Do intervertebral discs degenerate before they herniate, or after?

Association between vertebral cross-sectional area and lumbar disc displacement - a population-based study

PURPOSE

Vertebral dimensions may constitute a potential risk factor for degenerative changes in the spine. Previous studies have found a positive association between vertebral height and both type 2 Modic changes and intervertebral disc height loss. Also, vertebral endplate size has been associated with disc degeneration. However, only a few studies have investigated the association between vertebral dimensions and lumbar disc displacement (LDD). This study aimed to investigate the association between vertebral cross-sectional area (CSA) and LDD among the general middle-aged Finnish population. We hypothesized that larger vertebral CSA is associated with LDD.

MATERIALS AND METHODS

The study was conducted by using data from the Northern Finland Birth Cohort 1966 (NFBC1966). At the age of 46, a subpopulation of NFBC1966 underwent clinical examinations including magnetic resonance imaging (MRI) (n = 1249). MRI scans were used to measure L4 CSA and evaluate the presence of LDD (bulge, protrusion, and extrusion/sequestration) in the adjacent discs. The association between L4 CSA and LDD was analysed using logistic regression, with adjustment for sex, education, body mass index, leisure-time physical activity, smoking, diet, and L4 height.

RESULTS

Larger L4 CSA was associated with LDD; an increase of 1 cm2 in vertebral CSA elevated the odds of LDD relative to no LDD by 10% (adjusted odds ratio 1.10, 95% CI 1.01-1.19). The association was similar among either sex.

CONCLUSIONS

Larger L4 vertebral CSA was associated with LDD in our study sample. Even though smaller vertebral size exposes our vertebrae to osteoporotic fractures, it simultaneously seems to protect us from LDD.

Injectable hydrogel induces regeneration of naturally degenerate human intervertebral discs in a loaded organ culture model

Low back pain resulting from disc degeneration is a leading cause of disability worldwide. However, to date few therapies target the cause and fail to repair the intervertebral disc (IVD). This study investigates the ability of an injectable hydrogel (NPgel), to inhibit catabolic protein expression and promote matrix expression in human nucleus pulposus (NP) cells within a tissue explant culture model isolated from degenerate discs. Furthermore, the injection capacity of NPgel into naturally degenerate whole human discs, effects on mechanical function, and resistance to extrusion during loading were investigated. Finally, the induction of potential regenerative effects in a physiologically loaded human organ culture system was investigated following injection of NPgel with or without bone marrow progenitor cells. Injection of NPgel into naturally degenerate human IVDs increased disc height and Young's modulus, and was retained during extrusion testing. Injection into cadaveric discs followed by culture under physiological loading increased MRI signal intensity, restored natural biomechanical properties and showed evidence of increased anabolism and decreased catabolism with tissue integration observed. These results provide essential proof of concept data supporting the use of NPgel as an injectable therapy for disc regeneration. STATEMENT OF SIGNIFICANCE: Low back pain resulting from disc degeneration is a leading cause of disability worldwide. However, to date few therapies target the cause and fail to repair the intervertebral disc. This study investigated the potential regenerative properties of an injectable hydrogel system (NPgel) within human tissue samples. To mimic the human in vivo conditions and the unique IVD niche, a dynamically loaded intact human disc culture system was utilised. NPgel improved the biomechanical properties, increased MRI intensity and decreased degree of degeneration. Furthermore, NPgel induced matrix production and decreased catabolic factors by the native cells of the disc. This manuscript provides evidence for the potential use of NPgel as a regenerative biomaterial for intervertebral disc degeneration.

Understanding the etiopathogenesis of lumbar intervertebral disc herniation: From clinical evidence to basic scientific research

Lumbar intervertebral disc herniation, as a leading cause of low back pain, productivity loss, and disability, is a common musculoskeletal disorder that results in significant socioeconomic burdens. Despite extensive clinical and basic scientific research efforts, herniation etiopathogenesis, particularly its initiation and progression, is not well understood. Understanding herniation etiopathogenesis is essential for developing effective preventive measures and therapeutic interventions. Thus, this review seeks to provide a thorough overview of the advances in herniation-oriented research, with a discussion on ongoing challenges and potential future directions for clinical, translational, and basic scientific investigations to facilitate innovative interdisciplinary research aimed at understanding herniation etiopathogenesis. Specifically, risk factors for herniation are identified and summarized, including familial predisposition, obesity, diabetes mellitus, smoking tobacco, selected cardiovascular diseases, disc degeneration, and occupational risks. Basic scientific experimental and computational research that aims to understand the link between excessive mechanical load, catabolic tissue remodeling due to inflammation or insufficient nutrient supply, and herniation, are also reviewed. Potential future directions to address the current challenges in herniation-oriented research are explored by combining known progressive development in existing research techniques with ongoing technological advances. More research on the relationship between occupational risk factors and herniation, as well as the relationship between degeneration and herniation, is needed to develop preventive measures for working-age individuals. Notably, researchers should explore using or modifying existing degeneration animal models to study herniation etiopathogenesis, as such models may allow for a better understanding of how to prevent mild-to-moderately degenerated discs from herniating.

Cell clusters in intervertebral disc degeneration: an attempted repair mechanism aborted via apoptosis

Cell clusters are a histological hallmark feature of intervertebral disc degeneration. Clusters arise from cell proliferation, are associated with replicative senescence, and remain metabolically, but their precise role in various stages of disc degeneration remain obscure. The aim of this study was therefore to investigate small, medium, and large size cell-clusters. For this purpose, human disc samples were collected from 55 subjects, aged 37-72 years, 21 patients had disc herniation, 10 had degenerated non-herniated discs, and 9 had degenerative scoliosis with spinal curvature <45°. 15 non-degenerated control discs were from cadavers. Clusters and matrix changes were investigated with histology, immunohistochemistry, and Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Data obtained were analyzed with spearman rank correlation and ANOVA. Results revealed, small and medium-sized clusters were positive for cell proliferation markers Ki-67 and proliferating cell nuclear antigen (PCNA) in control and slightly degenerated human discs, while large cell clusters were typically more abundant in severely degenerated and herniated discs. Large clusters associated with matrix fissures, proteoglycan loss, matrix metalloproteinase-1 (MMP-1), and Caspase-3. Spatial association findings were reconfirmed with SDS-PAGE that showed presence to these target markers based on its molecular weight. Controls, slightly degenerated discs showed smaller clusters, less proteoglycan loss, MMP-1, and Caspase-3. In conclusion, cell clusters in the early stages of degeneration could be indicative of repair, however sustained loading increases large cell clusters especially around microscopic fissures that accelerates inflammatory catabolism and alters cellular metabolism, thus attempted repair process initiated by cell clusters fails and is aborted at least in part via apoptosis.

In-vitro models of disc degeneration - A review of methods and clinical relevance

The intervertebral disc (IVD) provides flexibility, acts as a shock absorber, and transmits load. Degeneration of the IVD includes alterations in the biomechanics, extracellular matrix (ECM), and cellular activity. These changes are not always perceived, however, IVD degeneration can lead to severe health problems including long-term disability. To understand the pathogenesis of IVD degeneration and suitable testing methods for emerging treatments and therapies, this review documents in-vitro models of IVD degeneration including physical disruption, hyperphysiological loading, ECM degradation by enzyme digestion, or a combination of these methods. This paper reviews and critically analyses the models of degeneration published since the year 2000 in either in human or animal specimens. The results are categorised in terms of the IVD biomechanics, physical attributes, ECM composition, tissue damage and cellularity to evaluate the models with respect to natural human degeneration, and to provide recommendations for clinically relevant models for the various stages of degeneration. There is no one model that replicates the wide range of degenerative changes that occur as part of normal degeneration. However, cyclic overloading replicates many aspects of degeneration, with the advantage of a dose-response allowing the tuning of damage initiated. Models of severe degeneration are currently lacking, but there is potential that combining cyclic overloading and enzymatic digestion will provide model that closely resembles human IVD degeneration. This will provide an effective way to investigate the effects of severe degeneration, and the evaluation of treatments for the IVD, which would generally be indicated at this advanced stage of degeneration.

Mesenchymal stromal/stem cells and their exosomes application in the treatment of intervertebral disc disease: A promising frontier

Today, the application of mesenchymal stromal/stem cells (MSCs) and their exosomes to treat degenerative diseases has received attention. Due to the characteristics of these cells, such as self-renewability, differentiative and immunomodulatory effects, their use in laboratory and clinical studies shows promising results. However, the allogeneic transplantation problems of MSCs limit the use of these cells in the clinic. Scientists propose the application of exosomes to use from the therapeutic effect of MSCs and overcome their defects. These vesicles change the target cell behaviour and transcription profile by transferring various cargo such as proteins, mi-RNAs, and lipids. One of the degenerative tissue diseases in which MSCs and their exosomes are used in their treatment is intervertebral disc disease (IDD). Different factors such as genetics, nutrition, ageing, and environmental factors play a significant role in the onset and progression of this disease. These factors affect the cellular and molecular properties of the disc, leading to tissue destruction. Nucleus pulposus cells (NPCs) are among the most important cells involved in the pathogenesis of disc degeneration. MSCs exert their therapeutic effects by differentiating, reducing apoptosis, increasing proliferation, and decreasing senescence in NPCs. In addition, the use of MSCs and their exosomes also affects the annulus fibrosus and cartilaginous endplate cells in disc tissue and prevents disc degeneration progression.

Prospective, population-based study of occupational movements and postures of the neck as risk factors for cervical disc herniation

OBJECTIVE

We studied the associations between objectively measured occupational neck exposures in a job exposure matrix (JEM) and cervical disc herniation (CDH).

DESIGN

A cohort study of Danish workers who ever held at least one of 29 jobs (eg, dentists, hairdressers, childcare, carpenters) from 1981 to 2016 was formed. Representative whole work-day inclinometric measurements from previous studies using triaxial accelerometers measuring neck angular velocity and posture of the neck were used as exposure in a JEM. Job titles were retrieved from the Danish Occupational Cohort with eXposure data database. The risk of CDH by quintiles of cumulated exposure was assessed by incidence rate ratios (IRR), adjusted for age, sex, calendar-year, previous lumbar disc herniation and educational level, using Poisson regression models.

SETTING

Nationwide Danish registers.

PARTICIPANTS

852 625 Danish workers within 29 different job-titles.

OUTCOME MEASURES

First diagnosis of CDH was retrieved from the Danish National Patient Register.

RESULTS

We found 14 000 cases of CDH during 20.2 million person-years of follow-up. Increasing levels of neck angular velocity showed a decreasing risk with IRR 0.90 (95% CI 0.86 to 0.95) when the highest level of cumulative exposure (dynamic work) was compared with the lowest (static work). Similar results were found for extension and flexion of the neck, though not statistically significant for extension. Multiple sensitivity analyses did not change the results.

CONCLUSION

In this large register-based study based on a JEM, we found no evidence of an increased risk of CDH with increasing cumulated angular velocity, flexion or extension of the neck. Factors other than occupational dynamic neck movements and bent neck position seem to be important in the development of CDH.

TNF-α-stimulated nucleus pulposus cells induce cell apoptosis through the release of exosomal miR-16 targeting IGF-1 and IGF-1R in rats

Background

Exosomes may contain excess cellular components released by cells in response to harmful external stimuli to maintain cellular homeostasis. Inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), can induce cell apoptosis, alter cellular component expression levels, and stimulate exosome release. In this study, we examined whether exosomes released from nucleus pulposus cells (NPCs) under inflammatory conditions could induce normal NP cell apoptosis in rats and its underlining mechanism.

Methods

Exosomes were isolated from TNF-α‐treated NPCs and used to treat normal NPCs. The effects were assessed by flow cytometry and western blot analysis. Anti-apoptotic insulin-like growth factor-1 (IGF-1) expression in NPCs was assessed by western blot analysis. Given the exosomal miRNAs might be the key factors of exosomes, bioinformatics approaches and quantitative real-time polymerase chain reaction (qRT-PCR) were used to identify IGF-1-regulating micro RNAs (miRNAs), including miR-16. Luciferase reporter assay assessed miR-16 regulation of IGF-1 and IGF-1 receptor (IGF-1R). NPCs were transfected with miR-16 mimic, and exosomes were applied to normal NPCs. NPCs were pretreated with 10 ng/mL TNF-α, transfected with miR-16 inhibitors, and the exosomes were isolated. Cell and exosome miR-16 levels were detected by qRT-PCR. Western blot analysis determined IGF-1, IGF-1R, and apoptotic marker levels in exosome-treated NPCs.

Results

Exosomes from TNF-α-treated NPCs induced apoptosis in normal NPCs and repressed IGF-1 expression. Exosomal miR-16 regulated IGF-1 and induced NPC apoptosis. The dual-luciferase reporter assay revealed that miR-16 binds the 3' untranslated regions (3'-UTRs) of IGF-1 and IGF-1R. Exosomal miR-16 repressed IGF-1 and the IGF-1R/phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway which therefore induced NPC apoptosis. Rescue experiments using miR-16 inhibitors further validated these findings.

Conclusions

The inflammatory factor TNF-α stimulated exosome release from NPCs, which induced the apoptosis of normal NPCs through the actions of exosomal miR-16. Exosomal miR-16 directly repressed the anti-apoptotic IGF-1/IGF-1R pathway, increasing the apoptosis of NPCs.

The Correlation Between Facet Tropism and Intervertebral Disc Herniation in the Subaxial Cervical Spine

STUDY DESIGN

A retrospective case-control study.

OBJECTIVE

Investigating the correlation between the facet tropism (FT) and subaxial cervical disc herniation (CDH).

SUMMARY OF BACKGROUND DATA

Although debatable, it was widely reported that FT was associated with lumbar disc herniation. However, the exact correlation between FT and subaxial CDH is still unclear.

METHODS

Two-hundred patients with any disc herniation at C3/4, C4/5, C5/6, or C6/7 and 50 normal participants without CDH (normal control group) were included in this study. For patients, the cervical levels with CDH and the levels without herniation were classified into the "herniation group" and "patient control group," respectively. Bilateral facet joint angles at C3/4, C4/5, C5/6, and C6/7 on sagittal, axial, and coronal planes were measured on computed tomography (CT). The disc degeneration at each level was assessed on magnetic resonance imaging (MRI).

RESULTS

Both the mean difference between left and right facet angles and tropism incidence in herniation group were significantly greater than those in two control groups whenever at C3/4, C4/5, C5/6, or C6/7 level and whenever on sagittal, axial, or coronal plane. The mean differences of angles and tropism incidences in most patient control groups were not significantly greater than those of corresponding normal control groups. The incidence of greater facet angle at the left or right side was not significantly different among the left, central, and right herniation groups. The mean disc degeneration grades in both herniation and patient control groups were significantly higher than those in normal control groups while no difference between herniation and patient control groups.

CONCLUSION

The FT on the sagittal, axial, and coronal planes are all associated with CDH in the subaxial cervical spine. The greater facet angle at the left or right side does not affect the side of herniation. The severity of cervical disc degeneration is not associated with FT.Level of Evidence: 3.

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

Intervertebral disc (IVD) degeneration is a major risk factor of low back pain. It is defined by a progressive loss of the IVD structure and functionality, leading to severe impairments with restricted treatment options due to the highly demanding mechanical exposure of the IVD. Degenerative changes in the IVD usually increase with age but at an accelerated rate in some individuals. To understand the initiation and progression of this disease, it is crucial to identify key top-down and bottom-up regulations' processes, across the cell, tissue, and organ levels, in health and disease. Owing to unremitting investigation of experimental research, the comprehension of detailed cell signaling pathways and their effect on matrix turnover significantly rose. Likewise, in silico research substantially contributed to a holistic understanding of spatiotemporal effects and complex, multifactorial interactions within the IVD. Together with important achievements in the research of biomaterials, manifold promising approaches for regenerative treatment options were presented over the last years. This review provides an integrative analysis of the current knowledge about (1) the multiscale function and regulation of the IVD in health and disease, (2) the possible regenerative strategies, and (3) the in silico models that shall eventually support the development of advanced therapies.

Vascularization of the human intervertebral disc: A scoping review

Intervertebral discs (IVDs) are often referred to as the largest avascular structures of the human body, yet a collective resource characterizing the vascularization of the IVD does not exist. To address this gap, the objective of this study was to conduct a comprehensive search of the literature to review and summarize current knowledge of the prevalence and localization of blood supply in human IVDs, with a scoping review. A comprehensive search of peer-reviewed publications on the topic of IVD vascularization in humans was conducted across six electronic databases: PubMed, EMBASE, MEDLINE, Scopus, Web of Science, and BIOSIS Previews. Studies of humans were included regardless of age, sex, ethnicity, and health status, with the exception of IVD herniation. Two independent reviewers screened titles and abstracts and full-texts according to eligibility criteria. The review was conducted and reported according to Preferred Reporting Items for Systematic Reviews Extension for Scoping Reviews guidelines. Our search yielded 3122 articles, with 22 articles meeting the inclusion criteria. The study samples ranged in age from fetal to >90 years and included both sexes, various health statuses, and used different methodologies (eg, histology, medical imaging, and gross dissection) to assess vasculature. Overall, consistent observations were that (a) the nucleus pulposus of the IVD is avascular throughout life, (b) both the cartilage endplates and annulus fibrosus receive considerable blood supply early in life that diminishes over the lifespan, and (c) vascular ingrowth into the cartilage endplates and inner layers of the annulus fibrosus is commonly associated with damaged or disrupted tissue, irrespective of age. Histology and immunohistochemistry are often used to report vascularization of the IVD. The body of the current literature suggests that the IVD should not be generalized as an avascular tissue. Instead, vascularization of the IVD differs based on the constituent tissues, their age, and state of degeneration or damage.

Are Modic Changes Associated With Health-related Quality of Life After Discectomy: A Study on 620 Patients With Two-year Follow-up

STUDY DESIGN

A registry-based comparative cohort study with 2-year follow-up.

OBJECTIVE

To assess whether Modic changes (MCs) are associated with health-related quality of life, long-term physical disability, back- or leg pain after discectomy.

SUMMARY OF BACKGROUND DATA

Previous studies have failed to show a clinically significant association between MCs and patient-reported outcomes (PROs) after discectomy.

METHODS

Data from the Danish National Spine Registry on patients undergoing first-time lumbar discectomy at a single institution from 2014 to 2017 with an accessible preoperative lumbar magnetic resonance imaging, complete preoperative, and 2-year follow-up questionnaires were obtained. PROs including Oswestry disability index (ODI), European Quality of Life-Five Dimensions (EQ-5D), visual analogue scale (VAS) back and leg pain, and patient satisfaction were collected. Patients were stratified based on the presence (+MC) or absence (-MC) of MCs on the preoperative MRI.

RESULTS

Of 620 patients included, MCs were present in 290 patients (47%). Of these, MC type 1 (MC-1) was present in 73 (25%) and MC type 2 (MC-2) in 217 (75%) patients. Preoperative data for ODI, EQ-5D, VAS-BP, and VAS-LP were comparable for the +MC and -MC groups. Both groups had a statistically significant improvement in PROs from baseline compared with 2-year follow-up (P < 0.001). At 2-year follow-up, both groups had improved with no significant difference between them in regards to ODI (15.5 vs. 17.2, P = 0.208); EQ-5D (0.75 vs. 0.72, P = 0.167); VAS-BP (27.1 vs. 28.3, P = 0.617); VAS-LP (26.8 vs. 25.0, P = 0.446); and patient satisfaction (74% vs. 76%, P = 0.878).

CONCLUSION

MCs were not found to be associated with health-related quality of life, disability, back- or leg pain, or patient satisfaction 2 years after discectomy.

LEVEL OF EVIDENCE

2.

Signal Intensity of Lumbar Disc Herniations: Correlation With Age of Herniation for Extrusion, Protrusion, and Sequestration

Background

There is presently insufficient data on small groups of patients, without focus on time since herniation occurred and without establishing a valid method of measurement for signal intensity (SI) of a lumbar disc herniation (LDH) in a standard magnetic resonance imaging (MRI). SI could be reported in relation to SI of nucleus pulposus of herniated intervertebral disc, nucleus pulposus of a healthy "control" intervertebral disc, cerebral spinal fluid, or anterior anulus fibrosus. It is not known which signal intensity ratio (SIR) shows the highest correlation with time since onset of pain and how SIR of different Combined Task Forces (CTF)-types of herniation develop over time.

Methods

Out of 1053 patients, we enrolled 151 patients to a retrospective single-center analysis of standard MRIs of consecutive patients treated for LDH from February 2008 to December 2017 with confirmed (surgery, injection, or electrophysiologic testing) radicular pain by LDH and known exact date of onset of pain. We excluded patients < 18 or  > 70 years, with chronical pain syndrome, spinal deformity, and history of prior spinal surgery on the affected spinal level. Because data did not show normal distribution, we assessed correlation by Spearman rank correlation coefficient. Correlation (R) and coefficient of correlation (CC) are reported.

Results

SI of LDH referenced by SI of nucleus pulposus of the affected intervertebral disc and CTF type "extrusion" showed the highest correlations with time since onset of pain (R: -0.893; CC: 79.7), followed by CTF-type "sequestration" (R: -0.356; CC: 12.7).

Conclusions

SIR of extrusion referenced by nucleus pulposus of the affected intervertebral disc does show a high correlation with days since onset of herniation and may be applied to monitor changes of SI of LDH after herniation in standard MRIs of the lumbar spine.

Are viruses associated with disc herniation? A clinical case series

Background

There is some limited evidence for the presence of viruses in herniated disc material including a previous case series that claimed to provide “unequivocal evidence of the presence of herpes virus DNA in intervertebral disc specimens of patients with lumbar disc herniation suggesting the potential role of herpes viruses as a contributing factor to the pathogenesis of degenerative disc disease”. This study has not been replicated. The objective of our study was to determine if viruses were present in herniated disc fragments in participants with a prior history of back pain.

Methods

We recruited fifteen participants with a history of prior low-back pain prior to undergoing disc herniation surgery in the lumbar spine. Harvested disc samples were subject to next generation sequencing for detection of both RNA and DNA viral pathogens. Additionally, samples were analysed by a broadly reactive PCR targeting herpesviral DNA. Ethics approval was granted by the Human Research Ethics Committees of both Murdoch University, and St John of God Hospital, Western Australia.

Results

Of the fifteen research participants, 8 were female. Mean age was 49.4 years (SD 14.5 yrs) with a range of 24–70 years. All participants had prior back pain with mean time since first ever attack being 8.8 years (SD 8.8 yrs). No samples contained significant DNA sequences relating to known human viral agents. Inconsequential retroviral sequences were commonly found and were a mixture of putative animal and human retroviral protein coding segments. All samples were negative for herpesvirus DNA when analysed by pan-herpesvirus PCR.

Conclusions

This study found no viral pathogens in any intervertebral disc fragments of patients who had previous back pain and underwent discectomy for disc herniation and thus it is unlikely that viruses are associated with disc herniation, however given the contradiction between key studies enhanced replication of this experiment is recommended.

Physical disruption of intervertebral disc promotes cell clustering and a degenerative phenotype

To test the hypothesis that physical disruption of an intervertebral disc disturbs cell-matrix binding, leading to cell clustering and increased expression of matrix degrading enzymes that contribute towards degenerative disc cell phenotype. Lumbar disc tissue was removed at surgery from 21 patients with disc herniation, 11 with disc degeneration, and 8 with adolescent scoliosis. 5 μm sections were examined with histology, and 30-µm sections by confocal microscopy. Antibodies were used against integrin α5beta1, matrix metalloproteinases (MMP) 1, MMP-3, caspase 3, and denatured collagen types I and II. Spatial associations were sought between cell clustering and various degenerative features. An additional, 11 non-herniated human discs were used to examine causality: half of each specimen was cultured in a manner that allowed free 'unconstrained' swelling (similar to a herniated disc in vivo), while the other half was cultured within a perspex ring that allowed 'constrained' swelling. Changes were monitored over 36 h using live-cell imaging. 1,9-Di-methyl methylene blue (DMMB) assay for glycosaminoglycan loss was carried out from tissue medium. Partially constrained specimens showed little swelling or cell movement in vitro. In contrast, unconstrained swelling significantly increased matrix distortion, glycosaminoglycan loss, exposure of integrin binding sites, expression of MMPs 1 and 3, and collagen denaturation. In the association studies, herniated disc specimens showed changes that resembled unconstrained swelling in vitro. In addition, they exhibited increased cell clustering, apoptosis, MMP expression, and collagen denaturation compared to 'control' discs. Results support our hypothesis. Further confirmation will require longitudinal animal experiments.

Associations Between Intervertebral Disc Degeneration Grading Schemes and Measures of Disc Function

Disc degeneration is a major cause of spinal dysfunction and pain, but grading schemes concentrate on tissue changes rather than altered function. The aim of this study was to compare disc degeneration grading systems with each other, and with biomechanical measures of disc function. Sixty-six motion segments (T8-9 to L5-S1) were dissected from cadavers aged 48-98 years. Disc function was assessed by measuring nucleus pressure (IDP) and maximum stresses in the annulus under 1 kN of compression. Detailed "scores" of disc degeneration were based on independent radiographic, macroscopic, and microscopic evaluations. For each evaluation, scores were used to assign a degeneration "grade" (I-IV), and functional measures were then correlated with degeneration scores and grades. Results showed that all measures were reliable (intraclass correlation coefficients: 0.82-0.99). Macroscopic and microscopic assessments were highly correlated with each other (r: 0.57-0.89, p < 0.001) but only weakly correlated with radiographic features. The overall macroscopic and microscopic scores of degeneration increased significantly with age and at lower spinal levels, although the influence of age was less marked in the case of the microscopic scores. IDP decreased with age and at lower spinal levels, but annulus stresses were more variable. Importantly, IDP and annulus stresses decreased consistently with all measures of disc degeneration, and these associations remained strong after controlling for age, gender, and spinal level. We conclude that radiographic and tissue-based assessments of disc degeneration are consistent with each other, and are more closely related to mechanical (dys)function than to age or spinal level. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1946-1955, 2019.

Mesenchymal stem cell therapies for intervertebral disc degeneration: Consideration of the degenerate niche

We have previously reported a synthetic Laponite crosslinked poly N-isopropylacrylamide-co-N, N'-dimethylacrylamide (NPgel) hydrogel, which induces nucleus pulposus (NP) cell differentiation of human mesenchymal stem cells (hMSCs) without the need for additional growth factors. Furthermore NP gel supports integration following injection into the disc and restores mechanical function to the disc. However, translation of this treatment strategy into clinical application is dependent on the survival and differentiation of hMSC to the correct cell phenotype within the degenerate intervertebral disc (IVD). Here, we investigated the viability and differentiation of hMSCs within NP gel within a catabolic microenvironment. hMSCs were encapsulated in NPgel and cultured for 4 weeks under hypoxia (5% O2) with ± calcium, interleukin-1β (IL-1β), and tumor necrosis factor alpha (TNFα) either individually or in combination to mimic the degenerate environment. Cell viability and cellular phenotype were investigated. Stem cell viability was maintained within hydrogel systems for the 4 weeks investigated under all degenerate conditions. NP matrix markers: Agg and Col II and NP phenotypic markers: HIF-1α, FOXF1, and PAX1 were expressed within the NPgel cultures and expression was not affected by culture within degenerate conditions. Alizarin red staining demonstrated increased calcium deposition under cultures containing CaCl2 indicating calcification of the matrix. Interestingly matrix metalloproteinases (MMPs), ADAMTS 4, and Col I expression by hMSCs cultured in NPgel was upregulated by calcium but not by proinflammatory cytokines IL-1β and TNFα. Importantly IL-1β and TNFα, regarded as key contributors to disc degeneration, were not shown to affect the NP cell differentiation of mesenchymal stem cells (MSCs) in the NPgel. In agreement with our previous findings, NPgel alone was sufficient to induce NP cell differentiation of MSCs, with expression of both aggrecan and collagen type II, under both standard and degenerate culture conditions; thus could provide a therapeutic option for the repair of the NP during IVD degeneration.

Tandem Disc Herniation of the Lumbar and Cervical Spine: Case Series and Review of the Epidemiological, Pathophysiological and Genetic Literature

Introduction

Lumbar disc herniation (LDH) and cervical disc herniation (CDH) represent a relevant public health problem. Patients with symptomatic tandem herniations of the cervical and lumbar spine are rare and not described in the literature. In these patients, certain variables may predispose the development of disc herniation which could increase the understanding of the development of disc herniations. Our aim is to present the first case series of tandem disc herniation, and to elucidate whether tandem herniation is attributable to a certain propensity for disc herniation or not.

Methods 

From a prospective registry, patients with symptomatic tandem disc herniations were included, and the literature was reviewed on the comparative pathophysiology, genetics, and epidemiology of disc herniation and disc degeneration.

Results

Out of 3,156 patients with disc herniations in our registry, 16 presented with symptomatic tandem LDH and CDH that required discectomy. Therefore, we estimate the incidence of tandem disc herniation at 0.51% (95% confidence interval (CI): 0.26% - 0.75%) in the surgical population. The mean number of degenerated lumbar discs was 2.1 ± 1.1. Compared to the 1,241 patients with isolated LDH, no investigated factors were significantly associated with tandem herniations.

Conclusion

From a genetic, pathophysiological, and epidemiological position, disc herniation is not commonly a consequence of disc degeneration. Rather, degeneration and herniation seem to exist as two separate and distinctly different processes. Based on the literature, it is tenable that tandem disc herniation does not deviate from the normal pathophysiology, but rather occurs in the rare case that two individual herniated discs coincide.

[Disc hernia regression as a natural course of discogenic lumbosacral radiculopathy]

Disc herniation with radiculopathy is a common cause of severe back pain leading to significant disability and a decrease in patients' quality of life. The authors report a case of 38-year-old female patient with radiculopathy of the first sacral root due to a large (11 mm) sequestered disc herniation between the fifth lumbar and the first sacral vertebrae. Conservative treatment with fluoroscopically-guided epidural steroid injection provided a significant clinical improvement, the patient was able to return to normal daily and professional activity in a short time. MRI in 9 months showed the regression of disc herniation. Possible predictors and timing of disc herniation regression are discussed, as well as the proposed mechanisms, the main one of which is considered to be immune-mediated lysis.

Current concepts for lumbar disc herniation

PURPOSE

To present the pathophysiology, biology, clinical presentation, diagnosis, and current treatment options for lumbar disc herniation.

METHODS

A thorough literature search was undertaken in PubMed and Google Scholar to summarize the current knowledge and future perspectives on lumbar disc herniation.

RESULTS

Several changes in the biology of the intervertebral disc are thought to contribute to disc herniation; nevertheless, the exact inciting event leading to disc herniation is yet to be discovered. Non-operative treatments have stood the test of time as the first-line treatment for most patients with lumbar disc herniation; however, operative treatment remains the current gold standard, with minimally invasive endoscopic microdiscectomy techniques showing best results with respect to postoperative pain and function.

CONCLUSIONS

The exact event leading to disc herniation remains unclear. Non-operative treatments should be the first-line treatment for most patients with lumbar disc herniation. Operative treatment remains the current gold standard, with minimally invasive endoscopic microdiscectomy techniques showing best results with respect to postoperative pain and function. Regenerative medicine is promising.

Magnetic resonance imaging analysis of work-related chronic low back pain: comparisons of different lumbar disc patterns

Background

Currently, there is a lack of comparative research about different lumbar disc patterns in patients with work-related chronic low back pain (CLBP) based on magnetic resonance imaging (MRI) analysis. Therefore, this study, on different patterns of lumbar disc degeneration or herniation in patients with CLBP, is valuable. In this study, we retrospectively investigated lumbar degenerative changes in patients with CLBP by using MRI analysis.

Materials and methods

Two hundred and eighty-three patients (110 women and 173 men) with work-related CLBP were enrolled and divided into four groups based on intervertebral disc morphology from MRI analysis, including normal discs (ND) group, degenerative discs (DD) group, bulging discs (BD) group, and herniated discs (HD) group. Demographic characteristics, occupational information, Visual Analog Scale (VAS) scores, and Oswestry Disability Index (ODI) scores were analyzed. Moreover, multiple parameters were investigated in the MRI analysis.

Results

The mean age of all 283 patients was 41.8±12.0 years (range, 18-80) and the mean duration of CLBP for all patients was 24.5±24.9 months. There were no significant differences in the patients' BMI, history of smoking, and education level (P>0.05). The three most common occupational types were manual worker, desk worker, and technician. The VAS and ODI scores of patients with CLBP in the DD, BD, and HD groups were significantly higher than those of patients in the ND group (P<0.05). The degrees of degeneration of L4/5 and L5/S1 were significantly higher than those of other intervertebral discs (P<0.05). The disc heights of L4/5 in the BD and HD groups were significantly lower than those of the ND group (P<0.05) and the disc height of L5/S1 in the HD group was significantly lower than that of the ND group (P<0.05). At the neutral position, the distances of L3/4, L4/5, and L5/S1 discs' bulge/herniation in the BD and HD groups were significantly higher than those in the ND and DD groups (P<0.05).

Conclusion

In summary, more severe degenerative changes of lower lumbar discs (L4/5 and L5/S1) such as higher degree of degeneration of disc, lower disc height, and significant displacement of disc were found in patients with work-related CLBP based on MRI analysis.

Is elective degenerative lumbar spine surgery in older adults safe in a short-stay clinic? Data from an institutional registry

PURPOSE

Physicians are increasingly confronted with degenerative spinal pathologies and the possibility of elective surgical treatment in older adults. Little is known on safety and effectiveness of short-stay, elective lumbar spine surgery in this population. We aim to describe patient profiles of older adults undergoing surgery at a specialized short-stay clinic, and describe associated risk profiles and outcomes.

METHODS

From a prospective registry, patients older than 65 were compared to younger controls. All patients underwent a strict anesthesiologic screening preoperatively, leading to a carefully selected cohort of relatively robust older adults suited for safe treatment at a short-stay clinic. A range of perioperative data and reoperations were available from all patients, and a subgroup of patients completed outcome assessments for disability, pain, and health-related quality of life (HRQOL).

RESULTS

Of the 3279 included patients, 382 (12%) were older than 65. Older patients presented more often with spinal stenosis, and index levels were placed higher (p < 0.001). While there was no difference in complications, reoperations, and blood loss (p > 0.05), older people had longer surgical times and length of stay, although not by a clinically relevant margin (p < 0.001). Long-term patient-reported outcomes were equal (p > 0.05). However, older adults had worse 6-week outcomes for leg pain, functional disability, and HRQOL (all p < 0.05).

CONCLUSIONS

Higher age should not be considered a contraindication for elective lumbar spine surgery at short-stay clinics. If the anesthesiologic risk can be controlled, conservative treatments have failed, and muscle-sparing techniques are applied, favorable outcomes can be achieved with an acceptable risk profile in a safe manner.

Theoretical Explorations Generate New Hypotheses About the Role of the Cartilage Endplate in Early Intervertebral Disk Degeneration

Altered cell nutrition in the intervertebral disk (IVD) is considered a main cause for disk degeneration (DD). The cartilage endplate (CEP) provides a major path for the diffusion of nutrients from the peripheral vasculature to the IVD nucleus pulposus (NP). In DD, sclerosis of the adjacent bony endplate is suggested to be responsible for decreased diffusion and disk cell nutrition. Yet, experimental evidence does not support this hypothesis. Hence, we evaluated how moderate CEP composition changes related to tissue degeneration can affect disk nutrition and cell viability. A novel composition-based permeability formulation was developed for the CEP, calibrated, validated, and used in a mechano-transport finite element IVD model. Fixed solute concentrations were applied at the outer surface of the annulus and the CEP, and three cycles of daily mechanical load were simulated. The CEP model indicated that CEP permeability increases with the degeneration/aging of the tissue, in accordance with recent measurements reported in the literature. Additionally, our results showed that CEP degeneration might be responsible for mechanical load-induced NP dehydration, which locally affects oxygen and lactate levels, and reduced glucose concentration by 16% in the NP-annulus transition zone. Remarkably, CEP degeneration was a condition sine-qua-non to provoke cell starvation and death, while simulating the effect of extracellular matrix depletion in DD. This theoretical study cast doubts about the paradigm that CEP calcification is needed to provoke cell starvation, and suggests an alternative path for DD whereby the early degradation of the CEP plays a key role.

Nerves and blood vessels in degenerated intervertebral discs are confined to physically disrupted tissue

Nerves and blood vessels are found in the peripheral annulus and endplates of healthy adult intervertebral discs. Degenerative changes can allow these vessels to grow inwards and become associated with discogenic pain, but it is not yet clear how far, and why, they grow in. Previously we have shown that physical disruption of the disc matrix, which is a defining feature of disc degeneration, creates free surfaces which lose proteoglycans and water, and so become physically and chemically conducive to cell migration. We now hypothesise that blood vessels and nerves in degenerated discs are confined to such disrupted tissue. Whole lumbar discs were obtained from 40 patients (aged 37-75 years) undergoing surgery for disc herniation, disc degeneration with spondylolisthesis or adolescent scoliosis ('non-degenerated' controls). Thin (5-μm) sections were stained with H&E and toluidine blue for semi-quantitative assessment of blood vessels, fissures and proteoglycan loss. Ten thick (30-μm) frozen sections from each disc were immunostained for CD31 (an endothelial cell marker), PGP 9.5 and Substance P (general and nociceptive nerve markers, respectively) and examined by confocal microscopy. Volocity image analysis software was used to calculate the cross-sectional area of each labelled structure, and its distance from the nearest free surface (disc periphery or internal fissure). Results showed that nerves and blood vessels were confined to proteoglycan-depleted regions of disrupted annulus. The maximum distance of any blood vessel or nerve from the nearest free surface was 888 and 247 μm, respectively. Blood vessels were greater in number, grew deeper, and occupied more area than nerves. The density of labelled blood vessels and nerves increased significantly with Pfirrmann grade of disc degeneration and with local proteoglycan loss. Analysing multiple thick sections with fluorescent markers on a confocal microscope allows reliable detection of thin filamentous structures, even within a dense matrix. We conclude that, in degenerated and herniated discs, blood vessels and nerves are confined to proteoglycan-depleted regions of disrupted tissue, especially within annulus fissures.

Vertebral Endplate Defect as Initiating Factor in Intervertebral Disc Degeneration: Strong Association Between Endplate Defect and Disc Degeneration in the General Population

STUDY DESIGN

Cross-sectional study of spine magnetic resonance in a population, predominantly female, sample.

OBJECTIVE

To determine the relationship between vertebral endplate defect and intervertebral disc degeneration (DD) in general population.

SUMMARY OF BACKGROUND DATA

Precise understanding of the mechanisms leading to DD development is lacking. In a degenerating disc, mechanical and structural changes lead to further worsening of disc integrity. Increasing attention has been paid to vertebral endplate defects as having a possible role in the etiopathogenesis of DD.

METHODS

The study population comprised 831 twin volunteers from TwinsUK (mean age 54 ± 8 yr, 95.8% female). Lumbar T2-weighted magnetic resonance images were coded for endplate defects from 8310 endplates into six grades. Total endplate score (TEP score) was achieved by summing both endplate defect grades from the same disc level. DD was evaluated using two different classifications; Pfirrmann grading, and a quantitative trait for DD based on a 4-point grading system. Multivariable regression analysis was used to determine relationships between the traits of interest and the known risk factors for DD, age, and body mass index (BMI). A receiver operator curve for TEP score predicting DD was generated, and survival analysis paired with Cox proportional hazards models analysis performed.

RESULTS

There was statistically significant association between DD and age and BMI. These associations lost significance when TEP score was included as predictor in multivariable model. TEP score was strongly and independently associated at every lumbar disc level with DD (Pfirmann P≤0.001; 4-point grading systems P < 1e-16). A cut-off point score of 5 for TEP score was found above which there was a higher DD prevalence. Across all age subgroups, probabilities of having DD were significantly increased in those considered TEP score positive (≥5).

CONCLUSION

Our large, population-based study has shown that endplate defect was strongly and independently associated with DD at every lumbar disc level. These results provide a mechanism by which increasing age and BMI predispose to DD.

LEVEL OF EVIDENCE

2.

Lumbar Disc Herniation

PURPOSE OF REVIEW

Substantial advancements have been made in the cause, diagnosis, imaging, and treatment options available for patients with lumbar disc herniation (LDH). We examined the current evidence and highlight the concepts on the frontline of discovery in LDH.

RECENT FINDINGS

There are a myriad of novel etiologies of LDH detailed in recent literature including inflammatory factors and infectious microbes. In the clinical setting, recent data focuses on improvements in computer tomography as a diagnostic tool and non-traditional injection options including tumor necrosis alpha inhibitors and platelet-rich plasma. Operative treatment outcomes have focused on minimally invasive endoscopic approaches and demonstrated robust 5-year post-operative outcomes. Advances in the molecular etiology of LDH will continue to drive novel treatment options. The role of endoscopic treatment for LDH will continue to evolve. Further research into10-year outcomes will be necessary as this surgical approach continues to gain widespread popularity.

Static axial overloading primes lumbar caprine intervertebral discs for posterior herniation

Introduction

Lumbar hernias occur mostly in the posterolateral region of IVDs and mechanical loading is an important risk factor. Studies show that dynamic and static overloading affect the nucleus and annulus of the IVD differently. We hypothesize there is also variance in the effect of overloading on the IVD’s anterior, lateral and posterior annulus, which could explain the predilection of herniations in the posterolateral region. We assessed the regional mechanical and cellular responses of lumbar caprine discs to dynamic and static overloading.

Material and methods

IVDs (n = 125) were cultured in a bioreactor and subjected to simulated-physiological loading (SPL), high dynamic (HD), or high static (HS) overloading. The effect of loading was determined in five disc regions: nucleus, inner-annulus and anterior, lateral and posterior outer-annulus. IVD height loss and external pressure transfer during loading were measured, cell viability was mapped and quantified, and matrix integrity was assessed.

Results

During culture, overloaded IVDs lost a significant amount of height, yet the distribution of axial pressure remained unchanged. HD loading caused cell death and disruption of matrix in all IVD regions, whereas HS loading particularly affected cell viability and matrix integrity in the posterior region of the outer annulus.

Conclusion

Axial overloading is detrimental to the lumbar IVD. Static overloading affects the posterior annulus more strongly, while the nucleus is relatively spared. Hence, static overloading predisposes the disc for posterior herniation. These findings could have implications for working conditions, in particular of sedentary occupations, and the design of interventions aimed at prevention and treatment of early intervertebral disc degeneration.

Contaminants in commercial preparations of 'purified' small leucine-rich proteoglycans may distort mechanistic studies

The present study reports the perplexing results that came about because of seriously impure commercially available reagents. Commercial reagents and chemicals are routinely ordered by scientists and expected to have been rigorously assessed for their purity. Unfortunately, we found this assumption to be risky. Extensive work was carried out within our laboratory using commercially sourced preparations of the small leucine-rich proteoglycans (SLRPs), decorin and biglycan, to investigate their influence on nerve cell growth. Unusual results compelled us to analyse the composition and purity of both preparations of these proteoglycans (PGs) using both mass spectrometry (MS) and Western blotting, with and without various enzymatic deglycosylations. Commercial ‘decorin’ and ‘biglycan’ were found to contain a mixture of PGs including not only both decorin and biglycan but also fibromodulin and aggrecan. The unexpected effects of ‘decorin’ and ‘biglycan’ on nerve cell growth could be explained by these impurities. Decorin and biglycan contain either chondroitin or dermatan sulfate glycosaminoglycan (GAG) chains whereas fibromodulin only contains keratan sulfate and the large (>2500 kDa), highly glycosylated aggrecan contains both keratan and chondroitin sulfate. The different structure, molecular weight and composition of these impurities significantly affected our work and any conclusions that could be made. These findings beg the question as to whether scientists need to verify the purity of each commercially obtained reagent used in their experiments. The implications of these findings are vast, since the effects of these impurities may already have led to inaccurate conclusions and reports in the literature with concomitant loss of researchers’ funds and time.

How maturity influences annulus-endplate integration in the ovine intervertebral disc: a micro- and ultra-structural study

The annulus-endplate anchorage system plays a vital role in structurally linking the compliant disc to its adjacent much more rigid vertebrae. Past literature has identified the endplate as a region of weakness, not just in the mature spine but also in the immature spine. The aim of this structural study was to investigate in detail the morphological changes associated with annulus-endplate integration through different stages of maturity. Ovine lumbar motion segments were collected from two immature age groups: (i) newborn and (ii) spring lamb (roughly 3 months old); these were compared with a third group of previously analysed mature ewe samples (3-5 years). Sections from the posterior region of each motion segment were obtained for microstructural analysis and imaged in their fully hydrated state via differential interference contrast (DIC) optical microscopy. Selected slices were further prepared and imaged via scanning electron microscopy (SEM) to analyse fibril-level modes of integration. Despite significant changes in endplate morphology, the annular fibre bundles in all three age groups displayed a similar branching mechanism, with the main bundle splitting into several sub-bundles on entering the cartilaginous endplate. This morphology, previously described in the mature ovine disc, is thought to strengthen significantly annulus-endplate integration. Its prevalence from an age as young as birth emphasizes the critical role that it plays in the anchorage system. The structure of the branched sub-bundles and their integration with the surrounding matrix were found to vary with age due to changes in the cartilaginous and vertebral components of the endplate. Microscopically, the sub-bundles in both immature age groups appeared to fade into the surrounding tissue due to their fibril-level integration with the cartilaginous endplate tissue, this mechanism being particularly complex in the spring lamb disc. However, in the fully mature disc, the sub-bundles remained as separate entities throughout the full depth of their anchorage into the cartilaginous endplate. Cell morphology was also found to vary with maturity within the cartilaginous matrix and it is proposed that this relates to endplate development and ossification.

Catabolic effects of endothelial cell-derived microparticles on disc cells: Implications in intervertebral disc neovascularization and degeneration

Neovascularization of intervertebral discs, a phenomenon considered pathological since normal discs are primarily avascular structures, occurs most frequently in annulus fibrosus (AF) of degenerated discs. Endothelial cells (ECs) are involved in this process, but the mechanism of the interaction between AF and endothelial cells is unclear. In this study, we evaluated the effects on matrix catabolic activity of AF cells by the extracellular endothelial microparticles (EMPs) and soluble protein factors (SUP fraction) produced from ECs. Passage 1 human AF cells grown in monolayer cultures were treated for 72 h with 250 µg of EMPs or SUP fraction isolated from culture of the microvascular endothelial cell line, HEMC-I. Live-cell imaging revealed uptake of EMPs by AF cells. RT-PCR analysis demonstrated increased mRNA expression of MMP-1 (50.3-fold), MMP-3 (4.5-fold) and MMP-13 (5.5-fold) in AF cell cultures treated with EMPs compared to untreated control. Western analysis also demonstrated increased MMP protein expression in EMP-treated AF cells. AF cells treated with the SUP fraction also exhibited a dramatic increase in MMP mRNA and protein expression. Increased MMP expression is primarily due to EMP or SUP stimulation of AF cells since EMPs or SUP fraction alone contained negligible amount of MMPs. Interestingly, MMP activity was elevated in AF cell cultures treated with EMPs but not with SUP. This study revealed enhanced matrix catabolism as a molecular consequence of action of ECs on AF cells via EMPs, which might be expected during neo-angiogenesis of degenerating disc. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1466-1474, 2016.

Qualitative grading of disc degeneration by magnetic resonance in the lumbar and cervical spine: lack of correlation with histology in surgical cases

BACKGROUND

Clinically, magnetic resonance (MR) imaging is the most effective non-invasive tool for assessing IVD degeneration. Histological examination of the IVD provides a more detailed assessment of the pathological changes at a tissue level. However, very few reports have studied the relationship between these techniques. Identifying a relationship may allow more detailed staging of IVD degeneration, of importance in targeting future regenerative therapies.

OBJECTIVES

To investigate the relationship between MR and histological grading of IVD degeneration in the cervical and lumbar spine in patients undergoing discectomy.

METHODS

Lumbar (N = 99) and cervical (N = 106) IVD samples were obtained from adult patients undergoing discectomy surgery for symptomatic IVD herniation and graded to ascertain a histological grade of degeneration. The pre-operative MR images from these patients were graded for the degree of IVD (MR grade) and vertebral end-plate degeneration (Modic Changes, MC). The relationship between histological and MR grades of degeneration were studied.

RESULTS

In lumbar and cervical IVD the majority of samples (93%) exhibited moderate levels of degeneration (ie MR grades 3-4) on pre-operative MR scans. Histologically, most specimens displayed moderate to severe grades of degeneration in lumbar (99%) and cervical spine (93%). MR grade was weakly correlated with patient age in lumbar and cervical study groups. MR and histological grades of IVD degeneration did not correlate in lumbar or cervical study groups. MC were more common in the lumbar than cervical spine (e.g. 39 versus 20% grade 2 changes; p < 0.05), but failed to correlate with MR or histological grades for degeneration.

CONCLUSIONS

In this surgical series, the resected IVD tissue displayed moderate to severe degeneration, but there is no correlation between MR and histological grades using a qualitative classification system. There remains a need for a quantitative, non-invasive, pre-clinical measure of IVD degeneration that correlates with histological changes seen in the IVD.

Novel Immortal Cell Lines Support Cellular Heterogeneity in the Human Annulus Fibrosus

Introduction

Loss of annulus fibrosus (AF) integrity predisposes to disc herniation and is associated with IVD degeneration. Successful implementation of biomedical intervention therapy requires in-depth knowledge of IVD cell biology. We recently generated unique clonal human nucleus pulposus (NP) cell lines. Recurring functional cellular phenotypes from independent donors provided pivotal evidence for cell heterogeneity in the mature human NP. In this study we aimed to generate and characterize immortal cell lines for the human AF from matched donors.

Methods

Non-degenerate healthy disc material was obtained as surplus surgical material. AF cells were immortalized by simian virus Large T antigen (SV40LTAg) and human telomerase (hTERT) expression. Early passage cells and immortalized cell clones were characterized based on marker gene expression under standardized culturing and in the presence of Transforming Growth factor β (TGFβ).

Results

The AF-specific expression signature included COL1A1, COL5A1, COL12A1, SFRP2 and was largely maintained in immortal AF cell lines. Remarkably, TGFβ induced rapid 3D sheet formation in a subgroup of AF clones. This phenotype was associated with inherent differences in Procollagen type I processing and maturation, and correlated with differential mRNA expression of Prolyl 4-hydroxylase alpha polypeptide 1 and 3 (P4HA1,3) and Lysyl oxidase (LOX) between clones and differential P4HA3 protein expression between AF cells in histological sections.

Conclusion

We report for the first time the generation of representative human AF cell lines. Gene expression profile analysis and functional comparison of AF clones revealed variation between immortalized cells and suggests phenotypic heterogeneity in the human AF. Future characterization of AF cellular (sub-)populations aims to combine identification of additional specific AF marker genes and their biological relevance. Ultimately this knowledge will contribute to clinical application of cell-based technology in IVD repair.

Progression of lumbar disc herniations over an eight-year period in a group of adult Danes from the general population--a longitudinal MRI study using quantitative measures

Background

A lumbar disc herniation (LDH) is a localised displacement of disc material, which may initiate changes in the disc and adjacent structures such as the nerve root and the spinal canal. Knowledge about how morphological changes in the disc relate to changes in other spinal structures might give the clinician a better understanding of the natural history and consequences of lumbar disc herniations. However, few longitudinal studies have investigated this process using reliable measures from magnetic resonance imaging (MRI). The objectives of this study were to examine changes in and associations between the size of lumbar disc herniations, dural sac area and disc height over an eight-year period using MRI at three time-points.

Methods

Individuals from a population-based cohort, the ‘Backs on Funen Cohort’, had MRIs taken at age 41 years and again at 45 and 49 years. Only disc levels with MRI-confirmed disc herniations at 41 or 45 years were included. Cross-sectional areas (mm²) of the LDH, dural sac and disc height were calculated from measurements performed on sagittal T2-weighted images using a previously validated method. Changes over time for the three MRI findings were defined as “unchanged”, “increased “, “decreased”, or “fluctuating”. Only changes beyond 95 % limits of agreement of the same measurements were regarded as valid. Associations between the three types of measures were examined cross-sectionally and longitudinally.

Results

One hundred and forty disc levels, from 106 people (48 women and 58 men), were included. Over eight years, 65 % of the herniations remained unchanged, 17.5 % decreased, 12.5 % increased, and 5 % had a fluctuating pattern. Increased herniation size was associated with decreased dural sac area (β-0.25[−0.52;0.01]) and increased disc height (β 0.35[0.14;0.56]). Moreover, larger herniation size predicted a statistically significant reduction in both dural sac area (β-0.35[−0.58;-0.13]) and disc height (β-0.50[−0.81;-0.20]).

Conclusions

On average, most LDHs do not change over a four- to eight-year period. However, larger herniation size predicts a reduction in both dural sac area and disc height. Further research should be done to determine the correlations between the progression of LDH and resolution of patient symptoms.

Lumbar disc herniation: Is there an association between histological and magnetic resonance imaging findings?

BACKGROUND

Although validated radiological scoring systems and histological scoring system of surgically removed degenerated disc are used in assessment of progression of intervertebral disc degeneration, there have not been many studies that integrate these two aspects of assessments. The data available in this respect are very limited. This clinical study was designed to find the correlation between quantitative radiological score (Pfirmann grading system and Modic changes [MC]) and quantitative histological degeneration score (HDS).

MATERIALS AND METHODS

A cohort of 77 patients (45 males, 32 females; mean age of 38 years [range 18-58 years]) who presented with complaints of discogenic pain or radiculopathy at single level were assessed radiologically. They were graded according to the radiological pattern. The surgically excised disc specimen was graded according to HDS. The degree of radiological changes were correlated with the degree of histological changes.

RESULTS

Though the overall HDS (0-15) did not show statistically significant correlation with Pfirmann grading system, there were positive association found between mucoid degeneration, chondrocyte proliferation with the Pfirmann grading and mucoid degeneration, which were statistically significant. Female sex also had a higher association with instability pattern.

CONCLUSION

The study shows that the Pfirmann grading system, MCs and HDS can reliably be used as scoring systems for assessing lumbar disc degeneration. The radiological assessment can be used as a noninvasive tool to assess the probable change in content rather than the microstructure of a disc undergoing degeneration.

Mechanics and biology in intervertebral disc degeneration: a vicious circle

Intervertebral disc degeneration is a major cause of low back pain. Despite its long history and large socio-economical impact in western societies, the initiation and progress of disc degeneration is not well understood and a generic disease model is lacking. In literature, mechanics and biology have both been implicated as the predominant inductive cause; here we argue that they are interconnected and amplify each other. This view is supported by the growing awareness that cellular physiology is strongly affected by mechanical loading. We propose a vicious circle of mechanical overloading, catabolic cell response, and degeneration of the water-binding extracellular matrix. Rather than simplifying the disease, the model illustrates the complexity of disc degeneration, because all factors are interrelated. It may however solve some of the controversy in the field, because the vicious circle can be entered at any point, eventually leading to the same pathology. The proposed disease model explains the comparable efficacy of very different animal models of disc degeneration, but also helps to consider the consequences of therapeutic interventions, either at the cellular, material or mechanical level.

Expression of matrix factors in the process of neovascularization of intervertebral disc

<sec><title>OBJECTIVE:</title><p> To investigate the effects of proteins products of endothelial cells (ECs) on the annulus fibrosus (AF) cell metabolism in an in vitro culture.</p></sec><sec><title>METHODS:</title><p>Human AF cells were expanded in monolayer cultures and treated with proteins from the medium of cell line HMEC-1 (Human Microvascular Endothelial Cells) (125µg/ml). After 72h of treatment RNA was isolated from AF cells for analysis of gene expression and the culture medium was collected for protein expression analysis.</p></sec><sec><title>RESULTS:</title><p> The qRT-PCR analysis demonstrated increased gene expression of matrix metalloproteinases (MMPs) in AF cells treated with protein products of endothelial cells compared with cells from control group of AF cells: MMP-1 243.10 times (p<0.05), MMP-2 1.37 time (p<0.05), MMP-3 39.83 times (p<0.05) and MMP-13 5.70 times (p<0.05). In contrast, tissue inhibitors of metalloproteinases (TIMPs) were suppressed; TIMP-2 (0.55 time) (p<0.05) and TIMP-3 (0.60 time) (p<0.05) in the exposed groups. The expression of aggrecan gene (0.83 time) (p<0.05), an important extracellular matrix component, was also reduced. MMP-1 and MMP-3 detection was performed, confirming the results of PCR by Western Blot technique.</p></sec><sec><title>CONCLUSIONS:</title><p> In this study, we observed that the proteins produced by ECs induced the MMPs expression and suppressed the TIMPs as well as the aggrecan in primary cells of the human intervertebral disc, targeting the development of potential treatments for intervertebral disc degeneration and associated discogenic pain.</p></sec>

Do bacteria play an important role in the pathogenesis of low back pain?

Considerable interest has been generated recently regarding an alternative hypothesis for the pathogenesis of low back pain and radiculopathy in the presence of intervertebral disc prolapse. Traditionally, back pain and radicular (sciatic) symptoms have been attributed to mechanical compression of neural tissue by herniated disc material and to inflammation caused by exposure of the nerve roots to disc tissue. Recent research however has suggested that low-grade infection within the intervertebral disc by anaerobic bacteria may be responsible. The development of Modic changes in the corresponding adjacent vertebral endplates has also been suggested as an indicator of infection. This article is a thorough review of the current literature regarding the hypothesis that low-grade anaerobic bacterial infection may be the cause of disabling low back pain and radiculopathy.

Low-back pain

Low-back pain is one of the most common painful conditions experienced by humans throughout their life. Some occupational risk factors (namely, heavy manual material handling) may also contribute to the development of low-back pain: due to the high prevalence of both low-back pain and manual material handling in the adult working population, it has been estimated that low-back pain is probably the most common occupational disorder worldwide. Lifetime prevalence of low-back pain has been reported to be as high as 84%, depending on the case definition used, and no age group is spared, even children. Although low-back pain is not a lethal condition, it was estimated at the third rank among all diseases by disability-adjusted life-years in 2010 in the USA, after ischemic heart disease and chronic obstructive pulmonary disease, and at the first rank by years lived with disability. It also ranked high (13th) globally for the same year, in disability-adjusted life-years. Low-back pain is currently classified as nonspecific/specific as to putative cause and as acute (lasting less than 6 weeks), subacute (6-12 weeks), or chronic (more than 12 weeks) according to duration of symptoms. The distinction between nonspecific/specific and acute/subacute/chronic low-back pain is useful not only for epidemiologic studies, but also (mainly) for choosing the appropriate strategy for the diagnosis and treatment of the disorder. Workplace risk factors for low-back pain include manual lifting and whole-body vibration exposure. This chapter will provide an overview of modern concepts of low-back pain (in general) and will then outline some distinctive features of work-related low-back pain.

In vivo multifrequency magnetic resonance elastography of the human intervertebral disk

PURPOSE

To test in vivo magnetic resonance elastography (MRE) of the human intervertebral disk (IVD).

METHODS

The feasibility of MRE in IVD was demonstrated in ex vivo bovine disks. Sixteen asymptomatic volunteers underwent multifrequency MRE of the lumbar spine (IVD L3/4 and L4/5, n = 32) using a posterior plate transducer connected to a loudspeaker and operated at five frequencies from 50 to 70 Hz. Full wave field data were acquired in 10 transverse slices of 2 × 2 × 2 mm(3) resolution. High-resolution maps of magnitude |G*| and phase angle φ of complex shear modulus G* were generated by multifrequency dual elasto visco (MDEV) inversion. Disk morphology was assessed by the Pfirrmann score (Pf).

RESULTS

Morphological Pf was 1 in 25, 2 in 3, and 3 in 4 disks. |G*| decreased with Pf by a Pearson's linear correlation coefficient of R = -0.592 (P = 0.0004), while φ remained unchanged. Group mean mechanical parameters for Pf = 1 to 3 were |G*| = 6.51 ± 1.27, 5.29 ± 0.95, 4.03 ± 0.99 kPa, and φ = 1.190 ± 0.181, 1.170 ± 0.156, 1.088 ± 0.084 rad, respectively (p[Pf1-Pf3] < 0.001). The variability of mechanical parameters in one volunteer including diurnal changes was approximately 11%.

CONCLUSION

Multifrequency MRE with MDEV inversion allows measurement of in vivo mechanical properties of IVDs and may provide additional information in disc degeneration beyond standard morphological changes.

Why do some intervertebral discs degenerate, when others (in the same spine) do not?

This review suggests why some discs degenerate rather than age normally. Intervertebral discs are avascular pads of fibrocartilage that allow movement between vertebral bodies. Human discs have a low cell density and a limited ability to adapt to mechanical demands. With increasing age, the matrix becomes yellowed, fibrous, and brittle, but if disc structure remains intact, there is little impairment in function, and minimal ingrowth of blood vessels or nerves. Approximately half of old lumbar discs degenerate in the sense of becoming physically disrupted. The posterior annulus and lower lumbar discs are most affected, presumably because they are most heavily loaded. Age and genetic inheritance can weaken discs to such an extent that they are physically disrupted during everyday activities. Damage to the endplate or annulus typically decompresses the nucleus, concentrates stress within the annulus, and allows ingrowth of nerves and blood vessels. Matrix disruption progresses by mechanical and biological means. The site of initial damage leads to two disc degeneration "phenotypes": endplate-driven degeneration is common in the upper lumbar and thoracic spine, and annulus-driven degeneration is common at L4-S1. Discogenic back pain can be initiated by tissue disruption, and amplified by inflammation and infection. Healing is possible in the outer annulus only, where cell density is highest. We conclude that some discs degenerate because they are disrupted by excessive mechanical loading. This can occur without trauma if tissues are weakened by age and genetic inheritance. Moderate mechanical loading, in contrast, strengthens all spinal tissues, including discs.

Mesenchymal stem cells: potential application in intervertebral disc regeneration

Chronic low back pain is one of the leading public health problems in developed countries. Degeneration of the intervertebral disc (IVD) is a major pathological process implicated in low back pain, which is characterized by cellular apoptosis and senescence with reduced synthesis of extracellular matrix (ECM). Currently, there is no clinical therapy targeting the reversal of disc degeneration. Recent advances in cellular and molecular biology have provided an exciting approach to disc regeneration that focuses on the delivery of viable cells to the degenerative disc. Adult mesenchymal stem cells (MSCs) are multipotent stem cells with self-renewal capacities and are able to differentiate into diverse specialized cell types, including chondrocyte lineages. The potential of stem cell therapy in disc degeneration is to repopulate the disc with viable cells capable of producing the ECM and restoring damaged tissue. The present literature review summarizes recent advances in basic research and clinical trials of MSCs to provide an outline of the key roles of MSCs therapies in disc repair. The review also discusses the controversies, challenges and therapeutic concepts for the future.

Disc cell therapies: critical issues

BACKGROUND

Disc cell therapies, in which cells are injected into the degenerate disc in order to regenerate the matrix and restore function, appear to be an attractive, minimally invasive method of treatment. Interest in this area has stimulated research into disc cell biology in particular. However, other important issues, some of which are discussed here, need to be considered if cell-based therapies are to be brought to the clinic.

PURPOSE

Firstly, a question which is barely addressed in the literature, is how to identify patients with 'degenerative disc disease' who would benefit from cell therapy. Pain not disc degeneration is the symptom which drives patients to the clinic. Even though there are associations between back pain and disc degeneration, many people with even severely degenerate discs, with herniated discs or with spinal stenosis, are pain-free. It is not possible using currently available techniques to identify whether disc repair or regeneration would remove symptoms or prevent symptoms from occurring in future. Moreover, the repair process in human discs is very slow (years) because of the low cell density which can be supported nutritionally even in healthy human discs. If repair is necessary for relief of symptoms, questions regarding quality of life and rehabilitation during this long process need consideration. Also, some serious technical issues remain. Finding appropriate cell sources and scaffolds have received most attention, but these are not the only issues determining the feasibility of the procedure. There are questions regarding the safety of implanting cells by injection through the annulus whether the nutrient supply to the disc is sufficient to support implanted cells and whether, if cells are able to survive, conditions in a degenerate human disc will allow them to repair the damaged tissue.

CONCLUSIONS

If cell therapy for treatment of disc-related disorders is to enter the clinic as a routine treatment, investigations must examine the questions related to patient selection and the feasibility of achieving the desired repair in an acceptable time frame. Few diagnostic tests that examine whether cell therapies are likely to succeed are available at present, but definite exclusion criteria would be evidence of major disc fissures, or disturbance of nutrient pathways as measured by post-contrast MRI.

The cytokine and chemokine expression profile of nucleus pulposus cells: implications for degeneration and regeneration of the intervertebral disc

INTRODUCTION

The aims of these studies were to identify the cytokine and chemokine expression profile of nucleus pulposus (NP) cells and to determine the relationships between NP cell cytokine and chemokine production and the characteristic tissue changes seen during intervertebral disc (IVD) degeneration.

METHODS

Real-time q-PCR cDNA Low Density Array (LDA) was used to investigate the expression of 91 cytokine and chemokine associated genes in NP cells from degenerate human IVDs. Further real-time q-PCR was used to investigate 30 selected cytokine and chemokine associated genes in NP cells from non-degenerate and degenerate IVDs and those from IVDs with immune cell infiltrates (‘infiltrated’). Immunohistochemistry (IHC) was performed for four selected cytokines and chemokines to confirm and localize protein expression in human NP tissue samples.

RESULTS

LDA identified the expression of numerous cytokine and chemokine associated genes including 15 novel cytokines and chemokines. Further q-PCR gene expression studies identified differential expression patterns in NP cells derived from non-degenerate, degenerate and infiltrated IVDs. IHC confirmed NP cells as a source of IL-16, CCL2, CCL7 and CXCL8 and that protein expression of CCL2, CCL7 and CXCL8 increases concordant with histological degenerative tissue changes.

CONCLUSIONS

Our data indicates that NP cells are a source of cytokines and chemokines within the IVD and that these expression patterns are altered in IVD pathology. These findings may be important for the correct assessment of the ‘degenerate niche’ prior to autologous or allogeneic cell transplantation for biological therapy of the degenerate IVD.