Introduction. Vertebral compression fractures are the most common type of osteoporotic fracture. Though 89% of clinical fractures occur anteriorly, it is challenging to replicate these ex vivo with the underlying intervertebral discs (IVDs) present. Furthermore, the role of
Purpose of study and background. Degeneration of the intervertebral disc is a strong contributor of low back pain. Studies have shown that both, mechanical unloading and overloading, lead to
Intervertebral disc degeneration (DD) is a complex age-related condition that constitutes the main risk factor for disabling back pain. DD is assessed using different traits extracted from MR imaging (MRI), normally combined to give summary measures (e.g. Pfirmann score). The aetiology of DD is poorly understood and despite its high heritability (75%), the precise genetic predisposition is yet to be defined. Genome wide association study (GWAS) is used to discover genetic variants associated with a disease or phenotype. It tests variants across the whole genome. It requires large samples to provide adequate but unfortunately there is poor availability of spine imaging data due to the high cost of MRI. We have adopted new methods to examine different MRI traits independently and use the information of those traits to boost GWAS power using specialized statistical software for jointly analyse correlated traits. We examined DD MRI features disc narrowing, disc bulge, disc signal intensity and osteophyte formation in the TwinsUK cohort who had undergone T2-weighted sagittal spine MRI. GWAS were performed on the four traits. MTAG software was used to boost single trait GWAS power using the information in the other trait GWAS. 9 different loci were identified.Background
Methods/Results
Introduction. Risk factors for
Introduction. Delamination of the annulus fibrosus is an early feature of
Summary Statement. Spinal flexibility in bending and axial torque has been shown to exhibit very modest changes with advancing
Purpose &
Relevance: To examine the prevalence of degenerative findings in the thoracic spine in a population sample of adult men. Normative data on thoracic degenerative findings provide an essential reference for related observations in patients. Methods &
Results: Qualitative and quantitative assessments of thoracic
This short contribution aims to explain how intervertebral disc ‘degeneration’ differs from normal ageing, and to suggest how mechanical loading and constitutional factors interact to cause
Mechanical function and failure of intervertebral discs. In a healthy disc, the nucleus pulposus acts like a pressurised fluid which is restrained by tensile stress within the annulus. With increasing age, the nucleus becomes more fibrous, and biochemical changes cause the whole disc to become less elastic, and more yellow in colour. Mechanically, the hydrostatic nucleus shrinks with age, and concentrations of compressive stress appear in the posterior annulus. Experiments on cadaveric spines have shown that healthy discs can prolapse when loaded severely or repetitively in bending and compression, and that internal disruption of the disc probably follows damage to the vertebral endplates. However, mechanical loading is not necessarily harmful to living discs: on the contrary, moderate repetitive loading may lead to disc hypertrophy rather than injury.
Introduction:
Purpose: To evaluate the long term clinical outcomes as well as radiological changes in distal unfused mobile segments and to evaluate factors that may predispose to distal
Osteoporotic fractures are associated with bone loss following hormonal changes and reduced physical activity in middle age. But these systemic changes do not explain why the anterior vertebral body should be such a common site of fracture. We hypothesise that age-related degenerative changes in the intervertebral discs can lead to abnormal load-bearing by the anterior vertebral body. Cadaveric lumbar motion segments (mean age 50 ± 19 yrs, n = 33) were subjected to 2 kN of compressive loading while the distribution of compressive stress was measured along the antero-posterior diameter of the intervertebral disc, using a miniature pressure-transducer. “Stress profiles” were obtained with each motion segment positioned to simulate a) the erect standing posture, and b) a forward stooping posture. Stress measurements were effectively integrated over area in order to calculate the force acting on the anterior and posterior halves of the disc (
. 1. ). These two forces were subtracted from the applied 2 kN to determine the compressive force resisted by the neural arch. Discs were sectioned and their degree of
Introduction. Primary cilia are singular structures containing a microtubule-based axoneme which are believed to not only be mechanosensitive but also to co-ordinate many cell functions via signalling pathways including Hedgehog and Wnt. Primary cilia have previously been described on cells of mouse intervertebral discs (IVDs), but not in bovine or human IVDs. Our aim was to examine primary cilia in these species. Methods. Nucleus pulposus cells were obtained from cows with no overt
Summary Statement. DNA damage induced by systemic drugs or local γ-irradiation drives
Introduction Disc replacement surgery is being investigated as an alternative to spinal fusion surgery in the hope that maintaining segment spinal motion will not only relieve pain, but also prevent or reduce the likelihood of symptomatic adjacent segment degeneration that is believed to be a consequence of fusion surgery. The aim of this study was to identify evidence in the medical literature that indicates whether or not spinal fusion surgery increases the likelihood of symptomatic adjacent segment degeneration compared to disc replacement surgery or natural history. Methods A search of the Cochrane Controlled Trials Register, Medline and reference lists of retrieved articles was performed. Search terms included arthroplasty replacement, spinal fusion, prognosis, controlled clinical trials and cohort studies, Studies were included if abstracts were available electronically, were published in the English language before1/3/2005 and involved humans. Levels of evidence were determined using the Oxford Centre for Evidence-Based Medicine criteria (. http://www.cebm.net/levels of evidence.asp. ). Discussion The majority of identified studies were case series of patients presenting with adjacent level
Study Design: Experimental in vivo study on New Zealand White Rabbits. Summary of Background Data: We have developed an in-vivo rabbit model of lumbar
Objectives. A single degenerate intervertebral disc is suggested to promote rapid degeneration in its adjacent discs. We validated this hypothesis using discordant co-twin case-control design. Methods. 185 pairs of twins were selected from the TwinsUK database having cervical MRI scans at baseline and at follow-up, after 10 years. Isolated
Introduction and Aims: Lower back and/or leg pain is a symptom of a number of pathological conditions involving lumbosacral nerve roots. Disc herniation is one of the most common causes of LBP (after mechanical back pain). There is controversy regarding the progression of
Introduction: The development of laboratory techniques in the last ten years has enabled the successful harvest, in vitro selection, culture and transplant of chondrocytes. The study proposes that transplantation of autologous chondrocytes prevents degeneration of the intervertebral disc following outer annular injury in an ovine model. Methods: Eight sheep were anaesthetised and five contiguous lumbar discs were exposed via a left-sided posterolateral approach. Four of the animals were given full thickness annular incisions in three alternate discs. No annular incisions were made in the other 4 sheep. Costal cartilage was harvested from the left twelfth rib of all animals. Tissue was cultured and the chondrocytes were labelled in vitro with CFSE for verification following transplantation. Six weeks later autologous cultured chondrocytes were injected into the lower two alternate discs of all animals, leaving the uppermost discs and those untouched in between as internal controls. Animals were sacrificed after three, six, twelve and twenty-four weeks. Results were based on X rays, histological, and immunocytochemical assessments. Results: Preliminary histological results up to three months showed viability of cultured chondrocytes and matrix production post transplantation. Serial X rays suggested that progressive
INTRODUCTION: The development of laboratory techniques in the last ten years has enabled the successful harvest, in vitro selection, culture and transplant of chondrocytes. The study proposes that transplantation of autologous chondrocytes prevents degeneration of the intervertebral disc following outer annular injury in an ovine model. METHODS: Eight sheep were anaesthetised and five contiguous lumbar discs were exposed via a left-sided posterolateral approach. Four of the animals were given full thickness annular incisions in three alternate discs. No annular incisions were made in the other four sheep. Costal cartilage was harvested from the left twelfth rib of all animals. Tissue was cultured and the chondrocytes were labelled in vitro with CFSE for verification following transplantation. Six weeks later autologous cultured chondrocytes were injected into the lower two alternate discs of all animals, leaving the uppermost discs and those untouched in between as internal controls. Animals were sacrificed after three, six, twelve and twenty-four weeks. Results were based on X-rays, histological, and immunocytochemical assessments. RESULTS: Preliminary histological results up to three months showed viability of cultured chondrocytes and matrix production post transplantation. Serial X-rays suggested that progressive
Study Design and Objectives: The aim of this study is to analyse clinical results of total lumbar disc arthroplasty according to the type of
The lumbar spines of 22 patients were examined for
Introduction: The evidence of genetic background as an important causative factor in
Background. The majority of adults will experience an episode of low back pain during their life. Patients with non-specific low back pain and lumbar
Introduction The annulus fibrosus of the intervertebral disc is composed of a series of concentric collagenous lamellae that constrain the highly pressurised fluid of the nucleus pulposus. With advancing age and even after physical injury in youth the disc almost invariably becomes progressively degenerate due to the combined effects of dehydration of the nucleus and disruption of the annulus. There is conjecture however, about which of the two compartments shows degenerate changes first. Methods A histological and biochemical review is presented, based on a review of the literature and work carried out in our laboratories. Results Three distinct types of annulus tears are seen histologically. Rim tears are formed by detachment of the peripheral annular fibres from the vertebral rim. Autopsy studies show that these lesions are rare in subjects younger than 30 years but the incidence increases significantly with advancing age. Although granulation tissue grows into the outer layers of the annulus in a normal healing response, these lesions frequently extend deeper into the disc. Radiating tears course radially across several lamellae, most often extending from the vertebral rim across the nucleus to involve the posterior side of the disc. These lesions are seen mostly between the ages of 30 and 50 years. Concentric tears are characterised by separation of adjacent lamellae and may appear as early as the second decade of life. In advanced degeneration nuclear changes may be seen with any combination of annular lesions. Biochemical changes, including dehydration and reduced proteoglycan content of the nucleus, parallel the morphologic changes to the disc. Altered biochemistry is further reflected by MRI studies in which some scanning sequences can detect even modest loss of fluid from the nucleus as early as three months after experimental annular incision. Annular lesions also compromise the biomechanical properties of the disc. While internal fixation that aims to immobilise the injured disc may promote some recovery of the mechanical integrity, degeneration nevertheless advances in the long term. Attempts to seal peripheral annular defects in experimental studies using biocompatible glue have also failed to promote healing and to prevent progression of even minor structural defects. Conclusions Technological developments such as gene transfer into disc cells and direct implantation of either stem cells or more mature cells are emerging as potential candidates for the treatment of
Introduction. The usefulness of markers of non-specific low back pain (NSLBP), including MRI derived measurements of cross-sectional area (CSA) and functional CSA (FCSA, fat free muscle area) of the lumbar musculature, is in doubt. To our knowledge, such markers remain unexplored in Lumbar
Thirty-three patients who had undergone anterior cervical fusion for degenerative disc disease were reviewed to determine the efficacy of the procedure. Only patients who were available for examination and who had undergone operation at least one year previously were included in the review. Nearly all had had arm pain and three-quarters neck pain. Diminished neck movement and neurological abnormalities in the arms had been frequent findings. Diagnosis from the clinical features and plain radiographs is described. Myelography was not used routinely and discography was not used at all. Indications for operation and surgical technique are described. Results show that pain in the neck and arm was relieved in a high proportion of cases and that the neurological abnormalities often recovered. It is concluded that this operation is safe and has a definite place in the relief of pain from cervical
Study Design: Experimental study to assess tissue engineered solutions to
Background: The healthy, adult human disc is innervated but the nerves are restricted to the outer few millimetres of the annulus fibrosus. In degenerate discs with associated back pain, however, the nerves are more numerous and penetrate further in. We have used a sheep model of intervertebral disc degeneration to monitor the presence and organisation of nerves in the
The pathophysiology of intervertebral disc degeneration has been extensively studied. Various factors have been suggested as influencing its aetiology, including mechanical factors, such as compressive loading, shear stress and vibration, as well as ageing, genetic, systemic and toxic factors, which can lead to degeneration of the disc through biochemical reactions. How are these factors linked? What is their individual importance? There is no clear evidence indicating whether ageing in the presence of repetitive injury or repetitive injury in the absence of ageing plays a greater role in the degenerative process. Mechanical factors can trigger biochemical reactions which, in turn, may promote the normal biological changes of ageing, which can also be accelerated by genetic factors. Degradation of the molecular structure of the disc during ageing renders it more susceptible to superimposed mechanical injuries. This review supports the theory that degeneration of the disc has a complex multifactorial aetiology. Which factors initiate the events in the degenerative cascade is a question that remains unanswered, but most evidence points to an age-related process influenced primarily by mechanical and genetic factors.
We reviewed the radiographs of 325 unselected patients with defects in the pars interarticularis of L5 to study whether the incidence of vertebral slip in spondylolysis of L5 remained unchanged after the age of 20 years. MRI was also carried out on 111 of the patients to investigate the relationship between the shape of the transverse process of L5 and the degeneration of the discs adjacent to this level. The incidence of spondylolisthesis increased with age from 17% in the second decade to 51% in the sixth. The transverse process was significantly more slender in patients with less degeneration at L4/5 and advanced degeneration at L5/S1 than in patients with advanced degeneration at L4/5 and less degeneration at L5/S1. Vertebral slip secondary to an isthmic defect of L5 after the age of 20 years was confirmed and the adjacent
Introduction. Patients with recurrent low back pain (LBP) exhibit changes in postural control. Stereotypical muscle activations resulting from external perturbations include anticipatory (APAs) and compensatory (CPAs) postural adjustments. This study aimed to determine differences in postural control strategies (APAs and CPAs) between those with and without lumbar
Introduction: A computer model of the L4/5 human intervertebral disc is currently under development. An integral aspect of this model is the material properties assigned to its components. Detailed data on the material properties of the anulus fibrosus ground matrix are not available in the existing literature. To determine these properties, mechanical tests were carried out on specimens of anulus fibrosus harvested from sheep spines. The tests included unconfined uniaxial compression, simple shear and biaxial compression. Data on the strain required to cause permanent damage in the anulus ground matrix and data on the mechanical response of the anulus to repeated loading were obtained. Methods: Intervertebral discs were isolated from the lumbar spines of recently sacrificed sheep. These discs were sectioned into test specimens ensuring there were no continuous collagen fibres bearing load. The edge dimensions of the cubic specimens were 3 ± 0.2mm. To ascertain the strain to initiate tissue damage, the specimens underwent successive loadings, which were carried out 1 hour apart to allow recovery. The maximum strain in each test was increased incrementally by 5% until a reduction in stiffness was observed in the following test. Separate tests were carried out to quantify and characterise the response of the anulus ground matrix in the three modes of loading and to strains greater than that which initiates damage. Results: The strains at which permanent tissue damage occurred were between 20 and 27% in uniaxial compression and between 25 and 35% in simple shear. Testing the specimen beyond these strains showed an obvious reduction in stiffness. The biaxial compression tests showed similar changes but did not result in such pronounced losses in stiffness. The material characteristics were reproducible up to 20% strain. Following deformation to higher strains the altered mechanics were also shown to be reproducible indicating that the matrix had been deranged but not failed. Discussion: Average physiological strains in the L4/5 intervertebral disc are in the order of 10–50% based on maximum deformations observed in vivo. The current results demonstrate that this strain will cause some permanent damage to the anulus ground matrix, however, the matrix will still be capable of carrying stress upon repeated loading. Thompson et. al. 1. found that people over the age of 35 all exhibited signs of
INTRODUCTION: A computer model of the L4/5 human intervertebral disc is currently under development. An integral aspect of this model is the material properties assigned to its components. Detailed data on the material properties of the anulus fibrosus ground matrix are not available in the existing literature. To determine these properties, mechanical tests were carried out on specimens of anulus fibrosus harvested from sheep spines. The tests included unconfined uniaxial compression, simple shear and biaxial compression. Data on the strain required to cause permanent damage in the anulus ground matrix and data on the mechanical response of the anulus to repeated loading were obtained. METHODS: Intervertebral discs were isolated from the lumbar spines of recently sacrificed sheep. These discs were sectioned into test specimens ensuring there were no continuous collagen fibres bearing load. The edge dimensions of the cubic specimens were 3 ± 0.2 mm. To ascertain the strain to initiate tissue damage, the specimens underwent successive loadings, which were carried out one hour apart to allow recovery. The maximum strain in each test was increased incrementally by 5% until a reduction in stiffness was observed in the following test. Separate tests were carried out to quantify and characterise the response of the anulus ground matrix in the three modes of loading and to strains greater than that which initiates damage. RESULTS: The strains at which permanent tissue damage occurred were between 20 and 27% in uniaxial compression and between 25 and 35% in simple shear. Testing the specimen beyond these strains showed an obvious reduction in stiffness. The biaxial compression tests showed similar changes but did not result in such pronounced losses in stiffness. The material characteristics were reproducible up to 20% strain. Following deformation to higher strains the altered mechanics were also shown to be reproducible indicating that the matrix had been deranged but not failed. DISCUSSION: Average physiological strains in the L4/5 intervertebral disc are in the order of 10–50% based on maximum deformations observed in vivo. The current results demonstrate that this strain will cause some permanent damage to the anulus ground matrix, however, the matrix will still be capable of carrying stress upon repeated loading. Thompson et. al. 1. found that people over the age of 35 all exhibited signs of
Introduction: There are few long-term studies after Zielke ventral derotation spondylodesis (VDS). We present a minimum 17 year follow-up study to assess factors predicting distal adjacent
Low back pain is thought to relate to intervertebral disc (IVD) degeneration. Although the mechanisms have not been clearly identified, exhaustion of nucleus pulposus cells and their producing matrix is regarded as one cause. The matrix of the IVD is continuously replenished and remodeled by tissue-specialized cells and are crucial in supporting the IVD function. However, due to aging, trauma, and genetic and lifestyle factors, the cells can lose their potency and viability, thereby limiting their collective matrix production capacity. We have discovered the link between loss of angiopoietin-1 receptor (Tie2)-positive human NP progenitor cells (NPPC) and IVD degeneration. Tie2+ cells were characterized as undifferentiated cells with multipotency and possessing high self-renewal abilities. Thus we and others have proposed Tie2+ NPPC as a potent cell source for regenerative cell therapies against IVD degeneration. However, their utilization is hindered by low Tie2-expressing cell yields from NP tissue, in particular from commonly available older and degenerated tissue sources. Moreover, NPPC show a rapid Tie2 decrease due to cell differentiation as part of standard culture processes. As such, a need exists to optimize or develop new culture methods that enable the maintenance of Tie2-expressing NPPC. Trials to overcome these difficulties will be shared.
Background: Over several decades, investigators have been trying to identify the painful degenerate disc. Their work included two main methods. The first was to set criteria on the radiological investigations, mainly the MRI scan, to describe the severity of the degenerative disc disease (DDD); and the second was to perform discographies. Neither of these two methods precluded the need for the other. Purpose: Using Pfirrmann’s classification, we correlated static MRI images, for the severity of segmental
The factors influencing normal spine curvature in midlife are unknown. We performed an MR and plain radiograph study on well characterised, unselected twin volunteers from the TwinsUK register ( T2 weighted MR scans and long spine standing radiographs were obtained at the same morning visit on twin pairs. Midline sagittal MR images were coded for 4 degenerative features. SpineviewTM software was applied plain films and calculated the angles of curvature. A classical twin study was performed. Multivariate regression analysis was used to determine the association between spine curves, LDD and confounders (age, body mass index).Background
Methods
Aims. The presence of facet tropism has been correlated with an elevated susceptibility to lumbar disc pathology. Our objective was to evaluate the impact of facet tropism on chronic lumbosacral discogenic pain through the analysis of clinical data and finite element modelling (FEM). Methods. Retrospective analysis was conducted on clinical data, with a specific focus on the spinal units displaying facet tropism, utilizing FEM analysis for motion simulation. We studied 318 intervertebral levels in 156 patients who had undergone provocation discography. Significant predictors of clinical findings were identified by univariate and multivariate analyses. Loading conditions were applied in FEM simulations to mimic biomechanical effects on intervertebral discs, focusing on maximal displacement and intradiscal pressures, gauged through alterations in disc morphology and physical stress. Results. A total of 144 discs were categorized as ‘positive’ and 174 discs as ‘negative’ by the results of provocation discography. The presence of defined facet tropism (OR 3.451, 95% CI 1.944 to 6.126) and higher Adams classification (OR 2.172, 95% CI 1.523 to 3.097) were important predictive parameters for discography-‘positive’ discs. FEM simulations showcased uneven stress distribution and significant disc displacement in tropism-affected discs, where loading exacerbated stress on facets with greater angles. During varied positions, notably increased stress and displacement were observed in discs with tropism compared to those with normal facet structure. Conclusion. Our findings indicate that facet tropism can contribute to disc herniation and changes in intradiscal pressure, potentially exacerbating
The complex relationship between acetabular component position and spinopelvic mobility in patients following total hip arthroplasty (THA) renders it difficult to optimize acetabular component positioning. Mobility of the normal lumbar spine during postural changes results in alterations in pelvic tilt (PT) to maintain the sagittal balance in each posture and, as a consequence, markedly changes the functional component anteversion (FCA). This study aimed to investigate the in vivo association of lumbar degenerative disc disease (DDD) with the PT angle and with FCA during postural changes in THA patients. A total of 50 patients with unilateral THA underwent CT imaging for radiological evaluation of presence and severity of lumbar DDD. In all, 18 patients with lumbar DDD were compared to 32 patients without lumbar DDD. In vivo PT and FCA, and the magnitudes of changes (ΔPT; ΔFCA) during supine, standing, swing-phase, and stance-phase positions were measured using a validated dual fluoroscopic imaging system.Aims
Methods
One hundred and thirty-nine discs from cadaveric lumbar spines were injected with a mixture of radio-opaque fluid and dye. Discograms were taken and the discs were then sectioned in the sagittal plane. Examination of the sections revealed that injected fluid did not at first mix with the disc matrix but pushed it aside to form pools of injected fluid. The location of these pools, and hence the appearance of a discogram, depended on the stage of degeneration of the disc. It is concluded that useful clinical information can be obtained from discograms.
There are many difficulties associated with the localisation of the symptomatic segment in patients presenting with cervicobrachial pain with no evidence of impaired conduction in the nerve root. Ancillary radiological investigations such as myelography, epidural phlebography, and epidural myelograms are of unreliable diagnostic value. However, discography can be of value if the technique described here is used. Infiltration of the cervical nerve root with local anaesthetic has also proved useful in the localisation of the symptomatic segment. The techniques used in cervical discography and infiltration of the nerve root are described and their reliability is assessed.
CaSO4 and CaCO3 3% alginate hydrogels were injected into the NP cavity of a bovine tail. After 90 minutes the tail was dissected to reveal the gel. NP cells released from pooled bovine NP tissue were dispersed into the CaSO4 and CaCO3 alginate gels (10x106 cells.mL-1) with and without hylan (Synvisc®) and cultured for 21 days.
Injectable alginate suspensions formed solid viscoelastic gels, filling the exact shape of the NP cavity. NP DNA and ECM synthesis was significantly greater in the CaCO3 alginate gel than in the CaSO4 alginate gel (p<
0.05). Synvisc® significantly increased sulphated GAG (p<
0.01) and collagen (p<
0.05) production. These effects were supported histologically and immunohistologically where cells in the CaCO3 and Synvisc® gels stained more intensely for proteoglycan and collagen type II.
We studied 135 lumbar discs from 27 spines removed post-mortem from subjects of an average age of 31.5 years. Defects of the annulus fibrosus were classified as peripheral, circumferential or radiating; the nucleus pulposus as normal, moderately or severely degenerate. Peripheral tears were more frequent in the anterior annulus, except in the L5-S1 disc. Circumferential tears were equally distributed between the anterior and the posterior annulus. Almost all the radiating tears were in the posterior annulus, and closely related to the presence of severe nuclear degeneration. Histology suggested that peripheral tears were due to trauma rather than biochemical degradation, and that they developed independently of nuclear degeneration. The association of peripheral annular lesions with low back pain is uncertain but our study suggests that they may have a role in the pathogenesis of discogenic pain.
the mid-sagittal plane of 10 male and 10 female discs aged 13–79 years; 7 parasagittal slices through a single disc; discs showing various types of tears.
Most chondrocytes were unicellular but bicellular and multicellular chondrons were common in the margins of large tears and the nucleus in degenerate discs. Cellularity was highest in the right posterior quadrant, lowest in the left anterior quadrant, about equal in the left posterior and right anterior quadrants, and substantially higher in the right half of the nucleus. The correlation of increasing age with declining cell density was much stronger for the nucleus than for the annulus. Nucleus cellularity continued to decline throughout life whereas the annulus ceased its decline after the age of 50. Cell density was low in the vicinity of tears but elsewhere the disc was unaffected. Extensive inferior and superior end-plate separations reduced cellularity throughout the disc. Increased thickness of the cartilage end-plate was associated with higher cellularity in the nucleus.
Mesenchymal stem-cell based therapies have been
proposed as novel treatments for intervertebral disc degeneration,
a prevalent and disabling condition associated with back pain. The
development of these treatment strategies, however, has been hindered
by the incomplete understanding of the human nucleus pulposus phenotype
and by an inaccurate interpretation and translation of animal to
human research. This review summarises recent work characterising
the nucleus pulposus phenotype in different animal models and in
humans and integrates their findings with the anatomical and physiological
differences between these species. Understanding this phenotype
is paramount to guarantee that implanted cells restore the native
functions of the intervertebral disc. Cite this article: