The Graf stabilisation system: early results in 50 patients

Biomechanical Effect of Hybrid Dynamic Stabilization Implant on the Segmental Motion and Intradiscal Pressure in Human Lumbar Spine

The hybrid dynamic stabilization system, Dynesys-Transition-Optima, represents a novel pedicle-based construct for the treatment of lumbar degenerative disease. The theoretical advantage of this system is to stabilize the treated segment and preserve the range of motion within the adjacent segment while potentially decreasing the risk of adjacent segment disease following lumbar arthrodesis. Satisfactory short-term outcomes were previously demonstrated in the Dynesys-Transition-Optima system. However, long-term follow-up reported accelerated degeneration of adjacent segments and segmental instability above the fusion level. This study investigated the biomechanical effects of the Dynesys-Transition-Optima system on segment motion and intradiscal pressure at adjacent and implanted levels. Segmental range of motion and intradiscal pressure were evaluated under the conditions of the intact spine, with a static fixator at L4-5, and implanted with DTO at L3-4 (Dynesys fixator) and L4-5 (static fixator) by applying the loading conditions of flexion/extension (±7.5 Nm) and lateral bending (±7.5 Nm), with/without a follower preload of 500 N. Our results showed that the hybrid Dynesys-Transition-Optima system can significantly reduce the ROM at the fusion level (L4-L5), whereas the range of motion at the adjacent level (L3-4) significantly increased. The increase in physiological loading could be an important factor in the increment of IDP at the intervertebral discs at the lumbar spine. The Dynesys-Transition-Optima system can preserve the mobility of the stabilized segments with a lesser range of motion on the transition segment; it may help to prevent the occurrence of adjacent segment degeneration. However, the current study cannot cover all the issues of adjacent segmental diseases. Future investigations of large-scale and long-term follow-ups are needed.

Fatigue wear test comparing vitamin-E-blended crosslinked polyethylene and conventional polyethylene in a Posterior Dynamic Stabilization System of the spine in the laboratory

BACKGROUND

Although artificial joints using polyethylene have been developed for various joints, the development of Posterior Dynamic Stabilization system of the spine using polyethylene has proceeded at a much slower pace. There are no studies which compare the abrasion resistance of vitamin-E-blended crosslinked polyethylene (VE) and conventional polyethylene (Virgin) in the spinal region. The purpose of this study was to compare the wear resistance of VE and Virgin in a Posterior Dynamic Stabilization System of the spine.

METHODS

Posterior Dynamic Stabilization System of the spine uses a polyethylene ball as a sliding surface. A fatigue wear test was repeated up to 1 million cycles at a speed of ±5°, 1 Hz while the rod was being pulled at a load of 50 N. Balls were compared using VE and Virgin in 6 samples each. Ti-6AL-4 V (Ti 64) and Co-Cr-Mo (CoCr) rods were used. Abrasion loss and shape change of the polyethylene balls were compared.

RESULTS

When Ti 64 was used as the rod, the average wear amount was -0.01 mg (0.02 mg, 0.01 mg, -0.06 mg) for VE, and 0.23 mg (0.18 mg, 0.13 mg, 0.38 mg) for Virgin. When CoCr was used as the rod, the average wear amount was 0.42 mg (0.71 mg, -0.06 mg, 0.61 mg) for VE, and 0.73 mg (0.72 mg, 0.70 mg, 0.76 mg) for Virgin. Most polyethylene samples showed indentations of 0.1 m or less at the contact point with the set screw. In the combination of Virgin and CoCr, a white patch was observed on the inner side of the polyethylene samples, with a maximum depression of 0.1 mm.

CONCLUSIONS

A fatigue wear test showed VE to be more efficient in abrasion resistance than Virgin in a Posterior Dynamic Stabilization System of the spine in the laboratory.

Biomechanics of spinal implants-a review

Spinal instrumentations have been classified as rigid fixation, total disc replacement and dynamic stabilization system for treatment of various spinal disorders. The efficacy and biomechanical suitability of any spinal implant can be measured through in vitro, in vivo experiments and numerical techniques. With the advancement in technology finite element models are making an important contribution to understand the complex structure of spinal components along with allied functionality, designing and application of spinal instrumentations at preliminary design stage. This paper aimed to review the past and recent studies to describe the biomechanical aspects of various spinal implants. The literatures were grouped and reviewed in accordance to instrumentation category and their functionality in the spinal column at respective locations.

Temporary axial rotation stabilization for lumbar disc herniation surgery with the ARO® spinal system: a prospective analysis of safety and clinical efficacy

Background

Decompressive surgery has a failure rate of between 25% and 32% based on patient reported improvement in clinical symptoms. Significant back pain is associated with 53% of failures of decompressive surgery, while also being associated with abnormal axial rotation motion. We report on the clinical performance of subjects receiving a novel axial rotation stabilization implant (ARO Spinal System, ARO Medical), while undergoing a surgical decompression for a herniated lumbar disc, a condition associated with low back pain and abnormal movement.

Methods

This Danish Medicines Agency and Ethics Committee approved clinical trial prospectively investigated the use of the ARO^® Spinal System as part of lumbar discectomy surgery in 20 patients. All subjects had a single level posterolateral lumbar herniation with symptoms lasting more than 6 weeks. They underwent an open discectomy at the symptomatic level, and received the implant.

Results

No complications with the implant were observed. Four serious adverse events not related to the devices were reported, one subject had reoperation at 3 months. Leg pain median VAS score decreased from 70 to 2 at 1 year (P=0.01) back pain median VAS score from 48 to 6 (P=0.04). Satisfaction with surgery was 88%. Oswestry Disability Index scored likewise improvement going from 38 pre-operative to 5 at 1 year. Follow-up rate was excellent 100%.

Conclusions

Discectomy with the ARO Spinal System proves equally safe as a standard discectomy at 1 year follow-up. The subjects had significant improvements in both leg and back pain. In addition, they did better than historical controls, though not statistically so in this patient sample.

Durability and Biological Response of a New Posterior Dynamic Stabilization System Using Polyethylene with Vitamin E

Objective

The purpose of this study was to evaluate the durability and biological response of a new Posterior Dynamic Stabilization system using polyethylene with vitamin E on the sliding surface.

Summary of Background Data

The use of polyethylene with vitamin E on the sliding surface in Posterior Dynamic Stabilization has not been reported previously.

Methods

A developed pedicle screw-based Posterior Dynamic system consists of four parts: a set screw, a rod, a ball, and a pedicle screw. The rod is inserted into the through hole of the ball, and the ball is sandwiched by the set screw. (1) Fatigue Wear Test. Testing was conducted under a dynamic compressive load of 50N at a speed of 1 Hz for 1 million cycles. We examined the loss of polyethylene due to abrasion in 3 units. (2) Biological Response in Pigs. In two pigs, a new pedicle screw and a conventional pedicle screw were inserted in L2 and L3/4, and L4 and L2/3, respectively. After breeding for 6 months, autopsies were performed. CT imaging was used to evaluate bone union of the facet joint. Abrasive specimens were prepared, and abrasion powder and inflammatory cell infiltration were evaluated microscopically.

Results

The average loss of polyethylene due to abrasion was -0.01 mg. In all units, polyethylene showed a decrease of 0.1 mm or less at the contact point with the set screw. The facet joints between the conventional screws exhibited bone fusion, but the facet joint between the conventional and the new screw retained mobility with no bony fusion. No abrasion powder was found and inflammatory cell infiltration was only minimally observed.

Conclusion

The new Posterior Dynamic Stabilization system exhibited a high level of durability and biological safety.

Minimum ten-year follow-up of spinal stenosis with degenerative spondylolisthesis treated with decompression and dynamic stabilization

Background

The Dynesys system remains the most widely implanted posterior non-fusion pedicle screw system. Various study designs used in investigations with good to excellent short- and mid-term results have been reported in the current literature. However, there is a lack of information concerning long-term outcomes following treatment for spinal stenosis with degenerative spondylolisthesis.

Methods

The aim of our study was twofold. Firstly, to assess whether the dynamic stabilization in situ with the Dynesys System without bone grafting provides enough stability to prevent progression of spondylolisthesis and secondarily to maintain significant clinical improvement in a long-term follow-up (FU). Therefore, the consecutive patients due to inclusion criterions underwent interlaminar decompression and stabilization with Dynesys instrumentation. Patients were evaluated clinically and radiologically after a minimum FU of 10 years.

Results

At FU, the mean low back pain (LBP) post-operatively and leg pain (LP) post-operatively on visual analog scale (VAS) and North American Spine Society (NASS) improved significantly (P<0.001) compared to preoperative examination. The mean value of NASS neurogenic symptoms (19.13% and 4.72%) and activity subscores were 23.13% and 10.74% respectively. In plain and functional radiographs the mean listhesis grade in neutral position was 11.11%, 11.8% in reclination and 11.63% in inclination. There were 17 and 8 patients with progressing degenerative osteochondrosis/listhesis at adjacent segments.

Conclusions

Decompression and single and double level dynamic in situ stabilization with the Dynesys System demonstrate good clinical and radiological long-term results in elderly patients.

Posterolateral fusion versus Dynesys dynamic stabilization: Retrospective study at a minimum 5.5years' follow-up

INTRODUCTION

Lumbar fusion is one of the most widespread techniques to treat degenerative lumbar pathology. To prevent complications such as non-union or adjacent segment degeneration, dynamic stabilization techniques were developed, but with controversial results. The aim of the present study was to compare long-term radiologic and clinical results between fusion and dynamic stabilization.

MATERIAL AND METHODS

A single-center retrospective study included patients with recurrent lumbar discal hernia or lumbar canal stenosis managed by posterolateral fusion or by dynamic stabilization associated to neurologic release. Patients were seen in follow-up for radiological and clinical assessment: visual analog pain scale (VAS), Oswestry Disability Index (ODI), Short Form-12 (SF-12), adjacent segment disease (ASD), and intervertebral range of motion (ROM).

RESULTS

Fifty-eight patients were included: 25 in the fusion group (FG), and 33 in the Dynesys^® group (DG). VAS scores were significantly lower in DG than FG. ODI was 14.6±2.8 in DG, versus 19.4±3.3 in FG (P=0.0001). SF-12 physical subscore was significantly higher in DG. ROM was 4.1±2° in DG, vs. 0.7±0.5° in FG (P=0.001). Radiologic ASD was significantly greater in FG than DG (36% vs. 12.1%; P=0.012), without difference in clinical expression (DG, 1 case; FG, 2 cases).

CONCLUSION

Dynamic stabilization provided clinical and radiological results comparable to those of posterolateral fusion in these indications (although level L5-S1 was not studied).

LEVEL OF EVIDENCE

IV.

Adjacent segment degeneration after lumbar spinal fusion compared with motion-preservation procedures: a meta-analysis

PURPOSE

This meta-analysis aimed to evaluate the efficacy of motion-preservation procedures to prevent the adjacent segment degeneration (ASDeg) or adjacent segment disease (ASDis) compared with fusion in lumbar spine.

METHODS

PubMed, Embase and the Cochrane Library were comprehensively searched and a meta-analysis was performed of all randomized controlled trials and well designed prospective or retrospective comparative cohort studies assessing the lumbar fusion and motion-preservation procedures. We compared the ASDeg and ASDis rate, reoperation rate, operation time, blood loss, length of hospital stay, visual analogue scale (VAS) and oswestry disability index (ODI) improvement of the two procedures.

RESULTS

A total of 15 studies consisting of 1474 patients were included in this study. The meta-analysis indicated that the prevalence of ASDeg, ASDis and reoperation rate on the adjacent level were lower in motion-preservation procedures group than in the fusion group (P = 0.001; P = 0.0004; P < 0.0001). Moreover, shorter length of hospital stay was found in motion-preservation procedures group (P < 0.0001). No difference was found in terms of operation time (P = 0.57), blood loss (P = 0.27), VAS (P = 0.76) and ODI improvement (P = 0.71) between the two groups.

CONCLUSIONS

The present evidences indicated that the motion-preservation procedures had an advantage on reducing the prevalence of ASDeg, ASDis and the reoperation rate due to the adjacent segment degeneration compared with the lumbar fusion. And the clinical outcomes of the two procedures are similar.

Restoring lumbar spine stiffness using an interspinous implant in an ovine model of instability

BACKGROUND

The objective of this study was to determine the effect of an interspinous implant on lumbar spine stability and stiffness during dorsoventral loading.

METHODS

Twelve Merino lambs were mechanically tested in vivo. Oscillatory (2 Hz) loads were applied to L2 under load control while displacements were monitored. Tri-axial accelerometers further quantified adjacent L3-L4 accelerations. Dorsoventral lumbar spine stiffness and L3 and L4 dorsoventral and axial displacements were determined over six trials of 20 cycles of loading. Four conditions were examined: 1) initial intact, 2) following destabilization at L3-L4, 3) following the insertion of an InSwing(®) interspinous device at L3-L4, and 4) with the implant secured with a tension band. Comparisons were performed using a one-way ANOVA with repeated measures and post-hoc Bonferroni correction.

FINDINGS

Compared to the intact condition, destabilization significantly decreased lumbar stiffness by 4.5% (P=.001) which was only recovered by the interspinous device with tension band. The interspinous device caused a significant 9.75% (P=.001) increase in dorsoventral stiffness from destabilization that increased 14% with the tension band added (P=.001). The tension band was responsible for decreased displacements from the intact (P=.038), instability (P=.001), and interspinous device (P=.005) conditions. Dorsoventral L3-L4 motion significantly improved with the interspinous device (P=.01) and the addition of the tension band (P=.001). No significant differences in L3-L4 intersegmental stability were noted for axial motion in the sagittal plane.

INTERPRETATION

This ovine model provided objective in vivo biomechanical evidence of lumbar instability and its restoration by means of an interspinous implant during dorsoventral spinal loading.

Nonfusion Does Not Prevent Adjacent Segment Disease: Dynesys Long-term Outcomes With Minimum Five-year Follow-up

STUDY DESIGN

Case series.

OBJECTIVE

The aim of this study was to determine the relationship between fusion and adjacent segment disease via Dynesys long-term outcomes.

SUMMARY OF BACKGROUND DATA

Dynesys is a dynamic stabilization system meant to improve symptoms by stabilizing the spine without fusion and avoiding the development of adjacent segment disease. However, few studies have evaluated long-term outcomes.

METHODS

All patients were operated on with Dynesys from 2006 to 2009 by a single surgeon at a single institution. We prospectively collected 18 variables among the following categories: patient characteristics, comorbidities, surgical indications, and OR variables. We analyzed two primary endpoints: solid fusion on X-ray and clinical adjacent segment disease (ASD) both at 5 years. Secondary endpoints were time to fusion, time to ASD, reoperation, Oswestry disability index (ODI), and visual analogue scale (VAS) leg pain. We conducted a multivariate analysis via the random forest method. Mann-Whitney U test and Fisher exact test were then used to qualify relationship between variables.

RESULTS

We had 52 patients to review in the database. Eight had preexisting ASD. Mean follow-up was 92 months (median 87 months). Fifteen had ASD (29%) during follow-up at a mean 45 months (Median 35 months). Nine had a solid fusion (17%), 2 of which also had ASD. Mean time to fusion was 65 months (median 71 months). Differences in improvement of ODI (P = 0.005) and VAS leg pain (P = 0.002) were significant favoring patients without ASD. The multivariate analysis revealed four variables associated with ASD: prior ASD (OR 11.3, P = 0.005), neurological deficit (OR 8.5, P = 0.018), revision OR (OR 8.5, P = 0.018), and multilevel degeneration (OR 0.184, P = 0.026). No variable was associated with fusion.

CONCLUSION

Dynesys was associated with a high rate of ASD over long-term follow-up despite maintaining a low fusion rate. Prior ASD was the strongest predictor of progressive ASD.

LEVEL OF EVIDENCE

3.

In Vitro Comparison of Dynesys, PEEK, and Titanium Constructs in the Lumbar Spine

Introduction. Pedicle based posterior dynamic stabilization systems aim to stabilize the pathologic spine while also allowing sufficient motion to mitigate adjacent level effects. Two flexible constructs that have been proposed to act in such a manner, the Dynesys Dynamic Stabilization System and PEEK rod, have yet to be directly compared in vitro to a rigid Titanium rod. Methods. Human lumbar specimens were tested in flexion extension, lateral bending, and axial torsion to evaluate the following conditions at L4-L5: Intact, Dynesys, PEEK rod, Titanium rod, and Destabilized. Intervertebral range of motion, interpedicular travel, and interpedicular displacement metrics were evaluated from 3rd-cycle data using an optoelectric tracking system. Results. Statistically significant decreases in ROM compared to Intact and Destabilized conditions were detected for the instrumented conditions during flexion extension and lateral bending. AT ROM was significantly less than Destabilized but not the Intact condition. Similar trends were found for interpedicular displacement in all modes of loading; however, interpedicular travel trends were less consistent. More importantly, no metrics under any mode of loading revealed significant differences between Dynesys, PEEK, and Titanium. Conclusion. The results of this study support previous findings that Dynesys and PEEK constructs behave similarly to a Titanium rod in vitro.

Clinical significance of achieving a flexion limitation with a tension band system in grade 1 degenerative spondylolisthesis: a minimum 5-year follow-up

STUDY DESIGN

Retrospective clinical study.

OBJECTIVE

To evaluate the effect of the limitation of flexion rotation clinically and radiologically after interspinous soft stabilization using a tension band system in grade 1 degenerative spondylolisthesis.

SUMMARY OF BACKGROUND DATA

Although several studies have been published on the clinical effects of limiting rotatory motion using tension band systems, which mainly targets the limitation of flexion rather than that of extension, they were confined to the category of pedicle screw-based systems, revealing inconsistent long-term outcomes.

METHODS

Sixty-one patients with a mean age of 60.6 years (range, 28-76 yr) who underwent interspinous soft stabilization after decompression for grade 1 degenerative spondylolisthesis with stenosis between 2002 and 2004 were analyzed. At follow-up, the patients were divided into 2 groups on the basis of their achievement or failure to achieve flexion limitation. The clinical and radiological findings were analyzed. A multiple linear regression analysis was performed to determine the prognostic factors for surgical outcomes.

RESULTS

At a mean follow-up duration of 72.5 months (range, 61-82 mo), 51 patients were classified into the flexion-limited group and 10 into the flexion-unlimited group. Statistically significant improvements were noted only in the flexion-limited group in all clinical scores. In the flexion-unlimited group, there were significant deteriorations in flexion angle (P = 0.009), axial thickness of the ligamentum flavum (P = 0.013), and the foraminal cross-sectional area (P = 0.011), resulting in significant intergroup differences. The preoperative extension angle was identified as the most influential variable for the flexion limitation and the clinical outcomes.

CONCLUSION

The effects of the limitation of flexion rotation achieved through interspinous soft stabilization using a tension band system after decompression were related to the prevention of late recurrent stenosis and resultant radicular pain caused by flexion instability. The extension potential at the index level was recognized as a major prognostic factor that can predict the flexion limitation and the clinical results.

LEVEL OF EVIDENCE

4.

Load sharing in lumbar spinal segment as a function of location of center of rotation

Object

The center (axis) of rotation (COR) in the lumbar spine has been studied well. However, there is limited information on the kinetic and kinematic consequences of imposed shift in the location of the COR, although this type of shift can be seen after surgeries using motion preservation or dynamic stabilization devices. The objective of this study was to assess the kinetic and kinematic changes in the lumbar spinal segment due to various imposed CORs.

Methods

A 3D finite element model of the L4–5 segment was constructed and validated. The segment was loaded under a 7.5-Nm bending moment while constrained to rotate about various imposed CORs in the sagittal and axial motion planes. Range of motion, ligament forces, facet loads, and disc stresses were measured.

Results

The present model showed an agreement with previous in vitro and finite element studies under the same load and boundary conditions. Range of motion, facet forces, disc stresses, and ligament loads showed a strong association with the location of the COR.

Conclusions

Acute alterations in the location of the COR can significantly change the load sharing characteristics within the spine segment. The normal location of the COR is a result of the tendency of the vertebra to move in the path of least cumulative resistance.

Pedicle-Based Non-fusion Stabilization Devices: A Critical Review and Appraisal of Current Evidence

Over the last decades, spinal fusion has become one of the most important principles in surgical treatment of spinal pathologies. Despite the undoubted benefits of fusion surgery, there are several drawbacks associated with this technique, including adjacent segment degeneration and pseudoarthrosis. Based on biomechanical data, dynamic stabilization of the spine is intended to ameliorate adjacent level degeneration by stabilizing vertebral motion in defined planes and mimicking natural spine movements.In this paper, we review the literature and discuss past and present pedicle-based non-fusion dynamic stabilization devices. Although there is a paucity of high-quality prospective trials, studies have indicated both promising and disappointing results. In comparison to 360° fusion surgery, the perioperative risk seems to be lower. Other complications like screw loosening, however, have been reported with various systems, while a reduction of adjacent segment disease has not yet been demonstrated. The necessary degree of restabilization to achieve pain-free motion seems to vary greatly between patients and current systems are far from perfection. If these problems can be solved, dynamic stabilization may nevertheless be an important option of spinal surgery in the future.

A short history of posterior dynamic stabilization

Interspinous spacers were developed to treat local deformities such as degenerative spondylolisthesis. To treat patients with chronic instability, posterior pedicle fixation and rod-based dynamic stabilization systems were developed as alternatives to fusion surgeries. Dynamic stabilization is the future of spinal surgery, and in the near future, we will be able to see the development of new devices and surgical techniques to stabilize the spine. It is important to follow the development of these technologies and to gain experience using them. In this paper, we review the literature and discuss the dynamic systems, both past and present, used in the market to treat lumbar degeneration.

Role of dynesys as pedicle-based nonfusion stabilization for degenerative disc disorders

Posterior nonfusion pedicle-screw-based stabilization remains a controversial area of spine surgery. To date, the Dynesys system remains the most widely implanted posterior nonfusion pedicle screw system. We review the history of Dynesys and discuss clinical outcome studies and biomechanical evaluations regarding the Dynesys system. Indications for surgery and controversies are discussed. Recommendations are made regarding technical implantation.

Pedicle screw-based posterior dynamic stabilization: literature review

Posterior dynamic stabilization (PDS) indicates motion preservation devices that are aimed for surgical treatment of activity related mechanical low back pain. A large number of such devices have been introduced during the last 2 decades, without biomechanical design rationale, or clinical evidence of efficacy to address back pain. Implant failure is the commonest complication, which has resulted in withdrawal of some of the PDS devices from the market. In this paper the authors presented the current understanding of clinical instability of lumbar motions segment, proposed a classification, and described the clinical experience of the pedicle screw-based posterior dynamic stabilization devices.

A review of current treatment of lumbar posterior ring apophysis fracture with lumbar disc herniation

PURPOSE

Lumbar posterior ring apophysis fracture (PRAF) is an uncommon disorder frequently accompanied by lumbar disc herniation (LDH). Over the years, there have constantly been published studies concerning this disorder. Due to its rarity, there is lack of an agreed treatment strategy, and lots of different opinions exist, including the choice of decompressive modalities, whether removal of apophyseal fragments or/and disc material, and the necessity of additional spinal fusion. The purpose of this review is to provide a collective opinion on the treatment of PRAF with LDH.

METHODS

A MEDLINE search in the English language literature was performed from 1980 to 2012. To be included in the study, it was strictly necessary for each clinical article to provide information about the description of apophyseal fracture such as location, treatment methods and clinical outcome. The studies were mainly analyzed for general features, the related classifications and treatments.

RESULTS

The literature searching yielded 19 articles reporting 366 patients experiencing 380 sites of fractures. All of them were case reports or case series. The classification systems of PRAF were various based on the morphology, mobilization, size or localization, and relationship between disc and fragment. The most used surgical options were posterior discectomy simultaneous excision of apophyseal fragments without spine fusion. Surgical treatment for PRAF with LDH had equally excellent clinical outcome compared with LDH alone.

CONCLUSIONS

The diverse features of apophyseal fracture lead to various modalities of classifications and operation options. Prior to operation, the surgeons should carefully make a plan to consider decompressive scope, removal of apophyseal fragment or/and disc and fusion or not. Because of methodological shortcomings in publications, it is not possible to definitively conclude what treatment modality is the best for the treatment of PRAF. More high-quality clinical studies are needed to draw more confirmable conclusions.

Outcome of a dynamic neutralization system for the spine

One hundred fourteen patients (66 men and 48 women; mean age, 49 years) underwent spine stabilization using a dynamic neutralization system between January 1999 and August 2010 for degenerative disk disease, spinal instability, or spinal stenosis. Mean follow-up was 6.8 years (range, 1-11 years). Seven patients were lost to follow-up. Radiological examination and clinical evaluation, including the Oswestry Disability Index, the Roland-Morris Disability Questionnaire, and patient satisfaction, were performed.Mean Oswestry Disability Index score improved from 57% (severe disability) preoperatively to 22% (moderate disability) postoperatively. Mean Roland-Morris Disability Questionnaire score improved from 52% preoperatively to 35% postoperatively; 79 (74%) patients declared themselves very satisfied with the end result of the operation. Postoperatively, 27 (25%) patients experienced complications, including screw loosening (n=22), infection (n=2), back (n=5) and leg (n=2) pain, and endplate vertebral fracture (n=1). Three patients with screw loosening, 2 with deep infection, and 1 with severe persistent back and leg pain underwent rigid spine arthrodesis.Dynamic neutralization systems can be considered for degenerative disk disease, spinal instability, and stenosis. Patient satisfaction with the procedure is excellent. However, in the long term, the complication rate, most commonly screw loosening, is high and reoperations are common. In this setting, long-term follow-up is recommended, and the use of this system should be reconsidered.

Which radiographic parameters are linked to failure of a dynamic spinal implant?

BACKGROUND

Knowledge about factors leading to failure of posterior dynamic stabilization implants is essential to design future implants and establish surgical indications. Therefore, we analyzed an implant for single-level or hybrid configuration (adjacent to spondylodesis), which was recalled due to high failure rates.

QUESTIONS/PURPOSES

We asked: (1) Were postoperative radiographic changes linked to implant failure? (2) Were radiographic parameters different between the two configurations? And (3) was implant failure related to inferior clinical scores?

METHODS

The implant was used in 18 patients with lumbar single-level spinal stenosis or with (recurrent) disc herniation and concurrent degenerative disc disease and in 22 patients with an initially degenerated segment adjacent and superior to a fusion site. We prospectively obtained preoperative and postoperative (immediate, 6-, 12- and 24-month) clinical and radiographic evaluations; 37 of the 40 patients completed the 24-month followup. Using plain and extension-flexion radiographs, we compared implant failure rates and their association with postoperative implant translation, anterior and posterior disc height, and ROM for each configuration and between configurations. We assessed associations between clinical scores (VAS pain scores for back and leg, Oswestry Disability Index) and implant failure.

RESULTS

Implant failure occurred in 10 of the 37 implants and corresponded to greater posterior disc height (single-level only) and implant translation. Adjacent-segment ROM increases and posterior disc height decreases over time were greater with the hybrid configuration. Implant failure rate related to higher Oswestry Disability Index (single-level only) and higher back pain scores.

CONCLUSIONS

Implant translation is associated with failure likely due to insufficient resistance to shear forces. Load transfer may cause progressive degeneration in the dynamic and adjacent segments, especially in the hybrid configuration.

STABILIZATION EFFECTS OF GRAF LIGAMENTOPLASTY

Graf ligamentoplasty with or without decompression was performed consecutively in 22 patients of lumbar degenerative diseases with segmental instability. The clinical course of the patients was evaluated using the criteria of the Japanese Orthopaedic Association (JOA) for assessing treatment of low back pain (29 points in total), and radiological alteration in angular and translational displacements were measured in flexion, extension, or neutral position. The change of an intervertebral vacuum phenomenon (Knutsson's sign), as a sign of segmental instability, was observed before and after the surgery.

A preoperative JOA score of 13.7 points was significantly improved to 25.0 points with an improvement rate of 75.7% on average by Graf ligamentoplasty. Radiological measurements revealed that the operation reduced the range of motion of the involved segment in both angular and translational modes with the segment realigned in extension. The short-term results of Graf ligamentoplasty was acceptable for lumbar degenerative diseases. The patients in whom Knutsson's sign was reduced or disappeared after Graf ligamentoplasty had a better outcome than those with the sign unchanged or increased in size. This suggests that Knutsson's sign can be a predictive indicator of the outcome of the surgery.

TREATMENT OF FLEXION INSTABILITY OF LUMBAR SPINE WITH GRAF BAND

This study focused mainly on the long-lasting effectiveness of Graf band stabilization system on the stabilized lumbar motion segment together with the band fate and the final outcome. Graf soft stabilization operation was carried out to suppress the forward flexion and rotatory instability. Fifty-one patients were subjected to this study. Forty-five had pure forward flexion instability preoperatively. Among the 51 patients, 20 were irreducible mild spondylolisthesis and 8 reducible mild spondylolisthesis; 17 excessive flexion angular motion; one disc disease with mild stenotic symptoms; and 5 post-laminectomy instability.

In this series, good or excellent results were obtained in 40 cases (78.7%); fair in 4; no improvement in 4; and poor in 3. JOA lumbar score increased from 16 at preoperative exam to 26.5 on average at the final examination. In 3 cases screws were malpositioned. In 2 cases, mild transient drop foot developed, and spontaneous fusion occurred in one disc surgery patient. There was no implant loosening or breakage, and no overstretch and tear of bands or disengagement. There was no recurrence of segmental instability at the immobilized segment. Also, there were no adjacent joint problems.

In summary, the Graf procedure appears to be a good alternative to spinal fusion for the stabilization of the unstable segment with forward flexion instability.

Motion-preserving technologies for degenerative lumbar spine: The past, present, and future horizons

Over the past few decades, remarkable advancements in the understanding of the origin of low-back pain and lumbar spinal disorders have been achieved. Spinal fusion is generally considered the “gold standard” in the treatment of low-back pain; however, fusion is also associated with accelerated degeneration of adjacent levels. Spinal arthroplasty and dynamic stabilization technologies, as well as the continuous improvement in diagnosis and surgical interventions, have opened a new era of treatment options. Recent advancements in nonfusion technologies such as motion-preservation devices and posterior dynamic stabilization may change the gold standard. These devices are designed with the intent to provide stabilization and eliminate pain while preserving motion of the functional spinal unit. The adaption of nonfusion technologies by the surgical community and payers for the treatment of degenerative spinal conditions will depend on the long-term clinical outcome of controlled randomized clinical studies. Although the development of nonfusion technology has just started and the adoption is very slow, it may be considered a viable option for motion preservation in coming years. This review article provides technical and surgical views from the past and from the present, as well as a glance at the future endeavors and challenges in instrumentation development for lumbar spinal disorders.

© 2011 SAS - The International Society for the Advancement of Spine Surgery. Published by Elsevier Inc. All rights reserved.

Hybrid dynamic stabilization with posterior spinal fusion in the lumbar spine

Background

Instrumented lumbar arthrodesis has been established as the gold standard in the care of patients with degenerative disc disease. However, spinal fusion results in the elimination of motion of the functional spinal unit and has been implicated in the development of adjacent-level degeneration. Motion-preserving devices such as the dynamic rod allow for stabilization of a pathologic motion segment above a fused segment and create a transitional zone (index level) that decreases the loads applied to the supra-adjacent normal segment.

Methods

After institutional review board approval, 28 patients were included in this prospective, consecutive, nonrandomized clinical trial. Each subject was consented for dynamic stabilization. There was no attempt at fusion at the dynamic level. The cohort underwent a posterior lateral spinal fusion with single- or 2-level transforaminal lumbar interbody fusion by use of a cage, with superior-level posterior dynamic instrumentation. Functional clinical outcomes were measured with a 100-point visual analog scale, Oswestry Disability Index, and Short Form 36 questionnaire. Radiographic measurements, fusion evaluation, complications, and screw loosening were recorded.

Results

A minimum of 24 months’ follow-up data included 22 patients. No device failure or screw breakage was identified. Postoperative range of motion averaged 2.5° at the index level, and the superior adjacent-level range of motion remained unchanged (P > .05). Disc height was preserved at all levels (P > .05). Of 180 screws, 6 (3%) showed radiographic loosening. Functional outcomes showed significant improvement in mean postoperative visual analog scale score by 24.7 points (P < .01) and Oswestry Disability Index by 27.6 points (P < .01), as well as the Short Form 36 physical (P < .01) and mental (P < .05) components from baseline to 2-year follow-up.

Conclusions

Our preliminary results at 2 years are satisfactory.

Clinical Relevance

Ultimately, further follow-up will assess the potential for this treatment to delay adjacent-level changes in the long term.

Biomechanical evaluation of posterior lumbar dynamic stabilization: an in vitro comparison between Universal Clamp and Wallis systems

Treatment of chronic low back pain due to degenerative lumbar spine conditions often involves fusion of the symptomatic level. A known risk of this procedure is accelerated adjacent level degeneration. Motion preservation devices have been designed to provide stabilization to the symptomatic motion segment while preserving some physiologic motion. The aim of this study was to compare the changes in relative range of motion caused as a result of application of two non-fusion, dynamic stabilization devices: the Universal Clamp (UC) and the Wallis device. Nine fresh, frozen human lumbar spines (L1-Sacrum) were tested in flexion-extension, lateral bending, and axial rotation with a custom spine simulator. Specimens were tested in four conditions: (1) intact, (2) the Universal Clamp implanted at L3-4 (UC), (3) the UC with a transverse rod added (UCTR), and (4) the Wallis device implanted at L3-4. Total range of motion at 7.5 N-m was determined for each device and compared to intact condition. The UC device (with or without a transverse rod) restricted motion in all planes more than the Wallis. The greatest restriction was observed in flexion. The neutral position of the L3-4 motion segment shifted toward extension with the UC and UCTR. Motion at the adjacent levels remained similar to that observed in the intact spine for all three constructs. These results suggest that the UC device may be an appropriate dynamic stabilization device for degenerative lumbar disorders.

Pedicle screw-based posterior dynamic stabilization in the lumbar spine

Traditionally, management of spinal pathology has centered on decompression, correction of deformity, and stabilization. Deformity correction and stabilization have been accomplished largely by spinal fusion at the pathologic levels. In addition to the risks and potential complications, there are sequelae to a successful fusion. Therefore, attention is being directed toward disk replacement in the lumbar spine. In addition to their preserving motion in the anterior column, several posterior motion-preservation devices have been developed in an effort to prevent pathologic motion at both a decompressed level and a segment adjacent to a fusion. Initial studies suggest that the results of posterior dynamic stabilization may be comparable to those of fusion; however, longer periods of clinical and radiographic follow-up are required to fully define the role these devices may play in the management of the degenerative lumbar spine.

Efficacy and safety of dynamic stabilization for patients with degenerative disc, spinal stenosis and low back pain: a systematic review of randomized controlled clinical trials

STUDY DESIGN: Systematic review of the literature. OBJECTIVE: To perform a systematic review of the literature to organize, critical appraisal and select the best evidence available about the efficacy and safety of non-fusion fixation and its potential use for patients with degenerative disc, spinal stenosis and low back pain. SUMMARY OF BACKGROUND DATA: Recent reports have increased debate about the role of dynamic stabilization in the treatment of chronic back pain associated with lumbar disc degeneration and spinal stenosis. We conducted a systematic review of randomized trials through a more sensitivity search strategy and rigorous criteria applied for the type of studies. METHODS: An electronic search was made in the databases of the Cochrane Central Register of Controlled Trials, Medline, Embase, and Latin American and Caribbean Health Sciences (Lilacs) extended to November 31, 2008, with no linguistic restrictions. RESULTS: One randomized controlled trial that fulfilled the inclusion criteria described above was included in this review. CONCLUSION: The data included in this review show that the use of non-fusion stabilization could be a suitable alternative to another therapies in well selected patients with spinal stenosis and degenerative disc disease. This review highlighted the need for continued research into the use of non-fusion stabilization in the treatment of spinal disorders. There is an urgency need to conduct randomized clinical trials. Long-term efficacy should be evaluated.

Transforaminal lumbar interbody fusion for failed Graf ligamentoplasty: a report of two cases

We report 2 cases of transforaminal lumbar interbody fusion for failed Graf ligamentoplasty. Both patients had residual or recurrent low back pain and leg pain after Graf ligamentoplasty, caused by lumbar segmental instability or narrowing of their intervertebral foramens. The pain improved markedly after the revision surgery. We recommend transforaminal lumbar interbody fusion for failed Graf ligamentoplasty, as it provides rigid interbody bony fusion and obviates complete exposure of the dural sac or dural tube.

Does Wallis implant reduce adjacent segment degeneration above lumbosacral instrumented fusion?

Delayed complications following lumbar spine fusion may occur amongst which is adjacent segment degeneration (ASD). Although interspinous implants have been successfully used in spinal stenosis to authors' knowledge such implants have not been previously used to reduce ASD in instrumented lumbar fusion. This prospective controlled study was designed to investigate if the implantation of an interspinous implant cephalad to short lumbar and lumbosacral instrumented fusion could eliminate the incidence of ASD and subsequently the related re-operation rate. Groups W and C enrolled initially each 25 consecutive selected patients. Group W included patients, who received the Wallis interspinous implant in the unfused vertebral segment cephalad to instrumentation and the group C selected age-, diagnosis-, level-, and instrumentation-matched to W group patients without interspinous implant (controls). The inclusion criterion for Wallis implantation was UCLA arthritic grade <II, while the exclusion criteria were previous lumbar surgery, severe osteoporosis or degeneration >UCLA grade II in the adjacent two segments cephalad to instrumentation. All patients suffered from symptomatic spinal stenosis and underwent decompression and 2-4 levels stabilization with rigid pedicle screw fixation and posterolateral fusion by a single surgeon. Lumbar lordosis, disc height (DH), segmental range of motion (ROM), and percent olisthesis in the adjacent two cephalad to instrumentation segments were measured preoperatively, and postoperatively until the final evaluation. VAS, SF-36, and Oswestry Disability Index (ODI) were used. One patient of group W developed pseudarthrosis: two patients of group C deep infection and one patient of group C ASD in the segment below instrumentation and were excluded from the final evaluation. Thus, 24 patients of group W and 21 in group C aged 65+ 13 and 64+ 11 years, respectively were included in the final analysis. The follow-up averaged 60 +/- 6 months. The instrumented levels averaged 2.5 + 1 vertebra for both groups. All 45 spines showed radiological fusion 8-12 months postoperatively. Lumbar lordosis did not change postoperatively. Postoperatively at the first cephalad adjacent segment: DH increased in the group W (P = 0.042); ROM significantly increased only in group C (ANOVA, P < 0.02); olisthesis decreased both in flexion (P = 0.0024) and extension (P = 0.012) in group W. The degeneration or deterioration of already existed ASD in the two cephalad segments was shown in 1 (4.1%) and 6 (28.6%) spines in W and C groups, respectively. Physical function (SF-36) and ODI improved postoperatively (P < 0.001), but in favour of the patients of group W (P < 0.05) at the final evaluation. Symptomatic ASD required surgical intervention was in 3 (14%) patients of group C and none in group W. ASD remains a significant problem and accounts for a big portion of revision surgery following instrumented lumbar fusion. In this series, the Wallis interspinous implant changed the natural history of ASD and saved the two cephalad adjacent unfused vertebra from fusion, while it lowered the radiographic ASD incidence until to 5 years postoperatively. Longer prospective randomized studies are necessary to prove the beneficial effect of the interspinous implant cephalad and caudal to instrumented fusion. We recommend Wallis device for UCLA degeneration I and II.

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 degrees to 5.3 +/- 2.7 degrees. The addition of the tension band resulted in a 43% reduction in total sagittal ROM to 3.6 +/- 1.9 degrees 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.

The myth of lumbar instability: the importance of abnormal loading as a cause of low back pain

Spinal fusion became what has been termed the "gold standard" for the treatment of mechanical low back pain, yet there was no scientific basis for this. Operations of fusion for low back pain were initially done at the beginning of the last century for back pain thought to be related to congenital abnormalities or for past spinal infection. The recognition of the disc as a cause of sciatica, commonly associated with back pain, and the recognition that a degenerate disc led to abnormal movement suggested the concept that this abnormal movement was the cause of pain, and this abnormal movement came to be called "instability". Much biomechanical expertise confirmed the fact that degenerate discs led to abnormal movement, there were many hypothesis as to why this caused pain. However clinical results of fusion for back pain were unpredictable. The failure of pedicle screws and cage fusion to improve the clinical results of fusion despite near 100% fusion success, and the introduction of "flexible stabilization" and artificial discs, which demonstrated that despite the often unpredictable movement permitted by of these devices, clinical success was similar to fusion, directed attention to the other role of the disc, that of load transfer, which these devices also affected. Abnormal load transfer was already known to be critical in other joints in the body and had led to the use of osteotomy to realign joints. The relevance of load transfer to the future design of spinal implants used in the treatment of low back pain is discussed, and some finite element studies are reported demonstrating the likely effect of abnormal loading beneath an incompletely incorporated plate of an artificial disc, perhaps explaining in part the somewhat disappointing clinical results to date of the implantation of artificial discs.

The Dynesys lumbar spinal stabilization system: a preliminary report on positional magnetic resonance imaging findings

STUDY DESIGN

We present the positional magnetic resonance imaging findings of a prospective case series of patients undergoing surgery with the Dynesys spinal stabilization device (Zimmer, Inc., Warsaw, IN).

OBJECTIVE

To explore the biomechanical impact of the Dynesys device in vivo.

SUMMARY OF BACKGROUND DATA

Spinal fusion surgery is widely used for painful degenerative conditions of the lumbar spine that have not responded to conservative measures. It often produces good outcomes but can be associated with adjacent segment hypermobility that may lead to further degeneration and pain. Previous cadaveric biomechanical studies claim that the Dynesys Dynamic Spinal Stabilization System allows some lumbar movement, behaving similar to a normal spine in extension but similar to rigid fixation in flexion.

METHODS

Twenty-four patients with dominant low back pain, with or without leg pain, were treated with the Dynesys. All patients underwent positional magnetic resonance imaging before surgery and 9 months after surgery. Measurements were made to assess the differences at the operated level, adjacent level, and whole lumbar spine.

RESULTS

There was a statistically significant reduction in flexion-extension range of movement of both the whole lumbar spine by 13.37 degrees (P = 0.002) and at the instrumented segments by 4.08 degrees (P < 0.001) following surgery. There was an insignificant reduction in range of movement at the level above instrumentation (P = 0.807). Mean anterior disc height at the instrumented level reduced by 0.7 mm following insertion of the Dynesys (P < 0.027). Mean posterior disc height reduced by 0.3 mm (P = 0.453). In a neutral posture, the Dynesys had no significant impact on lordosis or inclination of operated or adjacent levels. Contrary to cadaveric study findings, the Dynesys appears to restrict extension more than flexion with respect to a neutral posture.

CONCLUSIONS

In vivo, the Dynesys Stabilization System allows movement at the instrumented level, albeit reduced, with no significant increased mobility at the adjacent segments. There was reduction of the anterior disc height without a significant increase of the posterior disc height.

Randomized clinical study to compare the accuracy of navigated and non-navigated thoracic pedicle screws in deformity correction surgeries

STUDY DESIGN

Randomized clinical trial (level I evidence).

OBJECTIVE

To compare the accuracy of non-navigation and Iso-C based navigation in pedicle screw fixation in thoracic spine deformities.

SUMMARY OF BACKGROUND DATA

Thoracic pedicle screw insertion for spinal deformity correction can be associated with increased pedicle breaches. Iso-C based navigation has been reported to improve the accuracy of pedicle screw placement, but its use in the presence of deformity has not been reported.

METHODS

Twenty-seven patients with scoliosis and 6 patients with kyphosis had a total of 478 thoracic pedicle screws. The average Cobb angle was 58.4 degrees +/- 8 degrees (range 50 degrees -80 degrees), and the mean kyphotic angle was 54.6 degrees +/- 4 degrees (range 51 degrees -76 degrees). By random allocation, 17 patients had screw insertion under navigation (242 screws) and 16 under fluoroscopic control (236 screws). The 2 groups were compared for accuracy of screw placement, time for screw insertion, and the number of times the C-arm had to be brought into the field. Two independent blinded observers determined accuracy using postoperative computed tomography assessments.

RESULTS

There were 54 (23%) pedicle breaches in the non-navigation group as compared to only 5 (2%) in the navigation group (P < 0.001). Thirty-eight screws (16%) in the non-navigation group had penetrated the anterior or lateral cortex compared to 2 screws (0.8%) in the navigation group. Average screw insertion time in the non-navigation group was 4.61 +/- 1.05 minutes (range 1.8-6.5) compared to 2.37 +/- 0.72 minutes (range 1.16-4.5) in navigation group (P < 0.01). The C-arm had to be moved into the operation field on an average of 1.5 +/- 0.25 times (range 1-3) per screw. With single screening data, an average of 11.4 pedicles (range 9-14) could be visualized without necessity to bring the C-arm into operating field again.

CONCLUSIONS

Iso-C navigation increases accuracy, and reduces surgical time and radiation in thoracic deformity correction surgeries.

Biomechanical evaluation of a new total posterior-element replacement system

STUDY DESIGN

In vitro study to characterize the flexibility of a new total posterior-element system when instrumented to L4-L5 segments.

OBJECTIVE

The goal of this in vitro study was to investigate whether an optimized version of the TOPS implant (Impliant Ltd., Ramat Poleg, Israel) is capable to restore the physiologic motion characteristic of a spinal segment after facetectomy.

SUMMARY OF BACKGROUND DATA

The TOPS implant is designed to replace the posterior elements of a functional spinal unit, to provide flexible restabilization and spinal alignment, while maintaining the intervertebral disc. The implant is composed of bilateral pedicle screws, connected with 2 crossbars in the transversal plane. The crossbars are joined together by an elastic element capable of transmitting tensile and compressive loads, as well as shear forces.

METHODS

Six human cadaver specimens (L3-S1) (median age 61 years: minimum 47 and maximum 74 years) were used for this in vitro experiment. The specimens were loaded with pure moments of +/-7.5 Nm in flexion/extension, lateral bending, and axial rotation. The following states were investigated: (1) intact; (2) after bilateral laminectomy, including facetectomy of the lower facet joints, of the upper vertebra L4; and (3) after device implantation. The range of motion (ROM), neutral zone, and intradiscal pressure were determined from a third cycle. In a second step, the ROM in axial rotation was determined as a function of different flexion/extension postures.

RESULTS

In the neutral position, the laminectomy and facetectomy increased the median values of the ROM in flexion plus extension, lateral bending right plus left, and significantly in axial rotation left plus right from: 8.2 degrees, 7.6 degrees, 3.6 degrees to 12.1 degrees, 8.5 degrees, and 8.5 degrees (Wilcoxon signed rank test; P < 0.05). After fixation of the implant, the ROM was again reduced to 6.8 degrees, 7.8 degrees, and 3.8 degrees. In a flexed posture, the ROM in axial rotation was slightly increased compared to the neutral position. With increasing extension, the axial rotation decreased linearly from 3.7 degrees in neutral position to 2.3 degrees in 4 degrees extension in the segment L4-L5. The characteristic of the intradiscal pressure versus load with the implant was similar to that of the intact specimen.

CONCLUSION

The TOPS implant almost ideally restored the ROM in lateral bending and axial rotation compared to that of the intact specimen. In the sagittal plane, 85% of the intact ROM could be obtained. The ROM in axial rotation as a function of flexion and extension angle also mimics the biomechanical behavior of the posterior complex of a lumbar spine. This relationship between ROM and posture emphasizes the importance of a proper implantation.

Mid-term and long-term follow-up data after placement of the Graf stabilization system for lumbar degenerative disorders

Object

The Graf pedicle screw and ligament device is designed to provide flexible stabilization to prevent abnormal spinal movement. The purpose of this study was to investigate radiographic and clinical outcomes during a minimal 5-year follow-up period.

Methods

Between 1991 and 1997, 43 consecutive patients (whose mean age was 61 years) with lumbar degenerative disease underwent decompression and stabilization in which the Graf system was placed. Data were available for 31 patients who attended follow up for the minimal 5-year period. In a retrospective review, the authors assessed measurements on radiographs, clinical results (using Japanese Orthopaedic Association [JOA] Scale scores), and low-back pain (using a visual analog scale [VAS] score), preoperatively and postoperatively at 1, 3, 5, and/or 10 years. Radiographic measurements included sagittal and frontal range of motion (ROM), regional lordosis, and posterior disc height as well as the extent of degenerative spondylolisthesis.

Final follow-up JOA and VAS scores were significantly better than preoperative scores. Sagittal and frontal ROM was significantly reduced at 1 and 5 years, respectively, compared with preoperative values, and a gradual reduction persisted throughout the follow-up period. Compared with its preoperative status, the disc height ratio (adjacent segments to the operated level) was reduced 5 years after surgery. A significant inhibition of the vertebral slippage was detected only in the flexion position.

Conclusions

Analysis of these data indicated that the Graf system eventually leads to successful fusion, suggesting the presence of stability in all three dimensions. The use of the Graf system should continue to be evaluated as an alternative device in the treatment of lumbar degenerative disease.

Influence of a dynamic stabilisation system on load bearing of a bridged disc: an in vitro study of intradiscal pressure

In recent years, non-fusion implants to stabilise the lumbar spine have become more and more popular. However, little is known on the load bearing of such dynamic stabilisation systems. In order to investigate the load bearing of discs bridged with rigid and dynamic stabilisation systems, six lumbar cadaver spines were mounted in a spine tester and loaded with pure moments in the three main motion planes. Four different states of the specimens were studied: intact, destabilised, stabilisation with a Dynesys and stabilisation with an internal fixator. Intradiscal pressure (IDP) measurements were used to assess the load bearing of the bridged disc. In the neutral unloaded position, there were small but not significant differences in disc pressure for the four states of the treated disc (P>0.05). Concerning the disc pressure during the course of loading, both the Dynesys and internal fixator did significantly reduce the pressure change from neutral to extension in comparison to the intact state (-0.05, -0.04 and +0.24 MPa, respectively) (P<0.05). Compared to the intact state, there was no significant pressure change from neutral to flexion (0.14, 0.15 and 0.18 MPa, respectively) (P>0.05). The devices apparently eliminated the pressure change from neutral to lateral bending (Dynesys 0.01 MPa, Fixator 0.01 MPa and intact 0.24 MPa), but due to large variations in the intact and defect states the differences were not significant (P>0.05). In axial rotation, the pressure change for the internal fixator was reduced compared to the intact state; however, the change was only significant in left axial rotation (P<0.05). The Dynesys showed no significant differences (P>0.05) in axial rotation. No changes in IDP were seen in the adjacent discs for either the Dynesys or the internal fixator. Our results showed that the IDPs for both devices were similar, but altered compared to the intact disc.

Dynamic stabilization in the surgical management of painful lumbar spinal disorders

STUDY DESIGN

A literature review.

OBJECTIVE

To evaluate the mechanisms of action and effectiveness of posterior dynamic stabilization devices in the management of painful spinal disorders.

SUMMARY OF BACKGROUND DATA

Dynamic stabilization may provide pain relief by altering the transmission of abnormal loads across the degenerated disc space.

METHODS

A Medline search was conducted.

RESULTS

Articles supporting abnormal load transmission across the disc space and clinical reviews of currently available posterior dynamic systems were included.

CONCLUSIONS

Posterior dynamic stabilization systems may provide benefit comparable to fusion techniques, but without the elimination of movement. Further study is required to determine optimal design and clinical indications.

Biomechanics of nonfusion implants

Although spine fusion is a versatile and effective technique in the treatment of spinal disorders, increased stresses on adjacent unfused levels lead to symptomatic adjacent level degeneration in many patients. The goal of nonfusion devices in spine surgery is to ablate or unload painful structures while preserving segmental motion. The intended performance of nonfusion devices such as disc replacement, nucleus pulposus replacement, and posterior stabilization devices can be understood from the biomechanics of the functional spinal unit in health and disease and the interplay between the motion segment and the device. Implant design issues can also markedly affect performance.

Lumbar disc herniation associated with separation of the ring apophysis: is removal of the detached apophyses mandatory to achieve satisfactory results?

There are three questions to be addressed in lumbar disc herniation with separation of the ring apophysis: does this lesion occur only in adolescents, does any trauma predispose this lesion, and is removal of the detached apophyses mandatory to achieve satisfactory results? We prospectively investigated 32 consecutive patients (22 men, 10 women; mean age, 25.4 years; mean followup, 4 years 8 months). This lesion occurred not only in adolescents, but also in adults older than 30 years. Eight patients (25%) were younger than 20 years, whereas 14 patients (43.8%) were in the third decade, and 10 (31.2%) were in the fourth decade. Only five patients (15.6%) had antecedent traumatic episodes. Resection of the fragment did not influence the clinical results. Excision of the herniated disc and mobile bony fragment was done in 11 patients (34.4%). Discectomy alone was done in 21 patients (65.6%) with immobile bony fragments. Satisfactory results were obtained in both groups. Lumbar disc herniation with detachment of the ring apophysis can occur, without any relationship to trauma, in adults and adolescents. Removal of the bony fragment is not always needed to achieve satisfactory results.

Correlation between inter-vertebral disc morphology and the results in patients undergoing Graf ligament stabilisation

BACKGROUND

Previous studies have shown Graf ligament stabilisation procedure to give mixed results in the short to medium term. The aim of this study was to correlate the pre-operative state of the disc, multifidus muscles, age of the patient, levels operated and the clinical outcome after a mean follow-up of 47 months.

METHODS

Graf ligament stabilisation procedure was carried out in 38 patients between 1996 and 1999. Their post-operative status was assessed using MacNab criteria. The post-operative follow-up was by postal questionnaires and review of the clinical notes. Disc morphology and multifidus muscle wasting was graded blindly and independently. The intra- and interobserver reliability was measured with kappa score and classified using the kappa classification of Landis and Koch. Correlation was measured with the help of Spearman correlation coefficient.

RESULTS

Thirty-eight patients (100%) returned the questionnaires. Mean follow-up time was 47.55 months. Fifty-nine levels were operated on. Mean age was 39.68 years. The overall re-operation rate was 15.8%. The intra- and interobserver reliability was graded as good to substantial. Twenty-two patients (57.89%) were satisfied with the procedure. There was no statistically significant correlation between disc morphology, multifidus muscle wasting, sex, age, number of levels operated, the levels operated, and the satisfaction rate.

CONCLUSIONS

The indications of Graf ligament stabilisation procedure are not clear. Further work is necessary to clearly identify the indication for the procedure.

Dynamic stabilization devices in the treatment of low back pain

Soft stabilization has an important role in the treatment of the degenerative lumbar spine. Fusion of one or two motion segments may not make a big difference in the total range of motion of the lumbar spine, but preserving flexibility of a motion segment may prevent adjacent segment disease and may permit disc replacement, even when facet joints need to be excised. If a favorable environment is created in the motion segment by unloading the disc and permitting near normal motion, the disc may be able to repair itself or may supplement the reparative potential of gene therapy. Although soft stabilization seems promising, one should take a cautious approach to any new implant system. An implant for fusion only has to serve a temporary stabilization until fusion has taken place; on the other hand, a soft stabilization system has to provide stability throughout its life. Implant loosening following fusion surgery is common in the presence of pseudarthrosis. After soft stabilization, the implant has to stay anchored to the bone despite allowing movement. This sounds like a daunting task. The flexibility of the implant system, however, should be able to protect it from loosening at the anchor point into the bone. Finally, the soft stabilization system is intended to load-share with the disc and the facet joint only partially and unloads the motion segment. Any mismatch between the kinematics of the implant system and the motion segment, in particular any discrepancy between their IAR, would result in the implant bearing unexpected load at certain ranges of motion. If that happens, it would guarantee an early implant failure or loosening. The need for strict bench testing in the laboratory, therefore, cannot be over-emphasized. The few soft stabilization systems that have had clinical applications so far have produced a clinical outcome comparable to that of fusion. No prospective randomized controlled trial has been reported yet, which is an essential requirement for practice of evidence-based medicine.

Dynamic stabilization of the lumbar spine and its effects on adjacent segments: an in vitro experiment

In recent years, nonfusion stabilization of the lumbar spine has gained more and more popularity. These nonfusion systems intend to maintain or restore the intersegmental motions to magnitudes of the intact spine and have no negative effects on the segments adjacent to the stabilized one. This study investigated the DYNESYS, a dynamic nonfusion system, which is designed to stabilize the bridged segments while maintaining the disc and the facet joints. To determine the magnitude of stabilization and the effect of the stabilization on the adjacent segment, six lumbar cadaver spines were fixed in a spine tester and loaded with pure moments in the three main motion planes. For each spine, four different stages were tested: intact, defect of the middle segment, fixation with the DYNESYS, and fixation with the internal fixator. Intersegmental motions were measured at all levels. For the bridged segment, the DYNESYS stabilized the spine and was more flexible than the internal fixator. This difference between the internal fixator and the DYNESYS was most pronounced in extension (P < 0.05), with the DYNESYS restoring the motion back to the level of the intact spine. The motion in the adjacent segments was not influenced by either stabilization method. Our results suggest that the DYNESYS provides substantial stability in case of degenerative spinal pathologies and can therefore be considered as an alternative method to fusion surgery in these indications while the motion segment is preserved.

Outcome of the Graf ligamentoplasty procedure compared with anterior lumbar interbody fusion with the Hartshill horseshoe cage

The objective of our study was to assess the efficacy of Graf ligamentoplasty in comparison with rigid fixation and fusion with the Hartshill horseshoe cage for similar severity of disc degeneration. Although studies have been done on the Graf ligamentoplasty procedure and the Hartshill horseshoe cage, their efficacy has never been compared in any study. This study was done to decide whether retaining mobility and stabilizing the spine is best or stiffening the lumbar segment by fusion is preferable. Between 1995 and 1997, a prospective randomized study was performed comparing Graf ligament stabilization and anterior lumbar interbody fusion. Twenty-eight patients had single-level Graf ligaments inserted and 27 patients had single-level anterior lumbar interbody fusion (ALIF) with a Hartshill horseshoe cage and tricortical iliac crest autograft. The two groups were similar in age, sex, symptoms, severity of the disc degeneration, and duration of follow-up. The chi-square test and t-test were used to evaluate the outcome. At a minimum follow-up of 2.1 years, we found that 93% of patients who had undergone Graf ligamentoplasty had a satisfactory outcome (rated "excellent" or "better") compared to 77.8% of patients who had been treated with ALIF with Hartshill horseshoe cage stabilization and fusion, when measured on the Oswestry Disability Index ( P<0.05). Retaining mobility in the lumbar segments gives better results after stabilisation with Graf ligaments than rigid fixation and fusion with the Hartshill horseshoe cage in the short term. We will be watching this cohort of patients over the next few years.

Effect of surgical treatment on physical activity and bone resorption in patients with neurogenic intermittent claudication

The effect of surgical treatment on physical activity and bone resorption was examined in patients with neurogenic intermittent claudication. Nineteen patients, 50-77 years of age, with neurogenic intermittent claudication (mean, 162 m; range, 20-400 m) caused by degenerative lumbar disease were included in the study. Decompressive laminectomy alone was performed for 7 patients with lumbar spinal stenosis (LSS) and 5 patients with degenerative lumbar spondylolisthesis (DLSL), and decompressive laminectomy, with a Graf stabilization system, was performed for 7 patients with DLSL associated with flexion instability. Clinical symptoms and levels of urinary cross-linked N-telopeptides of type I collagen (NTx) were assessed before and 12 months after surgery. Subjective symptoms, including low back pain, leg pain and/or tingling, and gait disturbance, as well as restriction of activities of daily living were significantly alleviated by the surgical treatment, resulting in an increase in physical activity. Urinary NTx levels were significantly decreased by the surgical treatment, from 63.1 +/- 16.9 (mean +/- SD) nmol BCE/mmol Cr to 52.1 +/-11.2 nmol BCE/mmol Cr (P < 0.05). These findings suggest that surgical treatment appears to alleviate the clinical symptoms and increase physical activity in patients with LSS or DLSL, potentially resulting in the suppression of bone resorption. Surgical treatment may contribute to the prevention of physical inactivity-induced osteoporosis in elderly patients with neurogenic intermittent claudication caused by degenerative lumbar disease.

Adjacent-segment morbidity after Graf ligamentoplasty compared with posterolateral lumbar fusion

OBJECT

Of concern to spine surgeons are accelerated degenerative changes of motion segments located above and below where spinal fusion has been performed. Graf artificial ligament stabilization has been developed to avoid the adverse effect of spinal fusion. The object of this study was to assess the adjacent-segment morbidity of Graf ligamentoplasty compared with posterolateral fusion (PF) in which instrumentation was used.

METHODS

Data obtained in 45 patients who underwent L4-5 Graf ligamentoplasty (18 patients) or PF with instrumentation (27 patients) were reviewed retrospectively. The minimum follow-up period was 5 years. In the PF group a solid fusion rate of 92.6% was achieved. Radiographic evaluation included assessment of lumbar sagittal alignment, range of motion (ROM), and adjacent-disc degeneration. Adjacent-segment morbidity was clinically assessed by determining the reoperation rate. Graf ligamentoplasty maintained regional lordosis and flexibility (13 degrees in L4-5 lordosis; 4.4 degrees in L4-5 ROM). Although there was no difference in preoperative adjacent-disc condition between the two groups, radiographic evidence of adjacent-disc deterioration was observed more frequently in patients in the PF group than the Graf group (25% and 6% at L1-2; 38% and 6% at L2-3; 38% and 18% at L3-4; and 43% and 18% at L5-sacrum, respectively). One case in the Graf group (5.6%) and five cases in the PF group (18.5%) required additional surgeries for adjacent-segment lesions.

CONCLUSIONS

Graf ligamentoplasty cannot completely replace spinal fusion. In a well-selected group of patients, however, it was shown to maintain lumbar mobility and sagittal alignment, and it decreased the risk of adjacent-segment deterioration compared with PF with instrumentation.