Micro-CT quantification of subchondral endplate changes in intervertebral disc degeneration

Kartogenin-loaded polyvinyl alcohol/nano-hydroxyapatite composite hydrogel promotes tendon-bone healing in rabbits after anterior cruciate ligament reconstruction

Accumulating evidence supports the role of cartilage tissue engineering in cartilage defect repair, but the biological function has yet to be fully explained. In this work, kartogenin (KGN), an emerging chondroinductive nonprotein small molecule, was incorporated into a composite hydrogel of polyvinyl alcohol/nano-hydroxyapatite (PVA/n-HA) to fabricate an appropriate microenvironment for tendon-bone healing after anterior cruciate ligament (ACL) reconstruction. KGN/PVA/n-HA composite hydrogel scaffolds were prepared by in situ synthesis and physical adsorption, followed by characterization under a scanning electron microscope. The scaffolds were transplanted into healthy New Zealand White (NZW) rabbits. It was confirmed that KGN/PVA/n-HA scaffolds were successfully prepared and exhibited good supporting properties and excellent biocompatibility. Unilateral ACL reconstruction was constructed with tendon autograft in NZW rabbits, and the morphology and diameter of collagen fiber were analyzed. The scaffolds were shown to promote ACL growth and collagen fiber formation. Furthermore, microcomputerized tomography analysis and bone formation histology were performed to detect new bone formation. KGN/PVA/n-HA scaffolds effectively alleviated cartilage damage and prevented the occurrence of osteoarthritis. Meanwhile, ligament-bone healing and bone formation were observed in the presence of KGN/PVA/n-HA scaffolds. In conclusion, these results suggest that the KGN/PVA/n-HA scaffolds can facilitate tendon-bone healing after ACL reconstruction and might be considered novel hydrogel biomaterials in cartilage tissue engineering.

Mechanical crosstalk between the intervertebral disc, facet joints, and vertebral endplate following acute disc injury in a rabbit model

Background

Vertebral endplate sclerosis and facet osteoarthritis have been documented in animals and humans. However, it is unclear how these adjacent pathologies engage in crosstalk with the intervertebral disc. This study sought to elucidate this crosstalk by assessing each compartment individually in response to acute disc injury.

Methods

Eleven New Zealand White rabbits underwent annular disc puncture using a 16G or 21G needle. At 4 and 10 weeks, individual compartments of the motion segment were analyzed. Discs underwent T 1 relaxation mapping with MRI contrast agent gadodiamide as well T 2 mapping. Both discs and facets underwent mechanical testing via vertebra-disc-vertebra tension-compression creep testing and indentation testing, respectively. Endplate bone density was quantified via μCT. Discs and facets were sectioned and stained for histology scoring.

Results

Intervertebral discs became more degenerative with increasing needle diameter and time post-puncture. Bone density also increased in endplates adjacent to both 21G and 16G punctured discs leading to reduced gadodiamide transport at 10 weeks. The facet joints, however, did not follow this same trend. Facets adjacent to 16G punctured discs were less degenerative than facets adjacent to 21G punctured discs at 10 weeks. 16G facets were more degenerative at 4 weeks than at 10, suggesting the cartilage had recovered. The formation of severe disc osteophytes in 16G punctured discs between 4 and 10 weeks likely offloaded the facet cartilage, leading to the recovery observed.

Conclusions

Overall, this study supports that degeneration spans the whole spinal motion segment following disc injury. Vertebral endplate thickening occurred in response to disc injury, which limited the diffusion of small molecules into the disc. This work also suggests that altered disc mechanics can induce facet degeneration, and that extreme bony remodeling adjacent to the disc may promote facet cartilage recovery through offloading of the articular cartilage.

High Endplate Hounsfield Units Value Indicate Intervertebral Disc Degeneration Following Transforaminal Lumbar Interbody Fusion Surgery

OBJECTIVE

Lumbar disc degeneration (LDD) is a common cause of low back pain and disability, and its prevalence increases with age. The aim of this study is to investigate whether endplate Hounsfield unit (HU) values have an effect on lumbar disc degeneration (LDD) after transforaminal lumbar interbody fusion (TLIF) surgery in patients with degenerative lumbar stenosis.

METHODS

This study was a retrospective analysis of patients who underwent TLIF surgery in January 2016 to October 2019. One hundred and fifty-seven patients who underwent TLIF surgery for degenerative lumbar stenosis were enrolled in this study. Demographic data was recorded. VAS and ODI values were compared to assess the surgical outcomes in patients with or without process of LDD after TLIF surgery. Correlation analysis was performed to investigate associations between LDD and endplate HU value. Binary logistic regression analysis was carried out to study relationships between the DDD and the multiple risk factors.

RESULTS

There was a statistically significant correlation between LDD, body mass index (BMI), age, paraspinal muscle atrophy, and total endplate scores (TEPS). Also, a strong and independent association between endplate HU value and LDD was found at every lumbar disc level (p < 0.01). After conditioning on matching factors, multivariate logistic regression analysis showed that higher endplate HU (odds ratio [OR]: 1.003, p = 0.003), higher TEPS (OR: 1.264, p = 0.002), higher BMI (odds ratio [OR]: 1.202, p = 0.002), a smaller cross-sectional area (CSA) of the paraspinal muscle preoperatively (OR: 0.096, p < 0.001) were significant predictors of LDD development after TLIF surgery.

CONCLUSIONS

There is a significant association between LDD and endplate HU value after TLIF surgery in patients with degenerative lumbar stenosis. Beyond that, results from this study provide a mechanism by which high endplate HU value predisposes to LDD after TLIF surgery.

Radiological analysis of minimally invasive treatment of type A thoracolumbar fractures based on a series of 135 fractures

INTRODUCTION

Although the reduction of traumatic fractures of the thoracolumbar spine is of good quality during conventional so-called open procedures, the alternative minimally invasive approach also appears to confer good results. The aim of this study was to measure the radiological parameters before and after minimally invasive surgery, in order to assess the quality of the reduction of thoracolumbar compression fractures.

MATERIALS AND METHODS

This retrospective, monocentric study included 112 patients with a mean age of 48.9years, presenting with 135 type A thoracolumbar compression fractures treated by a posterior minimally invasive surgical approach comprising vertebral augmentation or posterior osteosynthesis or a mixed procedure.

RESULTS

The parameters analyzed were significantly lower whatever the procedure in the immediate postoperative period. Mean regional and local kyphosis, posterior wall displacement, and mean vertebral height were significantly lower (p<0.01). Fracture reduction was better when osteosynthesis was associated with vertebral augmentation. In the osteosynthesis subgroup with osteosynthesis hardware removal but without vertebral augmentation, we found a significant worsening of the regional kyphosis (p<0.05).

CONCLUSION

The management of thoracolumbar compression fractures by a posterior minimally invasive approach allows excellent fracture reduction with a restoration of the spinal canal, vertebral height and kyphosis.

LEVEL OF EVIDENCE

IV.

Intervertebral disc degeneration and osteoarthritis: a common molecular disease spectrum

Intervertebral disc degeneration (IDD) and osteoarthritis (OA) affecting the facet joint of the spine are biomechanically interdependent, typically occur in tandem, and have considerable epidemiological and pathophysiological overlap. Historically, the distinctions between these degenerative diseases have been emphasized. Therefore, research in the two fields often occurs independently without adequate consideration of the co-dependence of the two sites, which reside within the same functional spinal unit. Emerging evidence from animal models of spine degeneration highlight the interdependence of IDD and facet joint OA, warranting a review of the parallels between these two degenerative phenomena for the benefit of both clinicians and research scientists. This Review discusses the pathophysiological aspects of IDD and OA, with an emphasis on tissue, cellular and molecular pathways of degeneration. Although the intervertebral disc and synovial facet joint are biologically distinct structures that are amenable to reductive scientific consideration, substantial overlap exists between the molecular pathways and processes of degeneration (including cartilage destruction, extracellular matrix degeneration and osteophyte formation) that occur at these sites. Thus, researchers, clinicians, advocates and policy-makers should consider viewing the burden and management of spinal degeneration holistically as part of the OA disease continuum.

Macrophages and Intervertebral Disc Degeneration

The intervertebral disc (IVD) aids in motion and acts to absorb energy transmitted to the spine. With little inherent regenerative capacity, degeneration of the intervertebral disc results in intervertebral disc disease, which contributes to low back pain and significant disability in many individuals. Increasing evidence suggests that IVD degeneration is a disease of the whole joint that is associated with significant inflammation. Moreover, studies show elevated macrophage accumulation within the IVD with increasing levels of disease severity; however, we still need to understand the roles, be they causative or consequential, of macrophages during the degenerative process. In this narrative review, we discuss hallmarks of IVD degeneration, showcase evidence of macrophage involvement during disc degeneration, and explore burgeoning research aimed at understanding the molecular pathways regulating macrophage functions during intervertebral disc degeneration.

Correlation between Adrenoceptor Expression and Clinical Parameters in Degenerated Lumbar Intervertebral Discs

Despite advanced knowledge of the cellular and biomechanical processes of intervertebral disc degeneration (IVDD), the trigger and underlying mechanisms remain unclear. Since the sympathetic nervous system (SNS) has been shown to exhibit catabolic effects in osteoarthritis pathogenesis, it is attractive to speculate that it also influences IVDD. Therefore, we explored the adrenoceptor (AR) expression profile in human IVDs and correlated it with clinical parameters of patients. IVD samples were collected from n = 43 patients undergoing lumbar spinal fusion surgery. AR gene expression was analyzed by semi-quantitative polymerase chain reaction. Clinical parameters as well as radiological Pfirrmann and Modic classification were collected and correlated with AR expression levels. In total human IVD homogenates α1A-, α1B-, α2A-, α2B-, α2C-, β1- and β2-AR genes were expressed. Expression of α1A- (r = 0.439), α2A- (r = 0.346) and β2-AR (r = 0.409) showed a positive and significant correlation with Pfirrmann grade. α1A-AR expression was significantly decreased in IVD tissue of patients with adjacent segment disease (p = 0.041). The results of this study indicate that a relationship between IVDD and AR expression exists. Thus, the SNS and its neurotransmitters might play a role in IVDD pathogenesis. The knowledge of differential AR expression in different etiologies could contribute to the development of new therapeutic approaches for IVDD.

Regenerating and repairing degenerative intervertebral discs by regulating the micro/nano environment of degenerative bony endplates based on low-tension mechanics

Background

Conservative treatment is the recommended first-line treatment for degenerative disc diseases. Traction therapy has historically been one of the most common clinical methods to address this, but the clinical effect remains controversial.

Methods

Forty-two six-month-old male Sprague-Dawley rats were randomly divided into six groups: the model group (Group A, four coccyx vertebrae (Co7-Co10) were fixed with customized external fixators, and the vertebral disc degeneration model was constructed by axial compression of the target segment Co8 - Co9 for 4 weeks), the experimental control group (Group B, after successful modeling, the external fixation device was removed and self-rehabilitation was performed) and four intervention groups (Groups C to F): Groups C and E: Co8 - Co9 vertebrae compressed for 4 weeks followed by two or 4 weeks of high tension traction (HTT), respectively, and Groups D and F: vertebrae compressed for 4 weeks followed by two or 4 weeks of low-tension traction (LTT), respectively. Imaging tests (X-ray and MRI) were performed to assess disc height and T2 signal intensity at each time point. After the experiment, the animals were euthanized, and the caudal vertebrae were collected for analysis of intervertebral disc histopathology, proteoglycan content, and micronanostructure of the annulus fibrosus, nucleus pulposus and bony endplate.

Results

Signs of tissue regeneration were apparent in all four intervention groups. After two to 4 weeks of intervention (HTT and LTT), the morphology of pores in the bony endplate, their number, and diameter had recovered significantly compared with those in Group A. The LTT group was superior to the HTT group, and the 4w in situ group was significantly superior to the 2w group. Meanwhile, the histological scores of discs, the mean fibril diameter and modulus of annulus fibrosus were significantly improved compared with the control groups, and the LTT group was superior to HTT group.

Conclusions

Low-tension traction better promotes active reconstruction of bony endplates and improves the elastic modulus and micro/nanostructure of the disc. Thus, it further promotes the regeneration and repair of intervertebral discs.

N(6)-methyladenosine RNA methyltransferase like 3 inhibits extracellular matrix synthesis of endplate chondrocytes by downregulating sex-determining region Y-Box transcription factor 9 expression under tension

OBJECTIVE

Tension stimulation is an important inducer of endplate cartilage degeneration, but the specific regulatory mechanism remains unclear. This study was the first to reveal the mechanism by which methyltransferase-like 3 (METTL3)-mediated N(6)-methyladenosine (m6A) modification affected the extracellular matrix anabolism by tension-induced endplate chondrocytes.

METHOD

We examined the differences in METTL3 expression and m6A methylation levels in human endplate chondrocytes and human cartilage endplate tissues under in vitro tension. The effect on endplate cartilage degeneration was evaluated by manipulating m6A methylation mediated by METTL3 in vivo and in vitro. The effect of METTL3-mediated m6A methylation on the stability of sex-determining region Y-box transcription factor 9 (SOX9) gene expression was determined experimentally.

RESULTS

METTL3 expression and m6A methylation levels were significantly increased in degenerative human endplate cartilage tissue. Similarly, tension stimulation inhibited the ability of human endplate chondrocytes to synthesize extracellular matrix, which was accompanied by an increase in METTL3-mediated m6A methylation. The ability of endplate chondrocytes to resist tension was significantly enhanced by inhibiting METTL3 expression and subsequently downregulating m6A methylation in vitro and in vivo, thereby reducing intervertebral disc degeneration. Furthermore, METTL3 mediated SOX9 RNA methylation and disrupted SOX9 mRNA stability, thereby inhibiting the gene expression of the downstream collagen type II alpha 1 chain.

CONCLUSION

Tension stimulation downregulated SOX9 expression through METTL3-mediated m6A methylation, thereby inhibiting the synthesis of extracellular matrix in endplate chondrocytes.

Intradiscal vacuum phenomenon and spinal degeneration: a cross-sectional analysis of 219 subjects

INTRODUCTION

Intradiscal vacuum phenomenon (IVP) is the collection of gas within the intervertebral discs. It has been reported with various spinal disorders. The exact role of IVP in spinal degeneration leading to low back pain (LBP) is unclear. We aimed to obtain the prevalence of IVP in patients with LBP. Our second aim was to understand whether IVP was associated with intervertebral disc degeneration (IVDD), Modic changes, and subchondral sclerosis (SS).

METHODS

A total of 12.450 consecutive patients with chronic LBP were evaluated in terms of having abdominal computed tomography (CT) scan concomitant with lumbar spine magnetic resonance imaging (MRI) using radiological database of three spine centers. We excluded the patients with a history of malignancy, metabolic disease, spinal infection, traumatic or osteoporotic spine fracture, and spine surgery. All lumbar levels were evaluated in terms of IVDD and Modic changes on MRI, while they were evaluated in terms of IVP and SS on CT scans.

RESULTS

We included 219 patients. Severe IVDD, Modic changes, IVP, and SS were seen in 53.9% (n: 118), 38.8% (n: 85), 26.5% (n: 58), and 16% (n: 35) of the patients, respectively. Intradiscal vacuum phenomenon was closely associated with severe IVDD (OR: 8.204), Modic changes (OR: 3.547) and SS (OR: 4.231).

DISCUSSION

Intradiscal vacuum phenomenon was closely associated with severe IVDD, Modic changes, and SS. Further prospective clinical and laboratory studies are necessary to better delineate the pathogenesis of IVP.

Circ_0022382 ameliorated intervertebral disc degeneration by regulating TGF-β3 expression through sponge adsorption of miR-4726-5p

Circular RNAs (circRNAs) participate in the progression of many diseases, but knowledge on the role of circRNAs in intervertebral disc degeneration (IDD) is limited. In this study, we discovered the characteristics of a new circRNA (circ_0022382) in human endplate chondrocytes. Currently, real-time quantitative polymerase chain reaction (RT-qPCR) showed that the relative expression level of circ_0022382 was significantly lower under intermittent cyclic tension stimulation than in the control group. circ_0022382, miR-4726-5p and Transforming growth factor 3 (TGF-β3) were evaluated by RT-qPCR, Western Blot and immunofluorescence assay. Additionally, the role and mechanism of circ_0022382 in vivo were also consistent in the rat model. Furthermore, Intermittent cyclic mechanical tension can cause degeneration of endplate chondrocytes. The tension-sensitive circRNA_0022382 was decreased, and we found that circRNA_0022382 promoted morphology of endplate chondrocytes by sponge-binding miR-4726-5p down-regulation of target gene the TGF-β3 expression, thereby alleviating IDD. In a rat model of acupuncture, intervertebral disc injection of circ_0022382 relieved the progression of IDD in vivo. In conclusion, the circ_0022382/miR-4726-5p/TGF-β3 axis plays a key role in the anabolism and catabolism of the endplate chondrocyte extracellular matrix (ECM). It is suggested that circ_0022382 may provide a new approach for the prevention and treatment of IDD.

Intervertebral disc degeneration and regeneration: a motion segment perspective

Back and neck pain have become primary reasons for disability and healthcare spending globally. While the causes of back pain are multifactorial, intervertebral disc degeneration is frequently cited as a primary source of pain. The annulus fibrosus (AF) and nucleus pulposus (NP) subcomponents of the disc are common targets for regenerative therapeutics. However, disc degeneration is also associated with degenerative changes to adjacent spinal tissues, and successful regenerative therapies will likely need to consider and address the pathology of adjacent spinal structures beyond solely the disc subcomponents. This review summarises the current state of knowledge in the field regarding associations between back pain, disc degeneration, and degeneration of the cartilaginous and bony endplates, the AF-vertebral body interface, the facet joints and spinal muscles, in addition to a discussion of regenerative strategies for treating pain and degeneration from a whole motion segment perspective.

Multiscale structural characterization of the vertebral endplate in animal models

Research in the field of spinal biomechanics, including analyses of the impact of implants on the stability of the spine, is conducted extensively in animal models. One of the basic problems in spinal implantation is the transfer and distribution of loads carried by the spine on the surfaces of the vertebral bodies. An important factor in proper cooperation of spinal implants with the vertebrae is the endplate (EP), which is why the EP in the animal model used for testing should be as similar as possible to the human EP. Therefore, this study involved multiscale structural and morphometric analyses of the animal models most commonly used in spinal biomechanics research, i.e. pig, ovine, and bovine tail. The tests were performed on 28 lumbar porcine, ovine, and bovine vertebrae. Both cranial and caudal EPs were analysed in three selected areas: anterior, middle, and posterior EPs. The conducted tests included a morphometric analysis of the trabecular bone (TB) layer of the EP as well as microscopic analysis at the mesoscale (total thickness) and microscale (thickness of the individual EP layers). The porcine EP had a characteristic increased circumferential thickness (~3 mm) with a significant narrowing in the central region (50%-60%). The convex cranial ovine EP had a constant thickness throughout the cross-section and the concave caudal EP showed ~35% narrowing in the central region. The thickest EPs were observed in the bovine tail model with negligibly small narrowing in the central region (~5%). The thickness of the cartilaginous layer in the porcine and bovine models reached up to 1 mm in the peripheral regions and decreased in the central part. The growth plate layer had a similar thickness in all the models. On the other hand, the narrowing of the total thickness of the EPs in the central region was mainly due to a decrease in the VEP thickness. In the ovine and bovine models, the central region of the EP was characterized by large isotropy and trabeculae of mixed or rod-like shape. By contrast, in the pig, this region had plate-like trabeculae of anisotropic nature. The porcine model was identified as best reflecting the shape and structure of the human EP and as the best surrogate model for the human EP model. This choice is particularly important in the context of biomechanical research.

Degeneration alters structure-function relationships at multiple length-scales and across interfaces in human intervertebral discs

Intervertebral disc (IVD) degeneration and associated back pain place a significant burden on the population. IVD degeneration is a progressive cascade of cellular, compositional, and structural changes, which results in a loss of disc height, disorganization of extracellular matrix architecture, tears in the annulus fibrosus which may involve herniation of the nucleus pulposus, and remodeling of the bony and cartilaginous endplates (CEP). These changes to the IVD often occur concomitantly, across the entire motion segment from the disc subcomponents to the CEP and vertebral bone, making it difficult to determine the causal initiating factor of degeneration. Furthermore, assessments of the subcomponents of the IVD have been largely qualitative, with most studies focusing on a single attribute, rather than multiple adjacent IVD substructures. The objective of this study was to perform a multiscale and multimodal analysis of human lumbar motion segments across various length scales and degrees of degeneration. We performed multiple assays on every sample and identified several correlations between structural and functional measurements of disc subcomponents. Our results demonstrate that with increasing Pfirrmann grade there is a reduction in disc height and nucleus pulposus T2 relaxation time, in addition to alterations in motion segment macromechanical function, disc matrix composition and cellular morphology. At the cartilage endplate-vertebral bone interface, substantial remodeling was observed coinciding with alterations in micromechanical properties. Finally, we report significant relationships between vertebral bone and nucleus pulposus metrics, as well as between micromechanical properties of the endplate and whole motion segment biomechanical parameters, indicating the importance of studying IVD degeneration as a whole organ.

METTL3 promotes IL-1β-induced degeneration of endplate chondrocytes by driving m6A-dependent maturation of miR-126-5p

METTL3 is an important regulatory molecule in the process of RNA biosynthesis. It mainly regulates mRNA translation, alternative splicing and microRNA maturation by mediating m6A‐dependent methylation. Interleukin 1β (IL‐1β) is an important inducer of cartilage degeneration that can induce an inflammatory cascade reaction in chondrocytes and inhibit the normal biological function of cells. However, it is unclear whether IL‐1β is related to METTL3 expression or plays a regulatory role in endplate cartilage degeneration. In this study, we found that the expression level of METTL3 and methylation level of m6A in human endplate cartilage with different degrees of degeneration were significantly different, indicating that the methylation modification of m6A mediated by METTL3 was closely related to the degeneration of human endplate cartilage. Next, through a series of functional experiments, we found that miR‐126‐5p can play a significant role in IL‐1β–induced degeneration of endplate chondrocytes. Moreover, we found that miR‐126‐5p can inhibit the PI3K/Akt signalling pathway by targeting PIK3R2 gene, leading to the disorder of cell vitality and functional metabolism. To further determine whether METTL3 could regulate miR‐126‐5p maturation, we first confirmed that METTL3 can bind the key protein underlying pri‐miRNA processing, DGCR8. Additionally, when METTL3 expression was inhibited, the miR‐126‐5p maturation process was blocked. Therefore, we hypothesized that METTL3 can promote cleavage of pri‐miR‐126‐5p and form mature miR‐126‐5p by combining with DGCR8.

Evaluation of disc degeneration adjacent to AOspine A fractures: pre- and post-operative MRI analysis

INTRODUCTION

The management of type A thoracolumbar fractures varies from conservative treatment to multiple level fusion. Indeed, although Magerl defined the type A fracture as a strictly bone injury, several authors suggested associated disc lesions or degeneration after trauma. However, the preservation of mobility of the adjacent discs should be a major issue. This study was conducted to analyze the presence of immediate post-traumatic disc injuries and to know if discs degenerate after receiving treatment.

METHODS

We retrospectively reviewed the files of 27 patients with an AOspine A fracture, corresponding to 34 fractures (64 discs) with pre and post-operative MRI (mean follow-up: 32.4 months). Based on Pfirrmann's and Oner's classifications of disc injuries, two observers analyzed independently the type of lesion in the discs adjacent to the fractured vertebra in immediate post-trauma and at the last follow-up.

RESULTS

The immediate post-traumatic analysis according to Pfirrmann's classification found 97% of the cranial adjacent discs and 100% of the caudal discs classified Pfirrmann 3 or less. The analysis on the secondary MRI revealed that 78% of cranial adjacent discs and 88% of caudal adjacent discs still were classified Pfirrmann 3 or less.

CONCLUSIONS

Since, the great majority of type A fractures does not cause immediate disc injuries, these fractures are, as described by Magerl, strictly bony injuries. The quality of the body reduction seems to prevent secondary degeneration. These results may encourage surgeons not to perform arthrodesis on type A fractures even for A3 and A4.

Curcumin prevents tension-induced endplate cartilage degeneration by enhancing autophagy

AIMS

Intermittent cyclic tension stimulation(ICMT) was shown to promote degeneration of endplate chondrocytes and induce autophagy. However, enhancing autophagy can alleviate degeneration partly. Studies have shown that curcumin can induce autophagy and protect chondrocytes, we speculated that regulation of autophagy by curcumin might be an effective method to improve the stress resistance of endplate cartilage. In this study, human cervical endplate cartilage specimens were collected, and expression of autophagy markers was detected and compared.

MAIN METHODS

Human cervical endplate chondrocytes were cultured to establish a tension-induced degeneration model, for which changes of functional metabolism and autophagy levels were detected under different tension loading conditions. Changes in functional metabolism of endplate chondrocytes were observed under high-intensity tension loading in the presence of inhibitors, inducers, and curcumin to regulate the autophagy level of cells. In addition, a rat model of lumbar instability was established to observe the degeneration of lumbar disc after curcumin administration.

KEY FINDINGS

Through a series of experiments, we found that low-intensity tension stimulation can maintain a stable phenotype of endplate chondrocytes, but high-intensity tension stimulation has a negative effect. Moreover, with increasing tension intensity, the degree of degeneration of endplate chondrocytes was gradually aggravated and the level of autophagy increased. Besides, curcumin upregulated autophagy, inhibited apoptosis, and reduced phenotype loss of endplate chondrocytes induced by high-intensity tension loading, thereby relieving intervertebral disc degeneration induced by mechanical imbalance.

SIGNIFICANCE

Curcumin mediated autophagy and enhanced the adaptability of endplate chondrocytes to high-intensity tension load, thereby relieving intervertebral disc degeneration.

Microanatomy of the lumbar vertebral bony endplate of rats using scanning electron microscopy

INTRODUCTION

The bony endplate of a vertebra is a porous structure containing a large number of capillaries. To date, not very much is known regarding the appearance of the bony endplate microstructure, or the distribution of foramina in the bony endplate.

HYPOTHESIS

The purpose of this study was to provide information on this microstructure based on scanning electron microscopy (SEM) images.

MATERIALS AND METHODS

The bony endplates of rats was observed by SEM scanning. The resulting SEM images were used to evaluate the structural characteristics of the bony endplates, such as the shape and the foramen distribution. Quantitative data were analyzed using SPSS software.

RESULTS

A bony endplate resembled a concave lens and had a unique three-dimensional structure with a large number of surface and interior foramina. The anterior side of the bony endplate had a large number of heterogeneous foramina. The majority of the foramina were seen concentrated toward the center of the bony endplate, as the density decreased further away from the center with few foramina at the margins. The posterior side of the bony endplate had numerous, larger, and more evenly distributed foramina. The integral structure resembled a sponge, and most of the foramina contained capillary structures.

DISCUSSION

The spongy structure of the bony endplate is the structural basis of nutrient transport. Depending on the location of the bony endplate, capillaries can penetrate it and contact to the cartilage endplate, thus supporting nutritional transport. The findings provide a theoretical basis for future studies on intervertebral disc degeneration.

Autologous fibroblasts induce fibrosis of the nucleus pulposus to maintain the stability of degenerative intervertebral discs

Lumbar degenerative disc diseases cause low back pain (LBP). The maintenance of the height and stability of the intervertebral disc (IVD) space is an effective treatment for LBP. The following study evaluated the effects of fibroblast injection on intervertebral disc degeneration (IDD) in a preclinical setting. Compared with the IDD group, the fibroblast treatment group demonstrated effective maintenance of IVD height, reduced endplate degeneration, and improved nuclear magnetic resonance signals and overall histological structure. In doing so, fibrotic IVDs maintained the stability and biomechanics of the vertebra. This finding is in agreement with clinical findings that human nucleus pulposus (NP) fibrosis is essential for the maintenance of IVD height and mechanical properties in patients following percutaneous endoscopic lumbar discectomy (PELD). Mechanistically, we demonstrated that injected fibroblasts not only proliferated but also induced NP cells to adopt a fibrotic phenotype via the secretion of TGF-β. Finally, to better mimic human conditions, the efficacy of autologous fibroblast injection in the treatment of IDD was further examined in a nonhuman primate cynomolgus monkey model due to their capacity for upright posture. We showed that the injection of fibroblasts could maintain the IVD height and rescue IVD signals in cynomolgus monkeys. Taken together, the results of our study reveal that autologous fibroblast injection can enhance the natural process of fibrosis during acute and subacute stages of stress-induced IDD. Fibrotic IVDs can maintain the stability, biological activity, and mechanical properties of the intervertebral space, thus providing a new direction for the treatment of intervertebral space-derived lumbar degenerative diseases.

Visualization of intervertebral disc degeneration in a cadaveric human lumbar spine using microcomputed tomography

Gross features of disc degeneration (DD) that are associated with back pain include tears in the anulus fibrosus, structural changes of the endplates, and a collapse of the anulus. The aim of this study is the detailed visualization and microstructural characterization of DD using microcomputed tomography (μCT) and a dedicated image post‐processing pipeline. In detail, we investigate a cadaveric spine that shows both types of DD between L1 and L2 and between L2 and L3, respectively. The lumbar spine was obtained from a male donor aged 74 years. The complete specimen was scanned using μCT with an isometric voxel size of 93 μm. Subsequently, regions of interest (ROI) were prepared featuring each complete intervertebral disc including the adjacent endplates. ROIs were then additionally scanned with a voxel size of 35 μm and by means of magnetic resonance imaging. The collapsed endplate of the superior L2 showed explicit signs of an endplate‐driven degeneration, including bony endplate failures. In contrast, the intervertebral disc between L2 and L3 showed indications of an annulus‐driven DD including severe disc height loss and concentric tears. Using μCT we were able to visualize and quantify bone and cartilage features in DD. We showed that in both cases a suite of structural changes accompanies cartilage degeneration, including microstructural bony adaptions to counteract changes in the biomechanical loading regimen.

circRNA_0058097 promotes tension-induced degeneration of endplate chondrocytes by regulating HDAC4 expression through sponge adsorption of miR-365a-5p

Excessive mechanical tension can lead to the degeneration of endplate chondrocytes. The presence of tension-sensitive circRNA_0058097 molecules has been detected in human endplate chondrocytes, where it was found to be a potential competing endogenous RNA. Indeed, inhibiting the expression of circRNA_0058097 effectively enhanced the stress resistance of endplate chondrocytes, suggesting that it may be an important trigger point for the degeneration of endplate cartilage. Through a series of experiments, we reveal that circRNA_0058097 can upregulate the expression of downstream target gene histone deacetylase 4 by sponge adsorption of miR-365a-5p, which promoted morphological changes of endplate chondrocytes, and increased extracellular matrix degradation and degeneration of endplate cartilage. Therefore, circRNA_0058097 may provide a new way to prevent and treat endplate cartilage degeneration.

Immediate and late discal lesions on MRI in Magerl A thoracolumbar fracture: Analysis of 76 cases

INTRODUCTION

Magerl type A thoracolumbar fracture is frequent, but consensus is lacking on management, which ranges from non-operative treatment to corpectomy. It is, however, essential to spare adjacent discs in young patients. Historically, Magerl defined type A fracture in terms of isolated bone involvement. Subsequently, several authors suggested that discal lesions are associated, but results were inconsistent. The present study assessed the presence of immediate post-trauma discal lesions and late degeneration.

HYPOTHESIS

Type A fracture does not entail discal lesion.

MATERIAL AND METHOD

Fifty-four patients with type A fracture and immediate post-trauma MRI (76 fractures, 138 discs) were retrospectively reviewed. Twenty-seven also had follow-up MRI at a mean 32 months. Two observers analyzed adjacent discs on Oner's classification, on the immediate post-trauma MRI, and on follow-up MRI to assess disc degeneration.

RESULTS

Immediate post-trauma analysis of the cranial discs of the fractured vertebrae found 81% normal (type 1), none type 2, 7% type 3, 4% type 4, 7% type 5 and 1% type 6. Caudal discs were 97% type 1. Analysis at follow-up found degeneration in only 15% of cranial and 9% of caudal discs.

DISCUSSION

A large majority of type A fractures lead to no immediate discal lesions, and only 15% of cranial discs subsequently degenerate. MRI analyzing disc signal and morphology is essential before removing material.

LEVEL OF EVIDENCE

IV, retrospective study.

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.

Dynamic adaptation of vertebral endplate and trabecular bone following annular injury in a rat model of degenerative disc disease

BACKGROUND CONTEXT

Degenerative disc disease (DDD) is associated with longitudinal remodeling of paravertebral tissues. Although chronic vertebral changes in advanced stages of DDD are well-studied, very little data exists on acute vertebral bone remodeling at the onset and progression of DDD.

PURPOSE

To longitudinally characterize bony remodeling in a rodent model of disc injury-induced DDD.

STUDY DESIGN

In vivo animal study involving a rat annulus fibrosus injury model of DDD.

METHODS

Eight female Lewis rats were assigned to intervertebral disc (IVD) injury (Puncture) or sham surgery (Sham). All rats underwent anterior, transperitoneal approach to the lumbar spine, and Puncture rats underwent annulus fibrosus injury at the L3-L4 and L5-L6 IVDs (n = 8 per group). Live micro computed tomography imaging (10-μm voxel size) was performed 1 week before surgery and postoperatively at 2-week intervals up to a 12-week endpoint. Bone morphology and densitometry of the cranial vertebral body and bony endplate were analyzed and reported with respect to the preoperative baseline scan. Sagittal Safranin-O/Fast-Green and Toluidine Blue histology evaluated using the Rutges IVD score and a custom vertebral endplate score.

RESULTS

Vertebral trabecular tissue mineral density (TMD), vertebral trabecular spacing, endplate TMD, and endplate apparent bone mineral density were all significantly greater in Puncture compared with Sham at 4 weeks and each subsequent timepoint. Puncture rats exhibited marginally lower endplate total volume. Anterior endplate osteophyte formation and central physeal ossification were observed in Puncture rats. Endpoint histological analysis demonstrated moderate evidence of IVD degeneration, indicating that vertebral bone adaptation occurs in the acute phases of DDD onset and progression.

CONCLUSIONS

Annulus injury-induced DDD leads to acute and progressive changes to the morphology and densitometry of bone in the adjacent vertebral bodies and endplates.

Asymmetry between the superior and inferior endplates is a risk factor for lumbar disc degeneration

Endplate pathology plays an important role in the development of lumbar disc degeneration. Previous research paid little attention to differences between the superior and inferior endplates as a possible risk factor for disc degeneration. The purpose of this study was to test the hypothesis that asymmetry between the superior and inferior endplates is a risk factor for the development of lumbar disc degeneration. A total of 134 patients with lumbar disc herniation (LDH) and 100 healthy adults ("Controls") underwent magnetic resonance imaging scans. Each disc was categorized as non-degenerated (Pfirrmann grades I-II) or degenerated (Pfirrmann grades III-V) and get the following three groups: "Degenerated LDH" discs (n = 145), "Non-degenerated LDH" discs (n = 525) and "Non-degenerated Control" discs (n = 500). On mid-sagittal image, the lumbar endplate morphology could be categorized into three types: Flat, concave, and irregular. Superior and inferior endplates of a given disc were "symmetric" if both were of the same type, and "asymmetric" if they were of different types. The proportion of asymmetric endplates at L4-5 was higher in the "Degenerated LDH" discs group (47%) than in the "Non-degenerated LDH" discs group (21%) or "Non-degenerated Control" discs group (7%) (p < 0.05). At L5-S1 the proportions were 73%, 55%, and 38% (p < 0.05). Asymmetry of superior and inferior endplates in the mid-sagittal plane is a risk factor for lumbar disc degeneration. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2469-2475, 2018.

Intradiscal delivery of celecoxib-loaded microspheres restores intervertebral disc integrity in a preclinical canine model

Low back pain, related to degeneration of the intervertebral disc (IVD), affects millions of people worldwide. Clinical studies using oral cyclooxygenase-2 (COX-2) inhibitors have shown beneficial effects, although side-effects were reported. Therefore, intradiscal delivery of nonsteroidal anti-inflammatory drugs can be an alternative treatment strategy to halt degeneration and address IVD-related pain. In the present study, the controlled release and biologic potency of celecoxib, a selective COX-2 inhibitor, from polyesteramide microspheres was investigated in vitro. In addition, safety and efficacy of injection of celecoxib-loaded microspheres were evaluated in vivo in a canine IVD degeneration model. In vitro, a sustained release of celecoxib was noted for over 28 days resulting in sustained inhibition of inflammation, as indicated by decreased prostaglandin E₂ (PGE₂) production, and anti-catabolic effects in nucleus pulposus (NP) cells from degenerated IVDs on qPCR. In vivo, there was no evidence of adverse effects on computed tomography and magnetic resonance imaging or macroscopic evaluation of IVDs. Local and sustained delivery of celecoxib prevented progression of IVD degeneration corroborated by MRI, histology, and measurement of NP proteoglycan content. Furthermore, it seemed to harness inflammation as indicated by decreased PGE₂ tissue levels and decreased neuronal growth factor immunopositivity, providing indirect evidence that local delivery of a COX-2 inhibitor could also address pain related to IVD degeneration. In conclusion, intradiscal controlled release of celecoxib from polyesteramide microspheres prevented progression of IVD degeneration both in vitro and in vivo. Follow-up studies are warranted to determine the clinical efficacy of celecoxib-loaded PEAMs in chronic back pain.

Calcium Microcrystal Formation in Recurrent Herniation Patients After Autologous Disc Cell Transplantation

Autologous disc cell transplantation (ADCT) is a cell-based therapy aiming to initiate regeneration of intervertebral disc (IVD) tissue, but little is known about potential risks. This study aims to investigate the presence of structural phenomena accompanying the transformation process after ADCT treatment in IVD disease. Structural phenomena of ADCT-treated patients (Group 1, n = 10) with recurrent disc herniation were compared to conventionally-treated patients with recurrent herniation (Group 2, n = 10) and patients with a first-time herniation (Group 3, n = 10). For ethical reasons, a control group of ADCT patients who did not have a recurrent disc herniation was not possible. Tissue samples were obtained via micro-sequestrectomy after disc herniation and analyzed by micro-computed tomography, scanning electron microscopy, energy dispersive spectroscopy, and histology in terms of calcification zones, tissue structure, cell density, cell morphology, and elemental composition. The major differentiator between sample groups was calcium microcrystal formation in all ADCT samples, not found in any of the control group samples, which may indicate disc degradation. The incorporation of mineral particles provided clear contrast between the different materials and chemical analysis of a single particle indicated the presence of magnesium-containing calcium phosphate. As IVD calcification is a primary indicator of disc degeneration, further investigation of ADCT and detailed investigations assessing each patient's Pfirrmann degeneration grade following herniation is warranted. Structural phenomena unique to ADCT herniation prompt further investigation of the therapy's mechanisms and its effect on IVD tissue. However, the impossibility of a perfect control group limits the generalizable interpretation of the results.

Comparison of Synchrotron Radiation-based Propagation Phase Contrast Imaging and Conventional Micro-computed Tomography for Assessing Intervertebral Discs and Endplates in a Murine Model

STUDY DESIGN

The synchrotron radiation-based micro-computed tomography (SRμCT) and micro-CT (μCT) were applied to comparatively assess the intervertebral disc (IVD) and endplate (EP).

OBJECTIVE

To explore a new approach to evaluate the detailed structure of the IVD and EP during maturation and aging in a murine model.

SUMMARY OF BACKGROUND DATA

Till date, methods to observe the morphological changes in the IVD and EP from rodents have been relatively limited. SRμCT has been recognized as a potential way to visualize the structures containing sclerous and soft tissue. Our study focused on comparing the capacity of SRμCT and μCT in evaluating the detailed structure of the IVD and EP.

METHODS

Both SRμCT and μCT were performed to depict the structure of spinal tissue from 4-month-old mice. Then, the imaging quality was evaluated in the three-dimensional (3D) reconstructed model. Further, the changes in the EP and IVD during the maturation and aging process were assessed morphologically and quantitatively using SRμCT.

RESULTS

The 3D reconstructed model of the EP from both μCT and SRμCT provided detailed information on its inner structure. However, the IVD was only depicted using SRμCT. Multi-angle observations of the 3D structure of EP and IVD from mice of different ages (15 days, 2 months, 4 months, and 18 months) were dynamically performed by SRμCT. Quantitative evaluations indicated that the total volume of EP and IVD, the average height of IVD and the canal-total volume ratio of EP increased from 15-day-old mice to 4-month-old mice and decreased in 18-month-old mice.

CONCLUSION

The EP and IVD were clearly visualized using SRμCT. Compared with μCT, SRμCT provided a better ultrahigh resolution image of soft tissue and hard tissue simultaneously, which makes it a promising approach for the noninvasive study of disc degeneration.

LEVEL OF EVIDENCE

N /A.

Micro-CT evaluation of asymmetrical ovine intervertebral disc height loss from surgical approach

PURPOSE

The primary goal of this study is to clearly define and evaluate new intervertebral disc height parameters in analysing the morphological pathology of disc degeneration for application in damage model and regeneration therapy development, as well as applying traditional variables to 3-D characterization methods.

METHODS

A posterolateral surgical approach was used to induce disc degeneration in an ovine model. At 12-months post-operation, sheep vertebral segments were removed and characterized using micro-CT to evaluate disc height parameters in regard to injury localization.

RESULTS

Statistically significant differences between the disc height loss of the left and right side of the disc, consistent with the lateral surgical approach used were seen using the modified average disc height method by Dabbs et al. However, convexity index and the newly proposed Cross Tilt Index did not conclusively demonstrate a difference.

CONCLUSION

Two-dimensional morphological evaluations can be applied in 3-D to provide a more complete picture of disc height loss for injury models. New 3-D parameters that are tailored to the type of surgical approach used should be investigated, with the 9-point system described herein providing a useful basis for derived values. Additionally, the surgical approach chosen when artificially injuring the disc can result in asymmetrical degeneration, as indicated by uneven disc height loss.

3D characterization of morphological changes in the intervertebral disc and endplate during aging: A propagation phase contrast synchrotron micro-tomography study

A better understanding of functional changes in the intervertebral disc (IVD) and interaction with endplate is essential to elucidate the pathogenesis of IVD degeneration disease (IDDD). To date, the simultaneous depiction of 3D micro-architectural changes of endplate with aging and interaction with IVD remains a technical challenge. We aim to characterize the 3D morphology changes of endplate and IVD during aging using PPCST. The lumbar vertebral level 4/5 IVDs harvested from 15-day-, 4- and 24-month-old mice were initially evaluated by PPCST with histological sections subsequently analyzed to confirm the imaging efficiency. Quantitative assessments of age-related trends after aging, including mean diameter, volume fraction and connectivity of the canals, and endplate porosity and thickness, reached a peak at 4 months and significantly decreased at 24 months. The IVD volume consistently exhibited same trend of variation with the endplate after aging. In this study, PPCST simultaneously provided comprehensive details of 3D morphological changes of the IVD and canal network in the endplate and the interaction after aging. The results suggest that PPCST has the potential to provide a new platform for attaining a deeper insight into the pathogenesis of IDDD, providing potential therapeutic targets.

A large animal model that recapitulates the spectrum of human intervertebral disc degeneration

OBJECTIVE

The objective of this study was to establish a large animal model that recapitulates the spectrum of intervertebral disc degeneration that occurs in humans and which is suitable for pre-clinical evaluation of a wide range of experimental therapeutics.

DESIGN

Degeneration was induced in the lumbar intervertebral discs of large frame goats by either intradiscal injection of chondroitinase ABC (ChABC) over a range of dosages (0.1U, 1U or 5U) or subtotal nucleotomy. Radiographs were used to assess disc height changes over 12 weeks. Degenerative changes to the discs and endplates were assessed via magnetic resonance imaging (MRI), semi-quantitative histological grading, microcomputed tomography (μCT), and measurement of disc biomechanical properties.

RESULTS

Degenerative changes were observed for all interventions that ranged from mild (0.1U ChABC) to moderate (1U ChABC and nucleotomy) to severe (5U ChABC). All groups showed progressive reductions in disc height over 12 weeks. Histological scores were significantly increased in the 1U and 5U ChABC groups. Reductions in T2 and T1ρ, and increased Pfirrmann grade were observed on MRI. Resorption and remodeling of the cortical boney endplate adjacent to ChABC-injected discs also occurred. Spine segment range of motion (ROM) was greater and compressive modulus was lower in 1U ChABC and nucleotomy discs compared to intact.

CONCLUSIONS

A large animal model of disc degeneration was established that recapitulates the spectrum of structural, compositional and biomechanical features of human disc degeneration. This model may serve as a robust platform for evaluating the efficacy of therapeutics targeted towards varying degrees of disc degeneration.

Solute transport at the interface of cartilage and subchondral bone plate: Effect of micro-architecture

Cross-talk of subchondral bone and articular cartilage could be an important aspect in the etiology of osteoarthritis. Previous research has provided some evidence of transport of small molecules (~370Da) through the calcified cartilage and subchondral bone plate in murine osteoarthritis models. The current study, for the first time, uses a neutral diffusing computed tomography (CT) contrast agent (iodixanol, ~1550Da) to study the permeability of the osteochondral interface in equine and human samples. Sequential CT monitoring of diffusion after injecting a finite amount of contrast agent solution onto the cartilage surface using a micro-CT showed penetration of the contrast molecules across the cartilage-bone interface. Moreover, diffusion through the cartilage-bone interface was affected by thickness and porosity of the subchondral bone as well as the cartilage thickness in both human and equine samples. Our results revealed that porosity of the subchondral plate contributed more strongly to the diffusion across osteochondral interface compared to other morphological parameters in healthy equine samples. However, thickness of the subchondral plate contributed more strongly to the diffusion in slightly osteoarthritic human samples.

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.

Histological features of endplates of the mammalian spine: from mice to men

STUDY DESIGN

Histological features of the intervertebral disc (IVD)-endplate interface were analyzed.

OBJECTIVE

To define cartilaginous and bony vertebral endplate in commonly used laboratory animals and compare with that of the humans.

SUMMARY OF BACKGROUND DATA

Endplates are crucial for the IVD nutrient supply: the IVDs have limited blood supply; most nutrients diffuse through endplates to nourish the discs. Various animal models of IVD and endplate degeneration have been used to study the etiology and treatments of spinal disorders. However, because humans are biped, the spine mechanics differ significantly from other mammals. Translation of animal research findings requires a characterization and comparison of the vertebral endplate in the respective species. In this study, we compared the endplate structure of laboratory animal species at the age range commonly used for modeling spine degeneration with that of an adult human.

METHODS

Mouse, rat, rabbit, goat, and human IVDs and the adjacent vertebral bodies were isolated from the lower lumbar spine. Tissues were stained with Alcian Blue, counterstained with hematoxylin and eosin.

RESULTS

Structure of the vertebral endplate varied significantly between the adult animal species and that of the humans. Growth plates persisted in all adult animals studied, whereas the growth plate is absent in the adult humans. In the mice and rats, the cartilaginous endplates are in continuation with the growth plates, with only a small bony center. Rabbits and goats have a bony layer between cartilaginous endplate and the growth plate. The human endplate consist of a cartilaginous layer and the bony endplate.

CONCLUSION

Significant differences exist in histological features of the endplate across animal species and that of the humans. Consideration should be given when animal models are used to study IVD degeneration and surgical treatments.

LEVEL OF EVIDENCE

5.

Factors regulating viable cell density in the intervertebral disc: blood supply in relation to disc height

The intervertebral disc is an avascular tissue, maintained by a small population of cells that obtain nutrients mainly by diffusion from capillaries at the disc-vertebral body interface. Loss of this nutrient supply is thought to lead to disc degeneration, but how nutrient supply influences viable cell density is unclear. We investigated two factors that influence nutrient delivery to disc cells and hence cell viability: disc height and blood supply. We used bovine caudal discs as our model as these show a gradation in disc height. We found that although disc height varied twofold from the largest to the smallest disc studied, it had no significant effect on cell density, unlike the situation found in articular cartilage. The density of blood vessels supplying the discs was markedly greater for the largest disc than the smallest disc, as was the density of pores allowing capillary penetration through the bony endplate. Results indicate that changes in blood vessels in the vertebral bodies supplying the disc, as well as changes in endplate architecture appear to influence density of cells in intervertebral discs.

Negative effects of ADAMTS-7 and ADAMTS-12 on endplate cartilage differentiation

The roles of ADAMTS-7 and ADAMTS-12 in disc degeneration have not been previously examined. The purpose of this study was to examine the expression of ADAMTS-7 and ADAMTS-12 in the endplate cells isolated from patients with degenerative disc disease and to see whether they are associated with the pathological change of endplate. Sixty-four degenerated lumbar endplate specimens were obtained from the patients with degenerative disc disease categorized as type Modic I or II in magnetic resonance imaging (MRI) and 12 nondegenerative specimens as control (vertebra burst fracture patients without degenerative change in MRI) during surgical procedures. The expression of ADAMTS-7 and ADAMTS-12 was examined by real-time PCR and Western blotting. A statistically significant increase in mRNA expression of ADAMTS-7 and ADAMTS-12 was observed in the endplate cells in degenerative discs compared with nondegenerative discs. The corresponding protein levels of ADAMTS-7 and ADAMTS-12 had the same expression patterns. Moreover, ADAMTS-7 and ADAMTS-12 down-regulated the expression of Col II, Sox9, and Col X the marker genes for chondrogenesis. Our results indicate that ADAMTS-7 and ADAMTS-12 appear to be potent negative regulators of endplate cartilage development.

Characterization of the annulus fibrosus-vertebral body interface: identification of new structural features

Current surgical treatments for degenerative intervertebral disc disease do not restore full normal spinal movement. Tissue engineering a functional disc replacement may be one way to circumvent this limitation, but will require an integration of the different tissues making up the disc for this approach to be successful. Hence, an in-depth characterization of the native tissue interfaces, including annulus insertion into bone is necessary, as knowledge of this interface is limited. The objective of this study was to characterize the annulus fibrosus-vertebral bone (AF-VB) interface in immature (6-9 months old) and mature (18-24 months old) bovine discs, as well as to define these structures for normal adult human (22 and 45 years old) discs. Histological assessment showed that collagen fibers in the inner annulus, which are predominantly type II collagen, all appear to insert into the mineralized endplate zone. In contrast, some of the collagen fibers of the outer annulus, predominantly type I collagen, insert into this endplate, while other fibers curve laterally, at an ∼ 90° angle, to the outer aspect of the bone, and merge with the periosteum. This is seen in both human and bovine discs. Where the AF inserts into the calcified zone of the AF-VB interface, it passes through a chondroid region, rich in type II collagen and proteoglycans. Annulus cells (elongated cells that are not surrounded by proteoglycans) are present at this interface. This cartilage zone is evident in both human and bovine discs. Type X collagen and alkaline phosphatase are localized to the interface region. Age-associated differences in bovine spines are observed when examining the interface thickness and the matrix composition of the cartilaginous endplate, as well as the thickness of the mineralized endplate. These findings will assist with the design of the AF-VB interface in the tissue engineered disc.

Intervertebral disk nutrition: a review of factors influencing concentrations of nutrients and metabolites

The biomechanical behavior of the intervertebral disk ultimately depends on the viability and activity of a small population of resident cells that make and maintain the disk's extracellular matrix. Nutrients that support these cells are supplied by the blood vessels at the disks' margins and diffuse through the matrix of the avascular disk to the cells. This article reviews pathways of nutrient supply to these cells; examines factors that may interrupt these pathways, and discusses consequences for disk cell survival, disk degeneration, and disk repair.