测试以验证有限元模型的可靠性。利用Ansys的后处理路径功能对比分析两种系统载荷下的屈曲角位移以及屈曲活动时内部应力大小。疲劳测试参照ASTM标准进行,制作测试模具,模具由测试块和夹具组成,二者以转轴相连,能够使上下两个测试块自由屈伸运动。将DIFS系统安装至测试块上,通过夹具连接至疲劳试验机,进行循环疲劳测试。测试采用位移控制控制模式,使DIFS系统在屈伸15°范围内往返运动,以达到1000万次循环为成功。
实验结果
稳定性测量的结果显示失稳模型明显地增加了节段在三个运动平面的活动范围(ROM)和中性区(NZ)。失稳节段的ROM在屈／伸、侧弯和旋转方向上分别增加了25%、38%和38%,而NZ在这些方向上分别增加了55%、38%和65%。三种内固定系统均对失稳节段有稳定作用,将失稳节段的ROM和NZ限制在完整状态水平范围内(P<0.05)。DIFS在前屈、后伸、侧弯和旋转方向上分别将ROM恢复至完整状态水平的78%、60%、62%和69%。半硬性固定系统在这些方向上分别恢复ROM至完整状态的35%、28%、46%和37%。SINO系统在屈伸、侧弯和旋转方向上恢复ROM至10%、25%和33%。与完整状态相比较,DIFS较理想的恢复ROM至前者的60%以上,达到动态固定的目的。与DIFS相比较,半硬性固定和SINO坚强固定系统明显地限制了节段的运动。邻近节段的ROM和NZ不受内固定系统的影响,各个状态之间没有明显的差异。
间盘内压力结果显示失稳模型对固定节段和邻近节段的间盘内压力没有明显影响。三种内固定物均对间盘负荷有承载作用。其中DIFS系统在侧弯、旋转和前屈方向上分别承载间盘负荷的43%、30%和39%,半硬性系统在这些方向上分别承载58%、72%和66%,SINO系统分别承载76%、88%和83%,后伸方向上三种内固定系统均承载了全部的间盘负荷。邻近节段的间盘内压力不受固定系统的影响,各个状态之间没有明显差异。
有限元分析结果显示有限元计算与力学试验机测试所得的载荷-位移曲线一致,载荷100N使DIFS系统发生9°屈曲角位移,DIFS系统的钉棒连接处出现高应力区,其中连接棒在距两端19mm的上下两处,即钉棒连接处出现最大应力；上、下螺钉均在距钉尖52mm处,即螺钉体尾交界处出现最大应力,这与临床上常见的断钉处一致。与普通医用钛合金相比较,DIFS系统的屈曲活动性更好,在相同负荷作用下其屈曲角位移为前者的2.3倍,而内部的最大应力在屈曲同样角度时仅为前者的57%。
结论
1、DIFS系统能够较理想地实现对腰椎失稳节段的动态稳定,在多个方向上能与脊柱节段共同承载负荷；
2、DIFS系统在动态稳定同时具有较小的内部应力,预示其具有较好疲劳性能,有待于疲劳测试证实；
3、DIFS系统的全金属设计具有机械性能优势,且操作使用简便,在临床上具有了很好的应应用前景。
Objective
Lumbar degenerative diseases have become common illness in the field of orthopaedics due to the development of social aging problem. Traditional surgical method is lumbar fusion with internal fixation and bone graft. But lumbar fusion failed to obtain good clinical results. By further researching, lumbar dynamic fixation become more and more popular. The dynamic fixation includes transpedicular system and interspinous system, which have some limitations at materials and biomechanical properties. In ous study, we utilize a new titanium alloy with super-low elastic modulus to design a new lumbar dynamic fixation system. The bridged segmental stability, intradiscal pressure, stress distribution and fatigue test are performed to identify the biomechanical properties for further clinical applications.
Materials and Methods
We utilized a new titanium alloy (Ti-24Nb-4Zr-7.9Sn) to design and construct the lumbar dynamic internal fixation system (DIFS) and simi-rigid fixator comparing with SINO rigid fixator. In the DIFS and simi-rigid fixator, pedicle screws are 6.0X 45mm sized, made of 75GPa new metal. The rods of DIFS have a diameter of 4.0mm made of 43GPa metal, and the rods of simi-rigid have a diameter of 4.8mm made of 43GPa metal. The pedicle screws of SINO is also 6.0 X 45mm sized with the rods of 6.0mm diameter made of normal medical titanium alloy (Ti-6A1-4V, 110GPa).
Eight calf lumbar spine specimens were used for stability and intradiscal pressure test, keeping the bone, disc, ligament and zygapophysial joint intact.. The half of cranial and caudal segment were embedded in PMMA to make the superior and inferior parallel plane, and inserted the markers from the anterior, lateral side of vertebra and spinous process to mark the motions of segments. The instruments of stability test include MTS tester, pulley block system and MotionAnalysis system. Before testing, the makers were recognized by the MotionAnalysis system. The 8Nm pure moment was loaded to specimens in three motion planes. Preload of 2 cycles was performed to eliminate the viscosity. The motion of segments were recorded from the third cycle. The ROM and NZ are calculated, and the load-displacement curve is drawn. The method of loading in the measurment of intradiscal pressure is similar to stability test. Before testing, a hole was made adjacant to intervertebral disc for placing the sensor. We use the KYOWA sensor system to measure the pressure through the cartilage end plate. When loading, the pressure is recorded for load-pressure curve. The randomized blocks analysis of variance is applied to analyze the data of ROM, NZ and intradiscal pressure, with two-two correction by post hoc test.
The Ansys11.0 was utilized to build finite element model of DIFS and normal medical titanium alloy fixator following loading and calculation. The compression test was performed to evaluate the validity of the model. By the postprocessing function, the angular displacement and internal stress were compared between DIFS and normal medical titanium alloy fixator.
Fatigue test is performed according to the ASTM standard. The test instruments include the test block and clamping apparatus, which can rotate with each other around an axis. DIFS was fixed in test block, and connect to tester through clamping apparatus. The displacement-controlled mode is used to perform the cycle motion in the range of 15°flexion/extension. The test will not stop until 10 million cycles.
Results
The results of stability test showed that the defect significantly increased the ROM and NZ in the three motion planes. ROM of the defect increased 25%,38%and 38%in flexion/extension, lateral bending and rotations, and NZ increased 55%,38%and 65% in these three planes. All the three fixator showed stabilizing effect to the defect, limiting the ROM and NZ below the level of the intact. DIFS restored the ROM to 78%, 60%,62%and 69%of the intact level in flexion, extension, lateral bending and rotation. Simi-rigid fixator restored the ROM to 35%,28%,46%and 37%of the intact level in flexion, extension, lateral bending and rotation. SINO restored the ROM to 10%,25% and 33%of the intact level in flexion/extension, lateral bending and rotation. Compared with intact state, DIFS almost ideally restored the ROM to>60%of the intact. Compared with the DIFS, the simi-rigid and rigid fixator significantly limited the bridged segmental motion. The ROM and NZ in adjacent segments are not affected by internal fixation.
The defect does not significantly affect the intradiscal pressure of bridged and adjacent segments. All three fixators bore the intradiscal pressure. DIFS bore the pressure of 43%,30%and 39%of the intact level in lateral bending, rotation and flexion, simi-rigid fixator bore 58%,72%and 66%, SINO bore 76%,88%and 83%. In the extension direction,100%pressure was born by the fixator. Adjacent segmental intradiscal pressure was not significantly affected by fixations.
The results of finite element analysis demonstrated that the load-displacement curves are similar between the finite element calculation and compression test. The 100N load produced 9°angualr displacement, and high stress area was present at the conjunctions of the screws and rods. The high stress zone is consisted with the common location of system breaking. Compared with the normal medical titanium alloy fixator, DIFS has better motion property (2.3 times) and lesser maximum internal stress (57%).
Conclusion
1. DIFS is able to dynamically stabilized the defect segments, and share the intradiscal pressure with the segments in the most directions.
2. DIFS has lesser internal stress during angular motion and better motion property indicating relatively good anti-fatigue performance, which needs to confirm by cycling fatigue test.
3. With simple structures, DIFS is convenient to utilize with good potential of clinical application.
引文
1 Bjarke CF, Stender HE, Laursen M, et al. Long-term functional outcome of pedicle screw instrumentation as a support for posterolateral spinal fusion:randomized clinical study with a 5-year follow-up. Spine 2002;27:1269-1277.
2 Kawakami M, Tamaki T, Ando M, et al. Lumbar sagittal balance influences the clinical outcome after decompression and posterolateral spinal fusion for degenerative lumbar spondylolisthesis. Spine 2002;27:59-64.
3 Korsgaard M, Christensen FB, Thomsen K, et al. The influence of lumbar lordosis on spinal fusion and functional outcome after posterolateral spinal fusion with and without pedicle screw instrumentation. J Spinal Disord Tech 2002;15:187-192.
4 McMillan DW, McNally DS, Garbutt G, et al. Stress distributions inside intervertebral discs: the validity of experimental "stress profilometry." Proc Inst Mech Eng [H] 1996;210:81-87.
5 McNally DS, Adams MA. Internal intervertebral disc mechanics as revealed by stress profilometry. Spine 1992;17:66-73.
6 Mulholland RC, Sengupta DK. Rationale, principles and experimental evaluation of the concept of soft stabilization. Eur Spine J 2002; 11(Suppl 2):S198-S205.
7 Kroeber M, Unglaub F, Guehring T,et al. Effects of controlled dynamic disc distraction on degenerated intervertebral discs:an in vivo study on the rabbit lumbar spine model. Spine 2005;30:181-187.
8 Guehring T, Unglaub F, Lorenz H, et al. Intradiscal pressure measurements in normal discs, compressed discs and compressed discs treated with axial posterior disc distraction:an experimental study on the rabbit lumbar spine model. Eur Spine J 2006; 15:597-604.
9 Sengupta DK. Dynamic stabilization devices in the treatment of low back pain. Orthop Clin North Am 2004;35:43-56.
10 Chen SH, Zhong ZC, Chen CS,et al. Biomechanical comparison between lumbar disc arthroplasty and fusion. Med Eng Phys 2009;31:244-253.
11 Hao YL, Li SJ, Sun SY, et al. Elastic deformation behavior of Ti-24Nb-4Zr-7.9Sn for biomedical applications. Acta Biomater 2007;3:277-286.
12 Quint U, Wilke HJ, Loer F, et al. Possibilities for static and dynamic stabilization of the spine in lesions of the anterior and posterior ligament complex. Unfallchirurg 1998; 101:684-690.
13 Gamer MD, Wolfe SJ, Kuslich SD. Development and preclinical testing of a new tension-band device for the spine:the Loop system. Eur Spine J 2002; 11:186-91.
14 Schwarzenbach O, Berlemann U, Stoll TM, et al. Posterior dynamic stabilization systems: DYNESYS._Orthop Clin N Am 2005;36:363-372.
15 Schmoelz W, Huber JF, Nydegger T, et al. Dynamic stabilization of the lumbar spine and its effects on adjacent segments:an in vitro experiment. J Spinal Disord Tech 2003;16:418-423.
16 Niosi CA, Zhu QA, Wilson DC, et al. Biomechanical characterization of the three-dimensional kinematic behaviour of the Dynesys dynamic stabilization system:an in vitro study. Eur Spine J 2006;15:913-922.
17 Huang RC, Girardi FP, Lim MR, et al. Range of motion and adjacent level degeneration after lumbar total disc replacement. Presented at the 39th Annual Meeting of the Scoliosis Research Society, Buenos Aires, Argentina:2004.
18 Rohlmann A, Calisse J, Bergmann G, et al. Internal spinal fixator stiffness has only a minor influence on stresses in the adjacent discs. Spine 1999;24:1192-1195.
19 Penta M, Sandhu A, Fraser RD. Magnetic resonance imaging assessment of disc degeneration 10 years after anterior lumbar interbody fusion. Spine 1995;20:743-747.
20 Panjabi MM. Biomechanical testing to quantify adjacent-level effects.Presented at IV World Congress of Biomechanics, Calgary,Canada,2002.
21 Wilke HJ, Wenger K, Claes L. Testing criteria for spinal implants:recommendations for the standardization of in vitro stability testing of spinal implants. Eur Spine J 1998;7:148-154.
22 Kumar MN, Baklanov A, Chopin D. Correlation between sagittal plane changes and adjacent segment degeneration following lumbar spine fusion. Eur Spine J 2001;10:314■319.
23 Lee CK. Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine 1988 13:375-377.
24 Lehmann TR, Spratt KF, Tozzi JE, et al. Long-term follow-up of lower lumbar fusion patients. Spine 1987;12:97-104.
25 Seitsalo S, Schlenzka D, Poussa M, et al. Disc degeneration in young patients with isthmic spondylolisthesis treated operatively or conservatively:a long-term follow-up. Eur Spine J 1997;6:393-397.
26 Link HD. History, design and biomechanics of the LINK SB Charite artificial disc. Eur Spine J2002;11:S98-S105.
27 Mayer HM, Wiechert K, Korge A, et al. Minimally invasive total disc replacement:surgical technique and preliminary clinical results. Eur Spine J 2002; 11:S124-S130.
28 Freudiger S, Dubois G, Lorrain M. Dynamic neutralisation of the lumbar spine confirmed on a new lumbar spine simulator in vitro. Arch Orthop Trauma Surg 1999;119:127-132.
29 Grevitt MP, Gardner AD, Spilsbury J, et al. The Graf stabilization system:early results in 50 patients. Eur Spine J 1995;4:169-175.
30 Korge A, Nydegger T, Polard JL, et al. A spiral implant as nucleus prosthesis in the lumbar spine. Eur Spine J 2002;11:S149-S153.
31 Stoll TM, Dubois G, Schwarzenbach O. The dynamic neutralization system for the spine:a multi-center study of a novel non-fusion system. Eur Spine J 2002;11:S170-S178.
32 Swanson KE, Lindsey DP, Hsu KY, et al. The effects of an interspinous implant on intervertebral disc pressures. Spine 2003;28:26-32.
33 Okuyama K, Abe E, Suzuki T, et al. Posteriorlumbar interbody fusion:a retrospective study of complications after facet joint excision and pedicle screw fixation in 148 cases. Acta Orthop Scand 1999;70:329-334.
34 Esses SI, Sachs BL, Dreyzin V. Complications associated with the technique of pedicle screw fixation. A selected survey of ABS members. Spine 1993;18:2231-8.
35 Nachemson A. The load on lumbar disks in different positions of the body. Clin Orthop 1966;45:107-122.
36 McNally DS, Adams MA. Internal intervertebral disc mechanics as revealed by stress profilometry. Spine 1992; 17:66-73.
37 Pollintine P, Przybyla AS, Dolan P, et al. Neural arch loadbearing in old and degenerated spines. J Biomech 2004;37:197-204.
38 Abe E, Nickel T, Buttermann GR, et al. Lumbar intradiscal pressure after posterolateral fusion and pedicle screw fixation. Tohoku J Exp Med 1998; 186:243-253.
39 Chow DH, Luk KD, Evans JH, et al. Effects of short anterior lumbar interbody fusion on biomechanics of neighboring unfused segments. Spine 1996;21:549-555.
40 Cunningham BW, Kotani Y, McNulty PS, et al. The effect of spinal destabilization and instrumentation on lumbar intradiscal pressure:an in vitro biomechanical analysis. Spine 1997;22:2655-2663.
41 Molz FJ, Partin JI, Kirkpatrick JS. The acute effects of posterior fusion instrumentation on kinematics and intradiscal pressure of the human lumbar spine. J Spinal Disord Tech 2003;16:171-179.
42 Rohlmann A, Neller S, Bergmann G, et al. Effect of an internal fixator and a bone graft on intersegmental spinal motion and intradiscal pressure in the adjacent regions. Eur Spine J 2001;10:301-308.
43 Rigby MC, Selmon GP, Foy MA, et al. Graf ligament stabilization:mid-to-long term follow up. Eur Spine J 2001; 10:234-236.
44 Schmoelz W, Huber JF, Nydegger T, et al. Dynamic stabilization of the lumbar spine and its effects on adjacent segments:an in vitro experiment. J Spinal Disord Tech 2003;16:418-423.
45 Schmoelz W, Huber JF, Nydegger T, et al. Influence of a dynamic stabilization system on load bearing of a bridged disc:an in vitro study of intradiscal pressure. Eur Spine J 2006;21:1-10.
46 Garner MD, Wolfe SJ, Kuslich SD. Development and preclinical testing of a new tension-band device for the spine:the Loop system. Eur Spine J 2002; 11:186-191.
47 Wilke H, Neef P, Hinz B, et al. Intradiscal pressure together with anthropometric data—a data set for the validation of models. Clin Biomech (Bristol, Avon) 2001;16:S1 11-S126.
48 Hukins DW. A simple model for the function of proteoglycans and collagen in the response to compression of the intervertebral disc. Proc R Soc Lond B Biol Sci 1992;249:281-285.
49 McMillan DW, McNally DS, Garbutt G, et al. Stress distributions inside intervertebral discs: the validity of experimental "stress profilometry." Proc Inst Mech Eng [H] 1996;210:81-87.
50 McNally DS, Adams MA. Internal intervertebral disc mechanics as revealed by stress profilometry. Spine 1992; 17:66-73.
51 Krag MH, Seroussi RE,Wilder DG, et al. Internal displacement distribution from in vitro loading of human thoracic and lumbar spinal motion segments:experimental results and theoretical predictions. Spine 1987;12:1001-1007.
52 Sengupta DK, Mulholland RC. Fulcrum assisted soft stabilization system:a new concept in the surgical treatment of degenerative low back pain. Spine 2005;30:1019-1029.
53 Schmoelz W, Huber JF, Nydegger T, et al. Influence of a dynamic stabilisation system on load bearing of a bridged disc:an in vitro study of intradiscal pressure. Eur Spine J 2006;15:1276-1285.
54 Nachemson AL. Disc pressure measurements. Spine 1981;6:93-97.
55 Wilke HJ, Kavanagh S, Neller S, et al. Effect of a prosthetic disc nucleus on the mobility and disc height of the L4-5 intervertebral disc postnucleotomy. J Neurosurg 2001; 95:208-214.
56 Adams MA, McMillan DW, Green TP, et al. Sustained loading generates stress concentrations in lumbar intervertebral discs. Spine 1996; 21:434-438.
57 Rohlmann A, Neller S, Bergmann G, et al. Effect of an internal fixator and a bone graft on intersegmental spinal motion and intradiscal pressure in the adjacent regions. Eur Spine J 2001;10:301-308.
58 Weinhoffer SL, Guyer RD, Herbert M, et al. Intradiscal pressure measurements above an instrumented fusion. A cadaveric study. Spine 1995;20:526-531.
59 崔显峰,朱悦,李春树等.腰椎新型合金动态内固定系统的稳定性研究.中华骨科杂志2008：28：592-595.
60 Mosekilde L, Danielsen CC. Biomechanical competence of vertebral trabecular bone in relation to ash density and age in normal individuals. Bone 1987;8:79-85.
61 ASTM F1717-04, Standard Test Methods for Spinal Implant Constructs in Vertebrectomy Model 2004.
62 McNally DS, Shackleford IM, Goodship AE, et al. In vivo stress measurement can predict pain on discography. Spine 1996;21:2580-2587.
63 Unglaub F, Guehring T, Omlor G, et al. Controlled distraction as a therapeutic option in moderate degeneration of the intervertebral disc—an in vivo study in the rabbit-spine model. Z Orthop Ihre Grenzgeb 2006; 144:68-73.
64 McAfee P, Khoo LT, Pimenta L, et al. Treatment of lumbar spinal stenosis with a total posterior arthroplasty prosthesis:implant description, surgical technique, and a prospective report on 29 patients. Neurosurg Focus 2007;22:E13.
1 Bjarke CF, Stender HE, Laursen M, et al. Long-term functional outcome of pedicle screw instrumentation as a support for posterolateral spinal fusion:randomized clinical study with a 5-year follow-up. Spine,2002,27:1269-1277.
2 Kawakami M, Tamaki T, Ando M, Yamada H, Hashizume H, Yoshida M. Lumbar sagittal balance influences the clinical outcome after decompression and posterolateral spinal fusion for degenerative lumbar spondylolisthesis. Spine,2002,27:59-64.
3 Korsgaard M, Christensen FB, Thomsen K, Hansen ES,Bunger C. The influence of lumbar lordosis on spinal fusion and functional outcome after posterolateral spinal fusion with and without pedicle screw instrumentation. J Spinal Disord Tech,2002,15:187-192.
4 Wippermann BW, Schratt HE, Steeg S, et al. Complications of spongiosa harvesting of the ilial crest. A retrospective analysis of 1,191 cases.Chirurg 1997,68:1286-1291.
5 Ghiselli G, Wang JC, Bhatia NN, et al. Adjacent segment degeneration in the lumbar spine. J Bone Joint Surg Am,2004,86:1497-1503.
6 Huang RC, Girardi FP, Lim MR, Cammisa FP Jr. Advantages and disadvantages of nonfusion technology in spine surgery. Orthop Clin North Am,2005,36:263-269.
7 Unglaub F, Guehring T, Omlor G, et al. Controlled distraction as a therapeutic option in moderate degeneration of the intervertebral disc— an in vivo study in the rabbit-spine model. Z Orthop Ihre Grenzgeb,2006,144:68-73.
8 Guehring T, Unglaub F, Lorenz H, et al. Intradiscal pressure measurements in normal discs, compressed discs and compressed discs treated with axial posterior disc distraction:an experimental study on the rabbit lumbar spine model. Eur Spine J,2006,15:597-604.
9 Caserta S,La Maida GA,Misaggi B,et al.Elastic stabilization alone or combined with rigid fusion in spinal surgery:a biomechanical study and clinical experience based on 82 cases.Eur Spine J,2002,11(suppl 2):192-197.
10 Garner MD,Wolfe SJ,Kuslich SD.Development and preclinical testing of a new tension-band device for the spine:the Loop system.Eur Spine J,2002,11(suppl 2):186-191.
11 Senegas J.Mechanical supplementation by non-rigid fixation in degenerative intervertebral lumbar segments:the Wallis system.Eur Spine J,2002,11 Suppl 2:164-169.
12 Zucherman JF,Hsu KY,Hartjen CA,et al.A prospective randomized multi-center study for the treatment of lumbar spinal stenosis with the X STOP interspinous implant:1-year results.Eur Spine J,2004,13:22-31.
13 Siddiqui M, Smith FW, Wardlaw D,et al. One-year results of X Stop interspinous implant for the treatment of lumbar spinal stenosis. Spine,2007,32:1345-1348.
14 Phillips FM, Voronov LI, Gaitanis IN,et al.Biomechanics of posterior dynamic stabilizing device (DIAM) after facetectomy and discectomy.Spine J,2006,6:714-722.
15 Graf H. Evaluation of the therapeutic effect of Graf stabilization system. European Spine Society Meeting,Rome,1991.
16 Wild A, Jaeger M, Bushe C,et al. Biomechanical analysis of Grafs dynamic spine stabilisation system ex vivo.Biomed Tech (Berl),2001,46:290-294.
17 Grevitt MP, Gardner AD, Spilsbury J, et al. The Graf stabilisation system:early results in 50 patients. Eur Spine J,1995,4:169-175.
18 Markwalder TM,Wenger M.Dynamic stabilization of lumbar motion segments by use of Grafs ligaments:results with an average follow-up of 7.4 years in 39 highly selected,consecutive patients.ActaNeurochir(Wien),2003,145:209-214.
19 Hadlow SV, Fagan AB, Hillier TM, et al. The Graf ligamentoplasty procedure. Comparison with posterolateral fusion in the management of low back pain. Spine,1998,23:1172-1179.
20 Mulholland RC, Sengupta DK. Rationale, principles and experimental evaluation of the concept of soft stabilization. Eur Spine J,2002,11 (suppl 2):S198-S205.
21 Schmoelz W, Huber JF, Nydegger T,et al. Influence of a dynamic stabilisation system on load bearing of a bridged disc:an in vitro study of intradiscal pressure. Eur Spine J,2006,21:1-10.
22 Stoll TM, Dubois G, Schwarzenbach O. The dynamic neutralization system for the spine:a multi-center study of a novel non-fusion system. Eur Spine J,2002,1 1(suppl 2):S170-S178.
23 Putzier M,Schneider SV,Funk JF,et al.The surgical treatment of the lumbar disc prolapse:nucleotomy with additional transpedicular dynamic stabilization versus nucleotomy alone.Spine,2005,30:109-114.
24 Schnake KJ, Schaeren S, Jeanneret B. Dynamic stabilization in addition to decompression for lumbar spinal stenosis with degenerative spondylolisthesis. Spine,2006,31:442-449.
25 Legaye J. Unfavorable influence of the dynamic neutralization system on sagittal balance of the spine.Rev Chir Orthop Reparatrice Appar Mot,2005,91:542-550.
26 Lee SE, Park SB, Jahng TA,et al. Clinical experience of the dynamic stabilization system for the degenerativespine disease. J Korean Neurosurg Soc,2008,43:221-226..
27 Sengupta DK,Webb JK,Mulholland RC.Can soft stabilization in the lumbar spine unload the disc and retain mobility? A biomechanical study with fulcrum assisted soft stabilization on cadaver spine.Proceedings of the ISSLS Annual meeting,Edinburgh,2001.129.
28 Sengupta DK,Mulholland RC.Fulcram assisted soft stabilization system:a new concept in the surgical treatment of degenerateive low back pain.Spine,2005,30:1019-1029.
29 Sengupta DK, Herkowitz HN, Hochschuler S,et al. Loads sharing characteristics of two novel soft stabilization devices in the lumbar motion segments:a biomechanical study in cadaver spine.Presented at Spine Arthroplasty Society Annual Conference,Scottsdale:2003.
30 Wilke HJ, Schmidt H, Werner K,et al. Biomechanical evaluation of a new total posterior-element replacement system. Spine,2006,31:2790-2796.
31 McAfee P, Khoo LT, Pimenta L,et al. Treatment of lumbar spinal stenosis with a total posterior arthroplasty prosthesis:implant description, surgical technique, and a prospective report on 29 patients. Neurosurg Focus,2007,22:E13.