Dynamic Neutralization System Research Articles

The Effect of Unintended Facet Arthrodesis on the Treatment Outcome of Dynamic Neutralization System for Lumbar Degenerative Diseases.

This study aimed to examine the influence of unintended facet arthrodesis on the therapeutic effectiveness of the dynamic neutralization system (Dynesys). This retrospective study enrolled consecutive patients who underwent posterior decompression and dynamic stabilization for lumbar spondylosis or spinal stenosis. Follow-up assessments included lumbar radiography, lumbar vertebral computerized tomography (CT), visual analog scale (VAS), and Oswestry disability index (ODI). Patients were classified into the facet fusion and non-fusion groups. The differences in the VAS scores for back pain and leg pain, ODI, intervertebral range of motion (ROM) at the surgical segments, and upper adjacent segments were assessed before and after treatment. A total of 49 patients (29 males and 20 females) aged 31-65years were enrolled and followed-up for over 40months. Among the patients, 16 (32.7%) experienced unintended facet arthrodesis and were assigned to the fusion group, whereas the remaining patients were assigned to the non-fusion group. There was a significant increase in the incidence of facet arthrodesis in the surgical segments over time post-surgery (χ2 = 6.2, p < 0.05). The ROM of the surgical and upper adjacent segments, VAS scores for back pain and leg pain, and ODI were all significantly different before and after the operation (p < 0.05), but not between the fusion and non-fusion groups (p > 0.05). Although unintended facet arthrodesis is common after Dynesys procedure, the presence of facet arthrodesis does not significantly affect the efficacy of Dynesys in treating lumbar degenerative diseases.

Evaluation of outcomes of discectomy with a dynamic neutralization system in treatment of lumbar disk herniation

ObjectiveThe study aimed to explore the clinical outcomes of discectomy with dynamic neutralization system (Dynesys) for single-segmental lumbar disk herniation (LDH) versus simple discectomy. MethodsThe eligible patients with single-segmental LDH were randomly divided into the discectomy with Dynesys group (group A) and the simple discectomy group (group B). The Oswestry disability index (ODI), visual analog score (VAS), radiological results of intervertebral height and range of motion (ROM) of the treated segment were evaluated pre- and post-operatively in both groups. Operation duration and blood loss were recorded. Complications, reoperation, and mortality were also assessed. All patients received a 2-year follow-up. Results123 (96.1%) participants completed the follow-up. The operation duration and blood loss of group B were significantly lower than those of group A (p<0.05). After operation, ODI and VAS were improved significantly in both groups, and there was no significant difference between the two groups immediately after surgery. But a rising trend was found in ODI and VAS of group B, especially after the 1-year follow-up (p<0.05). X-rays showed a continuing loss of intervertebral height of the treated segment in group B, while it was preserved in group A (p<0.05). ROM of the treated segment was also maintained stable in group A. ConclusionDiscectomy with Dynesys is safe and effective for LDH treatment.

Evaluation of outcomes of discectomy with a dynamic neutralization system in treatment of lumbar disk herniation

ObjectiveThe study aimed to explore the clinical outcomes of discectomy with dynamic neutralization system (Dynesys) for single-segmental lumbar disk herniation (LDH) versus simple discectomy. MethodsThe eligible patients with single-segmental LDH were randomly divided into the discectomy with Dynesys group (group A) and the simple discectomy group (group B). The Oswestry disability index (ODI), visual analog score (VAS), radiological results of intervertebral height and range of motion (ROM) of the treated segment were evaluated pre- and post-operatively in both groups. Operation duration and blood loss were recorded. Complications, reoperation, and mortality were also assessed. All patients received a 2-year follow-up. Results123 (96.1%) participants completed the follow-up. The operation duration and blood loss of group B were significantly lower than those of group A (p<0.05). After operation, ODI and VAS were improved significantly in both groups, and there was no significant difference between the two groups immediately after surgery. But a rising trend was found in ODI and VAS of group B, especially after the 1-year follow-up (p<0.05). X-rays showed a continuing loss of intervertebral height of the treated segment in group B, while it was preserved in group A (p<0.05). ROM of the treated segment was also maintained stable in group A. ConclusionDiscectomy with Dynesys is safe and effective for LDH treatment.

Short-term effects of minimally invasive dynamic neutralization system for the treatment of lumbar spinal stenosis: An observational study.

The aim of the study was to evaluate the safety and short-term effects of dynamic stabilization via minimally invasive system for degenerative lumbar spinal stenosis. Patients with degenerative lumbar spinal stenosis and treated with Transforaminal Lumbar Interbody Fusion via minimally invasive minimally system (mis-TLIF) were served as the control group.From April 2011 to March 2015, 47 patients (29 male, 18 female; mean age 47.6 [range, 26–52] years) with lumbar spinal stenosis were treated with decompression and excision of herniated disk via the minimally invasive system combined with the dynamic fixation technique, and 42 patients as control group with mis-TLIF. Minimally invasive surgeries were performed via the posterior incision approach. The clinical outcomes were evaluated by comparing the Visual Analog Scale (VAS) score, Oswestry Disability Index (ODI) scores, and the ROMs of the adjacent segment before and after surgery. The postoperative complications related to the implants were identified.A total of 83 patients (43 of Dynesys group and 40 of mis-TLIF group) were followed for an average duration of >35 months. Dynesys stabilization resulted in significantly higher preservation of motion at the index level (P < .05), and significantly less hypermobility at the adjacent segments. VAS for the back and leg pain and ODI improved significantly (P < .05) in 2 groups; however, there is no significant difference between the groups. In Dynesys group, 3 cases suffered skin flay necrosis, 1 of them had a wound infection that was treated with washing and drainage combined with antibiotic therapy. Skin flay necrosis were also observed in 2 cases of mis-TLIF group. Reoperation was performed in one case of Dynesys group for rupture of the internal fixation. No rupture of internal fixation was observed in mis-TLIF group.The nonfusion fixation system Dynesys may be used to treat degenerative spinal stenosis without posterior element damage. This surgical technique is safe and effective. However, utilizing higher preservation of motion may lead to the failure of internal fixation.

Clinical experiences of dynamic stabilizers: Dynesys and Dynesys top loading system for lumbar spine degenerative disease

Dynesys (Dynamic Neutralization System) was designed to overcome the shortcomings of fusion. The Dynesys top loading (DTL) system is a new alternative Dynesys system that can be applied via a minimally invasive procedure. This study aimed to ascertain whether DTL is a suitable device for motion preservation and prevention of instability, and to compare the clinical and radiological outcomes between DTL and Dynesys. In this study, 12 patients were treated with Dynesys and 21 patients were treated with DTL. Back and leg pain were evaluated using the visual analog scale. The Oswestry Disability Index was used to evaluate the patients' function. Range of motion (ROM) at the operative level and for the whole lumbar spine was measured pre- and postoperatively. The length of wound, blood loss, length of hospital stay, and operation duration were also compared. All patients were followed up for 12–76 months. Scores on the visual analog scale and Oswestry Disability Index were significantly improved postoperatively. The median ROM of the whole spine and index level ROM in all patients showed 12.5% and 79.6% loss, respectively. The DTL group exhibited significantly better results in terms of blood loss, wound length, and operation duration, in addition to early ambulation. In conclusion, Dynesys and DTL are semirigid fixation systems that can significantly improve clinical symptoms and signs. Our results suggested that DTL was better than Dynesys as a result of it being a minimally invasive procedure. However, further study with large sample sizes and longer follow-up durations is required to validate the effects of these dynamic stabilizers.

Short-term effects of a dynamic neutralization system (Dynesys) for multi-segmental lumbar disc herniation

To determine the safety and short-term curative effects of internal fixation using a dynamic neutralization system (Dynesys) for multi-segmental lumbar disc herniation (ms-LDH) with the control group treated by posterior lumbar interbody fusion (PLIF). Forty-five patients with ms-LDH were selected as study group treated with Dynesys and 40 patients as control group with PLIF. The surgical efficacy was evaluated by comparing the visual analogue scale (VAS) scores, the Oswestry Disability Index (ODI) scores and the ROMs of the adjacent segment before and after surgery. The postoperative complications related to the implants were identified. All patients were followed up for an average duration of over 30months. Dynesys stabilization resulted in significantly higher preservation of motion at the index level (p<0.001), and significantly less (p<0.05) hypermobility at the adjacent segments. VAS for back and leg pain and ODI improved significantly (p<0.05) with both the methods, but there was no significant difference between the groups. The non-fusion fixation system Dynesys is safe and effective regarding short-term curative effects for the treatment of ms-LDH.

Short term outcome of posterior dynamic stabilization system in degenerative lumbar diseases.

Background:Decompression and fusion is considered as the ‘gold standard’ for the treatment of degenerative lumbar diseases, however, many disadvantages have been reported in several studies, recently like donor site pain, pseudoarthrosis, nonunion, screw loosening, instrumentation failure, infection, adjacent segment disease (ASDis) and degeneration. Dynamic neutralization system (Dynesys) avoids many of these disadvantages. This system is made up of pedicle screws, polyethylene terephthalate cords, and polycarbonate urethane spacers to stabilize the functional spinal unit and preserve the adjacent motion after surgeries. This was a retrospective cohort study to compare the effect of Dynesys for treating degenerative lumbar diseases with posterior lumbar interbody fusion (PLIF) based on short term followup.Materials and Methods:Seventy five consecutive patients of lumbar degenerative disease operated between October 2010 and November 2012 were studied with a minimum followup of 2 years. Patients were divided into two groups according to the different surgeries. 30 patients underwent decompression and implantation of Dynesys in two levels (n = 29) or three levels (n = 1) and 45 patients underwent PLIF in two levels (n = 39) or three levels (n = 6). Clinical and radiographic outcomes between two groups were reviewed.Results:Thirty patients (male:17, female:13) with a mean age of 55.96 ± 7.68 years were included in Dynesys group and the PLIF group included 45 patients (male:21, female:24) with a mean age of 54.69 ± 3.26 years. The average followup in Dynesys group and PLIF group was 2.22 ± 0.43 year (range 2-3.5 year) and 2.17 ± 0.76 year (range 2-3 year), respectively. Dynesys group showed a shorter operation time (141.06 ± 11.36 min vs. 176.98 ± 6.72 min, P < 0.001) and less intraoperative blood loss (386.76 ± 19.44 ml vs. 430.11 ± 24.72 ml, P < 0.001). For Dynesys group, visual analogue scale (VAS) for back and leg pain improved from 6.87 ± 0.80 to 2.92 ± 0.18 and 6.99 ± 0.81 to 3.25 ± 0.37, (both P < 0.001) and for PLIF, VAS for back and leg pain also improved significantly (6.97 ± 0.84–3.19 ± 0.19 and 7.26 ± 0.76–3.56 ± 0.38, both P < 0.001). Significant improvement was found at final followup in both groups in Oswestry disability index (ODI) score (both P < 0.001). Besides, Dynesys group showed a greater improvement in ODI and VAS back and leg pain scores compared with the PLIF group (P < 0.001, P = 0.009 and P = 0.031, respectively). For radiological, height of the operated level was found increased in both groups (both P < 0.001), but there was no difference between two groups (P = 0.93). For range of motion (ROM) of operated level, significant decrease was found in both groups (P < 0.001), but Dynesys showed a higher preservation of motion at the operative levels (P < 0.001). However, no significant difference was found in the percentage change of ROM of adjacent levels between Dynesys and PLIF (0.74 ± 8.92% vs. 0.92 ± 4.52%, P = 0.91). Some patients suffered from degeneration of adjacent intervertebral disc at final followup, but there was no significant difference in adjacent intervertebral disc degeneration between two groups (P = 0.71). Moreover, there were no differences in complications between Dynesys and PLIF (P = 0.90), although the incidence of complication in Dynesys was lower than PLIF (16.67% vs. 17.78%).Conclusion:Dynamic stabilization system treating lumbar degenerative disease showed clinical benefits with motion preservation of the operated segments, but does not have the significant advantage on motion preservation at adjacent segments, to avoid the degeneration of adjacent intervertebral disk.

Continuous clinical observation of the Dynesys dynamic neutralization system for degenerative lumbar spine diseases

Objective To evaluate the clinical indications and outcomes of dynesys neutralization system in the treatment of degenerative lumbar diseases.Methods From January 2007 to December 2011,102 consecutive patients with degenerative lumbar spine diseases underwent posterior decompression and internal fixation with the Dynesys dynamic neutralization system.Among them,69 patients were followed up,including 39 males and 30 females,aged from 30 to 62 years (average,44 years).The series of cases were composed of 24 cases of lumber disc herniation,35 cases of degenerative spinal stenosis,10 cases of degenerative changes of lumbar discs.Results The mean follow-up period was 35 months (range,6-44 months).The visual analogue scale (VAS) score decreased from preoperative 8.6 (range,6-9) to postoperative 2.8 (range,0-5),and the Oswestry disability index (ODI) improved from preoperative 73％ (range,30％-91％) to postoperative 30％ (range,0-61％).There were no implant failure or infection.According to the evaluation criteria of surgical treatment for low back pain,which was established by the Chinese Orthopaedic Association,the result was excellent in 53 patients,good in 12 patients,fair in 4 patients and poor in 1 patient.Conclusion The Dynesys dynamic neutralization system is effective in the treatment of degenerative lumbar spine disease,which can reserve the range of motion of stabilized segments,prevent degeneration of adjacent segments and improve clinical outcomes. Key words: Lumbar vertebrae; Internal fixators; Treatment outcome

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.

Effect of Spacer Diameter of the Dynesys Dynamic Stabilization System on the Biomechanics of the Lumbar Spine

A finite element analysis to simulate the behavior of lumbar spines implanted with a posterior dynamic neutralization system, Dynesys, under displacement-controlled loading. To investigate whether Dynesys spacers with different diameters would alter the distribution of range of motion, disk stress, and facet contact force at the Dynesys bridging level and the cranial adjacent level. The Dynesys system is designed to preserve intersegmental motion and reduce loading at adjacent levels, but clinical reports do not support these claims. This system has been shown to be almost as stiff as rigid fixation, which acts to hinder intersegmental motion. Few studies have investigated methods of reducing this stiffness. In the finite element study, a previously validated lumbar spine model was used. Five Dynesys constructs with different spacer diameters (0.8, 0.9, 1.0, 1.1, and 1.2 times the original standard size) were implanted into the spine model and bore 4 displacement-controlled loading cases: flexion, extension, torsion, and lateral bending. Resultant range of motions (ROMs), disk stress, and facet contact forces at the bridged level and the cranial adjacent level were compared with the results of a spine model without Dynesys implantation. The results of ROMs, disk stress, and facet contact forces at the bridged levels were all less than those in the intact spine, except for contact forces at the left facet under lateral bending, facet contact forces at the right facet under torsion, and disk stress under torsion. The results of ROMs, disk stress, and facet contact forces at the cranial adjacent levels were all higher than those in the intact spine. The results of the present study show that changing the diameter of the spacers will alter the stiffness of the Dynesys construct. Dynesys constructs with larger diameters behave stiffer under flexion but behave softer under extension, torsion, and lateral bending. Changing the diameter of the Dynesys spacers does not significantly influence the load distribution at adjacent levels.

Late infections after dynamic stabilization of the lumbar spine with Dynesys

Dynamic stabilization of the spine was developed as an alternative to rigid fusion in chronic back pain to reduce the risk of adjacent segment degeneration. Dynamic neutralization system (Dynesys, Zimmer CH) is one of the most popular systems available, but some midterm studies show revision rates as high as 30 %. Some late infectious complications in our patients prompted us to review them systematically. Propionibacterium recently has been shown to cause subtle infections of prosthetic material. Here, we report on a consecutive series of 50 Dynesys implants. In a median follow-up of 51 months (range 0-91), we identified 12 infectious and 11 non-infectious complications necessitating reoperation or removal of the implant in 17 patients. Material infections occurred after a median of 52 months (2-77) and were due to Propionibacterium alone (n = 4) or in combination (n = 3) in seven out of 11 patients. Clinical presentation combines new or increasing pain associated with signs of screw loosening on conventional X-rays; however, as many as 73.5 % of patients present some degree of screw loosening without being at all symptomatic of infection. The high rate of late infections with low-grade germs and the frequency of screw loosening signs made us suspect a lack of integration at the bone-screw interface. Surgeons should be suspicious if the patient presents a combination of new or increasing pain and signs of screw loosening, and aggressive revision is recommended in these cases.

Mid-term evaluation of the effects of dynamic neutralization system on lumbar intervertebral discs using quantitative molecular MR imaging

To evaluate the mid-term effects of implant of dynamic neutralization system (Dynesys) on disc tissue in patients with lumbar discopathy, through the quantification of glycosaminoglycans (GAG) concentration, both in treated and adjacent levels, by analysis of delayed gadolinium-enhanced MRI contrast (dGEMRIC) images. Ten patients with low back pain underwent the dGEMRIC diagnostic protocol before, 6-months and after 2 years from surgery. Each patient was also evaluated with visual analog (VAS), Oswestry, and Prolo scales both at presurgery and during follow-up. From dGEMRIC images, a ΔT1 parametric map was obtained for each disc, as quantitative indicator of its GAG concentration, and divided in 13 sectors, which were classified at presurgery as normal or abnormal, based on a 70-ms threshold. Evolution of ΔT1 was studied during the follow-up. Nine of ten patients completed the follow-up. VAS, Oswestry, and Prolo grades showed an improvement. This was accompanied by a reduction of ΔT1 in abnormal segments while normal segments showed a pattern of initial worsening at 6 months, followed by an improvement after 2 years. Our study confirmed the improvement in clinical evaluation, and for the first time related this to the changes in discs GAG concentration.

Short‐term clinical observation of the Dynesys neutralization system for the treatment of degenerative disease of the lumbar vertebrae

To explore the safety and short-term efficacy of the posterior approach of the Dynesys dynamic neutralization system for degenerative disease of the lumbar vertebrae. From March 2008 to March 2010, 32 cases of degenerative lumbar vertebral disease, 19 men and 13 women, (mean age 58 ± 5.2, range, 43-78 years), were treated with posterior laminectomy and Dynesys internal fixation. All patients had a history of over 3 months waist or leg pain that had not been relieved by conservative treatment. There were 10 cases of single lumbar intervertebral disc protrusion, 14 of degenerative lumbar spinal stenosis, 5 of degenerative lumbar isthmic spondylolisthesis, and 3 of recurrent lumbar disc protrusion after surgery. A visual analogue score (VAS) was used for pain assessment, and the Oswestry disability index (ODI) for functional evaluation of clinical outcomes. All patients were followed up for 6-23 months (mean, 16.4 ± 5.5 months). Forty-one segments in 32 patients were stabilized; 23 cases (71.9%) underwent single-segmental stabilization, and 9 (28.1%) two-segmental stabilization. VAS of leg pain, root and low back pain was significantly improved postoperatively. The ODI improved from preoperative 69% ± 12.6% to postoperative 28% ± 15.7% (P < 0.001). On the stabilized segment and adjacent segments above and below, the range of movement showed no statistical difference; no loosening of screws, cord and polyester spacer occurred. The Dynesys dynamic neutralization system combined with decompression can achieve satisfactory short-term clinical results in lumbar degenerative disease. This procedure system not only reduces back and leg pain, but also preserves the mobility of fixed segments, minimizes tissue injury and avoids taking bone for spinal fusion.

Dynamische dorsale Stabilisierung mithilfe des Pedikelschrauben-Systems DYNESYS®

The dynamic neutralization system for the spine (DYNESYS®) is a pedicle screw based system intending mobile restabilization substituting physiological tissue restraints and thus approximating the unstable motion pattern to a normal pattern. It consists of titanium alloy screws, connected by an elastic synthetic compound (PET band and PCU spacer) controlling motion in any plane. DYNESYS® can be used for mono- or multilevel stabilizations in the lumbar spine. DYNESYS® is indicated in the treatment of degenerative disease of the lumbar motion segment with instability and most often in combination with functional or structural spinal canal stenosis. Primary and secondary bone tumors of the spine. Spinal fractures. Infections. Lytic/isthmic spondylolisthesis. Degenerative spondylolisthesis > I°-II°. Facetectomy. Stabilization of thoracic and cervical spine. Allergies to components of DYNESYS®. Pregnancy. Standard midline approach. Decompression of the segment by laminotomy if indicated. Place the screws lateral to the facet joints. Measure the distance between the screw heads. Cut the spacers. Introduce spacer and cord on both sides. The length of the PCU spacer is determined by the distance of the pedicle screws and depends on the pathology of the lumbar motion segment. Tighten set screws under correct compression of the system. Mobilisation at the first day after surgery. No bracing necessary if there is no doubt about primary fixation of the screws. Physical strenuous work not earlier than 8 weeks postoperatively. DYNESYS® is a reliable dynamic stabilization system with good clinical results if used in correct indications.

Dynamic simulation of universal spacer in Dynesys dynamic stabilization system for human vertebra

The aim of this study is to analyze the simulated behavior of universal spacer in Dynesys dynamic stabilization system inserted in human vertebra. Dynesys, so-called “Dynamic neutralization system for the spine”, dynamic stabilization system is a new concept in the surgical treatment of lower back pain recently. Universal spacer used as flexible material is to stabilize the spine and the material property of universal spacer is polycarbonate urethane. Universal spacer may apply different kinematic behaviors at implanted level in vertebra. Spinal range of motion(SROM) of inter-vertebra with installed Dynesys dynamic stabilization system was studied using Adams+LifeMOD as simulation software package. The vertebra model was set up to closely resemble the in-vivo conditions. Inter-vertebra rotations were measured by post processor of Adams and compared with the intact values. SROMs of the flexion, extension, lateral bending, and axial rotation of human virtual models were measured, where three spinal fixation systems such as rigid system, Dynesys system, and fused system were installed. As a result, the value of SROM is decreased in flexion-extension and lateral bending when the spinal fixation system is implanted. The movement of Dynesys system is similar to that of intact model by allowing the movement of lumbar. This means that the Dynesys system is proved to be safe and effective in the treatment of unstable spinal condition.

Stabilization of the Lumbar Spine Using the Dynamic Neutralization System

The records of 68 patients (42 men and 26 women) who underwent 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 and/or 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. Within a 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.

Clinical outcomes of the Dynesys dynamic neutralization system: 1-year preliminary results

In this study the authors present the preliminary clinical outcomes of dynamic stabilization with the Dynesys spinal system as part of a multicenter randomized prospective Food and Drug Administration (FDA) investigational device exemption (IDE) clinical trial. This study included 101 patients from six IDE sites (no participants were omitted from the analysis) who underwent dynamic stabilization of the lumbar spine with the Dynesys construct. Patient participation was based on the presence of degenerative spondylolisthesis or retrolisthesis (Grade I), lateral or central spinal stenosis, and their physician's determination that the patient required decompression and instrumented fusion for one or two contiguous spinal levels between L-1 and S-1. Participants were evaluated preoperatively, postoperatively at 3 weeks, and then at 3-, 6-, and 12-month intervals. The 100-mm visual analog scale was used to score both lower-limb and back pain. Patient functioning was evaluated using the Oswestry Disability Index (ODI), and the participants' general health was assessed using the Short Form-12 questionnaire. Overall patient satisfaction was also reported. One hundred one patients (53 women and 48 men) with a mean age of 56.3 years (range 27-79 years) were included. The mean pain and function scores improved significantly from the baseline to 12-month follow-up evaluation, as follows: leg pain improved from 80.3 to 25.5, back pain from 54 to 29.4, and ODI score from 55.6 to 26.3%. The early clinical outcomes of treatment with Dynesys are promising, with lessening of pain and disability found at follow-up review. Dynesys may be preferable to fusion for surgical treatment of degenerative spondylolisthesis and stenosis because it decreases back and leg pain while avoiding the relatively greater tissue destruction and the morbidity of donor site problems encountered in fusion. However, long-term follow-up care is still recommended.

P32. Dynamic Spinal Stabilization: An Alternative to Spinal Fusion? A Report on Positional MRI Findings at 2 Years

BACKGROUND CONTEXT: The Dynamic Neutralization System (Dynesys) is a semirigid spinal stabilization device that uses transpedicular screws linked by cords and spacers.

Conséquences défavorables sur l’équilibre sagittal du rachis du système de neutralisation dynamique

Purpose of the study The dynamic neutralization system (Dynesis™) has been proposed for the treatment of symptomatic lumbar discopathy. This system preserves the mobility of the instrumented vertebral segment and restores discal height by posterior distraction on pedicular screws, stabilization being ensured by compression on a spacer. The potential kyphosing effect of this system and the impact on sagittal morphology of the spine were analyzed. Material and methods Twenty-six patients were studied. Lateral x-rays of the lumbar spine in the upright position were obtained before and after the surgical procedure and at mean 9.5 ± 3.3 months follow- up.Comparisons were made between the pre- and postoperative presentation with measurement of the pelvic and spinal sagittal parameters described by Duval-Beaupère: inclination of the pelvic segement on the sacrum, lordosis, and disc wedge angles at each level (particularly the instrumented levels). Sagittal morphology was assessed pre- and postoperatively. Results Mean kyphosing effect was 6 ± 1.4°, induced by the posterior distraction system. This accentuated the initial lumbar hypolordosis related to the degenerative disease. Comparison of the pre- and postoperative films revealed four types of sagittal reaction of the lumbopelvic segment: no modification (type A), significant loss of lordosis without change at the pelvis level (type B) or with compensatory pelvic retroversion (type C), accentuation of the lordosis with pelvic anteversion (type D). Conclusion The dynamic neutralization system (Dynesis™) can stabilize degenerative discopathy and protect the adjacent levels. Posterior distraction perturbs the initial hypokyphosis and can lead to pelvic compensation to achieve better dynamic balance. This loss of lordosis is however a cause of excessive mechanical stress on the lumbar structures and can lead to long-term degradation. Future developments of this dynamic system should take into account the essential factor of sagittal balance.

Clinical Experience With the Dynesys Semirigid Fixation System for the Lumbar Spine

Retrospective study on a consecutive series of patients. To examine patient-oriented outcome after Dynesys implantation. The dynamic neutralization system for the spine, Dynesys, is a nonfusion pedicle screw stabilization system, which was developed in an attempt to overcome the inherent disadvantages of rigid instrumentation and fusion. Although the system has been in clinical use for more than 5 years, no studies from disinterested research groups have reported on patient-oriented outcome after surgery with Dynesys. A total of 50 consecutive patients instrumented with Dynesys over the preceding 40 months were invited to complete a postal, patient-oriented follow-up questionnaire. The data from 31 of 31 of these, with at least 2 years' follow-up, were analyzed (mean age, 50 years; SD, 13 years; 20 women, 11 men). The primary indication for surgery was degenerative disease (disc/stenosis) with associated "instability"; 11 of 31 (35%) patients had had prior spinal surgery. In 32% cases, 1 level was instrumented, in 52% 2 levels, 13% 3 levels, and 3% 4 levels. Thirteen of 31 (42%) patients underwent additional decompression. Within the 2-year follow-up period, 6 of 31 (19%) patients had required or were scheduled for a further surgical intervention. At follow-up, mean (SD) back and leg pain (0-10 VAS) were 4.7 (3.2) and 3.8 (3.6), respectively. The following global outcomes were reported: back symptoms, 67% improved, 30% same, 3% worse; leg symptoms, 64% improved, 21% same, 14% worse; ability to do physical activities/sports, 40% improved, 33% same, 27% worse; quality of life, 50% improved, 37% same, 13% worse; how much the operation helped, 29% helped a lot, 23% helped, 10% only helped a little, 35% didn't help, 3% made things worse. The results of the present study indicate that both back and leg pain are, on average, still moderately high 2 years after instrumentation with the Dynesys system. Only half of the patients declared that the operation had helped and had improved their overall quality of life; less than half reported improvements in functional capacity. The reoperation rate after Dynesys was relatively high. The results provide no support for the notion that semirigid fixation of the lumbar spine results in better patient-oriented outcomes than those typical of fusion.