ORTHO SuperSite - Printable version

New from Ingenil-'

Seite 1 von 8

-

S P E C W INTRODUCTORY SAVINGS Save 25% on an essential billing

resource for Orthopaedics Ractices.

Stabilization of the Lumbar Spine Using the Dynarnic Neutralization System By George S. Sapkas, MD; George S. Themistocleous, MD; Andreas F. Mavrogenis, MD; loannis S. Benetos, MD; Nikolaos Metaxas, MD; Panayiotis J. Papagelopoulos, MD, DSc ORTHOPEDICS 2007; 30:859 October 2007 The records of 68 patients (42 men and 26 women) who undetwent spine stabilization with a dynamic neutralization system were reviewed. Mean patient age at operation was 42.8 years. The primary indication for surgery was degenerative spine disease and instability with neurogenic or radicular pain andlor chronic back pain. Forty-one (60.2%) patients had degenerative diskopathy or disk herniation, and 27 (39.8%) patients had lumbar spine stenosis. One-motion segment spine stabilization was performed in 30 patients, 2-motion segment spine stabilization in 32 patients, and 3-motion segment spine stabilization in 6 patients. W~thina mean follow-up of 36.2 months (range, 12.9-75.3 months), there were 2 re-operations, and 3 patients with screw loosening. Re-operations were for a deep infection in 1 patient and left leg pain in another patient. Both patients were managed with early implant removal and spinal arthrodesis. Self-assessment questionnaires showed improvement of patients' clinical and functional status. The Oswestry Disability Index and the Roland-Morris Disability Questionnaire score improved from a mean preoperative score of 55.4% (severe disability) and 52% respectively to a mean postoperative score of 22.9% (moderate disability) and 35% respectively. The overall results of this study are highly comparable to fusion procedures. The dynamic neutralization system can be a safe and effective alternative technique to spine arthrodesis in selected cases of degenerative lumbar spine instability.

An arthrodesed spine is not a normal state. When lumbar spine segments are fused together, either as a congenital abnormality or by surgery, significant stresses are directed to the adjacent spinal segments.l This could result in failure of the instrumentation or degenerative changes of the spine and significant disability of the ~ a t i e n t . l - ~ Recent studies showed that solid fusion can generate a considerable amount of morbidity, high rates of c o m p l i ~ a t i o n s ,a~ -high ~ ~ frequency of r e - o p e r a t i o n ~ , l - ~and ~~~ variable - ~ 9 patient satisfaction regardless of the quality of fusion .5.7.15.20-24 The future of spine stabilization needs to involve more physiologic and patient-friendly methods. Flexible stabilization is a commonly used term to describe various developed systems that allow a restricted spine m o t i ~ n . ~ ~ - ~ ~ The dynamic neutralization system for spine stabilization (Dynesys; Centerpulse Ltd, Zurich, Switzerland) is a pedicle screw system for flexible stabilization of the spine. This system consists of titanium alloy screws connected by an elastic synthetic compound that controls motion in any plane (nonfusion system) (Figure 1). The Dynesys instrumentation system re-stabilizes unstable segments ("neutralization") without involving the intervertebral disks and the facet joints; the segments remain mobile within a controlled range ("dynamic stabilization") permitting limited motion of the arthrodesed lumbar ~ e r t e b r a e .The ~ ~ 'spine ~ ~ is thus returned to an anatomical function that is closer to the healthy status. This study evaluated the effectiveness and safety of the dynamic neutralization pedicle screw system in the treatment of patients with spine instability associated with degenerative lumbar disease who have failed conservative treatment. All patients would have been considered for solid spine fusion if a flexible instrumentation system such as the Dynesys system was unavailable.

Materials and Methods The medical records of 68 patients who had spine stabilization using the Dynesys instrumentation system were retrospectively reviewed. These were 42 men and 26 women, with a mean age at operation of 42.8 years (range, 25-65 years). All patients presented with low back pain, with or without radicular leg pain that was resistant to conservative treatment over at least three months. Twenty-five of the patients had neurologic impairment. The primary indication for surgery was degenerative spine disease associated with degenerative disk disease or disk herniation in 41 (60.2%) patients and lumbar stenosis in 27 (39.8%) patients. These conditions resulted in instability associated with neurogenic or radicular leg pain andlor chronic back pain.

I

ORTHO SuperSite - Printable version

Seite 3 von 8

Figure 2: A 43-year-old patient with low back pain and right L5 and SI radiculopathy. Preoperative MRI of the lumbar spine shows right L5-SI disk protrusion (A). Postoperative AP (B) and lateral (C) radiographs of the lumbar spine show extensive right side laminotomy of L5

lamina and stabilization using the Dynesys System. Two years postoperatively, AP (D) and lateral (E) radiographs of the lumbar spine show no hardware failure and satisfactory intervertebral disk height and foramina space.

Results Sixty-six of the 68 patients were available for re-examination, and their records have been retrospectively reviewed for the purpose of this study. Two patients were lost to follow-up. Mean follow-up was 36.2 months (range, 12.9-75.3 months). Neurological deticits completely resolved in all patients. The mean preoperative Oswestry Disability Index score was 55% (severe disability). This improved to a mean postoperative score of 25% (moderate disability) in patients with I 8 months follow-up. The Roland-Morris Disability Questionnaire score improved from a mean preoperative value of 52% to a mean postoperative value of 35%. Fifty-seven (86%) of the 66 patients reported that they would undergo the operation again and 53 (80%) of the 66 patients reported having a satisfactory postoperative result. Eight patients, who had a previous lumbar surgery, reported the poorest results. Sixty-four of the 66 patients returned to work and previous activities of daily living after a maximum of 3 months. In the 41 patients with disk disease, the mean postoperative disk height was 2 mm (range, 1-3 mm) wider compared to the respective mean preoperative disk height. In the 27 patients with lumbar stenosis, the disk height changes were negligible. The postoperative dynamic flexion-extension radiographs showed spinal stability in all patients.

Complications No intraoperative complications were reported. Within a mean follow-up of 36.2 months, no late complications were observed related to the implants and mechanical failure or instability, such as breakage of the pedicle screws, the spacer or the cord, and alteration of the initial postoperative height of the intervertebral space (Figures 2D-E).

ORTHO SuperSite - Printable version

Seite 4 von 8

However 3 cases of screw loosening were reported. Deep spine infection occurred 1 month postoperatively in one patient. This has been treated with implant removal and reoperation for rigid spine arthrodesis 3 months later. Another patient had persistent left leg pain because of nerve root compression, and had a reoperation 15.6 months after the initial operation for implant removal, thorough foramina decompression and rigid spine arthrodesis.

Discussion Degenerative spondylosis can create spinal instability predisposing to axial low-back pain radicular pain or neurological deficits.14 Moreover decompressive procedures rnay aggravate preexisting instability or cause iatrogenic spine i n ~ t a b i l i t y . ~ e ~ ~ - ~ ~ Traditional surgical treatments of degenerative or iatrogenic instability is non-instrumented, instrumented, or pedicular fusion, posterior lumbar interbody fusion, transforaminal lumbar interbody fusion, anterior lumbar interbody fusion.14 Considering spinal fusion as the optimal treatment was based on the assumption that a degenerated motion segment either is unstable or moves out of normal range. This has been associated with generation of pain; therefore fusion offers the desired stability and subsequently prevents movement associated with pain deterioration. However recent studies showed that spine fusion surgery can generate a considerable amount of morbidity, high complication rate,4-17high frequency of r e o p e r a t i ~ n , l -and ~-~ variable ~ ~ ~ ~ patient satisfaction of the end-result of the Moreover fusion eliminates motion of the functional spinal segment and subsequently overloads the adjacent segments, thereby generating the "transition ~ y n d r o m e . " l ~ - ~ ~ The above results show that the prevention of movement per Se rnay not be the most important factor accounting for the success of fusion, challenging the original a ~ s u m p t i o nThe . ~ ~aforementioned drawbacks led to alternative procedures and techniques for stabilization without fusion, nonfusion systems. ~~ a concept where abnormal loading patterns due to disk In 2002 Mulholland and S e n g ~ p t aproposed disorganization occurring in degenerative disk disease were responsible for low back pain. Range of motion usually is not increased after disk degeneration, and motion by itself is not the cause of pain. According to these authors, the cause of pain is the abnormal quality of motion that rnay be in abnormal direction or in an increased degree of translation thus distributing abnormal loads across the disk space. The authors suggested that a dynamic stabilization system either restricts movement to a Zone where normal or near normal loading rnay occur, or prevents the spine from adopting a position where abnormal loading rnay ~ c c u ~A dynamic . ~ ~ - stabilization ~ ~ system would ideally restore normal function of the functional spinal segments on one hand, and protect the adjacent segments on the other.I4 Dynamic stabilization is a commonly used term to describe various systems that have been developed thus far, and that permit only restricted movement within the range of normal motion. In recent years, ideas of dynamic neutralization of the lumbar spine have become more p ~ p u l a rProposed .~~ systems range from complete replacement of the disk,45e46 to replacing the disk while maintaining the a n n u l u ~ ,or~ maintaining ~.~~ the disk with a controlled motion of the ~ e g m e n t . ~ ~ . ~ " ~ ~ The dynamic neutralization system for the spine (Dynesys) is a nonfusion pedicle screw stabilization system for the stabilization of the lumbar spine.14,22e25 This system provides flexible stabilization while controlling motion in any plane. It is designed for the treatment of degenerative conditions of the lumbar spine that present with unstable motion s e g m e n t ~as , ~ well ~ as unstable forms of dynamic or permanent patterns of lumbar stenosis. Dynesys is also capable of haltering the progression of minor deformities, that are frequently associated with spinal stenosis, including degenerative spondylolisthesis andlor early degenerative s c o l i ~ s i s . ~ ~ In view of the above mentioned arguments, the implantation of flexible instrumentation systems such as the Dynesys system have several advantages compared to rigid spine arthrodesis. Dynesys provides a more physiological condition compared to the sole decompression or fusion of an unstable segment. This system reduces movement both in flexion and extension. Moreover, the intervertebral disks and vertebral joints of the affected segments remain intact, and the adjacent spine segments are protected. The mobility obtained after flexible spine stabilization has a role in keeping up the patient's quality of life. However, in spine arthrodesis a cushioning element is removed from the spine, and the load on the remaining disks of the adjacent segments is greatly increased leading to the "transition syndrome."14,29~50-51 If a decompressive procedure is required, the Dynesys system re-establishes stability and prevents postoperative iatrogenic instability. In addition to restricting the range of motion, the Dynesys flexible instrumentation system rnay also unload the disk; this is an important feature of a flexible stabilization system.29-50Neural elements are indirectly decompressed and the loads are not transferred to the adjacent spinal levels avoiding early degenerative evolution. Dynesys instrumentation is less complicated than rigid spine arthrodesis. Among other advantages, bone grafting is

. ,.;,-.,.; ...,...-&--,.

ORTHO SuperSite - Printable version

-

Seite 5 von 8

not necessary. The patient is mobilized on postoperative day 1 and is discharged from the hospital within 3 to 4 days. The implant is relatively flat and does not irritate the patient. However, a precondition for implanting Dynesys is that the disk is not completely degenerated. If a spontaneous arthrodesis of the vertebrae or the facet joints has already occurred, rigid arthrodesis is recommended. Dynesys usually is used as a monosegmental implant; however, up to 4 segments can be treated. The system has now been in clinical use for almost a decade, with a number of relevant studies reporting on patientoriented outcome after Dynesys implantation.7~14~27-42~52-55 Schwarzenbach et a127operated on 54 patients with a mean patient age 60.5 years, for spinal stenosis (24), degenerative spondylolisthesis (4), low back diskogenic pain (12), primary disk herniation (2), and failed low-back pain surgery syndrome (6). Dynesys instrumentation operation consisted of decompression (27), decompression and arthrodesis (12), or arthrodesis of a single level alone (2). Within 26.8 months, the Oswestry Disability lndex improved from a mean preoperative score of 43% to a mean postoperative score of 20%. They also reported that the pain scale for low back pain improved from a mean preoperative value of 47.8% to a mean postoperative value of 32%, and the pain scale for leg pain also improved from a mean preoperative value of 63.2% to a mean postoperative value of 24.3%. Stoll et aIs2in a multicentric prospective study evaluated the efficacy of mobile stabilization using a pedicle system Dynesys in the treatment of 33 patients with degenerative lumbar spondylolisthesis and spinal stenosis, with a mean age of 59.9 years. Within a mean follow-up of 43.7 months, 4 patients underwent re-operation. At the latest followup, the Oswestry Disability lndex improved from a mean preoperative score of 58.5% to a mean postoperative score of 20.5%; back pain (visual analog score [VAS]) improved from 77.8% to 23.2%, and leg pain from 80% to 15.3%. Stoll et aIq4presented their first results with Dynesys in a prospective study of 83 consecutive patients. In this series, spinal instability was mainly associated with spinal stenosis (60.2%) and degenerative diskopathy (24.1 %), and in some cases with disk herniation (8.4%) and spine revision surgery (6.0%). Thirty-nine patients additionally had degenerative spondylolisthesis, and 30 patients had previous lumbar surgery. In 56 patients instrumentation was combined with direct spine decompression. Mean patient age at operation was 58.2 years (range, 26.8-85.3 years), mean follow-up was 38.1 months (range, 11.2-79.1 months). Nine complications were unrelated to the implant, and 1 was due to a screw misplacement. Mean pain and function scores significantly improved from baseline to followup; back pain scale improved from 7.4 to 3.1 points, leg pain scale improved from 6.9 to 2.4 points, and Oswestry Disability lndex improved from 55.4% to 22.9%. In another study, Stoll et a152evaluated the safety and efficacy of Dynesys in a consecutive series of 83 patients. In 56 patients, instrumentation was combined with direct decompression. Within a mean follow-up of 38.1 months, 9 complications were unrelated to the implant and 1 was due to screw misplacement. Four required early reoperation. In 7 cases, there were radiological signs of screw loosening. In 7 cases, adjacent segment degeneration required further surgery. Mean pain and function scores improved significantly during the f ~ l l o w - u p . ~ ~ Satisfactory results of the application of the Dynesys in patients with degenerative disk disease have been reported by Putzier et aLS3They concluded that Dynesys is able to compensate initial morphologic changes and prevent progression of segment degeneration. Cakir et a154presented the results of a retrospective analysis of the outcome of patients with degenerative lumbar instability and spinal stenosis who underwent decompression surgery combined with dorsoventral fusion, or decompression surgery combined with posterior dynamic stabilization. In 20 patients, the Dynesys group showed a slightly better outcome, and shorter operation time and hospital stay. Grob et al,42in a retrospective study of 50 consecutive patients with a mean patient age of 50 years reported less encouraging results. The primary indication for surgery was degenerative disk disease or spinal stenosis associated with instability. Only half of the patients reported satisfaction from the operation and improvement of their overall quality of life. Less than half reported functional improvement. Putzier et aIs5evaluated the outcome afler nucleotomy combined with dynamic stabilization compared with nucleotomy alone. Eighty-four patients underwent nucleotomy of the lumbar spine for the treatment of symptomatic disk prolapse. Dynamic stabilization using the Dynesys instrumentation system was performed in 35 of the 84 patients. Mean follow-up was 34 months. At 3-month follow-up, Oswestry Disability lndex and VAS improved significantly in both groups. However, at long-term follow-up, Oswestry Disability lndex and VAS improved significant only in the nonstabilized group. In the dynamically stabilized group, no progression of disk degeneration was observed, whereas radiographic signs of accelerated segmental degeneration were found in the nucleotomized-only group. There were no implant-associated complications. In the present series, the primary indication for a stabilization procedure using the Dynesys system was degenerative spine disease associated with degenerative diskopathy, disk herniation, and lumbar stenosis. These conditions resulted in instability associated with neurogenic or radicular pain andlor chronic back pain. A substantial improvement in the patient's functional Status was demonstrated postoperatively, at least for the first 2 years. The

I

ORTHO SuperSite - Printable version fact that 86% of the patients reported that they would undergo the operation again indicates their overall satisfaction. In this series, the overall complication rate was 3%. This rate is lower than the previously reported rates in rigid spine arthrodesis s t ~ d i e s . There ~ - ~ ~were . ~ ~no serious implant-related complications compared to those reported in rigid pedicle systems, such as screw m i s p l a ~ e m e n t ,or~ screw ~ ~ - ~ f~a i l ~ r e . lHowever, ~ - ~ ~ in line with the literature, implant loosening related complications can be expected in time.14 In this series, the implantation of a dynamic instrumentation system without fusing the bridged segment may excessively distress the screws leading to loosening or migration. lnfection rate was low and this was explained by the fact that Dynesys is less invasive compared to most posterior arthrodesis procedures. The overall results of the present study are in accordance with the results of previously published studies, and highly comparable to the results of fusion procedures.

Conclusion The Dynesys mobile spine stabilization system can be considered for all types of spinal instability, including excessive or pathologic motion and gradually developing deformity and iatrogenic instability. The results of the present study favor the aforementioned technique. The dynamic neutralization system can be a safe and effective alternative technique to spine arthrodesis in selected cases of degenerative or iatrogenic lumbar spine instability.

What is already known on this topic Rigid spine fusion can generate a considerable amount of morbidity, high complication rates, high frequency of reoperations, and variable patient satisfaction regardless of the quality of fusion. The future of spine stabilization needs to involve more physiologic and patientfriendly methods.

What this article adds The dynamic neutralization pedicle screw system is a flexible spine stabilization system that allows a restricted spine motion. The dynamic neutralization system can be a safe and effective alternative technique to spine arthrodesis in selected cases of degenerative or iatrogenic lumbar spine instability.

References Schlegel JD, Smith JA, Schleusener RL. Lumbar motion segment pathology adjacent to thoracolumbar, lumbar, and lumbosacral fusions. Spine. 1996; 21 :970-981. Aota Y, Kumano K, Hirabayashi S. Postfusion instability at the adjacent segments after rigid pedicle screw fixation for degenerative lumbar spinal disorders. J Spinal Disord. 1995; 8:464-473. Lehmann TR, Spratt KF, Tozzi JE, et al. Long-term follow-up of lower lumbar fusion patients. Spine. 1987; 12197-104. Abumi K, Panjabi MM, Kramer KM, Duranceau J, Oxland T, Crisco JJ. Biomechanical evaluation of lumbar spinal stability after graded facetectomies. Spine. 1990; 15:1142-1147. Bjarke CF, Stender HE, Laursen M, Thomsen K, Bunger CE. Long-term functional outcome of pedicle screw instrumentation as a support for posterolateral spinal fusion: randomized clinical study with a 5-year followup. Spine. 2002; 27:1269-1277. Esses SI, Sachs BL, Dreyzin V. Complications associated with the technique of pedicle screw fixation. A selected survey of ABS members. Spine. 1993; 18:2231-2238. Fritzell P, Hagg 0 , Wessberg P, Nordwall A. Swedish Lumbar Spine Study Group. Chronic low back pain and fusion: a comparison of three surgical techniques: a prospective multicenter randomized study from the Swedish lumbar spine study group. Spine. 2002; 27:1131-1141. Matsuzaki H, Tokuhashi Y, Matsumoto F, Hoshino M, Kiuchi T, Toriyama S. Problems and solutions of pedicle screw plate fixation of lumbar spine. Spine. 1990; 15:1159-1165. Okuyama K, Abe E, Suzuki T, Tamura Y, Chiba M, Sato K. Posterior lumbar 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. Pihlajamaki H, Myllynen P, Bostman 0 . Complications of transpedicular lumbosacral fixation for nontraumatic disorders. J Bone Joint Surg Br. 1997; 79:183-189. Rompe JD, Eysel P, Zöllner J, Nafe B, Heine J. Degenerative lumbar spinal stenosis. Long-term results after undercutting decompression compared with decompressive laminectomy alone or with instrumented fusion. Neurosurg Rev. 1999; 22: 102-106. Schwarzenbach 0 , Berlemann U, Stoll TM, Dubois G. Posterior dynamic stabilization systems: DYNESYS. Orthop Clin North Am. 2005; 36:363-372. Soini J, Laine T, Pohjolainen T, Hurri H, Alaranta H. Spondylodesis augmented by transpedicular fixation in the treatment of olisthetic and degenerative conditions of the lumbar spine. Clin Orthop Relat Res. 1993;

-

ORTHO SuperSite - Printable version

14. 15. 16. 17. 18. 19. 20. 21. 22.

23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38, 39. 40. 41. 42. 43. 44. 45.

.-

.i..i-duiT,i~.v

Seite 7 von 8

2971111-116. Stoll TM, Dubois G, Schwarzenbach 0 . The dynamic neutralization system for the spine: a multi-center study of a novel non-fusion system. Eur Spine J. 2002; Il(suppl2):S170-S178. Turner JA, Ersek M, Herron L, et al. Patient outcomes after lumbar spinal fusions. JAMA. 1992; 268:907-911. West JL III, Ogilvie JW, Bradford DS. Complications of the variable screw plate pedicle screw fixation. Spine. 1991; 161576-579. Whitecloud TS III, Davis JM, Olive PM. Operative treatment of the degenerated segment adjacent to a lumbar fusion. Spine. 1994; 19:531-536. Rahm MD, Hall BB. Adjacent-segment degeneration after lumbar fusion with instrumentation: a retrospective study. J Spinal Disord. 1996; 9:392-400. Schulitz KP, Wiesner L, Wittenberg RH, Hille E. The mobile segment above fusion [in German]. Z Orthop Ihre Grenzgeb. 1996; 134:171-1 76. Agazzi S, Reverdin A, May D. Posterior lumbar interbody fusion with cages: an independent review of 71 cases. J Neurosurg. 1999; 91(2 suppl):I 86-192. Buttermann GR, Garvey TA, Hunt AF, et al. Lumbar fusion results related to diagnosis. Spine. 1998; 23:116127. Fischgrund JS, Mackay M, Herkowitz HN, Brower R, Montgomery DM, Kurz LT. 1997 Volvo Award winner in clinical studies. Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective, randomized study comparing decompressive laminectomy and arthrodesis with and without spinal instrumentation. Spine. 1997; 2212807-2812. Fritzell P, Hagg 0 , Wessberg P, Nordwall A; Swedish Lumbar Spine Study Group. 2001 Volvo Award Winner in Clinical Studies: Lumbar fusion versus nonsurgical treatment for chronic low back pain: a multicenter randomized controlled trial from the Swedish Lumbar Spine Study Group. Spine. 2001; 26:2521-2532. Thomsen K, Christensen FB, Eiskjaer SP, Hansen ES, Fruensgaard S, Bunger CE. 1997 Volvo Award winner in clinical studies. The effect of pedicle screw instrumentation on functional outcome and fusion rates in posterolateral lumbar spinal fusion: a prospective, randomized clinical study. Spine. 1997; 22:2813-2822. Dubois G, de Germay B, Schaerer NS, Fennema P. Dynamic neutralization, a new concept for restabilization of the spine. In: Szpalski M, Pope MH, eds. Lumbar Segmental Instability. Philadelphia, Pa: Lippincott Williams & Wilkins; 1998:233-240. Freudiger S, Dubois G, Lorrain M. Dynamic neutralisation of the lumbar spine contirmed on a new lumbar spine simulator in vitro. Arch Orthop Trauma Surg. 1999; 119:127-132. Schwarzenbach 0 , Launer R, Els M. Dynamic Neutralization with DYNESYS for the treatment of degenerative Spine disease. Eur Spine J. 2001 ; 10(suppl):S57. Stoll TM, Dubois G, Schwarzenbach 0 . Mobile stabilization of degenerative lumbar Spondylolisthesis. Eur Spine J. 2001; 10(suppl):S57. Mulholland RC, Sengupta DK. Rationale, principles and experimental evaluation of the concept of soft stabilization. Eur Spine J. 2002; II(suppl 2):S198-S205. Fairbank JC, Couper J, Davies JB, O'Brien JP. The Oswestry low back pain disability questionnaire. Physiotherapy. 1980; 66:271-273. Gronblad M, Hupli M, Wennerstrand P, et al. lntercorrelation and test-retest reliability of the Pain Disability Index (PDI) and the Oswestry Disability Questionnaire (ODQ) and their correlation with pain intensity in low back pain patients. Clin J Pain. 1993; 9:189-195. Boscainos PJ, Sapkas G, Stilianessi E, Prouskas K, Papadakis SA. Greek versions of the Oswestry and Roland-Morris Disability Questionnaires. Clin Orthop Relat Res. 2003; 41 1:40-53. Roland M, Morris R. A study fo the natural history of back pain, I: Development of a reliable and sensitive measure of disability in low-back pain. Spine. 1983; 8:141-144. Roland M, Fairbank J. The Roland-Morris Disability Questionnaire and the Oswestry Disability Questionnaire. Spine. 2000; 2531 15-3124. Nydegger T, Husson JL, Schneider W. Evaluation of an implant material for surgical treatment of degenerative pathologies in the lumbar spine. Presented at: 76th Annual Meeting of the French Society of Orthopaedic Surgery and Traumatology; November 6-9, 2001; Paris, France. Roland M, Morris R. A study of the natural history of back pain: I, development of a reliable and sensitive measure of disability in low-back pain. Spine. 1983; 8:141-144. Baumgartner W, Grob D, Kramers-de Quervain I, Stossi E, Niederer P. Novel in viv0 motion analysis of the healthy lower lumbar spine during standardized movements and complex daily activities. Presented at: International Society of Biomechanics; July 8-13, 2001; Zurich, Switzerland. Boden SD, Martin C, Rudolph R, Kirkpatrick JS, Moeini SM, Hutton WC. lncrease of motion between lumbar vertebrae after excision of the capsule and cartilage of the facets. A cadaver study. J Bone Joint Surg Am. 1994; 76: 1847-1853. Frymoyer JW, Selby DK. Segmental instability. Rationale for treatment. Spine. 1985; 10:280-286. Johnsson B, Akesson M, Jonsson K, Stromqvist B. Low risk for vertebral slipping after decompression with facet joint preserving technique for lumbar spinal stenosis. €ur Spine J. 1992; 1: I 00-104. Johnsson KE, Willner S, Johnsson K. Postoperative instability after decompression for lumbar spinal stenosis. Spine. 1986; 11: I 07-1 10. Grob D, Benini A, Junge A, Mannion AF. Clinical experience with the Dynesys semirigid fixation system for the lumbar spine: surgical and patient-oriented outcome in 50 cases after an average of 2 years. Spine. 2005; 301324-331. 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. Schmoelz W, Huber JF, Nydegger T, Dipl-lng, Claes L, Wilke HJ. Dynamic stabilization of the lumbar spine and its effects on adjacent segments: an in vitro experiment. J Spinal Disord Tech. 2003; 16:418-423. Mayer HM, Wiechert K, Korge A, Qose I. Minimally invasive total disc replacement: surgical technique and

ORTHO SuperSite - Printable version

Seite 8 von 8

preliminary clinical results. Eur Spine J. 2002; II(suppl 2):S124-S130. Link HD. History, design and biomechanics of the LINK SB Charite artificial disc. Eur Spine J. 2002; II(suppl 2):S98-SI 05. Korge A, Nydegger T, Polard JL, Mayer HM, Husson JL. A spiral implant as nucleus prosthesis in the lumbar spine. Eur Spine J. 2002; II(suppl 2):S149-S153. Ray CD. The PDN prosthetic disc-nucleus device. Eur Spine J. 2002; II(suppl 2):S137-S142. Grevitt MP, Gardner AD, Spilsbury J, et al. The Graf stabilisation system: early results in 50 patients. Eur Spine J. 1995; 4:169-175. 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; II(suppl 2):S192-S197. Korovessis P, Papazisis Z, Koureas G, Lambiris E. Rigid, semirigid versus dynamic instrumentation for degenerative lumbar spinal stenosis: a correlative radiological and clinical analysis of short-term results. Spine. 2004; 29:735-742. Stoll TM, Dubois G, Schwarzenbach 0. The dynamic neutralization system for the spine: a multi-center study of a novel non-fusion system. Eur Spine J. 2002; Il(suppl 2):S170-S178. Putzier M, Schneider SV, Funk J, Perka C. Application of a dynamic pedicle screw system (DYNESYS) for lumbar segmental degenerations-comparison of clinical and radiological results for different indications [in German]. Z Orthop lhre Grenzgeb. 2004; 142:166-173. Cakir B, Ulmar B, Koepp H, Huch K, Puhl W, Richter M. Posterior dynamic stabilization as an alternative for dorso-ventral fusion in spinal stenosis with degenerative instability [in German]. Z Orthop lhre Grenzgeb. 2003; 1411418-424. Putzier M, Schneider SV, Funk JF, Tohtz SW, Perka C. The surgical treatment of the lumbar disc prolapse: nucleotomy with additional transpedicular dynamic stabilization versus nucleotomy alone. Spine. 2005; 30:E109-E114. Prolo DJ, Oklund SA, Butcher M. Toward uniformity in evaluating results of lumbar spine operations. A paradigm applied to posterior lumbar interbody fusions. Spine. 1986; 11:601-606. Amiot LP, Lang K, Putzier M, Zippel H, Labelle H. Comparative results between conventional and computerassisted pedicle screw installation in the thoracic, lumbar, and sacral spine. Spine. 2000; 25:606-614. Ohlin A, Karlsson M, Duppe H, Hasserius R, Redlund-Johnell I. Complications after transpedicular stabilization of the spine. A survivorship analysis of 163 cases. Spine. 1994; 19:2774-2779.

Authors Drs Sapkas, Themistocleous, Mavrogenis, Benetos, and Papagelopoulos are from the First Department of Orthopedics, Athens University Medical School; and Dr Metaxas is from the Department of Neurosurgery, Metropolitan Hospital, Athens Greece. Correspondence should be addressed to: Panayiotis J. Papagelopoulos, MD, DSc, 4 Christovassili Str, 15451, Neo Psychikon, Athens, Greece.

Copyright @ 2008 SLACK Incorporated.All rights reserved.