Intervertebral disc autografting in a bipedal animal model

Comparative study of outcomes between allograft intervertebral disc transplantation and anterior cervical discectomy and fusion: a retrospective cohort study at least 5 years of follow-up

PURPOSE

Adjacent segment degeneration (ASDeg) after anterior cervical discectomy and fusion (ACDF) seriously affects the long-term efficacy of the operation. Therefore, our team has done a lot of research on allograft intervertebral disc transplantation (AIDT) to prove its feasibility and safety. This study will compare the efficacy between AIDT and ACDF in the treatment of cervical spondylosis.

METHODS

All patients who received ACDF or AIDT in our hospital from 2000 to 2016 and followed up for at least 5 years were recruited and divided into ACDF and AIDT groups. The clinical outcomes including functional scores and radiological data of both groups were collected and compared preoperatively and postoperatively at 1 week, 3 months, 6 months, 12 months, 24 months, 60 months and last follow-up. Functional scores included Japanese Orthopedic Association score (JOA), Neck Disability Index (NDI), Visual Analog Scale of Neck (N-VAS) and Arms (A-VAS) pain, the Short Form Health Survey-36 (SF-36) and imaging dates including digital radiographs in the lateral, hyperextension and flexion positions to assess the stability, sagittal balance and mobility of the cervical spine and magnetic resonance imaging (MRI) scans to assess the degeneration of adjacent segment.

RESULTS

There were 68 patients with 25 in AIDT group and 43 in ACDF group. Satisfactory clinical results were obtained in both groups, but the long-term NDI score and N-VAS score in the AIDT group were better. The AIDT obtained the same stability and sagittal balance of the cervical spine as fusion surgery. The range of motion of adjacent segments can be restored to the preoperative level after transplantation, but this increases significantly after ACDF. There were significant differences in the superior adjacent segment range of motion (SROM) between two groups at 12 months (P = 0.039), 24 months (P = 0.035), 60 months (P = 0.039) and the last follow-up (P = 0.011). The inferior adjacent segment range of motion (IROM) and SROM had a similar trend in the two groups. The ratio value of the greyscale (RVG) of adjacent segments showed a downward trend. At the last follow-up, the RVG decreased more significantly in the ACDF group. At the last follow-up, there was a significant difference in the incidence of ASDeg between the two groups (P = 0.000). And the incidence of adjacent segment disease (ASDis) is 22.86% in the ACDF group.

CONCLUSION

The allograft intervertebral disc transplantation may be as an alternative technique to traditional anterior cervical discectomy and fusion for the management of cervical degenerative diseases. For the more, the results showed it would improve cervical kinematics and reduce the incidence of adjacent segment degeneration.

Species variation in the cartilaginous endplate of the lumbar intervertebral disc

Backgrounds

Cartilaginous endplate (CEP) plays an essential role in intervertebral disc (IVD) health and disease. The aim was to compare the CEP structure of lumbar IVD and to reveal the detailed pattern of integration between the CEP and bony endplate (BEP) from different species.

Methods

A total of 34 IVDs (5 human, 5 goat, 8 pig, 8 rabbit, and 8 rat IVDs) were collected, fixed and midsagittally cut; in each IVD, one‐half was used for histological staining to observe the CEP morphology, and the other half was used for scanning electron microscopy (SEM) analysis to measure the diameters and distributions of collagen fibers in the central and peripheral CEP areas and to observe the pattern of CEP‐BEP integration from different species.

Results

The human, pig, goat, and rabbit IVDs had the typical BEP‐CEP structure, but the rat CEP was directly connected with the growth plate. Human CEP was the thickest (896.95 ± 87.71 μm) among these species, followed by pig, goat, rat, and rabbit CEPs. Additionally, the mean cellular density of the rabbit CEP was the highest, which was 930 ± 202 per mm², followed by the rat, goat, pig, and human CEPs. In all the species, the collagen fiber diameter in the peripheral area was much bigger than that in the central area. The collagen fiber diameters of CEP from the human, pig, goat, and rat were distributed between 35 nm and 65 nm. The BEP and CEP were connected by the collagen from the CEP, aggregating into bundles or cross links with each other to form a network, and anchored to BEP.

Conclusions

Significant differences in the thickness, cellular density, and collagen characterization of CEPs from different species were demonstrated; the integration of BEP‐CEP in humans, pigs, goats, and rabbits was mainly achieved by the collagen bundles anchoring system, while the typical BEP‐CEP interface did not exist in rats.

Development, Pathogenesis, and Regeneration of the Intervertebral Disc: Current and Future Insights Spanning Traditional to Omics Methods

The intervertebral disc (IVD) is the fibrocartilaginous joint located between each vertebral body that confers flexibility and weight bearing capabilities to the spine. The IVD plays an important role in absorbing shock and stress applied to the spine, which helps to protect not only the vertebral bones, but also the brain and the rest of the central nervous system. Degeneration of the IVD is correlated with back pain, which can be debilitating and severely affects quality of life. Indeed, back pain results in substantial socioeconomic losses and healthcare costs globally each year, with about 85% of the world population experiencing back pain at some point in their lifetimes. Currently, therapeutic strategies for treating IVD degeneration are limited, and as such, there is great interest in advancing treatments for back pain. Ideally, treatments for back pain would restore native structure and thereby function to the degenerated IVD. However, the complex developmental origin and tissue composition of the IVD along with the avascular nature of the mature disc makes regeneration of the IVD a uniquely challenging task. Investigators across the field of IVD research have been working to elucidate the mechanisms behind the formation of this multifaceted structure, which may identify new therapeutic targets and inform development of novel regenerative strategies. This review summarizes current knowledge base on IVD development, degeneration, and regenerative strategies taken from traditional genetic approaches and omics studies and discusses the future landscape of investigations in IVD research and advancement of clinical therapies.

Decellularized Intervertebral Discs: A Potential Replacement for Degenerate Human Discs

Intervertebral disc (IVD) degeneration is a major cause of back pain. Current surgical interventions have limitations. An alternative approach is to replace degenerated IVDs with a natural biological scaffold. The removal of cellular components from human IVDs should render them nonimmunogenic upon implantation. The aim of this initial proof of technical feasibility study was to develop a decellularization protocol on bovine IVDs with endplates (EPs) and assess protocol performance before application of the protocol to human IVDs with attached EP and vertebral bone (VB). A decellularization protocol based on hypotonic low concentration sodium dodecyl sulfate (0.1% w/v) with proteinase inhibitors, freeze/thaw cycles, and nuclease and sonication treatments was applied to IVDs. Histological, biochemical, and biomechanical comparisons were made between cellular and decellularized tissue. Cell removal from bovine IVDs was demonstrated and total DNA levels of the decellularized inner annulus fibrosus (iAF), outer annulus fibrosus (oAF), and EP were 40.7 (±11.4), 25.9 (±3.8), and 29.3 (±3.1) ng.mg⁻¹ dry tissue weight, respectively (n = 6, ±95% confidence level [CL]). These values were significantly lower than in cellular tissue. No significant difference in DNA levels between bovine cellular and decellularized nucleus pulposus (NP) was found. Glycosaminoglycans (GAGs) were largely retained in the NP, iAF, and oAF. Cyclic compression testing showed sufficient sensitivity to detect an increase in stiffness of bovine IVD postdecellularization (2957.2 ± 340.8 N.mm⁻¹) (predecellularization: 2685.4 ± 263.1 N.mm⁻¹; n = 5, 95% CL), but the difference was within natural tissue variation. Total DNA levels for all decellularized tissue regions of human IVDs (NP, iAF, oAF, EP, and VB) were below 50 ng.mg⁻¹ dry tissue weight (range: 2 ng.mg⁻¹, iAF to 29 ng.mg⁻¹, VB) and the tissue retained high levels of GAGs. Further studies to assess the biocompatibility and regenerative potential of decellularized human IVDs in vitro and in vivo are now required; however, proof of technical feasibility has been demonstrated and the retention of bone in the IVD samples would allow incorporation of the tissue into the recipient spine.

Novel Intervertebral Technologies

Surgical procedures, such as spinal fusion and disk replacement, are commonly used for treatment following failure of conservative treatment in degenerative spine disease. However, there is growing consensus that currently available surgical technologies may have long-term inefficacy for successful management. Intervertebral disk degeneration is the most common manifestation of degenerative spine disease, hence, replacement/repair of this tissue is an important component of surgical treatment. Restoration of spinal alignment and preservation of natural kinematics is also essential to a good outcome. This article reviews novel intervertebral implant technologies that have the potential to significantly impact elective spine surgery for degenerative spine disease.

Biomaterials for intervertebral disc regeneration: Current status and looming challenges

A biomaterial-based strategy is employed to regenerate the degenerated intervertebral disc, which is considered a major generator of neck and back pain. Although encouraging enhancements in the anatomy and kinematics of the degenerative disc have been gained by biomaterials with various formulations in animals, the number of biomaterials tested in humans is rare. At present, most studies that involve the use of newly developed biomaterials focus on regeneration of the degenerative disc, but not pain relief. In this review, we summarise the current state of the art in the field of biomaterial-based regeneration or repair for the nucleus pulposus, annulus fibrosus, and total disc transplantation in animals and humans, and we then provide essential suggestions for the development and clinical translation of biomaterials for disc regeneration. It is important for researchers to consider the commonly neglected issues instead of concentrating solely on biomaterial development and fabrication.

Decellularization and characterization of a whole intervertebral disk xenograft scaffold

Intervertebral disk (IVD) degeneration is a multifactor process that results in the physical destruction of the nucleus pulposus (NP) and annulus fibrosus (AF). This compromises IVD function and causes significant disability and economic burden. Strategies to replace the entire composite structure of the IVD are limited and most approaches do not recapitulate the heterogenous biochemical composition, microarchitecture or mechanical properties of the native tissue. Our central hypothesis was that donor IVDs which resemble the size and biochemistry of human lumbar IVDs could be successfully decellularized while retaining the tissue's structure and function with the long-term goal of creating a composite scaffold for tissue engineering the human IVD. Accordingly, we optimized a procedure to decellularize bovine tail IVDs using a combination of detergents, ultrasonication, freeze-thaw cycles, and nucleases. The resultant decellularized whole IVD xenografts retained distinct AF and NP regions which contained no visible intact cell nuclei and minimal residual bovine deoxyribose nucleic acid (DNA; 65.98 ± 4.07 and 47.12 ± 13.22 ng/mg, respectively). Moreover, the NP region of decellularized IVDs contained 313.40 ± 50.67 µg/mg glycosaminoglycan. The presence of collagen type II was confirmed via immunohistochemistry. Additionally, histological analysis of the AF region of decellularized IVDs demonstrated retention of the native angle-ply collagen microarchitecture. Unconfined compression testing demonstrated no significant differences in swelling pressure and toe-region modulus between fresh and decellularized IVDs. However, linear region moduli, peak stress and equilibrium moduli were all significantly reduced. Together, this research demonstrates a successful initial step in developing a biomimetic acellular whole IVD xenograft scaffold for use in IVD tissue engineering. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2412-2423, 2018.

Imaging Evaluation and Relative Significance in Cases of Cervical Disk Allografting: Radiographic Character After Total Disk Transplantation

STUDY DESIGN

The clinical and radiologic data of total disk allografting (TDA) cases were collected and analyzed to explore the correlation between neurological function improvements and imaging changes.

OBJECTIVE

The aim of the study was to assess the medium-term and long-term outcome and radiographic character after TDA, and, furthermore, to explore the significance of the changes of imaging signs after the transplantation.

SUMMARY OF BACKGROUND DATA

Spinal fusion may result in the adjacent segment degeneration. The anxiousness urged the necessity for the development of TDA to reduce the risk of adjacent segment degeneration. Both animal studies and recent clinical trials have shown promising results to support the use of intervertebral disk allograft as a natural mobile disk replacement.

METHODS

The conditions of 13 cases that underwent TDA after cervical discectomy were recorded in detail. Axial symptoms and neurological function in various periods were assessed, and, meanwhile, radiologic examination was performed for the comprehensive evaluation of the relevant indicators before and after surgery.

RESULTS

(1) There was significant improvement in the neurological function after TDA. Postoperatively, the Visual Analog Score of axial symptoms did not increase significantly. (2) Both the entire and local segment maintained a satisfactory curve after allografting. There was no obvious correlation between the neurological function recovery and the cervical curve. Besides, the motion of the cervical spine did not change postoperatively. (3) Postoperatively, the spinal cord area at the index level increased significantly, whereas the signal value of the transplanted disk decreased sharply.

CONCLUSIONS

(1) Disk allografting is one of the effective and safe methods in treating the diseases of cervical disk herniation. (2) Although some degeneration occurs in the transplanted disk, the allograft can still be alive and can successfully maintain and improve the biological characters of the cervical spine in both radiologic and practical aspects.

A Review of Animal Models of Intervertebral Disc Degeneration: Pathophysiology, Regeneration, and Translation to the Clinic

Lower back pain is the leading cause of disability worldwide. Discogenic pain secondary to intervertebral disc degeneration is a significant cause of low back pain. Disc degeneration is a complex multifactorial process. Animal models are essential to furthering understanding of the degenerative process and testing potential therapies. The adult human lumbar intervertebral disc is characterized by the loss of notochordal cells, relatively large size, essentially avascular nature, and exposure to biomechanical stresses influenced by bipedalism. Animal models are compared with regard to the above characteristics. Numerous methods of inducing disc degeneration are reported. Broadly these can be considered under the categories of spontaneous degeneration, mechanical and structural models. The purpose of such animal models is to further our understanding and, ultimately, improve treatment of disc degeneration. The role of animal models of disc degeneration in translational research leading to clinical trials of novel cellular therapies is explored.

Biologic response of degenerative living human nucleus pulposus cells to treatment with cytokines

PURPOSE

To investigate the molecular responses of various genes and proteins related to disc degeneration upon treatment with cytokines that affect disc-cell proliferation and phenotype in living human intervertebral discs (IVDs). Responsiveness to these cytokines according to the degree of disc degeneration was also evaluated.

MATERIALS AND METHODS

The disc specimens were classified into two groups: group 1 (6 patients) showed mild degeneration of IVDs and group 2 (6 patients) exhibited severe degeneration of IVDs. Gene expression was analyzed after treatment with four cytokines: recombinant human bone morphogenic protein (rhBMP-2), transforming growth factor-β (TGF-β), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α). Molecular responses were assessed after exposure of cells from the IVD specimens to these cytokines via real-time polymerase chain reaction and immunofluorescence staining.

RESULTS

mRNA gene expression was significantly greater for aggrecan, type I collagen, type II collagen, alkaline phosphatase, osteocalcin, and Sox9 in group 1 than mRNA gene expression in group 2, when the samples were not treated with cytokines. Analysis of mRNA levels for these molecules after morphogen treatment revealed significant increases in both groups, which were much higher in group 1 than in group 2. The average number of IVD cells that were immunofluorescence stained positive for alkaline phosphatase increased after treatment with rhBMP-2 and TGF-β in group 1.

CONCLUSION

The biologic responsiveness to treatment of rhBMP-2, TGF-β, TNF-α, and IL-1β in the degenerative living human IVD can be different according to the degree of degeneration of the IVD.

Surgical technique for lumbar intervertebral disc transplantation in a goat model

PURPOSE

Fresh-frozen intervertebral disc transplantation was determined to be an effective treatment for degenerative disc diseases in rhesus monkeys and in humans. Further research in improving different aspects of disc allografts transplantation is needed and will be investigated in large animal models. This study reports the detailed surgical technique of intervertebral disc transplantation without internal fixation and the important notes to ensure success in goats.

METHODS

Fifty-one male goats were used in this study. Ten goats were used as intervertebral disc allograft donors; the remaining forty-one goats were used to develop the surgical technique for intervertebral disc allograft transplantation. Radiographs, ex vivo MRI and gross observation were used to monitor the stability and healing of the disc allografts at 3 months, postoperatively.

RESULTS

Size matching of the disc allograft, preservation of the anterior longitudinal ligament and an appropriate portion of the annulus fibrosus at the recipient site were crucial for stable graft retention. Additionally, a slightly reduced height of the disc allograft compared to that of the recipient slot may avoid graft endplate fracture.

CONCLUSIONS

Lumbar intervertebral disc transplantation without internal fixation can be successfully performed in goats.

The effect of gamma irradiation on the biological properties of intervertebral disc allografts: in vitro and in vivo studies in a beagle model

Study Design

An animal experiment about intervertebral disc allograft.

Objective

To explore the feasibility to decellularize disc allografts treated by ⁶°Co Gamma Irradiation, and simultaneously, to assess the possibility to make use of the decellularized natural disc scaffold for disc degeneration biotherapy.

Summary of Background Data

Studies of both animal and human disc allograft transplantation indicated that the disc allograft may serve as a scaffold to undertake the physiological responsibility of the segment.

Methods

Experiment in vitro: 48 discs of beagles were harvested and divided randomly into four groups including a control group and three irradiated groups. Immediate cell viability and biomechanical properties of the discs were checked and comparisons were made among these groups. Experiment in vivo: 24 beagles accepted single-level allografted disc treated with different doses of gamma irradiation. Plain X-rays and MRIs were taken before and after surgery. Then, the spinal columns were harvested en bloc from the sacrificed beagles and were examined morphologically.

Results

There were significant differences of both the annulus fibrosus and nucleus pulposus immediate cell viabilities among the various groups. There were no obvious differences of the biomechanical properties among the four groups. The disc height and range of motion decreased significantly in all groups as time went on. The observed indexes in irradiated groups were much smaller than those in the control group, but the indexes in 18-kGy group were larger than those in 25-kGy and 50-kGy groups. Both MRI and macroscopic findings showed that the segmental degeneration in the control and 18-kGy group was less severe than that in 25-kGy and 50-kGy groups.

Conclusion

Gamma Irradiation can decellularize disc allograft successfully to provide natural scaffold for the study of degenerative disc disease therapy, and also can be used as an effective method to produce adjustable animal models.

The effect of remodeling on the kinematics of the malpositioned disc allograft transplantation

STUDY DESIGN

A postoperative biomechanical study.

OBJECTIVE

This study aimed to assess whether the mal-alignment of the intervertebral disc (IVD) allograft during transplantation would negatively affect the biomechanics of the spinal segment.

SUMMARY OF BACKGROUND DATA

Studies of human IVD allograft transplantation have observed remodeling of the allograft implant, suggesting that the remodeling of the allograft may be able to restore the natural mechanics of the IVD.

METHODS

Eighteen male goats (age: 6-12 months; weight: 25-30 kg) were randomly assigned into control (n = 5), aligned (n = 5), or malpositioned (n = 5) groups. Transplantation of a size-matched cryopreserved IVD allograft was performed in the lumbar region (L4-L5) after disc excision. In the aligned group, the IVD allografts were placed aligned and flush with the anterior vertebral margin. In the malpositioned group, the allografts were placed proud anteriorly by 25% of the anterior-posterior diameter of the allograft. The lumbar spines were harvested at 6 months after transplantation. Three-dimensional kinematic assessment of the lumbar spines was performed using an MTS testing machine and an optoelectronic camera system. The range of motion, neutral zone, and instantaneous axis of rotation were calculated.

RESULTS

No significant difference in range of motion was noted between the groups in flexion, axial rotation, and lateral bending. Significance was noted with extension range of motion as detected in both the aligned (17.51 ± 1.97 degrees; P = 0.019) and malpositioned groups (16.61 ± 2.35 degrees; P = 0.027) compared with the control (10.11 ± 1.03 degrees). No significant difference was detected in the neutral zone between the groups. Significant difference in the instantaneous axis of rotation orientation between the malpositioned and control groups was detected in the sagittal plane during lateral bending motion (P = 0.036).

CONCLUSION

Kinematic parameters in both the aligned and malpositioned allograft were similar to those of the intact spine. This suggests that precise positioning of the IVD allograft may not be an essential factor affecting the biomechanics of the spinal segment after transplantation.

Intervertebral disc transplantation: a biological approach to motion preservation

Intervertebral disc transplantation was developed in a bipedal animal model through the stages of autograft, fresh allograft and fresh frozen allograft. Results showed that the allografts were able to survive through a deep freezing protocol and maintain cell viability after transplantation without significant immunoreaction. Although degeneration of the allograft appeared to be inevitable, it was able to maintain stability and mobility of the functional spinal unit. These findings were similarly reproduced in the human clinical trial with excellent mid-term clinical results at 5 years. The process of evolution and findings were summarized in this review.

Tissue engineering and the intervertebral disc: the challenges

Disc degeneration is a common disorder. Although the back pain that can develop in association with this is rarely life-threatening, the annual cost in terms of morbidity, lost productivity, medical expenses and workers' compensation benefits is significant. Surgical intervention as practised currently is directed towards removing the damaged or altered tissue. Development of new treatment modalities is critical as there is a growing consensus that the strategies used currently for symptomatic degenerative disc disease may not be effective. Accordingly, there is a need to develop an entirely new way to treat this disorder; regenerative medicine and tissue engineering approaches appear particularly promising in this regard. This paper reviews some of the challenges that currently are limiting the clinical application of this approach to the treatment of disc degeneration.

Scaffolding in tissue engineering: general approaches and tissue-specific considerations

Scaffolds represent important components for tissue engineering. However, researchers often encounter an enormous variety of choices when selecting scaffolds for tissue engineering. This paper aims to review the functions of scaffolds and the major scaffolding approaches as important guidelines for selecting scaffolds and discuss the tissue-specific considerations for scaffolding, using intervertebral disc as an example.

Strategies for regeneration of the intervertebral disc

Low back pain resulting from degenerative disc disease is the most common cause of disability in the UK. Current low back pain treatments are aimed at either treating the symptoms of pain, or removing the source of pain itself, but do not address the biological basis of the disease. Our increasing understanding of the molecular biological basis for degenerative disc disease has enabled the development of strategies aimed at tackling the causes of degeneration. Here we review the progress that has been made in strategies using cells, biomaterials and growth factors aimed at regenerating the human intervertebral disc.

Tissue-engineering approach to regenerating the intervertebral disc

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

Intervertebral disc transplantation in the treatment of degenerative spine disease: a preliminary study

BACKGROUND

Spinal fusion can be complicated by accelerated degeneration of the adjacent segments. Artificial disc replacements have been developed, but results are variable. Successful transplantations of intervertebral disc autografts, fresh allografts, and fresh-frozen allografts-ie, a non-fusion strategy-in which the mobility and stability of the spinal segment were preserved have been done in a primate model. Our aim was to determine the feasibility, safety, and long-term clinical results of disc transplantation in human beings.

METHODS

Five patients, average age 47 years, with cervical disc herniation underwent transplantation of fresh-frozen composite disc allografts after disc excision. Serial MRI and static and dynamic radiographs were used to monitor the status of the grafts and the sagittal stability and mobility of the segment.

FINDINGS

Good union of the graft endplates was seen by the end of 3 months after surgery in all patients. At a minimum follow-up of 5 years, the neurological symptoms of all patients had improved from before surgery levels. No immunoreaction was encountered. There was no olisthesis and only mild degenerative changes of the transplanted discs. All except one of the discs showed preservation of 7.0-11.3 degrees of sagittal motion at the final follow-up. MRI at 5 years showed preservation of hydration in at least two discs.

INTERPRETATION

Despite signs of mild disc degeneration, the motion and stability of the spinal unit was preserved after transplantation of fresh-frozen allogenic intervertebral discs in our patients. With further refinements, such transplantations could be an effective treatment for degenerative disc disease.

Molecular therapy of the intervertebral disc

Disc degeneration is the loss of the normal nucleus pulposus disc matrix to a more fibrotic and less cartilaginous structure. This change in disc micro-anatomy can be associated with pain and deformity, however, prevention and treatment options of disc degeneration are currently limited. Much research is going on to understand intervertebral discs at a molecular/ cellular level in hopes of creating clinically applicable options for treating disc degeneration. This review article will give insight into the current and developing status of treating intervertebral disc degeneration from a molecular standpoint.

Morphologic comparison of cervical, thoracic, lumbar intervertebral discs of cynomolgus monkey (Macaca fascicularis)

The aim was to analyze the morphological differences of the intervertebral disc and endplates at different levels. Forty-five vertebral motion segments were obtained from the spine of nine 3 to 4-year-old cynomolgus monkeys (Macaca fascicularis). From every spine, five discs were sectioned (C5-C6, T3-T4, T9-T10, L2-L3, L4-L5). In all the groups, tissue samples were collected and sections were stained with Masson's trichrome, Safranine-O and van Gieson's connective tissue stain to analyze the intervertebral discs. Immunohistochemistry was performed, using specific antibodies to detect collagens I and II. The intervertebral disc height, the maximum nucleus pulposus height, the superior and inferior endplate heights were histomorphometrically measured and different indexes were calculated to compare the differences between specimens of the same animal and between discs of the same level, and finally the differences between groups of discs of different levels. There were no differences existing in annular fibers anchoring on the endplate between discs of different levels. A positive immune reaction for type I collagen was observed in the longitudinal ligaments and in the annular region adjacent to them. Collagen II immune reactivity was found in the annulus close to the nucleus pulposus, in the endplates and in the nucleus. There were no differences between discs of different levels in the collagen I and II localization. The height of the discs varied along the spine. The smallest value was measured in T3-T4, with a larger increase caudally than cranially. The highest value was measured in L2-L3. A cervical disc was 55% the height of a lumbar one. The endplate height increased along the length of the spine. The inferior EP was always higher than the superior. The study provides a detailed structural characterization of the intervertebral disc and may be useful for further investigations on the disc degeneration process.

Molecular therapy of the intervertebral disc

BACKGROUND CONTEXT

Currently, no biologic treatment is available for disc degeneration. However, many different molecules of potential therapeutic benefit are being investigated.

PURPOSE

Review and categorize the molecules under investigation for potential therapy in preventing or reversing disc degeneration.

STUDY DESIGN

Review article.

METHODS

Review of published articles on molecules that may be useful in biologic therapy of the intervertebral disc.

RESULTS

The list of molecules under investigation for potential benefit in biologic therapy of the intervertebral disc repair continues to grow. These molecules are so diverse that they no longer all fall into the classic terminology of "growth factor." Some of these molecules are not growth factors at all and some are not even cytokines. At least four different classes of molecules may be effective in disc repair. These include anticatabolics (eg, tissue inhibitors of metalloproteinase [TIMPs]), mitogens (eg, insulin-like growth factor-1 [IGF-1], platelet-derived growth factor [PDGF]), chondrogenic morphogens (transforming growth factor beta [TGF-beta] and bone morphogenetic proteins [BMPs]), and intracellular regulators (LIM mineralization protein-1 [LMP-1] and Sox9). Although some in vitro data are available on all of these molecules, few of these molecules have been tested in vivo with an animal model of disc degeneration.

CONCLUSIONS

As the current screening experiments are concluded, more definitive in vivo systems involving a more realistic degeneration model will be a necessary step before attempting human studies.

Formation of a nucleus pulposus-cartilage endplate construct in vitro

Intervertebral disc (IVD) degeneration is a common problem and treatment options for persistent symptomatic disease are limited. Tissue engineering is being explored for its ability to reconstitute the functional components of the IVD. The purpose of this study was to determine whether it was possible to form in vitro a triphasic construct consisting of nucleus pulposus (NP), cartilage endplate (CEP), and a porous calcium polyphosphate (CPP) bone substitute. Bovine articular chondrocytes were placed on the top surface of a porous CPP construct and allowed to form cartilage in vitro. Nucleus pulposus cells were then placed onto the in vitro-formed hyaline cartilage. At 24 h scanning electron microscopy demonstrated that the NP cells maintained their rounded morphology, similar to NP cells placed directly on porous CPP. At 8 weeks histological examination of the triphasic constructs by light microscopy showed that a continuous layer of NP tissue had formed and was fused to the underlying cartilage tissue, which itself was integrated with the porous CPP. The incorporation of the cartilage layer was beneficial to the construct by improving tissue attachment to the CPP, as demonstrated by increased peak load and increased energy required for failure during shear loading when compared to a biphasic construct composed of nucleus pulposus-bone substitute only. This study demonstrates that it is possible to generate a multi-component construct with the incorporation of a CEP-like layer resulting in improved bone substitute-to-IVD tissue interface characteristics.

Cellular therapy for disc degeneration

STUDY DESIGN

Review article regarding the developing field of cellular therapies for symptomatic disc degeneration.

OBJECTIVE

To review the rationale and discuss the results of cellular strategies that have been proposed or investigated for disc degeneration.

SUMMARY OF BACKGROUND DATA

Disc degeneration is a substantial clinical problem. Disc degeneration begins with a loss of disc cells and alterations in the extracellular matrix of the disc. One promising approach for this problem involves the use of cells transplanted to the degenerative disc to achieve functional tissue repair.

METHODS

The rationale for using cellular therapy for disc degeneration is discussed. The basic science studies involving cellular transplantation to the disc are reviewed and future directions of this line of research are discussed.

RESULTS

Although substantial work remains, the future of cellular therapies for symptomatic disc degeneration appears promising.

CONCLUSION

Continued research is warranted to further define the optimal cell type, scaffolds, and adjuvants that will allow successful disc repair in human patients.

Tissue engineered nucleus pulposus tissue formed on a porous calcium polyphosphate substrate

STUDY DESIGN

This study describes the formation of nucleus pulposus tissue using a novel tissue engineering approach.

OBJECTIVES

To determine if a construct composed of nucleus pulposus tissue on the surface of a calcium polyphosphate substrate could be formed in vitro with properties similar to native nucleus pulposus tissue.

SUMMARY OF BACKGROUND DATA

There is no optimal treatment for the persistent pain associated with intervertebral disc degeneration. Disc replacement using artificial intervertebral discs has met with some success, and biologic transplantation is limited by the availability of donor tissues.

METHODS

Nucleus pulposus cells were isolated from bovine caudal intervertebral discs. Cells were seeded at high density on the upper surface of a porous bone substitute material (calcium polyphosphate) and maintained up to 6 weeks in culture. In vitro formed tissue was compared to native nucleus pulposus for histologic appearance, biochemical composition (tissue cellularity, proteoglycan and collagen accumulation), and compressive mechanical properties.

RESULTS

When maintained on the surface of a three-dimensional substrate, nucleus pulposus cells formed a continuous layer of tissue with a proteoglycan content equivalent to the native tissue. Although collagen accumulation attained only 26% than that of the native tissue, there was no difference in tissue stiffness, viscosity, or weight-bearing capacity of the in vitro formed tissue when compared with the native tissue.

CONCLUSION

Nucleus pulposus-like tissue formed in vitro on the surface of a calcium polyphosphate substrate resembles the native tissue in terms of proteoglycan content and compressive mechanical properties. These studies are the first step toward developing a functional spinal unit in vitro.

Fresh frozen intervertebral disc allografting in a bipedal animal model

STUDY DESIGN

An in vivo experimental study to examine the possibility of using fresh frozen intervertebral disc allograft in disc transplantation.

OBJECTIVES

To investigate the long-term radiographic, pathologic, biochemical, and biomechanical changes of fresh frozen disc allograft in a bipedal animal model.

SUMMARY OF BACKGROUND DATA

It has been shown that intervertebral disc autograft is able to survive and maintain some degree of tissue metabolism and segmental mobility after transplantation in a bipedal animal model. However, the long-term results of disc allografting and the associated problems of graft rejection are unknown.

METHODS

Seventeen rhesus monkeys (15 male, 2 female) between 5 and 8 years of age and weighing between 6.7 and 11.8 kg were used in this study. Of these 17 subjects, two were used as intervertebral disc donors and three were used as controls for the biomechanical testing. The remaining 12 monkeys were randomly divided into a short-term group (n = 4, followed up for 2, 4, 6, and 8 weeks, respectively), a midterm group (n = 6, 6 months), and a long-term group (n = 2, 24 months). Radiologic, histologic, biochemical, and biomechanical changes were investigated.

RESULTS

Radiography and macro- and microhistologic examination showed severe disc degeneration at 24 months of follow-up. Disc height decreased mainly in the early postoperative stage. Decreased water, proteoglycan, and hydroxyproline contents of the allograft were observed at 6 and 24 months of follow-up. The biomechanical properties of the transplanted allograft were similar to those of control.

CONCLUSION

Fresh frozen disc allografts can survive and maintain some degree of cell metabolism and segmental mobility at 24 months after transplantation. However, severe disc degeneration is also observed at this stage.

Current concepts in intervertebral disc restoration

A current focus of treatment for degenerative disk disease is the restoration of the intervertebral disk. This article summarizes the structure and function of the intervertebral disk, the pathogenesis of its degeneration, and the clinical relevance of degenerative disk disease. Current literature relating to intervertebral disk replacement and regeneration is reviewed.

Effects of freezing on the biomechanics of the intervertebral disc

Storage of anatomic specimens is possible only if there is a reliable method for preservation of the tissues. The establishment of such a procedure is thus of twofold importance: clinical (transplantation of segments of the vertebral column) and experimental (research and teaching programs). Simple freezing at -18 degrees C is the simplest and least expensive method for storing spinal specimens compared to other modes of storage such as cryo-preservation and lyophilization. Does this mode of storage affect the biomechanics of frozen anatomic specimens, in particular those of the intervertebral disc? This experiment dealt with the comparative biomechanical analysis before and after three months of freezing of 19 segments of the sheep vertebral column (4 functional C4-C5 units, 3 C7-T1 units, 6 T13-L1 units and 6 L5-L67 units). The results showed that there was no significant difference (risk of error 5%) between frozen and fresh segments of vertebral column in terms of amplitude and rigidity, except for the C7-T12 segment where the conditions of validity of the statistical tests were not met. The results of this experiment allowed us to validate a biomechanical model to assay the effects of freezing.