The effect of compressive force applied to the intervertebral disc in vivo. A study of proteoglycans and collagen

Biomechanical Analysis of Multilevel Posterior Cervical Spinal Fusion Constructs

STUDY DESIGN

Controlled Laboratory Study.

OBJECTIVE

To compare multilevel posterior cervical fusion (PCF) constructs stopping at C7, T1, and T2 under cyclic load to determine the range of motion (ROM) between the lowest instrumented level and lowest instrumented-adjacent level (LIV-1).

SUMMARY OF BACKGROUND DATA

PCF is a mainstay of treatment for various cervical spine conditions. The transition between the flexible cervical spine and rigid thoracic spine can lead to construct failure at the cervicothoracic junction. There is little evidence to determine the most appropriate level at which to stop a multilevel PCF.

METHODS

Fifteen human cadaveric cervicothoracic spines were randomly assigned to 1 of 3 treatment groups: PCF stopping at C7, T1, or T2. Specimens were tested in their native state, following a simulated PCF, and after cyclic loading. Specimens were loaded in flexion-extension), lateral bending, and axial rotation. Three-dimensional kinematics were recorded to evaluate ROM.

RESULTS

The C7 group had greater flexion-extension motion than the T1 and T2 groups following instrumentation (10.17±0.83 degree vs. 2.77±1.66 degree and 1.06±0.55 degree, P <0.001), and after cyclic loading (10.42±2.30 degree vs. 2.47±0.64 degree and 1.99±1.23 degree, P <0.001). There was no significant difference between the T1 and T2 groups. The C7 group had greater lateral bending ROM than both thoracic groups after instrumentation (8.81±3.44 degree vs. 3.51±2.52 degree, P =0.013 and 1.99±1.99 degree, P =0.003) and after cyclic loading. The C7 group had greater axial rotation motion than the thoracic groups (4.46±2.27 degree vs. 1.26±0.69 degree, P =0.010; and 0.73±0.74 degree, P =0.003) following cyclic loading.

CONCLUSION

Motion at the cervicothoracic junction is significantly greater when a multilevel PCF stops at C7 rather than T1 or T2. This is likely attributable to the transition from a flexible cervical spine to a rigid thoracic spine. Although this does not account for in vivo fusion, surgeons should consider extending multilevel PCF constructs to T1 when feasible.

LEVEL OF EVIDENCE

Not applicable.

Adjacent segment mobility after ACDF considering fusion status at the implant insertion site

PURPOSE

This paper sets out to analyse mobility changes in segments adjacent to the operated segment. Additionally, it investigates the relationship between the degree of fusion in the operated disc space and mobility changes in the adjacent segments.

METHODS

In total, 170 disc spaces were operated on in 104 consecutive patients qualified for one- or two-level surgery. The degree of mobility of segments directly above and below the implant insertion site was calculated. Measurements were performed the day before the surgery and 12 months post-surgery. Functional (flexion and extension) radiographs of the cervical spine and CT scans obtained 12 months post-surgery were used to evaluate the fusion status. The results were subjected to statistical analysis.

RESULTS

Statistically significant increase in mobility was recorded for the segments situated immediately below the operative site, with a mean change in mobility of 1.7 mm. Complete fusion was demonstrated in 101 cases (71.1%), and partial fusion in 43 cases (29.9%). In the complete fusion subgroup, the ranges of both flexion and extension in the segments directly below the operative site were significantly greater than those in the partial fusion (pseudoarthrosis) subgroup.

CONCLUSION

The mobility of the adjacent segment below the implant insertion site was significantly increased at 12 months post-ACDF surgery. The range of this compensatory hypermobility was significantly greater in patients with complete fusion at the ACDF site than in cases of pseudoarthrosis. Implant subsidence was not associated with mobility changes in the segments directly above or directly below the site of ACDF surgery.

The Evaluation of Proteoglycan Levels and the Possible Role of ACAN Gene (c.6423T>C) Variant in Patients with Lumbar Disc Degeneration Disease

BACKGROUND/AIM

The present study aimed to investigate the role of an aggrecan (ACAN) gene variant and proteoglycan levels in the risk of lumbar degenerative disc disease (LDDD).

MATERIALS AND METHODS

A total of 108 patients with LDDD and 103 healthy controls were enrolled. Molecular assessment of the ACAN gene (c.6423T>C) variant was determined by real time-polymerase chain reaction. Proteoglycan levels in serum were measured with enzyme-linked immunosorbent assay.

RESULTS

The frequency of all alleles and genotypes in all study groups were distributed according to the Hardy-Weinberg equilibrium. In addition, no association between the ACAN gene (c.6423T>C) variant and presence of risk factors for LDDD was detected. However, proteoglycan levels were significantly lower in patients with LDDD compared to the control group (p<0.00001).

CONCLUSION

Our findings suggest that proteoglycan has emerged as a potential novel biomarker which might be used for prediction of LDDD risk.

Mechanotransduction and cell biomechanics of the intervertebral disc

Mechanical loading of the intervertebral disc (IVD) initiates cell-mediated remodeling events that contribute to disc degeneration. Cells of the IVD, nucleus pulposus (NP) and anulus fibrosus (AF), will exhibit various responses to different mechanical stimuli which appear to be highly dependent on loading type, magnitude, duration, and anatomic zone of cell origin. Cells of the NP, the innermost region of the disc, exhibit an anabolic response to low-moderate magnitudes of static compression, osmotic pressure, or hydrostatic pressure, while higher magnitudes promote a catabolic response marked by increased protease expression and activity. Cells of the outer AF are responsive to physical forces in a manner that depends on frequency and magnitude, as are cells of the NP, though they experience different forces, deformations, pressure, and osmotic pressure in vivo. Much remains to be understood of the mechanotransduction pathways that regulate IVD cell responses to loading, including responses to specific stimuli and also differences among cell types. There is evidence that cytoskeletal remodeling and receptor-mediated signaling are important mechanotransduction events that can regulate downstream effects like gene expression and posttranslational biosynthesis, all of which may influence phenotype and bioactivity. These and other mechanotransduction events will be regulated by known and to-be-discovered cell-matrix and cell-cell interactions, and depend on composition of extracellular matrix ligands for cell interaction, matrix stiffness, and the phenotype of the cells themselves. Here, we present a review of the current knowledge of the role of mechanical stimuli and the impact upon the cellular response to loading and changes that occur with aging and degeneration of the IVD.

Gene Expression Profiling Identifies Interferon Signalling Molecules and IGFBP3 in Human Degenerative Annulus Fibrosus

Low back pain is a major cause of disability especially for people between 20 and 50 years of age. As a costly healthcare problem, it imposes a serious socio-economic burden. Current surgical therapies fail to replace the normal disc in facilitating spinal movements and absorbing load. The focus of regenerative medicine is on identifying biomarkers and signalling pathways to improve our understanding about cascades of disc degeneration and allow for the design of specific therapies. We hypothesized that comparing microarray profiles from degenerative and non-degenerative discs will lead to the identification of dysregulated signalling and pathophysiological targets. Microarray data sets were generated from human annulus fibrosus cells and analysed using IPA ingenuity pathway analysis. Gene expression values were validated by qRT-PCR, and respective proteins were identified by immunohistochemistry. Microarray analysis revealed 238 differentially expressed genes in the degenerative annulus fibrosus. Seventeen of the dysregulated molecular markers showed log₂-fold changes greater than ±1.5. Various dysregulated cellular functions, including cell proliferation and inflammatory response, were identified. The most significant canonical pathway induced in degenerative annulus fibrosus was found to be the interferon pathway. This study indicates interferon-alpha signalling pathway activation with IFIT3 and IGFBP3 up-regulation, which may affect cellular function in human degenerative disc.

Passive strain-induced matrix synthesis and organization in shape-specific, cartilaginous neotissues

Tissue-engineered musculoskeletal soft tissues typically lack the appropriate mechanical robustness of their native counterparts, hindering their clinical applicability. With structure and function being intimately linked, efforts to capture the anatomical shape and matrix organization of native tissues are imperative to engineer functionally robust and anisotropic tissues capable of withstanding the biomechanically complex in vivo joint environment. The present study sought to tailor the use of passive axial compressive loading to drive matrix synthesis and reorganization within self-assembled, shape-specific fibrocartilaginous constructs, with the goal of developing functionally anisotropic neotissues. Specifically, shape-specific fibrocartilaginous neotissues were subjected to 0, 0.01, 0.05, or 0.1 N axial loads early during tissue culture. Results found the 0.1-N load to significantly increase both collagen and glycosaminoglycan synthesis by 27% and 67%, respectively, and to concurrently reorganize the matrix by promoting greater matrix alignment, compaction, and collagen crosslinking compared with all other loading levels. These structural enhancements translated into improved functional properties, with the 0.1-N load significantly increasing both the relaxation modulus and Young's modulus by 96% and 255%, respectively, over controls. Finite element analysis further revealed the 0.1-N uniaxial load to induce multiaxial tensile and compressive strain gradients within the shape-specific neotissues, with maxima of 10.1%, 18.3%, and -21.8% in the XX-, YY-, and ZZ-directions, respectively. This indicates that strains created in different directions in response to a single axis load drove the observed anisotropic functional properties. Together, results of this study suggest that strain thresholds exist within each axis to promote matrix synthesis, alignment, and compaction within the shape-specific neotissues. Tailoring of passive axial loading, thus, presents as a simple, yet effective way to drive in vitro matrix development in shape-specific neotissues toward more closely achieving native structural and functional properties.

The Lumbar Spine as a Dynamic Structure Depicted in Upright MRI

Spinal canal stenosis is a dynamic phenomenon that becomes apparent during spinal loading. Current diagnostic procedures have considerable short comings in diagnosing the disease to full extend, as they are performed in supine situation. Upright MRI imaging might overcome this diagnostic gap.This study investigated the lumbar neuroforamenal diameter, spinal canal diameter, vertebral body translation, and vertebral body angles in 3 different body positions using upright MRI imaging.Fifteen subjects were enrolled in this study. A dynamic MRI in 3 different body positions (at 0° supine, 80° upright, and 80° upright + hyperlordosis posture) was taken using a 0.25 T open-configuration scanner equipped with a rotatable examination bed allowing a true standing MRI.The mean diameter of the neuroforamen at L5/S1 in 0° position was 8.4 mm on the right and 8.8 mm on the left, in 80° position 7.3 mm on the right and 7.2 mm on the left, and in 80° position with hyperlordosis 6.6 mm (P < 0.05) on the right and 6.1 mm on the left (P < 0.001).The mean area of the neuroforamen at L5/S1 in 0° position was 103.5 mm on the right and 105.0 mm on the left, in 80° position 92.5 mm on the right and 94.8 mm on the left, and in 80° position with hyperlordosis 81.9 mm on the right and 90.2 mm on the left.The mean volume of the spinal canal at the L5/S1 level in 0° position was 9770 mm, in 80° position 10600 mm, and in 80° position with hyperlordosis 9414 mm.The mean intervertebral translation at level L5/S1 was 8.3 mm in 0° position, 9.9 mm in 80° position, and 10.1 mm in the 80° position with hyperlordosis.The lordosis angle at level L5/S1 was 49.4° in 0° position, 55.8° in 80° position, and 64.7 mm in the 80° position with hyperlordosis.Spinal canal stenosis is subject to a dynamic process, that can be displayed in upright MRI imaging. The range of anomalies is clinically relevant and dynamic positioning of the patient during MRI can provide essential diagnostic information which are not attainable with other methods.

Biomechanical Determination of Distal Level for Fusions across the Cervicothoracic Junction

Study Design In vitro testing. Objective To determine whether long cervical and cervicothoracic fusions increase the intradiscal pressure at the adjacent caudal disk and to determine which thoracic end vertebra causes the least increase in the adjacent-level intradiscal pressure. Methods A bending moment was applied to six cadaveric cervicothoracic spine specimens with intact rib cages. Intradiscal pressures were recorded from C7-T1 to T9-10 before and after simulated fusion by anterior cervical plating and posterior thoracic pedicle screw constructs. The changes in the intradiscal pressure from baseline were calculated and compared. Results No significant differences where found when the changes of the juxtafusion intradiscal pressure at each level were compared for the flexion, extension, and left and right bending simulations. However, combining the pressures for all directions of bending at each level demonstrated a decrease in the pressures at the T2-T3 level. Exploratory analysis comparing changes in the pressure at T2-T3 to other levels showed a significant decrease in the pressures at this level (p = 0.005). Conclusions Based on the combined intradiscal pressures alone it may be advantageous to end long constructs spanning the cervicothoracic junction at the T2 level if there are no other mitigating factors.

Delivery systems for the treatment of degenerated intervertebral discs

The intervertebral disc (IVD) is the most avascular and acellular tissue in the body and therefore prone to degeneration. During IVD degeneration, the balance between anabolic and catabolic processes in the disc is deregulated, amongst others leading to alteration of extracellular matrix production, abnormal enzyme activities and production of pro-inflammatory substances like cytokines. The established treatment strategy for IVD degeneration consists of physiotherapy, pain medication by drug therapy and if necessary surgery. This approach, however, has shown limited success. Alternative strategies to increase and prolong the effects of bioactive agents and to reverse the process of IVD degeneration include the use of delivery systems for drugs, proteins, cells and genes. In view of the specific anatomy and physiology of the IVD and depending on the strategy of the therapy, different delivery systems have been developed which are reviewed in this article.

Adipose-derived stromal cells protect intervertebral disc cells in compression: implications for stem cell regenerative disc therapy

Introduction: Abnormal biomechanics plays a role in intervertebral disc degeneration. Adipose-derived stromal cells (ADSCs) have been implicated in disc integrity; however, their role in the setting of mechanical stimuli upon the disc's nucleus pulposus (NP) remains unknown. As such, the present study aimed to evaluate the influence of ADSCs upon NP cells in compressive load culture.

Methods: Human NP cells were cultured in compressive load at 3.0MPa for 48 hours with or without ADSCs co-culture (the ratio was 50:50). We used flow cytometry, live/dead staining and scanning electron microscopy (SEM) to evaluate cell death, and determined the expression of specific apoptotic pathways by characterizing the expression of activated caspases-3, -8 and -9. We further used real-time (RT-) PCR and immunostaining to determine the expression of the extracellular matrix (ECM), mediators of matrix degradation (e.g. MMPs, TIMPs and ADAMTSs), pro-inflammatory factors and NP cell phenotype markers.

Results: ADSCs inhibited human NP cell apoptosis via suppression of activated caspase-9 and caspase-3. Furthermore, ADSCs protected NP cells from the degradative effects of compressive load by significantly up-regulating the expression of ECM genes (SOX9, COL2A1 and ACAN), tissue inhibitors of metalloproteinases (TIMPs) genes (TIMP-1 and TIMP-2) and cytokeratin 8 (CK8) protein expression. Alternatively, ADSCs showed protective effect by inhibiting compressive load mediated increase of matrix metalloproteinases (MMPs; MMP-3 and MMP-13), disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs; ADAMTS-1 and 5), and pro-inflammatory factors (IL-1beta, IL-6, TGF-beta1 and TNF-alpha).

Conclusions: Our study is the first in vitro study assessing the impact of ADSCs on NP cells in an un-physiological mechanical stimulation culture environment. Our study noted that ADSCs protect compressive load induced NP cell death and degradation by inhibition of activated caspase-9 and -3 activity; regulating ECM and modulator genes, suppressing pro-inflammatory factors and preserving CK8. Consequently, the protective impact of ADSCs found in this study provides an essential understanding and expands our knowledge as to the utility of ADSCs therapy for intervertebral disc regeneration.

Occult neural foraminal stenosis caused by association between disc degeneration and facet joint osteoarthritis: demonstration with dedicated upright MRI system

PURPOSE

The aim of our study was to evaluate the presence of dynamic foraminal stenosis using a new low-field dedicated magnetic resonance (MR) unit with a balancing system that allows images to be acquired both in the recumbent and upright position. Imaging of lumbar spine with the patient in a supine, nonweight-bearing position is likely to misrepresent the degree and potential risk of spinal stenosis.

MATERIALS AND METHODS

In the period between September 2008 and May 2011, we selected 630 symptomatic patients aged 40-65 years (mean age 56) who underwent conventional MR in clinostatic position. The study only included selected patients (total 160) who underwent clinostatic and orthostatic evaluation using a dedicated MR system (G-scan). The biomechanical parameters were also considered. Changes in the dimension of the neural foramina were compared using the presence of disc and facet degeneration by statistical analysis.

RESULTS

Stenosis of the intervertebral foramen was never found in the presence of normal intervertebral discs either in the presence or in the absence of facet disease, in either clinostatic or orthostatic position. Sixty-one stenotic levels were detected which were visualised exclusively in scans obtained under weight-bearing conditions. We named this dynamic condition "occult stenosis". In all of these cases, disc disease was associated with facet pathology.

CONCLUSION

Our data show that the association between disc pathology and facet osteoarthrosis can cause occult foraminal stenosis. Strategies to image the spine under physiological load conditions may improve the clinical diagnosis of radicular pain.

CK8 phosphorylation induced by compressive loads underlies the downregulation of CK8 in human disc degeneration by activating protein kinase C

Cytokeratin 8 (CK8) is a member of the cytokeratins family with multiple functions on the basis of its unique structural hallmark. The aberrant expression of CK8 and its phosphorylation are pertinent with various diseases. We have previously shown that CK8 exists in normal human nucleus pulposus (NP) cells and decreases as the intervertebral disc degenerates. However, the underlying molecular regulatory machinery of CK8 in intervertebral disc degeneration (IDD) has not been clarified. Here, we collected NP samples from patients with idiopathic scoliosis as control and IDD as degenerate groups. We found that CK8 expression decreased in IDD with an increased phosphorylation in degenerate NP cells. Moreover, NP cells were cultured under different compressive load schemes for diverse time duration. We found that compressive loads resulted in phosphorylation and disassembly of CK8 in a time-dependent and degree-dependent manner in vitro. The activation of protein kinase C was a significant molecular factor contributing to this phenomenon. Taken together, this study is the first to address the molecular mechanisms of CK8 downregulation in NP cells. Importantly, our findings provide clues regarding a molecular link between compressive loads and CK8 alterations, which shed a novel light on the etiology of IDD.

Cervical spine alignment, sagittal deformity, and clinical implications: a review

This paper is a narrative review of normal cervical alignment, methods for quantifying alignment, and how alignment is associated with cervical deformity, myelopathy, and adjacent-segment disease (ASD), with discussions of health-related quality of life (HRQOL). Popular methods currently used to quantify cervical alignment are discussed including cervical lordosis, sagittal vertical axis, and horizontal gaze with the chin-brow to vertical angle. Cervical deformity is examined in detail as deformities localized to the cervical spine affect, and are affected by, other parameters of the spine in preserving global sagittal alignment. An evolving trend is defining cervical sagittal alignment. Evidence from a few recent studies suggests correlations between radiographic parameters in the cervical spine and HRQOL. Analysis of the cervical regional alignment with respect to overall spinal pelvic alignment is critical. The article details mechanisms by which cervical kyphotic deformity potentially leads to ASD and discusses previous studies that suggest how postoperative sagittal malalignment may promote ASD. Further clinical studies are needed to explore the relationship of cervical malalignment and the development of ASD. Sagittal alignment of the cervical spine may play a substantial role in the development of cervical myelopathy as cervical deformity can lead to spinal cord compression and cord tension. Surgical correction of cervical myelopathy should always take into consideration cervical sagittal alignment, as decompression alone may not decrease cord tension induced by kyphosis. Awareness of the development of postlaminectomy kyphosis is critical as it relates to cervical myelopathy. The future direction of cervical deformity correction should include a comprehensive approach in assessing global cervicalpelvic relationships. Just as understanding pelvic incidence as it relates to lumbar lordosis was crucial in building our knowledge of thoracolumbar deformities, T-1 incidence and cervical sagittal balance can further our understanding of cervical deformities. Other important parameters that account for the cervical-pelvic relationship are surveyed in detail, and it is recognized that all such parameters need to be validated in studies that correlate HRQOL outcomes following cervical deformity correction.

BMP-2 and TGF-β3 do not prevent spontaneous degeneration in rabbit disc explants but induce ossification of the annulus fibrosus

INTRODUCTION

Different approaches for disc regeneration are currently under investigation. Beside gene therapy and tissue engineering techniques, the application of growth and differentiation factors own promising potential. Studies using reduced intervertebral disc models, such as cell or tissue fragment cultures, have limited validity and show controversial results depending on the employed experimental model. Therefore, the goal of the current study was to investigate the effect of BMP-2 and TGF-β3 on intervertebral disc degeneration using an in vitro full-organ disc/endplate culture system.

MATERIALS AND METHODS

Intervertebral rabbit disc explants were cultured in the presence of 1 μg/ml BMP-2 or TGF-β3 for 21 days in DMEM/F12 media. Nucleus and annulus were analyzed for gene expression of collagen type I and II (Col I/II), aggrecan, collagenases (MMP-1/MMP-13) with RT-qPCR, histological changes with bone and proteoglycan-specific staining (von Kossa, toluidine blue) and differences in cellularity (DNA) and proteoglycan content (alcian blue binding assay).

RESULTS

The results demonstrate that disc proteoglycan concentration decreased with time in the TGF-β3 and BMP-2 groups. In the annulus fibrosus (AF), TGF-β3 and BMP-2 resulted in an up-regulation of Col I and type II, and of aggrecan gene expression. In contrast, MMP genes were inhibited. In the nucleus, the growth factors decreased gene expression of aggrecan and spontaneous Col I up-regulation was inhibited by TGF-β3, whereas expression of Col II was decreased with BMP-2. There was no effect on expression of MMP-1 and MMP-13 for most sampling points. However, TGF-β3 and BMP-2 induced ossification of the AF was demonstrated by histology.

CONCLUSION

It can be concluded that both growth factors, at the tested concentrations, may not be suitable to regenerate the whole intervertebral disc organ but they are interesting candidates for being injected alone or in combination into a painful intervertebral disc to induce osseous fusion (spondylodesis).

Regeneration of the intervertebral disc with nucleus pulposus cell-seeded collagen II/hyaluronan/chondroitin-6-sulfate tri-copolymer constructs in a rabbit disc degeneration model

STUDY DESIGN

Advancement in tissue engineering provides a promising approach to recover the functionality of the degenerated intervertebral disc. In our study, a nucleus pulposus (NP) cell-seeded collagen II/hyaluronan/chondroitin-6-sulfate (CII/HyA/CS) tri-copolymer construct was implanted into the disc space directly after nucleotomy in a rabbit model.

OBJECTIVE

The aim of this study was to investigate whether the NP cell-seeded CII/HyA/CS tri-copolymer constructs could regenerate the degenerated disc in vivo after implantation into the rabbit nucleotomy model.

SUMMARY OF BACKGROUND DATA

Nucleotomy is one of the most prevalent surgical modalities to treat degenerative disc disease, which could achieve good short-term effects of pain relieve, whereas removal of the entire or partial NP changes the biomechanical characteristics of the remaining disc and the adjacent vertebral segments and a series of long-term complications such as accelerated annulus and the facet joints degeneration may ensue. Therefore, it is necessary to think about possible procedures immediately after the primary nucleotomy surgery to avoid these complications.

METHODS

NP cells isolated from thoracic and lumbar spines of New Zealand White rabbits of approximately 3 weeks of age and 1 kg in weight were labeled with a 5- (and-6) -carboxyflurescein diacetate succinimidyl ester (CFDA-SE) fluorescent dye and seeded within the CII/HyA/CS scaffold by a centrifugation method. After in vitro culture for 1 week, NP cell-seeded CII/HyA/CS tri-copolymer constructs were allografted into the disc defects of recipient rabbit immediately after nucleotomy of the lumbar spine. The Bradner Disc Index and the T2-weighted signal intensity index were determined using lateral plane radiographs and magnetic resonance imaging at 4, 12, and 24 weeks after the operation. Finally, the operated discs were explanted for gross morphological observation, histological evaluation, and cell viability assessment. Animals with only nucleotomy and cell-free CII/HyA/CS scaffold implantation served as controls.

RESULTS

In our study, we could demonstrate that the T2-weighted signal intensity index of the operated discs decreased in all three groups 1 month after surgery and the index of the cell-containing scaffold insertion group was significantly higher than that of the other two groups. After 24 weeks, the index of the cell-containing scaffold insertion group increased significantly. However, further decline was observed in both the noninsertion group and the scaffold insertion group. In radiographic analysis, the narrowing of the intervertebral disc space was significantly retarded by the cell-scaffold hybrids implantation up to 24 postoperative weeks. Furthermore, the gross morphology and histological evaluation indicated that the allografted NP cells were viable and showed extracellular matrix production.

CONCLUSION

In our study, we had constructed rabbit NP cell-seeded CII/HyA/CS tri-copolymer implants in vitro. Immediately after nucleotomy of the recipient rabbit, we allografted the precultured cell-scaffold hybrids into the lacuna of the disc. Results documented survival of the allografted NP cells and extracellular matrix deposition, which finally resulted in maintenance of disc height and restoration of T2-weighted signal intensity on magnetic resonance imaging.

Biomechanical disc culture system: feasibility study using rat intervertebral discs

A small-scale biomechanical disc culture system was designed to stimulate intervertebral disc (IVD) 'motion segment' in culture environment with load-controlled compression and combined load (compression+shear). After 7 days of diurnal mechanical loading, cell viability of discs stimulated with static compression load (0.25 MPa) and static combined load (compression (0.25 MPa)+shear (1.5N)) were similar (>90 per cent) to unloaded controls. Mechanically stimulated discs showed decrease in static/dynamic moduli, early stress relaxation, and loss of disc height after 7 days of diurnal loading. Histological data of discs indicated load-induced transformations that were not apparent in controls. The feasibility of studying the mechanobiology of intact IVD as a motion segment was demonstrated. Media conditioning (improve tissue stability in long-term culture) and application of biochemical gene expression assays (differential tissue response to types of mechanical stimulation) are proposed as future improvements. The study suggests that the limitations in studying mechanobiology of IVD pathology in vitro can be overcome and it is possible to understand the physiologically relevant mechanism of IVD pathology.

Adjacent segment motion after anterior cervical discectomy and fusion versus Prodisc-c cervical total disk arthroplasty: analysis from a randomized, controlled trial

STUDY DESIGN

Post hoc analysis of data acquired in a prospective, randomized, controlled trial.

OBJECTIVE

To compare adjacent segment motion after anterior cervical discectomy and fusion (ACDF) versus cervical total disc arthroplasty (TDA).

SUMMARY OF BACKGROUND DATA

TDA has been designed to be a motion-preserving device, thus theoretically normalizing adjacent segment kinematics. Clinical studies with short-term follow-up have yet to demonstrate a consistent significant difference in the incidence of adjacent segment disease.

METHODS

Two hundred nine patients at 13 sites were treated in a prospective, randomized, controlled trial of ACDF versus TDA for single-level symptomatic cervical degenerative disc disease (SCDD). Flexion and extension radiographs were obtained at all follow-up visits. Changes in ROM were compared using the Wilcoxon signed-rank test and the Mann-Whitney U test. Predictors of postoperative ROM were determined by multivariate analysis using mixed effects linear regression.

RESULTS

Data for 199 patients were available with 24-month follow-up. The groups were similar with respect to baseline demographics. A significant increase in motion at the cranial and caudal adjacent segments after surgery was observed in the ACDF group only (cranial: ACDF: +1.4° (0.4, 2.4), P = 0.01; TDA: +0.8°, (-0.1, +1.7), P = 0.166; caudal: ACDF: +2.6° (1.3, 3.9), P < 0.0001; TDA: +1.3, (-0.2, +2.8), P = 0.359). No significant difference in adjacent segment ROM was observed between ACDF and TDA. Only time was a significant predictor of postoperative ROM at both the cranial and caudal adjacent segments.

CONCLUSION

Adjacent segment kinematics may be altered after ACDF and TDA. Multivariate analysis showed time to be a significant predictor of changes in adjacent segment ROM. No association between the treatment chosen (ACDF vs. TDA) and ROM was observed. Furthermore clinical follow-up is needed to determine whether possible differences in adjacent segment motion affect the prevalence of adjacent segment disease in the two groups.

Two-level noncontiguous versus three-level anterior cervical discectomy and fusion: a biomechanical comparison

STUDY DESIGN

Biomechanical study.

OBJECTIVE

To determine biomechanical forces exerted on intermediate and adjacent segments after two- or three-level fusion for treatment of noncontiguous levels.

SUMMARY OF BACKGROUND DATA

Increased motion adjacent to fused spinal segments is postulated to be a driving force in adjacent segment degeneration. Occasionally, a patient requires treatment of noncontiguous levels on either side of a normal level. The biomechanical forces exerted on the intermediate and adjacent levels are unknown.

METHODS

Seven intact human cadaveric cervical spines (C3-T1) were mounted in a custom seven-axis spine simulator equipped with a follower load apparatus and OptoTRAK three-dimensional tracking system. Each intact specimen underwent five cycles each of flexion/extension, lateral bending, and axial rotation under a ± 1.5 Nm moment and a 100-Nm axial follower load. Applied torque and motion data in each axis of motion and level were recorded. Testing was repeated under the same parameters after C4-C5 and C6-C7 diskectomies were performed and fused with rigid cervical plates and interbody spacers and again after a three-level fusion from C4 to C7.

RESULTS

Range of motion was modestly increased (35%) in the intermediate and adjacent levels in the skip fusion construct. A significant or nearly significant difference was reached in seven of nine moments. With the three-level fusion construct, motion at the infra- and supra-adjacent levels was significantly or nearly significantly increased in all applied moments over the intact and the two-level noncontiguous construct. The magnitude of this change was substantial (72%).

CONCLUSION

Infra- and supra-adjacent levels experienced a marked increase in strain in all moments with a three-level fusion, whereas the intermediate, supra-, and infra-adjacent segments of a two-level fusion experienced modest strain moments relative to intact. It would be appropriate to consider noncontiguous fusions instead of a three-level fusion when confronted with nonadjacent disease.

Development of an intact intervertebral disc organ culture system in which degeneration can be induced as a prelude to studying repair potential

The present work describes a novel bovine disc organ culture system with long-term maintenance of cell viability, in which degenerative changes can be induced as a prelude to studying repair. Discs were isolated with three different techniques: without endplates (NEP), with bony endplates (BEP) and with intact cartilage endplates (CEP). Swelling, deformation, and cell viability were evaluated in unloaded cultures. Degeneration was induced by a single trypsin injection into the center of the disc and the effect on cell viability and matrix degradation was followed. Trypsin-treated discs were exposed to TGFβ to evaluate the potential to study repair in this system. NEP isolated discs showed >75% maintained cell viability for up to 10 days but were severely deformed, BEP discs on the other hand maintained morphology but failed to retain cell viability having only 27% viable cells after 10 days. In CEP discs, both cell viability and morphology were maintained for at least 4 weeks where >75% of the cells were still viable. To mimic proteoglycan loss during disc degeneration, a single trypsin injection was administered to the center of the disc. This resulted in 60% loss of aggrecan, after 7 days, without affecting cell viability. When TGFβ was injected to validate that the system can be used to study a repair response following injection of a bio-active substance, proteoglycan synthesis nearly doubled compared to baseline synthesis. Trypsin-treated bovine CEP discs therefore provide a model system for studying repair of the degenerate disc, as morphology, cell viability and responsiveness to bio-active substances were maintained.

Alterations in gene expression in response to compression of nucleus pulposus cells

BACKGROUND CONTEXT

It is clear that mechanical forces are involved in initiating disc degeneration but also have the potential to exert beneficial effects. However, the signaling pathways initiated by mechanical stress and thresholds for these responses have not been elucidated. We have developed a metabolically active compression system with the advantages of having the ability to test cells in vitro as well as within their native matrix and control exposure to environmental factors. We hypothesized that nucleus pulposus cells would respond to compressive stress with different thresholds for alterations in catabolic and anabolic gene expression.

PURPOSE

The purpose of the study was to establish the utility of a novel compression chamber and examine the effects of various magnitudes and durations of compression on nucleus pulposus inflammatory, catabolic, and anabolic gene expression.

STUDY DESIGN

In vitro controlled examination of intervertebral disc cell responses to compression.

METHODS

A chamber capable of imparting 0 to 20 MPa of hydrostatic compression onto nucleus pulposus cells was fabricated. Healthy rabbit nucleus pulposus cells were cultured in alginate beads and exposed to static compression at 0.7, 2, and 4 MPa for 4 or 24 hours. Gene expression analysis (real-time polymerase chain reaction) was performed to compare markers of inflammation (inducible nitric oxide synthase, cyclooxygenase-2), matrix catabolism (matrix metalloproteinase-3), and anticatabolic/anabolic metabolism (tissue inhibitor of metalloproteinase-1, aggrecan) in control and compressed cells.

RESULTS

Compression resulted in magnitude- and duration-dependent changes in gene expression. Increasing magnitudes showed more anticatabolic gene expression changes, whereas increasing duration resulted in increases in procatabolic gene expression.

CONCLUSION

These data demonstrate favorable effects of compression in relation to genes involved in matrix homeostasis and procatabolic gene expression in response to sustained loading levels, consistent with traumatic effects. These data provide an improved understanding of how compression affects cell signaling, which has the potential to be exploited to initiate repair and prevent matrix breakdown.

The response of annulus fibrosus cell to fibronectin-coated nanofibrous polyurethane-anionic dihydroxyoligomer scaffolds

Tissue engineering of the annulus fibrosus(AF), a component of the intervertebral disc, has proven to be challenging due to its complex oriented lamellar structure. Previously it was demonstrated that polyurethane (PU) scaffolds containing an anionic dihydroxy oligomers (ADO) may be suitable to use in this application. The current study examines whether matrix protein(s) coatings (collagen type I, collagen type I and fibronectin, fibronectin, or vitronectin) would promote cell and collagen orientation that more closely mimics native AF. The greatest cell attachment occurred when scaffolds were pre-coated with Fn. Cells on Fn-coated scaffolds were aligned parallel to scaffold fibers, a process that involved α5β1 integrin, as determined by integrin-specific blocking antibodies, which in turn reduced AF cell spreading and alignment. Cell shape was regulated by the actin cytoskeleton as cells grown in the presence of cytochalasin D did not spread. Cells on Fn-coated PU scaffolds formed fibrillar Fn, synthesized significantly more collagen, and showed linear alignment of the secreted type I collagen when compared to cells grown on the other protein-coated scaffolds and the non-coated control. Thus Fn-coating of PU-ADO scaffolds appears to promote properly oriented AF cells and collagen, which should facilitate developing AF tissue that more closely mimics the native tissue.

The influence of exogenous cross-linking and compressive creep loading on intradiscal pressure

This study involves a biomechanical evaluation of a prospective injectable treatment for degenerative discs. The high osmolarity of the non-degenerated nucleus pulposus attracts water contributing to the hydrostatic behavior of the tissue. This intradiscal pressure is known to drop as fluid is exuded from the matrix due to compressive loading. The objective of this study was to compare the changes in intradiscal pressure in control and genipin cross-linked intervertebral discs. Thirty bovine lumbar motion segments were randomly divided into a phosphate-buffered saline control group and a 0.33% genipin group and soaked at room temperature for 2 days. A needle pressure sensor was held in the center of the disc while short-term and static creep compressive loads were applied. The control group demonstrated a 25% higher average intradiscal pressure compared to genipin-treated discs under 750 N compressive load (p=0.029). Depressurization during static compressive creep was 56% higher in the control than in the genipin group (p=0.014). These results suggest cross-linking induced changes in the poroelastic properties of the involved tissues affected the mechanics of compressive load support in the disc with lower levels of nucleus pressure, a corresponding decrease in the elastic expansion of the annulus, and an increased axial compressive loading of the inner and outer annulus tissues. It is possible that concurrent changes in hydraulic permeability and proteoglycan retention known to be associated with genipin cross-linking were also contributors to poroelastic changes. Reduction of peak pressures and moderation of pressure fluctuations could be beneficial relative to discogenic pain.

Construction of collagen II/hyaluronate/chondroitin-6-sulfate tri-copolymer scaffold for nucleus pulposus tissue engineering and preliminary analysis of its physico-chemical properties and biocompatibility

To construct a novel scaffold for nucleus pulposus (NP) tissue engineering, The porous type II collagen (CII)/hyaluronate (HyA)-chondroitin-6-sulfate (6-CS) scaffold was prepared using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS) cross-linking system. The physico-chemical properties and biocompatibility of CII/HyA-CS scaffolds were evaluated. The results suggested CII/HyA-CS scaffolds have a highly porous structure (porosity: 94.8 +/- 1.5%), high water-binding capacity (79.2 +/- 2.8%) and significantly improved mechanical stability by EDC/NHS crosslinking (denaturation temperature: 74.6 +/- 1.8 and 58.1 +/- 2.6 degrees C, respectively, for the crosslinked scaffolds and the non-crosslinked; collagenase degradation rate: 39.5 +/- 3.4 and 63.5 +/- 2.0%, respectively, for the crosslinked scaffolds and the non-crosslinked). The CII/HyA-CS scaffolds also showed satisfactory cytocompatibility and histocompatibility as well as low immunogenicity. These results indicate CII/HyA-CS scaffolds may be an alternative material for NP tissue engineering due to the similarity of its composition and physico-chemical properties to those of the extracellular matrices (ECM) of native NP.

In vivo remodeling of intervertebral discs in response to short- and long-term dynamic compression

This study evaluated how dynamic compression induced changes in gene expression, tissue composition, and structural properties of the intervertebral disc using a rat tail model. We hypothesized that daily exposure to dynamic compression for short durations would result in anabolic remodeling with increased matrix protein expression and proteoglycan content, and that increased daily load exposure time and experiment duration would retain these changes but also accumulate changes representative of mild degeneration. Sprague-Dawley rats (n = 100) were instrumented with an Ilizarov-type device and divided into three dynamic compression (2 week-1.5 h/day, 2 week-8 h/day, 8 week-8 h/day at 1 MPa and 1 Hz) and two sham (2 week, 8 week) groups. Dynamic compression resulted in anabolic remodeling with increased matrix mRNA expression, minimal changes in catabolic genes or disc structure and stiffness, and increased glysosaminoglycans (GAG) content in the nucleus pulposus. Some accumulation of mild degeneration with 8 week-8 h included loss of annulus fibrosus GAG and disc height although 8-week shams also had loss of disc height, water content, and minor structural alterations. We conclude that dynamic compression is consistent with a notion of "healthy" loading that is able to maintain or promote matrix biosynthesis without substantially disrupting disc structural integrity. A slow accumulation of changes similar to human disc degeneration occurred when dynamic compression was applied for excessive durations, but this degenerative shift was mild when compared to static compression, bending, or other interventions that create greater structural disruption.

Cumulative occupational lumbar load and lumbar disc disease--results of a German multi-center case-control study (EPILIFT)

Background

The to date evidence for a dose-response relationship between physical workload and the development of lumbar disc diseases is limited. We therefore investigated the possible etiologic relevance of cumulative occupational lumbar load to lumbar disc diseases in a multi-center case-control study.

Methods

In four study regions in Germany (Frankfurt/Main, Freiburg, Halle/Saale, Regensburg), patients seeking medical care for pain associated with clinically and radiologically verified lumbar disc herniation (286 males, 278 females) or symptomatic lumbar disc narrowing (145 males, 206 females) were prospectively recruited. Population control subjects (453 males and 448 females) were drawn from the regional population registers. Cases and control subjects were between 25 and 70 years of age. In a structured personal interview, a complete occupational history was elicited to identify subjects with certain minimum workloads. On the basis of job task-specific supplementary surveys performed by technical experts, the situational lumbar load represented by the compressive force at the lumbosacral disc was determined via biomechanical model calculations for any working situation with object handling and load-intensive postures during the total working life. For this analysis, all manual handling of objects of about 5 kilograms or more and postures with trunk inclination of 20 degrees or more are included in the calculation of cumulative lumbar load. Confounder selection was based on biologic plausibility and on the change-in-estimate criterion. Odds ratios (OR) and 95% confidence intervals (CI) were calculated separately for men and women using unconditional logistic regression analysis, adjusted for age, region, and unemployment as major life event (in males) or psychosocial strain at work (in females), respectively. To further elucidate the contribution of past physical workload to the development of lumbar disc diseases, we performed lag-time analyses.

Results

We found a positive dose-response relationship between cumulative occupational lumbar load and lumbar disc herniation as well as lumbar disc narrowing among men and women. Even past lumbar load seems to contribute to the risk of lumbar disc disease.

Conclusion

According to our study, cumulative physical workload is related to lumbar disc diseases among men and women.

Spinal hemiepiphysiodesis decreases the size of vertebral growth plate hypertrophic zone and cells

BACKGROUND

Hemiepiphysiodesis is a potential method to treat idiopathic juvenile scoliosis early. The purpose of the present study was to investigate a mechanism of curve creation in the pig thoracic model of spinal hemiepiphysiodesis by determining whether the structure of the vertebral growth plate varied with distance from the stapled, concave side of the spine. The hypotheses were that the heights of the hypertrophic zone, hypertrophic cells, and disc would be decreased on the treated side of the treated level as compared with both an unstapled control level and the side opposite the staple.

METHODS

Custom spine staples were implanted into six midthoracic vertebrae in each of five skeletally immature pigs. After eight weeks, the spines were harvested and histological sections were prepared. Hypertrophic zone height, hypertrophic cell height and width, and disc height were measured at discrete coronal plane locations at stapled and unstapled thoracic levels. Differences between stapled and unstapled levels and locations were compared with use of mixed linear modeling for repeated measures, followed by regression models to determine growth plate intercept and slope across the plane by thoracic level.

RESULTS

Zone height, cell height, and cell width were lowest on the stapled side of the stapled level, with significant differences in the overall statistical model (p < 0.02). Disc heights were significantly reduced (p < 0.0001) at the stapled levels across the coronal plane.

CONCLUSIONS

Unilateral control of intervertebral joint motion decreased growth plate height, cell size, and disc height.

Intervertebral disc cell death in the porcine and human injured cervical spine after trauma: a histological and ultrastructural study

STUDY DESIGN

Histologic and ultrastructural study of disc cell death after traumatic injury to the human cervical spine and postmortem (p-m) in the porcine cervical spine.

OBJECTIVE

To determine the changes in disc cell morphology, viability, and manner of cell death after trauma in human discs and p-m in porcine discs.

SUMMARY OF BACKGROUND DATA

Similarities in the morphology of human and porcine spine have been shown in many histologic and biomechanical investigations. It is known that compressive or traumatic injuries to cartilage and intervertebral discs can result in cell death by necrosis or apoptosis. An additional form of apoptosis, chondroptosis, has been reported in articular cartilage, but not to date in the disc.

METHODS

The anterior portion of intervertebral discs and endplates of 30 patients with traumatic injuries to the cervical spine were studied histologically (including trypan blue exclusion and TUNEL staining) and ultrastructurally. Fractures were classified according to Magerl and degeneration of the intervertebral disc according to Thompson and Benneker. Similar studies of disc and endplate were undertaken on porcine cervical spine 0 to 24 hours p-m.

RESULTS

Electron and light microscopy showed up to 75% of human disc cells die within the first 24 hours of trauma, mainly by necrosis, similar to that seen in pig discs p-m. This study reports on 2 morphologies, chondroptosis and balloon cells, previously not described in the disc. Chondroptosis had been significantly higher and ballooned cells were exclusively seen in discs from fractures with compression, where apoptosis was also most common. Porcine samples revealed comparable rates of apoptosis and chondroptosis as fractures with less compression. Glycogen was commonly found in disc cells after trauma.

CONCLUSION

Traumatic injuries of the human cervical spine lead to rapid changes in disc cell morphology and cell death, particularly via necrosis. The type of fracture and load seems to influence cell death.

Effects of static compression with different loading magnitudes and durations on the intervertebral disc: an in vivo rat-tail study

STUDY DESIGN

An in vivo rat-tail model was used to study the effects of static compression with different loading magnitudes and durations on the intervertebral disc.

OBJECTIVE

To investigate the effects of static compression with different loading magnitudes and durations on the intervertebral disc over a period of time.

SUMMARY OF BACKGROUND DATA

A disc degeneration model is essential for studying therapeutic effects on degenerated disc. Static compression can induce degenerative-like changes in the intervertebral disc. However, the consequences of the simulation model over a period of resting have not been clearly documented, which may have confounding effects on the experimental outcome.

METHODS

Thirty-five rats were used. Static compressions with different loads (11 or 17 N) and durations (1 hour daily or continuous) were applied to the rat-tail caudal 8-9 disc for 2 weeks, and followed with 3 weeks of rest. The disc height was quantified in vivo on days 4, 18, and 39. The rats were killed and the discs were harvested for morphologic examination on day 39 after the disc height measurement.

RESULTS

Significant decrease in disc height was observed after continuous static compression for both 11 and 17 N, and continued during the resting period. The morphologic evaluation of the continuous compressed disc showed a decreased nuclear size, reduced number of nuclear cells, and irregular nuclear shape with inward bulging of disorganized annular collagen lamellas. Daily compression of 1 hour was found to induce a transient increase in disc height, but restored after the 3-week resting period. Favorable morphologic changes, including vacuolated nuclear cells and oval nuclear shape with well-organized annular collagen lamellas, were seen in the rat disc specimens with daily compression of 1 hour.

CONCLUSION

Disc degenerative-like changes without recovery were demonstrated in the rat caudal disc after continuous compression. The changes in disc height and disc morphology were found to be dependent on the duration of load application and may have clinical implication.

The pathophysiology of disc degeneration: a critical review

The pathophysiology of intervertebral disc degeneration has been extensively studied. Various factors have been suggested as influencing its aetiology, including mechanical factors, such as compressive loading, shear stress and vibration, as well as ageing, genetic, systemic and toxic factors, which can lead to degeneration of the disc through biochemical reactions. How are these factors linked? What is their individual importance? There is no clear evidence indicating whether ageing in the presence of repetitive injury or repetitive injury in the absence of ageing plays a greater role in the degenerative process. Mechanical factors can trigger biochemical reactions which, in turn, may promote the normal biological changes of ageing, which can also be accelerated by genetic factors. Degradation of the molecular structure of the disc during ageing renders it more susceptible to superimposed mechanical injuries. This review supports the theory that degeneration of the disc has a complex multifactorial aetiology. Which factors initiate the events in the degenerative cascade is a question that remains unanswered, but most evidence points to an age-related process influenced primarily by mechanical and genetic factors.

Optimizing nonviral-mediated transfection of human intervertebral disc chondrocytes

BACKGROUND CONTEXT

The use of viral vectors for transfection of human disc chondrocytes has been well documented. However, because of immunological and cell toxicity concerns, nonviral reagents may provide gene delivery to intervertebral disc (IVD) chondrocytes without these associated obstacles. Several studies have been done using nonviral delivery systems with varying degrees of success.

PURPOSE

The purpose of the study was to determine the efficiency, toxicity, and optimal conditions for gene delivery into human degenerative IVD cells via nonviral reagents in vitro.

STUDY DESIGN/SETTING

In vitro viral and nonviral gene transfer.

PATIENT SAMPLE

Human disc chondrocytes from 21 patients undergoing discectomy for trauma, disc herniation, and fusion for scoliosis or degenerative low back pain.

OUTCOME MEASURES

Cell cytotoxicity and transfection efficiency as determined by microscopy, luciferase assay, and flow cytometry.

METHODS

Seventeen lipid-based nonviral reagents coupled to DNA plasmids coding for luciferase were transfected into cultured chondrocytes. Cells were transfected with varying ratios of DNA plasmid to reagent, harvested at 48 hours and analyzed for transfection rates and cell viability. Transfections with adenoviral constructs were comparisons. The three most efficient reagents were then coupled to green fluorescent protein and the experiments repeated. The most efficient reagent after these experiments (LT1) was tested in standard chondrocyte-maintenance medium and a minimal medium mixture devoid of antibiotics, buffers, and amino acids. Finally, LT1 in minimal medium with various hyaluronidase treatments was tested. The most effective reagents and relative toxicity as measured by flow cytometry were analyzed using repeated measures analysis of variance.

RESULTS

LT1 was most efficient and least toxic of nonviral reagents tested. LT1 had a mean percent survival of 78.1% versus 26.6% for TKO, 15.8% for T-Jurkat, and 70.8% in controls. Transfection was 1.5%. LT1 in minimal medium was significantly better than other reagents for both cell viability and transfection percentages. Minimal medium increased transfection with other reagents, yet cell viability with TKO and T-Jurkat was poor. Hyaluronidase had no effect on the viability of controls and decreased viability from 74.9% to an overall mean of 62.6% for all treatments. Transfection percentages increased from 1.8% without treatment to 15.2% with 40 units and 10.4% with four units of hyaluronidase given 24 hours before transfection and left in throughout the experiment. When treated at the time of transfection, efficiency was not significantly different to samples without hyaluronidase added. Additionally, hyaluronidase added 24 hours before transfection and washed out at the time of transfection significantly increased transfection percentages.

CONCLUSIONS

LT1 was the most efficient reagent in terms of transfection ability and cell toxicity compared with other reagents. Treatments in minimal medium yielded significant increases in transfection and no significant difference in toxicity as compared with controls. Hyaluronidase treatments improve transfection significantly but also increase toxicity. These results suggest that the nonviral reagent LT1 can be used to transfect IVD chondrocytes in vitro and may help facilitate gene transfection of IVD chondrocytes in vivo.

Better backs by better beds?

STUDY DESIGN

A "randomized"/stratified, single-blinded, parallel-group study. OBJECTIVE.: To evaluate 3 structurally different mattresses relative influence on patients with chronic low back pain (CLBP).

SUMMARY OF BACKGROUND DATA

In several advertisements, it is proclaimed that certain mattresses have a positive effect on LBP, and especially a hard mattress is commonly believed to have a positive effect.

METHODS

One hundred sixty CLBP patients were randomized to 1 of 3 groups, having a mattress/bed mounted in their sleeping room for 1 month. The beds were: (1) waterbed (Akva), (2) body-conforming foam mattress (Tempur), and (3) a hard mattress (Innovation Futon). At baseline and after 4 weeks, a blinded observer interviewed the patients on LBP levels (0-10), daily function (activities of daily living, 0-30), and on the amount of sleeping hours/night.

RESULTS

Because of dropout of 19 patients before baseline, the analyses were performed on 141 patients. During the 1-month trial period another 27 patients stopped ahead of time, which were accounted for by "worse case" as well as "no-change" analyses. Both the waterbed and the foam mattress seemed superior to the hard mattress, especially when using the probably most relevant "worst case" data. There were no relevant difference between the effects of the water bed and the foam bed.

CONCLUSION

The Waterbed and foam mattress' did influence back symptoms, function and sleep more positively as apposed to the hard mattress, but the differences were small.

Pharmacological enhancement of disc diffusion and differentiation of healthy, ageing and degenerated discs : Results from in-vivo serial post-contrast MRI studies in 365 human lumbar discs

Degenerative disc disease (DDD) is still a poorly understood phenomenon because of the lack of availability of precise definition of healthy, ageing and degenerated discs. Decreased nutrition is the final common pathway for DDD and the status of the endplate (EP) plays a crucial role in controlling the extent of diffusion, which is the only source of nutrition. The vascular channels in the subchondral plate have muscarinic receptors but the possibility of enhancing diffusion pharmacologically by dilation of these vessels has not been probed. Although it is well accepted that EP damage will affect diffusion and thereby nutrition, there is no described method to quantify the extent of EP damage. Precise definitions with an objective method of differentiating healthy, ageing and degenerated discs on the basis of anatomical integrity of the disc and physiological basis of altered nutrition will be useful. This information is an urgent necessity for better understanding of DDD and also strategizing prevention and treatment. Seven hundred and thirty endplates of 365 lumbar discs from 73 individuals (26 healthy volunteers and 47 patients) with age ranging from 10-64 years were evaluated by pre-contrast and 10 min, 2, 4, 6 and 12 h post contrast MRI after IV injection of 0.3 mmol/kg of Gadodiamide. End plates were classified according to the extent of damage into six grades and an incremental score was given for each category. A total endplate score (TEPS) was derived by adding the EP score of the two endplates for each concerned disc. The base line value (SI(base)) and the signal intensity at particular time periods were used to derive the enhancement percentage for each time period (Enhancement (%) = SI(tp) - SI(base)/SI(base) x 100). The enhancement percentage for each time period, the time for peak enhancement (T-max) and the time intensity curve (TIC) over 12 h were used to study and compare the diffusion characteristics. The differences in pattern of diffusion were obvious visually at 4 h which was categorized into five patterns-Pattern A representing normal diffusion to Pattern E representing a total abnormality in diffusion. Degeneration was classified according to Pfirrmann's grading and this was correlated to the TEPS and the alterations in diffusion patterns. The relationship of TEPS on the increase in DDD was evaluated by a logistic curve and the cut point for severe DDD was found by ROC curve. The influence of the variables of age, level, Modic changes, instability, annulus fibrosis defect (DEBIT), TEPS and diffusion patterns on DDD was analyzed by multiple and stepwise regression analysis. Oral nimodipine study: Additional forty lumbar end-plates from four young healthy volunteers were studied to document the effect of oral nimodipine. Pre-drug diffusion levels were studied by pre and post contrast MRI (0.3 mmol/kg of gadodiamide) at 10 min, 2, 4, 6, 12 and 24 h. Oral nimodipine was administered (30 mg QID) for 5 days and post-contrast MRI studies were performed similarly. Enhancement was calculated at vertebral body-VB; subchondral bone-SCB; Endplate Zone-EPZ and at superior and inferior peripheral nucleus pulposus-PNP and central nucleus pulposus-CNP, using appropriate cursors by a blinded investigator. Paired sample t test and area under curve (AUC) measurements were done.The incidence of disc degeneration had a significant correlation with increasing TEPS (Trend Chi-square, P < 0.01). Only one out of 83 (1.2%) disc had either Pfirrmann Grade IV or V when the score was 4 or below when compared to 34/190 (17.9%) for scores 5-7; 41 of 72 (56.9%) for scores 8-10 and 18 of 20 (90%) for scores 11 and 12 (P < 0.001 for all groups). Pearson's correlation between TEPS and DDD was statistically significant, irrespective of the level of disc or different age groups (r value was above 0.6 and P < 0.01 for all age groups). Logistic curve fit analysis and ROC curve analysis showed that the incidence of DDD increased abruptly when the TEPS crossed six. With a progressive increase of end plate damage, five different patterns of diffusion were visualized. Pattern D and E represented totally altered diffusion pattern questioning the application of biological method of treatment in such situations. Four types of time intensity curves (TIC) were noted which helped to differentiate between healthy, aged and degenerated discs. Multiple and stepwise regression analysis indicated that pattern of disc diffusion and TEPS to be the most significant factors influencing DDD, irrespective of age. Nimodipine increased the average signal intensity for all regions-by 7.6% for VB, 8% for SCB and EPZ and 11% for CNP at all time intervals (P < 0.01 for all cases). Although the increase was high at all time intervals, the maximum increase was at 2 h for VB, SCB and EPZ; 4 h for PNP and 12 h for CNP. It was also interesting that post-nimodipine, the peak signal intensity was attained early, was higher and maintained longer compared to pre-nimodipine values. Our study has helped to establish that EP damage as a crucial event leading to structural failure thereby precipitating DDD. An EP damage score has been devised which had a good correlation to DDD and discs with a score of six and above can be considered 'at risk' for severe DDD. New data on disc diffusion patterns were obtained which may help to differentiate healthy, ageing and degenerated discs in in-vivo conditions. This is also the first study to document an increase in diffusion of human lumbar discs by oral nimodipine and poses interesting possibility of pharmacological enhancement of lumbar disc nutrition.

Effects of reloading after simulated microgravity on proteoglycan metabolism in the nucleus pulposus and anulus fibrosus of the lumbar intervertebral disc: an experimental study using a rat tail suspension model

STUDY DESIGN

An experiment to measure proteoglycan (PG) content and PG-related gene mRNA expressions in the lumbar intervertebral disc (IVD) of rats tail-suspended (TS) for up to 6 weeks with subsequent reloading.

OBJECTIVE

To assess the effects of reloading after simulated microgravity on PG metabolism in nucleus pulposus (NP) and anulus fibrosus (AF).

SUMMARY OF BACKGROUND DATA

Although the PG content of rat lumbar IVD is reportedly decreased by low compressive force (due to so-called microgravity) during spaceflight, it is unknown whether it recovers completely on reloading and whether these effects differ between NP and AF.

METHODS

Eighty-five F344/N rats were divided as follows: caged control (C) or TS for either 3 or 6 weeks, with some TS rats reloaded for 1 or 2 days or 3 weeks after 3 weeks' suspension (TS+RL-1d, -2d, or -3w). The glycosaminoglycan content and mRNA levels for aggrecan, TIMP1, MMP3, and ADAMTS4 were measured in NP and AF.

RESULTS

The glycosaminoglycan contents of NP and AF were significantly decreased (by 27%-42%) in the TS groups, whereas in the TS+RL-3w group recovery was complete in NP, but incomplete in AF, without histologic degenerative changes at any time point. In NP, the aggrecan mRNA level was significantly downregulated in TS-3w, but recovered to control level on reloading (TS+RL-3w). In AF, the MMP3 mRNA level was significantly elevated in TS-6w. In the early (1-2 days) response of PG-related gene expressions to reloading, mRNA levels were significantly increased for aggrecan, TIMP1, and ADAMTS4 in NP and for MMP3 in AF, but significantly decreased for ADAMTS4 in AF (vs. the TS-3w group).

CONCLUSION

Our results suggest that in IVD maintenance against the present type of mechanical stress, modulation of PG plays an important role and may be associated with molecular changes in PG-related genes.

Biologic response of the intervertebral disc to static and dynamic compression in vitro

STUDY DESIGN

This study attempts to determine the biologic response of the intervertebral disc to static and dynamic compression in vitro.

OBJECTIVE

To quantitate and compare the changes of histology, Type I and II collagens, aggrecan, interleukin (IL)-1beta, and tumor necrosis factor (TNF)-alpha expression, and apoptosis in rabbit intervertebral discs following static and dynamic compression in vitro.

SUMMARY OF BACKGROUND DATA

Compressive stimuli associated with weight-bearing and loading of the intervertebral disc are thought to be important regulators of disc cell metabolism. Very little is known about the different types of mechanical stimuli that may achieve regulation of intervertebral disc cell metabolism. We examined the biologic response of the rabbit intervertebral discs when exposed to static and dynamic compression in vitro.

METHODS

The rabbit intervertebral disc explants were in vitro subjected to unconfined uniaxial compression. Static compression of 0.5 and 1 MPa and dynamic compression of 0.5 and 1 MPa were applied at the frequency of 0.1 and 1 Hz for 6 hours, respectively. After loaded with different types of mechanical stimuli, disc explants were examined for histologic changes, collagen I, collagen II, aggrecan, IL-1beta and TNF-alpha expression, and apoptosis.

RESULTS

The static compressive load was found to suppress gene expression for collagens and aggrecan in the disc, whereas the disc under dynamic compression exhibited significant anabolic change with increase in gene expression for Type I and II collagen and aggrecan. The regional difference of the responses to mechanical loading in vitro was found between the anulus fibrosus and nucleus pulposus. All loading conditions caused marked histologic changes, up-regulation of IL-1beta and TNF-alpha expression, and increase in TUNEL-positive cells in the intervertebral discs, with the most significant from control was that when statically loaded.

CONCLUSION

Mechanical loading is involved in the physiology and pathology of disc degeneration. Static and dynamic compression may induce different biologic response of the intervertebral disc: static compression has catabolic role on the disc, whereas the dynamic load at appropriate level may benefit the synthetic activity and anabolic response of the disc.

Tissue-engineering approach to regenerating the intervertebral disc

In today's world there is an ever increasing incidence of low back pain, which is generally attributed to degeneration of the intervertebral disc (IVD) in those in their second or third decade of life. The most prevalent treatment modalities involve conservative methods (physical therapy and medications) or surgical fusion of the upper and lower vertebral bodies. In the last 10 years, there has been a surge of interest in applying tissue-engineering principles to treat spinal problems associated with the IVD. Tissue engineering provides many promising advantages to treating disc degeneration; it adopts a more biological and reparative approach, whereby the main goal is to restore the properties of the disc to its pre-degenerative state. This review outlines the physiology of the IVD and the etiology of disc degeneration. Much of the research carried out in the field of tissue engineering is based on three predominant constituents: cells, scaffolds, and signals. Thus, specific attention is given to these constituents and their potential use in repairing the IVD. Some of the significant challenges involved in IVD tissue engineering are also identified, and a brief discussion regarding possible future areas of research follows.

Nucleus pulposus cellular longevity by telomerase gene therapy

STUDY DESIGN

Nonviral transfection of nucleus pulposus cells with a telomerase expression construct to assess the effects on cellular lifespan, function, karyotypic stability, and transformation properties.

OBJECTIVES

To investigate whether telomerase gene therapy can extend the cellular lifespan while retaining functionality of nucleus pulposus cells in a safe manner.

SUMMARY OF BACKGROUND DATA

Degeneration of the intervertebral disc is an age-related condition in which cells responsible for the maintenance and health of the disc deteriorate with age. Telomerase can extend the cellular lifespan and function of other musculoskeletal tissues, such as the heart, bones, and connective tissues. Therefore, extension of the cellular lifespan and matrix production of intervertebral disc cells may have the potential to delay the degeneration process.

METHODS

Ovine nucleus pulposus cells were lipofectamine transfected in vitro with a human telomerase reverse transcriptase (hTERT) expression construct. Cellular lifespan and matrix transcript levels were determined by cumulative population doublings and real-time RT-PCR, respectively. G1-cell cycle checkpoint, p53 functionality, growth of transfected cells in anchorage-independent or serum starvation conditions, and karyotypic analysis were performed.

RESULTS

Transfection was achieved successfully with 340% +/- 7% (mean +/- SD) relative telomerase activity in hTERT-transfected cells. hTERT transfection enabled a 50% extension in mean cellular lifespan and prolonged matrix production of collagen 1 and 2 for more than 282 days. Karyotypic instability was detected but G1-cell cycle checkpoint and p53 was functionally comparable to parental cells with no growth in serum starvation or anchorage-independent conditions.

CONCLUSIONS

Telomerase can extend the cellular lifespan of nucleus pulposus cells and prolong the production of extracellular matrix. Safety is still unresolved, as karyotypic instability was detected but no loss of contact inhibition, mitogen dependency, or G1-cell cycle checkpoint control was evident.

Anti-catabolic effect of OP-1 in chronically compressed intervertebral discs

Experimental animal models of disc degeneration have been used to assess the biomechanical behavior, biochemical composition, and biological changes in the intervertebral discs. The objective of our study was to evaluate the anabolic and anti-catabolic effects of intradiscal injection of Osteogenic Protein-1 (OP-1) by histology and immunohistochemistry in disc degeneration model. Thirty-four rats were divided into five groups: intact control; sham control; compressed nucleus pulposus (NP) injected with saline; and two OP-1 groups: COP-1 group (compression was continued after intradiscal OP-1 injection) and ROP-1 group (compression was released at the time of OP-1 injection). Anabolic and anti-catabolic effects of OP-1 were evaluated by histology and immunohistochemistry with the following antibodies: anti-pro- and anti-mature OP-1, anti-MMP-13, anti-aggrecanase, anti-substance P, anti-tumor necrosis factor-alpha (TNF-alpha), and anti-interleukin-1beta (IL-1beta). The OP-1 injection to the degenerative disc stimulated an anabolic response characterized by the restoration of the normal morphology of the disc, increased Safranin O staining in the NP, extention of the extracellular matrix, and stimulation of endogenous OP-1 synthesis in the NP, annulus fibrosis (AF), and end-plate. The anti-catabolic effect of OP-1 was documented by reduced immunostaining for aggrecanase, MMP-13, substance P, TNF-alpha, and IL-1beta. This study confirmed the anti-catabolic activity of OP-1 as demonstrated previously in human articular cartilage and provided critical evidence for the potential of OP-1 therapy in the treatment of disc degeneration. Because substance P is a neuropeptide linked with inflammation and pain, a reduction in the level of this protein may support our previously reported results on the effect of OP-1 on pain-related behavior.

Establishment of a novel intervertebral disc/endplate culture model: analysis of an ex vivo in vitro whole-organ rabbit culture system

STUDY DESIGN

Ex vivo in vitro study evaluating a novel intervertebral disc/endplate culture system.

OBJECTIVES

To establish a whole-organ intervertebral disc culture model for the study of disc degeneration in vitro, including the characterization of basic cell and organ function.

SUMMARY OF BACKGROUND DATA

With current in vivo models for the study of disc and endplate degeneration, it remains difficult to investigate the complex disc metabolism and signaling cascades. In contrast, more controlled but simplified in vitro systems using isolated cells or disc fragments are difficult to culture due to the unconstrained conditions, with often-observed cell death or cell dedifferentiation. Therefore, there is a demand for a controlled culture model with preserved cell function that offers the possibility to investigate disc and endplate pathologies in a structurally intact organ.

METHODS

Naturally constrained intervertebral disc/endplate units from rabbits were cultured in multi-well plates. Cell viability, metabolic activity, matrix composition, and matrix gene expression profile were monitored using the Live/Dead cell viability test (Invitrogen, Basel, Switzerland), tetrazolium salt reduction (WST-8), proteoglycan and deoxyribonucleic acid quantification assays, and quantitative polymerase chain reaction.

RESULTS

Viability and organ integrity were preserved for at least 4 weeks, while proteoglycan and deoxyribonucleic acid content decreased slightly, and matrix genes exhibited a degenerative profile with up-regulation of type I collagen and suppression of collagen type II and aggrecan genes. Additionally, cell metabolic activity was reduced to one third of the initial value.

CONCLUSIONS

Naturally constrained intervertebral rabbit discs could be cultured for several weeks without losing cell viability. Structural integrity and matrix composition were retained. However, the organ responded to the artificial environment with a degenerative gene expression pattern and decreased metabolic rate. Therefore, the described system serves as a promising in vitro model to study disc degeneration in a whole organ.

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited

OBJECTIVE

The objectives of this white paper are to review and summarize the basic science literature relevant to spinal fixation (subluxation) and spinal adjusting procedures and to make specific recommendations for future research.

METHODS

PubMed, CINAHL, ICL, OSTMED, and MANTIS databases were searched by a multidisciplinary team for reports of basic science research (since 1995) related to spinal fixation (subluxation) and spinal adjusting (spinal manipulation). In addition, hand searches of the reference sections of studies judged to be important by the authors were also obtained. Each author used key words they determined to be most important to their field in designing their individual search strategy. Both animal and human studies were included in the literature searches, summaries, and recommendations for future research produced in this project.

DISCUSSION

The following topic areas were identified: anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system. A relevant summary of each topic area and specific recommendations for future research in each area were the primary objectives of this project.

CONCLUSIONS

The summaries of the literature for the 6 topic sections (anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system) indicated that a significant body of basic science research evaluating chiropractic spinal adjusting has been completed and published since the 1997 basic science white paper. Much more basic science research in these fields needs to be accomplished, and the recommendations at the end of each topic section should help researchers, funding agencies, and other decision makers develop specific research priorities.

Influence of diurnal hyperosmotic loading on the metabolism and matrix gene expression of a whole-organ intervertebral disc model

It is generally agreed that the mechanical environment of intervertebral disc cells plays an important role in maintaining a balanced matrix metabolism. The precise mechanism by which the signals are transduced into the cells is poorly understood. Osmotic changes in the extracellular matrix (ECM) are thought to be involved. Current in-vitro studies on this topic are mostly short-term and show conflicting data on the reaction of disc cells subjected to osmotic changes which is partially due to the heterogenous and often substantially-reduced culture systems. The aim of the study was therefore to investigate the effects of cyclic osmotic loading for 4 weeks on metabolism and matrix gene expression in a full-organ intervertebral disc culture system. Intervertebral disc/endplate units were isolated from New Zealand White Rabbits and cultured either in iso-osmotic media (335 mosmol/kg) or were diurnally exposed for 8 hours to hyper-osmotic conditions (485 mosmol/kg). Cell viability, metabolic activity, matrix composition and matrix gene expression profile (collagen types I/II and aggrecan) were monitored using Live/Dead cell viability assay, tetrazolium reduction test (WST 8), proteoglycan and DNA quantification assays and quantitative PCR. The results show that diurnal osmotic stimulation did not have significant effects on proteoglycan content, cellularity and disc cell viability after 28 days in culture. However, hyperosmolarity caused increased cell death in the early culture phase and counteracted up-regulation of type I collagen gene expression in nucleus and annulus cells. Moreover, the initially decreased cellular dehydrogenase activity recovered with osmotic stimulation after 4 weeks and aggrecan gene down-regulation was delayed, although the latter was not significant according to our statistical criteria. In contrast, collagen type II did not respond to the osmotic changes and was down-regulated in both groups. In conclusion, diurnal hyper-osmotic stimulation of a whole-organ disc/endplate culture partially inhibits a matrix gene expression profile as encountered in degenerative disc disease and counteracts cellular metabolic hypo-activity.

Frequency response of pig intervertebral disc cells subjected to dynamic hydrostatic pressure

The pathogenesis of vibration-induced disorders of intervertebral disc at the cellular level is largely unknown. Dynamic loads with frequencies close to that of the in vivo human spine resonant frequency (4-6 Hz) have a destructive effect, which may induce extracellular disc matrix (ECM) degradation. To investigate this issue, three-dimensional (3D) alginate cultures of normal pig intervertebral disc nucleus and inner annulus cells were tested under dynamic hydrostatic loading. Alginate cultures of each region were divided into six groups; five groups were exposed to cyclic hydrostatic pressures of frequencies 1, 3, 5, 8, and 10 Hz with the same amplitude (1 MPa), and group 6 was the control group (no loading). Cultures of different groups were loaded for 3 days (30 min daily) in a hydraulic chamber. Effects of loading frequency on disc collagen and protein metabolism were investigated by measuring 3H-proline-labeled proteins associated with the cells in the extracellular matrix and release of 3H-proline-labeled molecules into culture medium. The results indicated a poor synthesis rate and more degradation near the 5 Hz frequency. The repeatability of experiments was verified by performing two experiments with the same protocol. Both experiments indicated that a threshold frequency of around 5 Hz disrupted protein metabolism.

Rat spinal motion segment in organ culture: a cell viability study

STUDY DESIGN

This study investigated tissue integrity and viability of cells in an organ culture system of intervertebral disc (IVD) with adjoining vertebral bodies.

OBJECTIVE

The goal of this study was to design a methodology to maintain an IVD motion segment in organ culture, thereby preserving viability and tissue architecture.

SUMMARY OF BACKGROUND DATA

Study of IVD mechanobiology in vitro necessitates availability of vertebral bodies for controlled application of complex loads.

METHODS

IVD motion segments were dissected from rat lumbar segments and maintained in organ culture and cell viability was evaluated histochemically using NitroBlue Tetrazolium. Tissue integrity and morphology were evaluated using conventional histologic techniques.

RESULTS

The in vitro organ culture of motion segments maintained the viability and tissue integrity for 14 days. More than 95% viability in all three regions of interest (anulus fibrosus, nucleus pulposus, end plates) was maintained for 14 days in culture.

CONCLUSION

Our initial results suggest that long-term motion segment culture is practical, and the inclusion of vertebral bodies will facilitate anchoring during biomechanical stimulation. Thus, we expect the culture system to provide us with an excellent model for studying the pathomechanics of IVD degeneration and the effects of mechanical stimulation on the biology of IVD cells.

Stepwise reduction of functional spinal structures increase vertebral translation and intradiscal pressure

To date, there are only a few studies that provide data to efficiently calibrate finite element models for the spine due to its complexity. In a recent study, we quantified the range of motion rotation and the lordosis angle. This paper provides complementary results regarding two more parameters, intradiscal pressure and vertebral translation. All parameters were obtained as a function of stepwise anatomical reduction, loading direction and magnitude. Eight lumbar spinal segments (L4-5) with a median age of 52 years (38-59 years) and no signs of disc degeneration were used for the in vitro testing. A miniaturized pressure probe was implanted into the nucleus. An ultrasound-based motion-tracking system was employed to record spatial movements of several landmarks on the specimens. The center of L4, the anterior, posterior, left and right point of the lower endplate of L4 were digitized as landmarks and its translation was determined. Specimens were loaded with pure moments (1-10Nm) in the three principal anatomical planes at a loading rate of 1.0 degrees /s. Anatomy was stepwise reduced by cutting different ligaments, facet capsules and joints and removing nucleus. Translation analysis showed that the L4 center point had its largest displacement in sagittal direction and almost none vertically. Removal of the supra- and interspinous, flaval ligaments showed a slight increase and further removal of structures, a higher increase of translation. Axial rotation also was accompanied with L4 to elevate when torsion was applied. This effect was found to be larger with progressing defects. Nucleotomy exhibited the most unstable situation for specimens. Results of the intradiscal pressure indicated a large increase after removing the facet capsules and joints. Furthermore, it was found that intradiscal pressure correlated well with data of range of motion for rotation. Predicting and simulating clinical defects, surgical intervention or treatment methods requires a well performed calibration based on in vitro data, whereas it is important to adapt all including structures with as many known parameters as possible. Results provided by these studies may be used as a database for researchers aiming to calibrate or validate finite element models of L4-5 segments.

A stimulation unit for the application of mechanical strain on tissue engineered anulus fibrosus cells: a new system to induce extracellular matrix synthesis by anulus fibrosus cells dependent on cyclic mechanical strain

A bioreactor system consisting of a multifunctional stimulation unit and common 6-well culture plate is introduced to activate extracellular matrix synthesis in intervertebral disc cells due to cyclic mechanical strain. The developed stimulation unit is sterilizable and reusable. It is viable for cultivation and mechanical stimulation of cartilage tissue and tissue engineered cell matrix constructs in combination with the common 6-well culture plate. The custom made device allows long-term cultivations in batch- or continuous operation mode. Manual handling and thereby the risk of contamination is reduced. Sampling, changing the medium, and addition of supplements are easily performed from the connected conditioning vessel. This bioreactor system enables stimulation of different samples independently during one run. For the work presented here anulus fibrosus cells from pigs were taken and immobilized in agarose to obtain three-dimensional cell matrix constructs. Over a period of 14 days the constructs were subjected to 10% compression under cyclic mechanical pressure with a frequency of 0.1 Hz. Afterwards the constructs were biochemically examined for hydroxyproline and sulphated glycosaminoglycanes. These proven constituents of extracellular matrix were found to be released depending on the applied compressive strain.

In vitro organ culture of the bovine intervertebral disc: effects of vertebral endplate and potential for mechanobiology studies

STUDY DESIGN

Whole bovine coccygeal discs were cultured under static load, with or without vertebral endplates (VEPs), and assessed for cell viability, biochemical stability, biosynthetic activity, and biosynthetic responsiveness to changes in mechanical load.

OBJECTIVES

To assess the effects of VEPs on biochemical and cellular stability of disc cells during in vitro culture of large disc explants. To determine whether cultured discs could respond to mechanical perturbation.

SUMMARY OF BACKGROUND DATA

Previous methods for culturing the intervertebral disc have focused on rabbit and rat discs, but the small size of these discs limits the relevance of these culture systems to the human condition. Bovine coccygeal discs have similar dimensions to the human lumbar disc (i.e., similar size and nominal stresses), but long-term culture of these discs has not been reported.

METHODS

Bovine coccygeal discs were harvested with or without VEPs, cultured under static load (5 kg, approximately 0.25 MPa, in situ swelling pressure) for up to 1 week, and evaluated for changes in hydration, glycosaminoglycan content, cell viability, and biosynthetic activity. Additionally, the biochemical and biosynthetic response of discs cultured without VEP to increasing the load to a 20-kg (approximately 1 MPa, the estimated stress in human lumbar disc during heavy lifting) static load for 6 hours was assessed.

RESULTS

During the first 24 hours, culturing discs with endplates was moderately better with regards to maintaining in situ anulus hydration and nucleus glycosaminoglycan levels. The endplates, however, obstructed media flow to the disc, resulting in a marked decrease in cell viability after 1 week of culture. Nucleus pulposus cell viability was maintained in discs cultured without endplates, but there was a significant drop in biosynthetic activity within 2 days of culture. Despite this drop, the disc cells in the discs without VEP remained biosynthetically responsive to changes in mechanical loading.

CONCLUSIONS

It is possible to maintain cell viability and the biosynthetic responsiveness of large discs for up to 1 week in vitro when the discs are cultured under static load and without VEP.