Molecular MR imaging for the evaluation of the effect of dynamic stabilization on lumbar intervertebral discs. Eur Spine J. 2009;18 Suppl 1:40-48. [PMID: 19396475 DOI: 10.1007/s00586-009-0996-7]

Promoting Regeneration in Degenerative Disc Disease

OBJECTIVE

The degenerative disc disease has a multifactorial etiology and mechanical stress is one of the most important etiological factor. The purpose of this study was to evaluate the intervertebral disc (IVD) after axial stress diminution from the point of view of its proteoglycan (PG) content, with preoteoglicans (PGs) being very important in the normal function but also in the degenerative or regenerative processes.

METHODS

This is a single-center, prospective, non-randomized study of 38 degenerated intervertebral discs treated with monosegmental or polisegmental posterior lumbar spinal fixation in 27 patients. During surgery, a posterior intervertebral distraction at operated levels was applied. Patients' mean age was 50.77 years and the mean follow-up 28.74 months. Both clinical (visual analog pain scale, Oswestry disability index) and radiological (lumbar spine lordosis, disc thickness) analyses were made before and after surgery. A new method of cartilage analysis, which was also validated for the IVD, delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) was used to determine the PG content before and after surgery for both the intervertebral degenerative disc and control level L1-L2 disc.

RESULTS

The clinical features improved significantly. The thickness of the operated discs increased by an average of 1.71 mm postoperatively and remained unchanged in the control group. The lumbar lordosis did not change significantly. In dGEMRIC studies, the discs accumulated in average 410.08 units /cm2 of gadolinium before surgery and 272.45 units/cm2 after surgery, without significant changes in the control group.

CONCLUSION

Our study shows an improvement of PG quantity in degenerated IVD due to a decrease in gadolinium binding seen in dGEMRIC study. Thus, we can ameliorate IVD homeostasis by eliminating mechanical stress, which could be a step towards the process of disc regeneration.

Shorter screw lengths in dynamic Dynesys fixation have less screw loosening: From clinical investigation to finite-element analysis

BACKGROUND

The dynamic Dynesys Stabilization System preserves lumbar mobility at instrumented levels. This study investigated the effect of screw length on screw loosening (SL) after dynamic Dynesys fixation and screw displacement during lumbar motion, using clinical investigation and finite-element (FE) analysis.

METHODS

Clinical data of 50 patients with degenerative spondylolisthesis treated with decompression and Dynesys fixation in 2011 were analyzed retrospectively. Horizontal sliding displacement and vertical displacement of screw tips at L4 were analyzed postoperatively using displacement-controlled FE analysis at the L4-L5 level with screw lengths 45 (long screw), 36 (median screw), and 27 (short screw), and 6.4 mm in diameter, under flexion, extension, lateral bending, and rotation.

RESULTS

In 13 patients (13/50, 26%), 40 screws (40/266, 15%) were loose at mean follow-up of 101.3 ± 4.4 months. Radiographic SL at 35, 40, 45, and 50 mm were 7.7%, 10.7%, 12.1%, and 37.5%, respectively, regardless of the fixation level ( p = 0.009). FE analysis revealed that the long screw model with corresponding longer lever arm had maximal horizontal sliding displacement under all directions and maximal vertical displacement, except for lateral bending.

CONCLUSION

Shorter screws in Dynesys fixation may help avoid dynamic SL. Clinically, 50 mm screws showed the greatest SL and median screw screws demonstrated the least displacement biomechanically.

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.

A comparative finite element analysis of artificial intervertebral disc replacement and pedicle screw fixation of the lumbar spine

Titanium alloy-based Pedicle screw-rod fusion is a very common technique to provide higher fusion regularity than other methods. In recent times, Carbon-fibre-reinforced (CFR)-PEEK rod is used to better reduce the fusion rate. Alternatively, total disc replacement (TDR) is also very common for the non-fusion treatment method for degenerative disc disease (DDD). This study aims to investigate flexibility (ROM), stability, stress condition in implant, implant adjacent bone of the implanted lumbar spine during different physiological movements and loading environments. The finite element (FE) intact model of the lumbar spine (L2-L5) with two-level pedicle screw-rod fusion at L3-L4-L5 and two-level artificial disc replacement was developed. CFR-PEEK was taken for rod for semi-rigid fusion. UHMWPE was taken as core part of the artificial disc. The FE models were simulated under 6, 8 and 10 Nm moments in left right lateral bending, flexion and extension movements. The total ROM was reduced for two-level pedicle screw fixation and increased for the artificial disc replacement model during flexion extension compared to the intact spine. The total ROM was reduced by around 54% and 25% for two-level fixation and increased by 30% and 19.5% for artificial disc replacement spine, under flexion-extension and left-right lateral bending respectively. For screw fixation, the ROM increased by 15% and 18% reduced by 4.5% and 14% for disc replacement at the adjacent segments for flexion-extension and left-right lateral bending.

Effect of Discectomy on Dynesys Dynamic Fixation in the Treatment of Lumbar Degenerative Diseases

Objective

To compare the effect of decompression of the spinal canal with or without discectomy on the clinical efficacy of Dynesys dynamic fixation treatment in lumbar degenerative diseases.

Methods

A total of 62 patients treated for single-segment lumbar degenerative disease from October 2010 to November 2017 were retrospectively analyzed. All patients underwent decompression of the spinal canal with Dynesys dynamic fixation and were divided into two groups. Twenty-seven patients in group A did not undergo discectomy, and 35 patients in group B underwent discectomy. The intervertebral height, range of motion, Pfirrmann grade of the surgical segment and the upper adjacent segment, function scores, and operation information were compared.

Results

All patients were followed up for an average of 30.7 ± 11.5 months. At the final follow-up, the intervertebral height and range of motion of the surgical segment decreased significantly in both group A and B (p < 0.05), the range of motion of the upper adjacent segment increased significantly (p < 0.05), and the intervertebral height did not change significantly (p < 0.05). The retained percentages of surgical segment intervertebral height and ROM in group A were significantly better than those in group B (p < 0.05). The intervertebral height (p > 0.05) and range of motion (p < 0.05) of the surgical segment in group A were higher than those in group B. The surgical segment Pfirrmann grading of group A was better than that of group B (p < 0.05).

Conclusion

Dynesys in the treatment of lumbar degenerative diseases may lead to a good clinical effect. In selected cases without discectomy, the range of motion and intervertebral height may be better preserved, and disc degeneration may be reduced.

The Optimal Timing of Hydrogel Injection for Treatment of Intervertebral Disc Degeneration: Quantitative Analysis Based on T1ρ MR Imaging

STUDY DESIGN

Animal experimental study.

OBJECTIVE

The aim of this study was to investigate the optimal time of hydrogel injection for regenerating intervertebral disc degeneration (IDD) based on T1ρ magnetic resonance imaging (MRI).

SUMMARY OF BACKGROUND DATA

Currently, different approaches are being pursued to regenerate the IDD. However, the optimal timing for the regenerative intervention is unclear.

METHODS

The slowly, progressive IDD models were established in 18 rhesus monkeys. On the basis of the MR T1ρ values of the discs, the rhesus monkeys were divided into severe (T1ρ values: <81 ms), moderate (T1ρ values: 81∼95 ms), and mild (T1ρ values: 96∼110 ms) degeneration groups. Biocompatible hydrogel was injected into the central part of the nucleus pulposus of the discs under fluoroscopic guidance. Treatment effects were investigated using radiography, T1ρ MRI, and histology until 12 months postoperatively.

RESULTS

After injection, the T1ρ values of all the discs increased significantly at 1 month postoperatively, and then remained at approximately 110 ms in the mild and moderate groups during the whole observation period, with no significant difference compared to the values at 1 month (P > 0.05). However, in the severe group, the T1ρ values decreased significantly after 1 month and leveled at approximately 70 ms after 6 months, with significant difference compared to the values at 1 month (P < 0.05). In the mild and moderate groups, there were no significant differences between preoperative histological scores and those at 12 months (P > 0.05). However, the histological score in the severe group at 12 months was significantly higher than the preoperative scores (P < 0.05).

CONCLUSION

This study suggested that the moderate degenerative stage of IDD (T1ρ values from 95 to 80 ms) could be the optimal time for hydrogel injection aimed at the regenerative intervention, based on T1ρ-MR imaging technique and quantitative analysis.

LEVEL OF EVIDENCE

N/A.

Lumbar disc rehydration in the bridged segment using the BioFlex dynamic stabilization system: A case report and literature review

BACKGROUND

In recent years, the mechanical concept of intervertebral disc regeneration has become more and more popular due to the increasing awareness of the importance of preservation of spine movement. Interestingly, there is increasing evidence, however, that dynamic stabilization systems may compensate non-physiological loads, limit pathological movement, normalize disc height and intradiscal pressure, and provide an adaptive environment for disc regeneration.

CASE SUMMARY

The patient was a 54-year-old man, who presented with a 10-year history of mechanical back pain, which had become progressively serious and radiated into the left lower limb with numbness 3 mo prior. He had decreased muscle strength (class IV) of the left dorsal extensor and plantar flexor. Magnetic resonance imaging scans showed L3-S1 disc degeneration and L4-L5 disc herniation. Because the patient did not respond to various conservative treatments, he underwent a posterior L4-5 discectomy with fixation of the BioFlex dynamic stabilization system (Bio-Spine, Seoul, Korea). Preoperative symptoms were relieved and lumbar function was markedly improved after the operation. L4-L5 disc rehydration of instrumented segment was noted on magnetic resonance imaging at the 2-year follow-up.

CONCLUSION

Rehydration of the degenerated disc in our patient indicates that the BioFlex dynamic stabilization system may promote disc regeneration. Further research is needed to provide more evidence to support lumbar disc rehydration in the bridged segment using this system.

MRI-biochemical follow up measurements of lumbar intervertebral disc in patients with leg length discrepancy: Is it possible to alter cartilage damage with conservative therapy?

Objective

Effect of conservative therapy on intervertebral discs (IVD) in patients with leg-length-discrepancy (LLD).

M&M

Seventy lumbar IVDs of 14 participants (five with LLD 10-20 mm) were examined using a 3T-MRI-scanner. Morphological (Pfirrmann) and molecular (glycosaminoglycan-chemical-exchange-saturation-transfer, gagCEST) grading was assessed before and after a four-month therapy (physiotherapy and shoe inlays).

Results

Significantly lower GAG values in patients with LLD were found (L5/S1, p = 0.02). After therapy, a trend towards higher gagCEST values in patients with LLD was observed (2.48 ± 1.77% vs. 1.79 ± 0.79%; p > 0.05).

Conclusion

LLD represents a risk factor for molecular alterations of lumbar IVDs. Only minor effects of conservative therapy on these alterations could be found.

Wallis interspinous device versus discectomy for lumbar disc herniation : A comparative study

The aim of this study was to assess the efficacy of the Wallis interspinous device for treating lumbar disc herniation (LDH) as well as to investigate whether the device could reduce the incidence of recurrent herniation in comparison with disc excision alone. A total of 72 patients with LDH were treated with primary discectomy and the Wallis interspinous device was implanted in 36. Clinical outcomes were evaluated with a visual analog scale (VAS) for low back and leg pain and the Oswestry Disability Index (ODI) before and after surgery. The incidence of recurrent disc herniation after the operation was also evaluated. There was a significant improvement (p < 0.01) in the clinical outcomes assessed by the VAS and ODI scores compared with preoperative values in both groups. Up to the final follow-up, there were no significant differences between the two groups in VAS and ODI scores (p > 0.05). In addition, there was no significant difference regarding the incidence of recurrent disc herniation between the two groups (13.9% vs. 16.6%, p > 0.05). Of the patients five underwent second discectomy or fusion surgery. The Wallis interspinous device was unable to improve the already good clinical outcome after discectomy for LDH and prevent or reduce recurrence of herniated disc in the current follow-up interval. Whether the device for should be used for LDH should be carefully considered before surgery.

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.

Effectiveness of Transpedicular Dynamic Stabilization in Treating Discogenic Low Back Pain

PURPOSE

To assess clinical outcomes after dynamic stabilization in discogenic low back pain.

METHODS

From April 2012 to January 2015, 23 patients with discogenic low back pain were treated with dynamic stabilization via the Wiltse approach. Main clinical assessments included visual analog scale, Oswestry Disability Index, and complications. Radiographs were evaluated for lumbar range of motion and intervertebral height. The Woodend classification was determined by magnetic resonance imaging.

RESULTS

There were 23 cases evaluated with a mean follow-up time of 39 months. At last follow-up, visual analog scale and Oswestry Disability Index scores improved significantly compared with preoperatively (P < 0.05). At the stabilized segments, the height of intervertebral discs was increased significantly after surgery (P < 0.05). At last follow-up, the height was reduced to the preoperative level. At the operated segment, 47.4% of the flexion/extension range of motion was retained. Six discs showed rehydration with 1 grade improvement on the Woodend classification.

CONCLUSIONS

Dynamic stabilization was a safe and effective treatment in carefully selected groups of patients with discogenic low back pain and promoted disc regeneration to some extent.

Value of delayed gadolinium-enhanced magnetic resonance imaging of cartilage for the pre-operative assessment of cervical intervertebral discs

The study was performed to preoperatively assess the cartilage integrity of cervical intervertebral discs (IVDs) using Delayed Gadolinium-Enhanced Magnetic Resonance Imaging of Cartilage (dGEMRIC). Therefore, 53 cervical intervertebral discs of nine preoperative patients with neck and shoulder/arm pain scheduled for discectomy (five females, four males; mean age: 47.1 ± 8.4 years; range: 36-58 years) were included for biochemical analysis in this retrospective study. The patients underwent 3T magnetic resonance imaging (MRI) including biochemical imaging with dGEMRIC and morphological, sagittal T2 weighted (T2w) imaging. Cervical IVDs were rated using an MRI based grading system for cervical IVDs on T2w images. Region-of-interest measurements were performed in the nucleus pulposus (NP) and annulus fibrosus (AF) and a dGEMRIC index was calculated. Our results demonstrated that IVDs scheduled for discectomy showed significantly lower dGEMRIC index compared to IVDs that did not require surgical intervention in NP and AF (NP: 898.4 ± 191.9 ms vs. 1,150.3 ± 320.7 ms, p = 0.008; AF: 738.7 ± 183.8 ms vs. 984.6 ± 178.9 ms, p = 0.008). For Miyazaki score 3, the dGEMRIC indices were significantly lower in IVDs scheduled for surgery compared to non-operated discs for NP (p = 0.043) and AF (p = 0.018). In conclusion we could demonstrate that biochemical imaging with dGEMRIC is feasible in cervical IVDs. Significantly lower dGEMRIC index suggested GAG depletion in degenerated cervical IVD, scheduled for discectomy. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1824-1830, 2017.

Medium-term effects of Dynesys dynamic stabilization versus posterior lumbar interbody fusion for treatment of multisegmental lumbar degenerative disease

Objective

To compare the medium-term clinical and radiographic outcomes of Dynesys dynamic stabilization and posterior lumbar interbody fusion (PLIF) for treatment of multisegmental lumbar degenerative disease.

Methods

Fifty-seven patients with multisegmental lumbar degenerative disease underwent Dynesys stabilization (n = 26) or PLIF (n = 31) from December 2008 to February 2010. The mean follow-up period was 50.3 (range, 46–65) months. Clinical outcomes were evaluated using a visual analogue scale (VAS) and the Oswestry disability index (ODI). Radiographic evaluations included disc height and range of motion (ROM) of the operative segments and proximal adjacent segment on lumbar flexion-extension X-rays. The intervertebral disc signal change was defined by magnetic resonance imaging, and disc degeneration was classified by the Pfirrmann grade.

Results

The clinical outcomes including the VAS score and ODI were significantly improved in both groups at 3 months and the final follow-up, but the difference between the two was not significant. At the final follow-up, the disc height of stabilized segments in both groups was significantly increased; the increase was more notable in the Dynesys than PLIF group. The ROM of stabilized segments at the final follow-up decreased from 6.20° to 2.76° and 6.56° to 0.00° in the Dynesys and PLIF groups, respectively. There was no distinct change in the height of the proximal adjacent segment in the two groups. The ROM of the proximal adjacent segment in both groups increased significantly at the final follow-up; the change was significantly greater in the PLIF than Dynesys group. Only one case of adjacent segment degeneration occurred in the PLIF group, and this patient underwent a second operation.

Conclusions

Both Dynesys stabilization and PLIF can improve the clinical and radiographic outcomes of multisegmental lumbar degenerative disease. Compared with PLIF, Dynesys stabilization can maintain the mobility of the stabilized segments with less influence on the proximal adjacent segment and may help to prevent the occurrence of adjacent segment degeneration. Dynesys is reliable for the treatment of multisegmental lumbar degenerative disease at the medium-term follow-up.

Biochemical validity of imaging techniques (X-ray, MRI, and dGEMRIC) in degenerative disc disease of the human cervical spine-an in vivo study

BACKGROUND CONTEXT

On a molecular level, maturation or degeneration of human intervertebral disc is among others expressed by the content of glycosaminoglycans (GAGs). According to the degenerative status, the disc content can differ in nucleus pulposus (NP) and annulus fibrosus (AF), respectively. Research in this area was conducted mostly on postmortem samples. Although several radiological classification systems exist, none includes biochemical features. Therefore, we focused our in vivo study on a widely spread and less expensive imaging technique for the cervical spine and the correlation of radiological patterns to biochemical equivalents in the intervertebral discs.

PURPOSE

The aim of this pilot study was to (1) measure the GAG content in human cervical discs, (2) to investigate whether a topographic biochemical GAG pattern can be found, and (3) whether there is a correlation between imaging data (X-ray and magnetic resonance imaging [MRI] including delayed gadolinium-enhanced MRI of cartilage [dGEMRIC] as a special imaging technique of cartilage) and the biochemical data.

STUDY DESIGN/SAMPLE

We conducted a prospective experimental pilot study.

PATIENT SAMPLE

Only non-responders to conservative therapy were included. All subjects were physically and neurologically examined, and they completed their questionnaires.

OUTCOME MEASURES

Visual analogue scale neck and arm, Neck Disability Index score, radiological parameters (X-rays, MRI, dGEMRIC), and the content of GAG in the cervical disc were assessed.

METHODS

After surgical removal of 12 discs, 96 fractions of AF and NP were biochemically analyzed for the GAG content using dimethylmethylene blue assay.

RESULTS

A quantitative pattern of GAGs in the human cervical disc was identified. There were (1) significantly (p<.001) higher values of GAGs (µg GAG/mg tissue) in the NP (169.9 SD 37.3) compared with the AF (132.4 SD 42.2), and (2) significantly (p<.005) higher values of GAGs in the posterior (right/left: 149.9/160.2) compared with the anterior (right/left: 112.0/120.2) part of the AF. Third, we found in dGEMRIC imaging a significantly (p<.008) different distribution of GAGs in the cervical disc (NP 1083.3 ms [SD 248.6], AF 925.9 ms [SD 137.6]). Finally, we found that grading of disc degeneration in X-ray and MRI was significantly correlated with neither AF- nor NP-GAG content.

CONCLUSIONS

The GAG content in human cervical discs can be detected in vivo and is subject to a significantly (p<.05) region-specific pattern (AF vs. NP; anterior vs. posterior in the AF). Up to the levels of AF and NP, this is reproducible in MRI in dGEMRIC technique, but not in X-ray or standard MRI sequences. Potentially, the MRI in dGEMRIC technique can be used as a non-invasive in vivo indicator for disc degeneration in the cervical spine.

Quantitative magnetic resonance imaging of the lumbar intervertebral discs

Human lumbar spine is composed of multiple tissue components that serve to provide structural stability and proper nutrition. Conventional magnetic resonance (MR) imaging techniques have been useful for evaluation of IVD, but inadequate at imaging the discovertebral junction and ligamentous tissues due primarily to their short T2 nature. Ultrashort time to echo (UTE) MR techniques acquire sufficient MR signal from these short T2 tissues, thereby allowing direct and quantitative evaluation. This article discusses the anatomy of the lumbar spine, MR techniques available for morphologic and quantitative MR evaluation of long and short T2 tissues of the lumbar spine, considerations for T2 relaxation modeling and fitting, and existing and new techniques for spine image post-processing, focusing on segmentation. This article will be of interest to radiologic and orthopaedic researchers performing lumbar spine imaging.

Comparison of the Dynesys Dynamic Stabilization System and Posterior Lumbar Interbody Fusion for Lumbar Degenerative Disease

BACKGROUND

There have been few studies comparing the clinical and radiographic outcomes between the Dynesys dynamic stabilization system and posterior lumbar interbody fusion (PLIF). The objective of this study is to compare the clinical and radiographic outcomes of Dynesys and PLIF for lumbar degenerative disease.

METHODS

Of 96 patients with lumbar degenerative disease included in this retrospectively analysis, 46 were treated with the Dynesys system and 50 underwent PLIF from July 2008 to March 2011. Clinical and radiographic outcomes were evaluated. We also evaluated the occurrence of radiographic and symptomatic adjacent segment degeneration (ASD).

RESULTS

The mean follow-up time in the Dynesys group was 53.6 ± 5.3 months, while that in the PLIF group was 55.2 ± 6.8 months. At the final follow-up, the Oswestry disability index and visual analogue scale score were significantly improved in both groups. The range of motion (ROM) of stabilized segments in Dynesys group decreased from 7.1 ± 2.2° to 4.9 ± 2.2° (P < 0.05), while that of in PLIF group decreased from 7.3 ± 2.3° to 0° (P < 0.05). The ROM of the upper segments increased significantly in both groups at the final follow-up, the ROM was higher in the PLIF group. There were significantly more radiographic ASDs in the PLIF group than in the Dynesys group. The incidence of complications was comparable between groups.

CONCLUSIONS

Both Dynesys and PLIF can improve the clinical outcomes for lumbar degenerative disease. Compared to PLIF, Dynesys stabilization partially preserves the ROM of the stabilized segments, limits hypermobility in the upper adjacent segment, and may prevent the occurrence of ASD.

Age-dependency of glycosaminoglycan content in lumbar discs: A 3t gagcEST study

PURPOSE

To analyze age-dependency of glycosaminoglycan content using gagCEST (glycosaminoglycan chemical exchange saturation transfer) imaging in lumbar intervertebral discs of healthy volunteers.

MATERIALS AND METHODS

In all, 70 volunteers without low back pain (mean age 44 ± 14 years, range: 21-69 years) were examined with T2 -weighted and gagCEST imaging with a 3T MR scanner, with approval of the local Ethics Committee after written informed consent was obtained. Pfirrmann grading and classification into discs without bulging and herniation, discs with bulging, and discs with herniation were performed. Only intervertebral discs without bulging and herniation were analyzed. A region-of-interest-based gagCEST analysis of nucleus pulposus (NP) and annulus fibrosus (AF) was performed. Correlation between age and gagCEST was tested within groups of equal Pfirrmann score.

RESULTS

GagCEST effects decreased significantly from 3.09 ± 1.12% in 20-29 years old volunteers to -0.24 ± 1.36% in 50-59 years old volunteers (P < 0.001). In the case of Pfirrmann scores 2 and 3, a significant correlation was observed between gagCEST effect and age (Pfirrmann score 2, NP: ρ = -0.558, P < 0.001; Pfirrmann score 3, NP: ρ = -0.337, P = 0.048). For Pfirrmann scores 1 and 4, no significant correlation was obtained (Pfirrmann score 1, NP: ρ = -0.046, P = 0.824; Pfirrmann score 4, NP: ρ = -0.316, P = 0.188).

CONCLUSION

We show a decreased gagCEST effect likely corresponding to decreasing glycosaminoglycans with aging. Hence, age-matched analysis of gagCEST imaging may be necessary in future studies.

Assessment of lumbar intervertebral disc glycosaminoglycan content by gadolinium-enhanced MRI before and after 21-days of head-down-tilt bedrest

During spaceflight, it has been shown that intervertebral discs (IVDs) increase in height, causing elongation of the spine up to several centimeters. Astronauts frequently report dull lower back pain that is most likely of discogenic origin and may result from IVD expansion. It is unknown whether disc volume solely increases by water influx, or if the content of glycosaminoglycans also changes in microgravity. Aim of this pilot study was to investigate effects of the spaceflight analog of bedrest on the glycosaminoglycan content of human lumbar IVDs. Five healthy, non-smoking, male human subjects of European descent were immobilized in 6° head-down-tilt bedrest for 21 days. Subjects remained in bed 24 h a day with at least one shoulder on the mattress. Magnetic Resonance Imaging (MRI) scans were taken according to the delayed gadolinium-enhanced magnetic resonance imaging (dGEMRIC) protocol before and after bedrest. The outcome measures were T1 and ΔT1. Scans were performed before and after administration of the contrast agent Gd-DOTA, and differences between T1-values of both scans (ΔT1) were computed. ΔT1 is the longitudinal relaxation time in the tissue and inversely related to the glycosaminoglycan-content. For data analysis, IVDs L1/2 to L4/5 were semi-automatically segmented. Zones were defined and analyzed separately. Results show a highly significant decrease in ΔT1 (p<0.001) after bedrest in all IVDs, and in all areas of the IVDs. The ΔT1-decrease was most prominent in the nucleus pulposus and in L4/5, and was expressed slightly more in the posterior than anterior IVD. Unexpected negative ΔT1-values were found in Pfirrmann-grade 2-discs after bedrest. Significantly lower T1 before contrast agent application was found after bedrest compared to before bedrest. According to the dGEMRIC-literature, the decrease in ΔT1 may be interpreted as an increase in glycosaminoglycans in healthy IVDs during bedrest. This interpretation seems contradictory to previous findings in IVD unloading.

Three-dimensional characterization of in vivo intervertebral disc degeneration using EPIC-μCT

OBJECTIVE

Small animal models are commonly employed to study progression of and potential treatment techniques for degenerative disc disease (DDD), but assessment using conventional imaging techniques is challenging due to resolution. The objective of this study was to employ equilibrium partitioning of an ionic contrast agent micro computed tomography (EPIC - μCT) to map three-dimensional (3D) degenerative changes in the rabbit intervertebral disc (IVD).

MATERIALS AND METHODS

In vivo degeneration was induced surgically in 12 New Zealand White rabbits via percutaneous annular puncture and percutaneous nucleotomy. IVDs were harvested after 3 and 6 weeks. EPIC-μCT imaging was performed on fresh, IVDs before and after formalin fixation, and 3D IVD volumes were segmented. IVDs were histologically stained with Safranin-O/Fast-Green and Hematoxylin & Eosin (H&E). EPIC-μCT attenuation and 3D morphological measurements were assessed in healthy and degenerate IVDs and compared to qualitative grading and disc height measurement from histology.

RESULTS

EPIC-μCT caused pronounced contrast enhancement of the IVD. Annular puncture and nucleotomy produced mild and severe degenerative changes, respectively. IVD attenuation following contrast enhancement increased significantly in nucleotomized discs at 3 and 6 weeks. IVD attenuation correlated significantly with histologic score and disc height measurements. Disc height decreased most extensively in the posterior and lateral aspects of the IVD. 3D morphological measurements correlated strongly to IVD attenuation and were more sensitive to degenerative changes than histologic measurements. Formalin fixation reduced the attenuation of IVDs by ∼10%.

CONCLUSION

EPIC-μCT is sensitive to in vivo DDD induced by nucleotomy and provides a high resolution 3D method for mapping degenerative changes in rabbit IVDs.

23Na-magnetic resonance imaging of the human lumbar vertebral discs: in vivo measurements at 3.0 T in healthy volunteers and patients with low back pain

BACKGROUND CONTEXT

1H magnetic resonance imaging (MRI) of the spine can rule out common causes of low back pain (LBP), such as disc protrusions or nerve root compression; however, no significant causal relation exists between morphology and the extent of symptoms. Functional MRI techniques, such as 23Na, may provide additional information, allowing indirect assessment of vertebral glycosaminoglycan concentrations, decreases in which are associated with early degenerative changes.

PURPOSE

To evaluate 23Na-MRI of asymptomatic healthy volunteers and symptomatic patients with LPB and correlate the results to the Pfirrmann classification of MRI disc morphology.

STUDY DESIGN

Retrospective cohort study at an academic medical center.

PATIENT SAMPLE

Two groups were studied: (1) 55 healthy volunteers (31 men, 24 women; mean age 28.8 years) and (2) 12 patients (6 men, 6 women; mean age: 35.3 years) with a recent history of LBP.

METHODS

Lumbar spines of the aforementioned groups were examined on a 3.0 T MRI scanner with morphological 1H and 23Na imaging. Intervertebral disc (IVD) 23Na at each level was normalized (23Nanorm). Distribution and differences between mean 23Nanorm corresponding to each Pfirrmann classification were evaluated in the two study groups (analysis of variance). Linear correlations between 23Nanorm, body mass index (BMI), and age were assessed (Pearson correlation coefficient). Gender-dependent differences were evaluated (paired t test).

OUTCOME MEASURES

Physiological measure: IVD 23Nanorm as determined by 23Na-MRI.

RESULTS

A normal distribution of 23Nanorm was confirmed for both groups (p=.072 and p=.073, respectively). The mean Pfirrmann score statistically significantly differed between them (p<.0001). 23Nanorm was statistically significantly reduced in degenerated IVDs (Pfirrmann scores 4+5) (p<.0001). No statistically significant differences were seen for the mean 23Nanorm of IVDs with the same Pfirrmann score in healthy volunteers and patients (.469<p<.967). Age (0.007<R2<0.202) and BMI (0.074<R2<0.288) showed either weak or no correlation to 23Nanorm. Mean 23Nanorm was significantly (p=.0002) greater in women relative to men.

CONCLUSIONS

The results underline the feasibility and robustness of 23Na-MRI of human IVDs and affirm, in a large cohort, decreases in 23Na IVD content seen with disc degeneration.

A new device used in the restoration of kinematics after total facet arthroplasty

Facet degeneration can lead to spinal stenosis and instability, and often requires stabilization. Interbody fusion is commonly performed, but it can lead to adjacent-segment disease. Dynamic posterior stabilization was performed using a total facet arthroplasty system. The total facet arthroplasty system was originally intended to restore the natural motion of the posterior stabilizers, but follow-up studies are lacking due to limited clinical use. We studied the first 14 cases (long-term follow-up) treated with this new device in our clinic. All patients were diagnosed with lumbar stenosis due to hypertrophy of the articular facets on one to three levels (maximum). Disk space was of normal height. The design of this implant allows its use only at levels L3-L4 and L4-L5. We implanted nine patients at the L4-L5 level and four patients at level L3-L4. Postoperative follow-up of the patients was obtained for an average of 3.7 years. All patients reported persistent improvement of symptoms, visual analog scale score, and Oswestry Disability Index score. Functional scores and dynamic radiographic imaging demonstrated the functional efficacy of this new implant, which represents an alternative technique and a new approach to dynamic stabilization of the vertebral column after interventions for spine decompression. The total facet arthroplasty system represents a viable option for dynamic posterior stabilization after spinal decompression. For the observed follow-up, it preserved motion without significant complications or apparent intradisk or adjacent-disk degeneration.

Functional and radiological outcomes of semi-rigid dynamic lumbar stabilization adjacent to single-level fusion after 2 years

OBJECTIVE

To prospectively evaluate the functional and radiological outcomes of Isobar semi-rigid dynamic posterior stabilization adjacent to single-level fusion up to and including 24 months postoperatively.

METHOD

A prospective follow-up for 24 months of 36 patients who underwent posterior Isobar dynamic stabilization due to single-level degenerative lumbar discopathy and instability (DLDI) with mild adjacent level degeneration, with collection of functional [visual analog scale (VAS) and Oswestry Disability Index (ODI)] and radiological data (resting, functional X-rays and MRI).

RESULTS

Functional outcomes at 24 months showed significant improvement in mean VAS score by 38.9 points (P < 0.01) and ODI by 22.4 points (P < 0.01). Compared with data preoperatively, disc height at the index and adjacent levels and intervertebral angle (IVA) at the index level showed a slight decreasing trend at each follow-up (P > 0.05), while IVA at the adjacent level showed a slight increasing trend (P > 0.05). Range of motion averaged 2.84° at the index level and remained unchanged at the adjacent level (P > 0.05). The mean Pfirrmann score changed from 2.86 preoperatively to 2.92 at 24 months postoperatively at the index level (P > 0.05), and from 1.92 preoperatively to 1.96 at 24 months postoperatively at the adjacent level (P > 0.05). No reoperation, loosening of screws or infection was recorded.

CONCLUSIONS

Patients with single-level DLDI and mild adjacent level degeneration treated with Isobar stabilization show a clinical improvement after 2 years. However, disc degeneration at the index and adjacent levels seems to continue despite using semi-rigid dynamic stabilization.

Biomechanical analysis and design of a dynamic spinal fixator using topology optimization: a finite element analysis

Surgeons often use spinal fixators to manage spinal instability. Dynesys (DY) is a type of dynamic fixator that is designed to restore spinal stability and to provide flexibility. The aim of this study was to design a new spinal fixator using topology optimization [the topology design (TD) system]. Here, we constructed finite element (FE) models of degenerative disc disease, DY, and the TD system. A hybrid-controlled analysis was applied to each of the three FE models. The rod structure of the topology optimization was modelled at a 39 % reduced volume compared with the rigid rod. The TD system was similar to the DY system in terms of stiffness. In contrast, the TD system reduced the cranial adjacent disc stress and facet contact force at the adjacent level. The TD system also reduced pedicle screw stresses in flexion, extension, and lateral bending.

The Prolo Scale: history, evolution and psychometric properties

BACKGROUND

The Prolo Scale (PS) is a widely accepted assessment tool for lumbar spinal surgery results. Nevertheless, in the literature there is a dearth of consensus about its application, interpretation and accuracy. The purpose of this review is to investigate the evolution of the PS from its introduction in 1986 to the present, including an analysis of different versions of the scale and research on the existing studies investigating its psychometric properties.

MATERIALS AND METHODS

PubMed, Cochrane Library and PEDro databases were searched. Studies in English, Italian, French, Spanish and German published from 1986 to December 2012 were analyzed.

RESULTS

The original lumbar surgery outcome scale consisted of two Likert-type scales (economic and functional). There are three more versions of the scale: Schnee proposed one consisting of 10 items, Brantigan made one with 20 items and introduced 2 more subscales (pain and medication), and Davis adapted the scale for the cervical spine. PS is often mentioned without any specific reference to the version used; therefore, a homogeneous comparison of studies is difficult to achieve. Several authors agree on the need to embrace a multidimensional measuring system to evaluate low back pain (LBP), but there is still no consensus regarding the most reliable tool. To date, PS has been mostly used as secondary outcome measure in association with validated primary measures for LBP.

CONCLUSIONS

The Prolo Scale has been adopted for clinical examination for 20 years because it is easy to administer and useful to compare significant amounts of data from surgical studies carried out at different times. Although several authors demonstrated the scale sensitivity among a battery of tests, no thorough validation study was found in the current literature.

Intervertebral disc rehydration after lumbar dynamic stabilization: magnetic resonance image evaluation with a mean followup of four years

Objective. To compare the clinical and radiographic outcomes in patients of different ages who underwent the Dynesys stabilization. Methods. This retrospective study included 72 patients (mean age 61.4 years) with one- or two-level lumbar spinal stenosis who underwent laminectomy and the Dynesys (Zimmer Spine, Minneapolis) dynamic stabilization system. Thirty-seven patients were younger than 65-year old while the other 35 were older. Mean followup was 46.7 months. Pre- and postoperative radiographic and clinical evaluations were analyzed. Results. The mean calibrated disc signal (CDS) at the index level was significantly improved from 60.2 ± 25.2 preoperatively to 66.9 ± 26.0 postoperatively (P > 0.001). Screw loosening occurred in 22.2% of patients and 5.1% of screws. The improvement in CDS at index level was seen to be significant in younger patients but not in older patients. Overall, the mean visual analogue scale (VAS) of back pain, VAS of leg pain, and the Oswestry disability index (ODI) scores improved significantly after operation. There were no significant differences in pre- and postoperative VAS and ODI and screw loosening rates between the younger and older patients. Conclusions. There is significant clinical improvement after laminectomy and dynamic stabilization for symptomatic lumbar spinal stenosis. Intervertebral disc rehydration was seen in younger patients.

Dynamic stabilization for challenging lumbar degenerative diseases of the spine: a review of the literature

Fusion and rigid instrumentation have been currently the mainstay for the surgical treatment of degenerative diseases of the spine over the last 4 decades. In all over the world the common experience was formed about fusion surgery. Satisfactory results of lumbar spinal fusion appeared completely incompatible and unfavorable within years. Rigid spinal implants along with fusion cause increased stresses of the adjacent segments and have some important disadvantages such as donor site morbidity including pain, wound problems, infections because of longer operating time, pseudarthrosis, and fatigue failure of implants. Alternative spinal implants were developed with time on unsatisfactory outcomes of rigid internal fixation along with fusion. Motion preservation devices which include both anterior and posterior dynamic stabilization are designed and used especially in the last two decades. This paper evaluates the dynamic stabilization of the lumbar spine and talks about chronologically some novel dynamic stabilization devices and thier efficacies.

Intervertebral disk degeneration: T1ρ MR imaging of human and animal models

PURPOSE

To evaluate disk degeneration in human and animal models by using a T1ρ magnetic resonance (MR) imaging technique to help in understanding the natural history and progression of intervertebral disk degeneration.

MATERIALS AND METHODS

After institutional review board approval was obtained, 80 subjects (54 men and 26 women; mean age ± standard deviation, 31.6 years ± 6.20) with 400 lumbar intervertebral disks were examined at MR imaging. With approval from the animal care committee, six rhesus monkeys received two levels of either annulus fibrosus puncture or pingyangmycin subendplate injection at L3-4 and L5-6 to mimic disk degeneration. Lumbar spines of all the animals were examined at radiography and MR imaging preoperatively and 1 day and 1, 3, 6, 9, and 13 months postoperatively. Pfirrmann grading system and T1ρ quantification were used to evaluate the degenerative degree of the disks of both humans and animals.

RESULTS

The mean T1ρ values of lumbar intervertebral disks of human subjects were 136.0 msec ± 31.4 and 76.1 msec ± 14.2 at Pfirrmann grades II and III, respectively. The T1ρ values in lumbar intervertebral disks of the rhesus monkey models of disk degeneration had a rapid decrease from approximately 110 msec to 80 msec and then tended to stabilize after operation. There was a large T1ρ value decrease between Pfirrmann grades II and III in human subjects that coincided with the rapid degeneration process of lumbar intervertebral disks in the rhesus monkeys. Pfirrmann grades were significantly correlated with T1ρ values in both humans (r = -0.681, P < .001) and rhesus monkeys (r = -0.824, P < .001).

CONCLUSION

The data demonstrate that rapid intervertebral disk degeneration occurs early in the degenerative cascade, between Pfirrmann grades II and III.

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.

Posterior dynamic stabilization in the treatment of degenerative lumbar stenosis: validity of its rationale

OBJECT

The authors undertook this study to investigate the validity of the rationale for posterior dynamic stabilization using the Device for Intervertebral Assisted Motion (DIAM) in the treatment of degenerative lumbar stenosis.

METHODS

A cohort of 31 patients who underwent single-level decompression and DIAM placement for degenerative lumbar stenosis were followed up for at least 2 years and data pertaining to their cases were analyzed prospectively. Of these patients, 7 had retrolisthesis. Preoperative and postoperative plain lumbar radiographs obtained in all patients and CT images obtained in 14 patients were analyzed. Posterior disc heights; range of motion (ROM) of proximal, distal, and implant segments; lordotic angles of implant segments; percentage of retrolisthesis; and cross-sectional area and heights of intervertebral foramina on CT sagittal images were analyzed. Clinical outcomes were evaluated using visual analog scale scores and Oswestry Disability Index scores.

RESULTS

The mean values for posterior disc height before surgery, at 1 week after surgery, and at the final follow-up visits were 6.4 ± 2.0 mm, 9.7 ± 2.8 mm, and 6.8 ± 2.5 mm, respectively. The mean lordotic angles at the implant levels before surgery, at 1 week after surgery, and at the final follow-up visits were 7.1° ± 3.3°, 4.1° ± 2.7°, and 7.0° ± 3.7°, respectively. No statistically significant difference was found between the preoperative values and values from final follow-up visits for posterior disc height and lordotic angles at implant levels (p = 0.17 and p = 0.10, respectively). There was no statistically significant difference between the preoperative and final follow-up visit values for intervertebral foramen cross-sectional area and heights on CT images. The ROMs of proximal and distal segments also showed no significant decrease (p = 0.98 and p = 0.92, respectively). However, the ROMs of implant segments decreased significantly (p = 0.02). The average 31.4-month improvement for all clinical outcome measures was significant (p < 0.001).

CONCLUSIONS

Based on radiological findings, the DIAM failed to show validity in terms of the rationale of indirect decompression, but it did restrict motion at the instrumented level without significant change in adjacent-segment ROM. The clinical condition of the patients, however, was improved, and improvement was maintained despite progressive loss of posterior disc height after surgery.

Radiographic and clinical results of posterior dynamic stabilization for the treatment of multisegment degenerative disc disease with a minimum follow-up of 3 years

BACKGROUND

This study aims to compare radiographic and clinical outcomes of Dynesys and posterior lumbar interbody fusion (PLIF) for the treatment of multisegment disease.

METHODS

Thirty-five consecutive patients who received Dynesys implantation at three levels from L1 to S1 from November 2006 to July 2007 were studied. A retrospective analysis of the medical records of 25 patients with the same indications who received 3-level PLIF (L1-S1) was also conducted. Radiographic and clinical outcomes between the groups were compared. All patients included in the analysis completed 3-year follow-up. Dynesys stabilization resulted in higher preservation of motion at the operative levels, as well as total range of motion from L1 to S1. A decrease of anterior disc height was seen in the Dynesys group and an increase was seen in the PLIF group. An increase in posterior disc height was noted in both groups; however, was greater in the PLIF group at 3 years.

RESULTS

The Dynesys group showed a greater improvement in Oswestry Disability Index and visual analogue scale back pain scores at 3 years postoperatively. There were no differences in complications between the two groups.

CONCLUSION

In conclusion, Dynesys is an acceptable alternative to PLIF for the treatment of multisegment lumbar disease.

Quantitative MRI analysis of the surface area, signal intensity and MRI index of the central bright area for the evaluation of early adjacent disc degeneration after lumbar fusion

PURPOSE

The aim of this study was to evaluate early ASD at short-term follow-up in fused and unoperated patients with degenerative disc disease, using quantitative magnetic resonance imaging (MRI) analysis of the area, signal intensity and their product, i.e., MRI index of the central bright area of the disc as well as measures of intervertebral disc height and Pfirrmann grading scale. The further purpose was to determine whether fusion accelerates ASD compared with non-surgical treatment in short-term follow-up.

METHODS

One hundred and eight chronic low back patients diagnosed as L4/L5 degeneration undertook either one-level instrumented posterior lumbar interbody fusion or conservative treatment. They were followed up for about 1 year. Finally 46 fused and 45 conservatively treated patients with MRI follow-up were included. Pre- and post-treatment MRIs were compared to determine the progression of disc degeneration at the two cranial adjacent segments.

RESULTS

The area, signal intensity and MRI index of the central bright area of the adjacent discs decreased in the operated and unoperated groups from pre-treatment to follow-up, except for an insignificant decrease of signal intensity at the second adjacent segment in the unoperated group. The changes in these parameters were statistically greater at the first than the second adjacent segment in the fused group, but not in the unoperated group. And the changes in the fused group were more pronounced than those at both neighbouring levels in the unoperated group. However, the Pfirrmann grading scale and intervertebral disc height did not detect any changes at adjacent discs in either group.

CONCLUSIONS

Decrease in the parameters of quantitative MRI analysis indicated early degeneration at discs adjacent to lumbar spinal fusion. Fusion had an independent effect on the natural history of ASD during short-term follow-up. Continued longitudinal follow-up is required to determine whether these MRI changes lead to pathologic changes.

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

OBJECTIVE

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.

METHODS

  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.

RESULTS

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.

CONCLUSION

  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.

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

PURPOSE

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.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSION

Our study confirmed the improvement in clinical evaluation, and for the first time related this to the changes in discs GAG concentration.

The effect of degenerative morphological changes of the intervertebral disc on the lumbar spine biomechanics: a poroelastic finite element investigation

Intervertebral disc degeneration involves changes in the spinal anatomical structures. The mechanical relevance of the following changes was investigated: disc height, endplate sclerosis, disc water content, permeability and depressurisation. A poroelastic nonlinear finite element model of the L4-L5 human spine segments was employed. Loads represented a daily cycle (500 N compression combined with flexion-extension motion for 16 h followed by 200 N compression for 8 h). In non-degenerative conditions, the model predicted a diurnal axial displacement of 1.32 mm and a peak intradiscal pressure of 0.47 MPa. Axial displacement, facet force and range of motion in flexion-extension are decreased by decreasing disc height. By decreasing the initial water content, axial displacement, facet force and fluid loss were all reduced. Endplate sclerosis did not have a significant influence on the calculated results. Depressurisation determined an increase of the disc effective stress, possibly inducing failure. Degenerative instability was not calculated in any simulations.

Effect of the cord pretension of the Dynesys dynamic stabilisation system on the biomechanics of the lumbar spine: a finite element analysis

The Dynesys dynamics stabilisation system was developed to maintain the mobility of motion segment of the lumbar spine in order to reduce the incidence of negative effects at the adjacent segments. However, the magnitude of cord pretension may change the stiffness of the Dynesys system and result in a diverse clinical outcome, and the effects of Dynesys cord pretension remain unclear. Displacement-controlled finite element analysis was used to evaluate the biomechanical behaviour of the lumbar spine after insertion of Dynesys with three different cord pretensions. For the implanted level, increasing the cord pretension from 100 to 300 N resulted in an increase in flexion stiffness from 19.0 to 64.5 Nm/deg, a marked increase in facet contact force (FCF) of 35% in extension and 32% in torsion, a 40% increase of the annulus stress in torsion, and an increase in the high-stress region of the pedicle screw in flexion and lateral bending. For the adjacent levels, varying the cord pretension from 100 to 300 N only had a minor influence on range of motion (ROM), FCF, and annulus stress, with changes of 6, 12, and 9%, respectively. This study found that alteration of cord pretension affects the ROM and FCF, and annulus stress within the construct but not the adjacent segment. In addition, use of a 300 N cord pretension causes a much higher stiffness at the implanted level when compared with the intact lumbar spine.

How does spinal canal decompression and dorsal stabilization affect segmental mobility? A biomechanical study

INTRODUCTION

When decompression of the lumbar spinal canal is performed, segmental stability might be affected. Exactly which anatomical structures can thereby be resected without interfering with stability, and when, respectively how, additional stabilization is essential, has not been adequately investigated so far. The present investigation describes kinetic changes in a surgically treated motion segment as well as in its adjacent segments.

MATERIAL AND METHODS

Segmental biomechanical examination of nine human lumbar cadaver spines (L1 to L5) was performed without preload in a spine-testing apparatus by means of a precise, ultrasound-guided measuring system. Thus, samples consisting of four free motion segments were made available. Besides measurements in the native (untreated) spine specimen further measurements were done after progressive resection of dorsal elements like lig. flavum, hemilaminectomy, laminectomy and facetectomy. The segment was then stabilised by means of a rigid system (ART((R))) and by means of a dynamic, transpedicularly fixed system (Dynesys((R))).

RESULTS

For the analysis, range of motion (ROM) values and separately viewed data of the respective direction of motion were considered in equal measure. A very high reproducibility of the individual measurements could be verified. In the sagittal and frontal plane, flavectomy and hemilaminectomy did not achieve any relevant change in the ROM in both directions. This applies to the segment operated on as well as to the adjacent segments examined. Resection of the facet likewise does not lead to any distinct increase of mobility in the operated segment as far as flexion and right/left bending is concerned. In extension a striking increase in mobility of more than 1degree compared to the native value can be perceived in the operated segment. Stabilization with the rigid and dynamic system effect an almost equal reduction of flexion/extension and right/left bending. In the adjacent segments, a slightly higher mobility is to be noted for rigid stabilization than for dynamic stabilisation. A linear regression analysis shows that in flexion/extension monosegmental rigid stabilisation is compensated predominantly in the first cranial adjacent segment. In case of a dynamic stabilisation the compensation is distributed among the first and second cranial, and by 20% in the caudal adjacent segment.

SUMMARY

Monosegmental decompression of the lumbar spinal canal does not essentially destabilise the motion segment during in vitro conditions. Regarding rigid or dynamic stabilisation, the ROM does not differ within the operated segment, but the distribution of the compensatory movement is different.