ISSLS prize winner: A study of diffusion in human lumbar discs: a serial magnetic resonance imaging study documenting the influence of the endplate on diffusion in normal and degenerate discs

Low back pain patients and controls display functional differences in endplates and vertebrae measured with T2-mapping

PURPOSE

The aim was to (1) verify our previous finding that endplates (EPs) display load-induced T2-changes, (2) investigate whether vertebrae display load-induced T2-changes and (3) investigate whether EPs and vertebrae in LBP patients and controls display T2-differences during conventional unloaded MRI and axial loaded MRI (alMRI).

METHODS

Twenty-seven patients (mean 39 years) and 12 (mean 38 years) controls were examined with T2-mapping on a 1.5 T scanner during conventional unloaded MRI and subsequently during alMRI (Dynawell^® loading device), separated by approximately 20 min. For determination of EP and vertebral T2-values, volumetric regions of interest were manually segmented. Each vertebra was then divided into half to obtain superior and inferior units. The presence of EP changes (visual inhomogeneity in the EP zone), Schmorl's nodules and Modic changes were registered.

RESULTS

For conventional unloaded MRI, the T2-values in the superior and inferior vertebral units and the EPs were significantly higher in the patients compared with controls (p < 0.03, p < 0.006) even when adjusted for the presence of Modic changes, Schmorl's nodules and EP signal changes. alMRI induced significant changes in the superior EPs of the patients (p < 0.001). Additionally, the T2-value differed significantly between the superior and inferior EP, as well as between the superior and inferior vertebra with higher values in the inferior units (p < 0.001).

CONCLUSION

This study demonstrated significantly higher EP and vertebral T2-values in LBP patients in comparison with controls. In addition, alMRI induced significant T2-changes in the superior EPs for patients but not for controls. Importantly, the T2-differences between the groups may indicate that EPs and vertebrae in LBP patients have altered biodynamical characteristics compared to controls and the higher T2-values measured in patients may represent early inflammation or impaired nutritional transport. These slides can be retrieved from electronic supplementary material.

Severe Lumbar Intervertebral Disc Degeneration Is Associated with Modic Changes and Fatty Infiltration in the Paraspinal Muscles at all Lumbar Levels, Except for L1-L2: A Cross-Sectional Analysis of 50 Symptomatic Women and 50 Age-Matched Symptomatic Men

BACKGROUND

Low back pain is a common public health problem associated with lumbar intervertebral disc degeneration. It is still unclear, however, whether intervertebral disc degeneration is an isolated process or accompanied by other degenerative events. We analyzed whether disc degeneration was associated with vertebral end-plate changes and fatty infiltration in the paraspinal muscles. We also aimed to identify whether the severity of disc degeneration influenced this association.

METHODS

Intervertebral disc degeneration, vertebral end-plate changes, and fatty infiltration in the multifidus, erector spinae, and psoas muscles at all lumbar intervertebral disc levels were evaluated on lumbar spine magnetic resonance images of 50 symptomatic women and 50 age-matched symptomatic men.

RESULTS

The women had greater lumbar intervertebral disc degeneration scores at L4-L5 and L5-S1 and in total. The women had more fatty infiltration in the multifidus and erector spinae muscles at L4-L5 and L5-S1. The men had more fatty infiltration in the psoas muscle at L5-S1. Patients with severe intervertebral disc degeneration were more likely to have increased fatty infiltration in the multifidus and erector spinae muscles. The rate of vertebral end-plate changes was also greater in the patients with severe intervertebral disc degeneration.

CONCLUSIONS

Severe disc degeneration in the lumbar spine is closely associated with Modic changes and fatty infiltration in the multifidus and erector spinae muscles. We suggest that disc degeneration is not an isolated event but, rather, a continuum of events that could more clearly be shown in future prospective, large sample-size studies.

Lumbar Schmorl's Nodes and Their Correlation with Spine Configuration and Degeneration

The aim of this study was to reveal whether demographic aspect, vertebral morphometry, and spine degeneration are associated with lumbar Schmorl's nodes (SNs). A retrospective cross-sectional study was performed using data from the Department of Radiology (Carmel, Medical Center, Israel) for 180 individuals: age range between 40 and 99 years; 90 males and 90 females. All participants had undergone high-resolution CT scans for abdominal diagnostic purposes in the same supine position prior to our study, which enabled the processing of the scans in all planes and allowed a 3D reconstruction of the lower lumbar region. Eighty individuals (44.4%) had at least one SN along the lumbar spine, particularly at L3-4 level (30%). Vertebral body length (L1 to L3) and width (L1 and L4) were significantly greater in the SNs group compared to non-SNs group. On contrast, disc height (L3-4 and L4-5) was significantly lesser in SNs group than non-SNs group. SNs was significantly associated with smoking (X²= 4.436, P=0.02) and degenerative lumbar spinal stenosis (X²= 5.197, P=0.038). Moreover, the prevalence of SN was significantly greater in individuals with vacuum phenomenon and osteophytes formation (L1-2 to L4-5 levels). This study indicates that vacuum phenomenon on L3-4 (OR: 4.7, P=0.034), smoking habit (OR: 3.2, P=0.003), disc height loss of L4-5 (OR: 0.798, P=0.008), vertebral body length of L1 (OR: 1.37, P<0.001), and age (OR: 1.05, P=0.002) increase the probability of developing lumbar SNs.

Contribution of the endplates to disc degeneration

Purpose of review

The endplates form the interface between the rigid vertebral bodies and compliant intervertebral discs. Proper endplate function involves a balance between conflicting biomechanical and nutritional demands. This review summarizes recent data that highlight the importance of proper endplate function and the relationships between endplate dysfunction, adjacent disc degeneration, and axial low back pain.

Recent findings

Changes to endplate morphology and composition that impair its permeability associate with disc degeneration. Endplate damage also associates with disc degeneration, and the progression of degeneration may be accelerated and the chronicity of symptoms heightened when damage coincides with evidence of adjacent bone marrow lesions.

Summary

The endplate plays a key role in the development of disc degeneration and low back pain. Clarification of the mechanisms governing endplate degeneration and developments in clinical imaging that enable precise evaluation of endplate function and dysfunction will distinguish the correlative vs. causative nature of endplate damage and motivate new treatments that target pathologic endplate function.

Standardisation of basal medium for reproducible culture of human annulus fibrosus and nucleus pulposus cells

Background

The lifetime prevalence of degenerative disc disease is dramatically high. Numerous investigations on disc degeneration have been performed on cells from annulus fibrosus (AF) and nucleus pulposus (NP) of the intervertebral disc (IVD) in cell culture experiments utilising a broad variety of basal culture media. Although the basal media differ in nutrient formulation, it is not known whether the choice of the basal media itself has an impact on the cell’s behaviour in vitro. In this study, we evaluated the most common media used for monolayer expansion of AF and NP cells to set standards for disc cell culture.

Methods

Human AF and NP cells were isolated from cervical discs. Cells were expanded in monolayer until passage P2 using six different common culture media containing alpha-Minimal Essential Medium (alpha-MEM), Dulbecco’s Modified Eagle’s Medium (DMEM) or Ham’s F-12 medium (Ham’s F-12) as single medium or in a mixture of two media (alpha/F-12, DMEM/alpha, DMEM/F-12). Cell morphology, cell growth, glycosaminoglycan production and quantitative gene expression of cartilage- and IVD-related markers aggrecan, collagen type II, forkhead box F1 and keratin 18 were analysed. Statistical analysis was performed with two-way ANOVA testing and Bonferroni compensation.

Results

AF and NP cells were expandable in all tested media. Both cell types showed similar cell morphology and characteristics of dedifferentiation known for cultured disc cells independently from the media. However, proceeding culture in Ham’s F-12 impeded cell growth of both AF and NP cells. Furthermore, the keratin 18 gene expression profile of NP cells was changed in alpha-MEM and Ham’s F-12.

Conclusion

The impact of the different media itself on disc cell’s behaviour in vitro was low. However, AF and NP cells were only robust, when DMEM was used as single medium or in a mixture (DMEM/alpha, DMEM/F-12). Therefore, we recommend using these media as standard medium for disc cell culture. Our findings are valuable for the harmonisation of preclinical study results and thereby push the development of cell therapies for clinical treatment of disc degeneration.

Mechanotransduction and cell biomechanics of the intervertebral disc

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

The degeneration of adjacent intervertebral discs negatively influence union rate of osteoporotic vertebral fracture: A multicenter cohort study

BACKGROUND

With the increasing aging population in developed countries, there has been an associated increased prevalence of osteoporotic vertebral fracture (OVF). Many previous reports have attempted to predict the risk of delayed union associated with OVF. However, the role of endplate failure and the degeneration of adjacent intervertebral discs, and their association with delayed union has received little attention. The aim of this study was to evaluate the endplate fracture and disc degeneration rank as risk factors for delayed union.

MATERIALS AND METHODS

Two hundred and eighteen consecutive patients with fresh OVF were enrolled in the study. MRI and X-ray were performed at the time of enrollment and at the 6 months follow-up. The MR images were used to assess the degeneration grade of adjacent intervertebral discs (using the modified Pfirrmann grading system), and endplate failure. Supine and weight-bearing radiographs were used to define angular motion and compression ratio of the anterior vertebral body wall.

RESULTS

A total of 139 patients (112 female, 27 male) completed the 6 month follow-up (a 65.1% follow-up rate). The study revealed 27 cases of delayed union (19.4%). A healthier adjacent caudal disc with low grade degeneration was found to be associated with an increased risk of delayed union (P = 0.008). Bi-endplate injury and significant compression of the anterior vertebral body wall were significantly associated with delayed union (P = 0.019, and P = 0.001 respectively). Rapid progression of the adjacent cranial disc degeneration was observed at the end of the 6 month follow-up period (P = 0.001).

CONCLUSION

Modified Pfirrmann grading system revealed that a healthier adjacent intervertebral disc at the caudal level and bi-endplate fracture were significantly associated with an increased risk of delayed union. These findings may influence the management strategy for patients with OVF.

Intervertebral Disk Nutrients and Transport Mechanisms in Relation to Disk Degeneration: A Narrative Literature Review

Objective

The purpose of this paper was to review the literature regarding the mechanisms leading to degeneration in intervertebral disks and to discuss contributing mechanical and biological factors.

Methods

The inclusion criteria for the literature review were research studies conducted in the last 3 decades with free full-text available in English. Review articles and articles pertaining to temporomandibular joints and joints of the body other than the intervertebral disk were excluded. The following databases were searched: PubMed, EBSCOhost, and Google Scholar through September 9, 2016.

Results

A total of 57 articles were used in this review. Intervertebral disk cells require glucose for sustainability and oxygen to synthesize matrix components. Nutrients enter the disk via 2 vascular supply routes: capillary beds of end plates and the peripheral annulus fibrosus. Solute size, shape and charge, compression, and metabolic demand all influence the efficiency of nutrient transport, and alterations of any of these factors may have effects on nutrient transport and, potentially, disk degeneration.

Conclusions

Progressive nutrient transport disruptions may actively contribute in advancing the phases of degenerative disk disease. Such disruptions include dysfunctional loading and spinal position, lack of motion, high frequency loading, disk injury, aging, smoking, an acidic environment, and a lack of nutrient bioavailability.

Modic type 1 change is an autoimmune response that requires a proinflammatory milieu provided by the 'Modic disc'

BACKGROUND CONTEXT

Modic changes (MCs) are magnetic resonance imaging (MRI) evidence of inflammatory and fibrotic vertebral bone marrow lesions that associate with adjacent disc degeneration and end plate damage. Although MC etiology is uncertain, historical data suggest a linkage to an autoimmune response of bone marrow triggered by the nucleus pulposus (NP).

PURPOSE

The aim of this study was to test whether bone marrow has an autoimmune response to NP cells that is amplified by an inflammatory milieu and ultimately leads to MC development in vivo. We hypothesized that an inflammatory co-stimulus is required for bone marrow/NP crosstalk to stimulate MC.

STUDY DESIGN

This is an in-vitro cell co-culture study plus in-vivo experiments in rat caudal vertebrae.

METHODS

In in-vitro study, bone marrow mononuclear cells (BMNCs) and NP cells (NPCs) from rats were co-cultured with and without interleukin (IL)-1α stimulation. Cell viability (n=3) of BMNCs and NPCs and gene expression (n=7) were analyzed. In in-vivo study, proinflammatory lipopolysaccharide (LPS) and control disc nucleus surrogates (NP micromass pellets) were generated in vitro from rat NPCs and implanted into rat tail vertebrae, and the response was compared with sham surgery (n=12 each). Tissue changes were investigated with T1w and T2w MRI (7T), histology, and immunohistochemistry (tumor necrosis factor, CD3) 1 (n=6) and 2 weeks (n=6) after implantation.

RESULTS

BMNC/NPC co-culture significantly increased lymphocyte viability (42%-69%, p<.05) and reduced NPC viability (96%-88%, p<.001), indicating immunogenicity of NPC. However, IL-1α was required to cause significant transcriptional upregulation of IL-1, IL-6, IL-10, and tropomyosin receptor kinase A. Therefore, an inflammatory activation is required to amplify the immune response. Immunogenicity of the NP was corroborated in vivo by CD3 cell accumulation around LPS and control disc surrogates at Day 7. However, only the LPS disc surrogate group demonstrated infiltration of CD3 cells at Day 14. Furthermore, end plate defects (p<.05, LPS: n=4/6, Ctrl: n=0/6, sham: n=0/6) and MC1-like MRI changes (T2w hyperintensity, p<.05) were only seen with LPS disc surrogates.

CONCLUSIONS

NPCs are immunogenic but cannot trigger MC without an additional proinflammatory stimulus. Our data suggest that MC requires end plate defects that allow marrow/NPC co-mingling plus an adjacent inflammatory "MC disc" that can amplify the immune response.

MRI evaluation of the effects of extension exercises on the disc fluid content and location of the centroid of the fluid distribution

BACKGROUND

McKenzie prone press-up exercises have been hypothesised to reduce intradiscal pressure, allowing fluid to be reabsorbed into the disc, which could improve the internal stability and local chemical milieu of the disc, potentially reducing symptoms.

OBJECTIVE

To investigate the immediate effects of prone press-up exercises on lumbar disc fluid content and movement.

DESIGN

Quantification of MRI changes before and after a single exercise session.

METHODS

The mid-sagittal T₂-weighted MR images of 22 volunteers with low back pain were obtained before and immediately after performing press-up exercises. The whole disc and nucleus regions of the L4-5 and L5-S1 discs were then segmented, and their mean signal intensity (MSI) and signal intensity weighted centroid (SIWC) were computed to estimate disc fluid content and displacement.

RESULTS

There were no significant differences between the MSI and the vertical position of the SIWC of the whole disc before and after extension at either disc level (effect size [ES]: -0.23 to 0.09). There was a significant anterior displacement (0.1 ± 5.4 mm) of the location of the SIWC of the disc after extension exercise at L4-5 (ES: 0.22), but not at L5-S1 (ES: 0.00) or at either level for the nucleus region (ES: -0.06; 0.16).

CONCLUSION

Little evidence was found supporting the hypothesis that press-up exercises affect disc fluid content and distribution. Novel parameters reflecting fluid distribution detected similar or larger effects of the extension than MSI. If such exercises are effective in reducing symptoms, it is likely through other mechanisms than by changing fluid content or distribution.

Cervical and thoracic intervertebral disc hydration increases with recumbency: a study in 101 healthy volunteers

BACKGROUND CONTEXT

Variation in the water content and the size of lumbar intervertebral discs (IVDs) is known to occur because of recumbency and has been associated with lumbar IVD herniation risk through the impact of IVD hydration on tissue mechanical properties. It is not clear if similar changes in cervical or thoracic IVDs occur with recumbency.

PURPOSE

The aim of this study was to determine whether increases in hydration of thoracic and cervical IVDs occur with short-duration recumbency.

STUDY DESIGN/SETTING

This study used a test-retest design in a magnetic resonance imaging facility.

METHODS

We examined expansion of all IVDs in the spine in 101 healthy individuals (54 women) aged 25-35 years on sagittal T2-weighted magnetic resonance images after a mean of 26.9 minutes lying in the scanner bore. All scans were performed after midday. To mitigate false positives, p-values were adjusted by the false discovery rate method.

RESULTS

At the end of lying, the cervical spine IVD volume increased by a mean (standard deviation) of 2.6 (5.6)% (p<.001) compared with a 1.0 (4.0)% (p=.024) increase in the upper thoracic spine IVD volume and a 2.0 (3.2)% (p<.001) increase at the lower thoracic spine. Lumbar IVD volume increased by 1.2 (2.4)% (p<.001). C2-C3 IVD volume (+4.1 [13.8]%, p=.011) increased the most at the cervical spine, followed by C5-C6 (+3.9 [9.8]%, p<.001) and C3-C4 (+3.8 [13.5]%, p=.014). Lumbar IVDs with higher degeneration grades showed more expansion with lying (p=.0031).

CONCLUSIONS

We established that cervical and thoracic IVD volumes increase with recumbency. We expect diurnal variation in cervical and thoracic IVD hydration will occur in the general population, with greater cervical and thoracic IVD hydration and size upon rising in the morning.

Axial loading during MRI induces significant T2 value changes in vertebral endplates-a feasibility study on patients with low back pain

BACKGROUND

The function of the endplate (EP) is the most important factor influencing nutritional supply to the avascular intervertebral disc (IVD). It is desired to have a non-invasive method to assess functional EP characteristics in vivo. Assessment of functional EP characteristics is important in order to understand its relation to IVD degeneration, which in turn might deepen the understanding of the pathophysiology behind low back pain (LBP). It was hypothesized that, by comparing quantitative MRI of EPs performed with conventional supine MRI (unloaded MRI) with axial loading during MRI (alMRI), dynamical properties of the EP can be displayed. The aim was therefore to investigate the feasibility of axial loading during MRI (alMRI) to instantaneously induce quantitative EP changes.

METHODS

T2 mapping of 55 vertebral EPs (L1-S1) in five LBP patients was performed during conventional supine MRI (unloaded MRI) and subsequent alMRI. With T2 mapping, the cartilaginous EP and bony EP cannot be separated; hence, the visualized EP was termed EP zone (EPZ). Each EPZ was segmented at multiple midsagittal views, generating volumetric regions of interest. EPZs demonstrating signal inhomogeneity and/or adjacent Modic changes (MC) were termed abnormal EPZs. EPZ mean T2 values were compared between unloaded MRI and alMRI, and their relationship with abnormal EPZs was determined.

RESULTS

alMRI induced significantly higher (p = 0.01) EPZ mean T2 values compared with unloaded MRI. Significantly higher mean T2 values were seen in inferior EPZs compared with superior EPZs, both with unloaded MRI (35%, p < 0.001) and with alMRI (26%, p = 0.04). Significant difference between unloaded MRI and alMRI was seen in normal (p = 0.02), but not in abnormal EPZs (p = 0.5; n = 12).

CONCLUSIONS

alMRI induces changes in human EPZ characteristics in vivo. The T2 value significantly increased in normal EPZs, with lack of such in abnormal EPZs. Combining T2 mapping with alMRI provides a clinical feasible, non-invasive method with potential to reveal biochemical behavioral patterns, thus adding another dimension of the EPZs characteristics compared with information obtained with solely unloaded MRI.

Detection of O-Linked-N-Acetylglucosamine Modification and Its Associated Enzymes in Human Degenerated Intervertebral Discs

Study Design

Human herniated discs were obtained from discectomy specimens for the immunohistochemical detection of O-GlcNAc and O-GlcNAcase (OGA)/O-GlcNAc transferase (OGT).

Purpose

This study aimed to quantify the extent of O-GlcNAcylation and its associated enzymes (OGT/OGA) in human degenerated intervertebral discs.

Overview of Literature

The O-GlcNAcylation of nuclear, cytoplasmic, and mitochondrial proteins as well as the effects of such post-translational modifications are currently the focus of extensive research. O-GlcNAcylation is believed to contribute to the etiology of chronic illnesses by acting as a nutrient and stress sensor in the cellular environment. Mature intervertebral disc cells are chondrocyte-like cells, and O-GlcNAc has been shown to promote chondrocyte apoptosis in vitro. We believe that O-GlcNAcylation is a key regulator of disc degeneration.

Methods

Fifty-six specimens were fixed for 24 hours in a 10% solution of neutral-buffered formaldehyde, dehydrated, and embedded in paraffin. Tissue slices (4-µm-thick) were used for hematoxylin-eosin staining and immunohistochemistry.

Results

We found that O-GlcNAcylation of cytoplasmic proteins was less than that of nuclear proteins in both single cells and cell clusters. Cytoplasmic O-GlcNAcylation occurs subsequent to nuclear O-GlcNAcylation and is directly proportional to disc degeneration. OGT and O-GlcNAc expression levels were identical in all specimens examined.

Conclusions

O-GlcNAc and OGA/OGT expression is shown to correlate for the first time with intervertebral disc cell degeneration. Increasing disc degeneration is associated with increasing O-GlcNAcylation in both nuclear and cytoplasmic proteins in human disc cells.

Spatial geometric and magnetic resonance signal intensity changes with advancing stages of nucleus pulposus degeneration

Background

With advancing stages of degeneration, denaturation and degradation of proteoglycans in the nucleus pulposus (NP) lead to tissue dehydration and signal intensity loss on T2-weighted MR images. Pfirrmann grading is widely used for grading degeneration of intervertebral discs (IVDs). The criterion to differentiate IVDs of Pfirrmann Grade I from the other grades is NP homogeneity. Pfirrmann grading is qualitative and its assessment may be subjective. Therefore, assessment of quantitative objective measures correlating with early disc degeneration may complement the grading. This study aimed to evaluate the applicability of the distance between the center weighted by signal intensity (weighted center) and the geometric center as a parameter of NP homogeneity. Other phenomena related to advancing stages of degeneration were also investigated.

Methods

MR images of 65 asymptomatic volunteers with a total of 288 lumbar IVDs with clearly identifiable nucleus pulposus boundary (Pfirrmann Grade I, II and III) were included in this study. A custom-written program was developed to determine the IVD longitudinal axis, define the NP boundary, and to locate the coordinates of geometric and weighted NP centers on the mid-sagittal image of each studied IVD. The distances between the weighted and geometric centers on the longitudinal axis and the perpendicular axis of each IVD were calculated.

Results

The weighted center located posterior to the geometric center, which indicated the signal intensity was lower at the anterior portion of the NP, in 85.8% of studied IVDs. The distance between the weighted and geometric center on the longitudinal axis was significantly shorter in homogeneous (Pfirrmann Grade I) than in inhomogeneous (Grade II) IVDs. The distance on the perpendicular axis in Grade III IVDs was significantly larger than that in Grade I and Grade II IVDs.

Conclusion

The relationship between the weighted and geometric centers can serve as an indicator for NP homogeneity. The distance between both centers through advancing stages of degeneration demonstrated decrease of signal intensity progressing along the longitudinal axis initially and then along the cranio-caudal direction at later stages. These findings could provide insights of initiation and subsequent progression of degenerative changes in IVDs.

Intervertebral Disc Aging, Degeneration, and Associated Potential Molecular Mechanisms

Intervertebral disc degeneration is a major cause of neck and back pain, a very common clinical problem. However, no effective treatment is available, which is largely due to the lack of understanding of molecular mechanisms underlying disc degeneration. Here, we briefly described the process of intervertebral disc aging and degeneration and summarized major findings in molecular signaling pathways implicated in disc aging and degeneration.

Non-invasive quantification of age-related changes in the vertebral endplate in rats using in vivo DCE-MRI

Background

Small animal models that can mimic degenerative disc disease (DDD) are commonly used to examine DDD progression. However, assessments such as histological studies and macroscopic measurements do not allow for longitudinal studies because they can only be completed after the animal is sacrificed. Dynamic contrast-enhanced MRI (DCE-MRI) may provide a reliable, non-invasive in vivo method for detecting the progression.

Methods

The present study investigated the progression of changes in lumbar discs and the effect of endplate conditions on diffusion into the lumbar discs of aging sand rats after intravenous administration of gadolinium-containing contrast medium through the tail vein. Contrast enhancement was measured in the lumbar intervertebral discs on each image. The results were compared with those from conventional histological characterizations.

Results

T2-weighted images revealed that with aging, the shape of L3–L4, L4–L5, L5–L6, and L6–S1 nucleus pulposus (NP) became irregular, while the mean areas, signal intensities, and T2 values of the NP were significantly decreased. Each of the observed disc changes demonstrated a progressive increase in phase during 2-min scout scans. Post-contrast MRI showed impaired endplate nutritional diffusion to the disc with aging, enhancement was significantly greater in young animals than in old animals. Endplate calcification or sclerosis was histologically confirmed; histologic score was correlated with the age. We found the histological score of the endplate negatively corresponded to the DCE-MRI results.

Conclusions

DCE-MRI studies offer a non-invasive in vivo method for investigating the progress of diffusion into the discs and the functional conditions of the endplate. We conclude that quantitative DCE-MRI can identify the severity of disc degeneration and efficiently reflect the progression of vertebral endplate changes in the aging sand rat lumbar spine via the NP contrast enhancement patterns.

Age-related differences in the response of the L5-S1 intervertebral disc to spinal traction

BACKGROUND

Lumbar traction is a common treatment for low back pain; however its mechanisms of action are poorly understood. It has been hypothesized that a key effect of lumbar traction is its capacity to influence fluid movement within the intervertebral disc (IVD).

OBJECTIVES

To determine differences in the apparent diffusion coefficient (ADC) obtained with lumbar diffusion-weighted imaging (DWI) of the L5-S1 IVD before, and during, the application of lumbar traction.

DESIGN

Case series, repeated measures.

METHODS

A static traction load of ∼50% of body-weight was applied to the low back using a novel "MRI-safe" apparatus. DWI of the lumbar spine was performed prior to, and during the application of the traction load.

RESULTS

Participants were currently asymptomatic and included a young adult group (n = 18) and a middle-aged group (n = 15). The young adult group had a non-significant 2.2% increase in ADC (mean change = 0.03 × 10^-3 mm²/s, SD = 0.24, 95% CI = -0.09, 0.15). The ADC for the middle-aged group significantly increased by 20% (mean change of 0.18 × 10^-3 mm²/s, SD = 0.19; 95% CI = 0.07, 0.28; p = 0.003; effect size = 0.95). There was an inverse relationship between the ADC obtained before traction and the percent increase in ADC that was measured during traction.

CONCLUSION

Static traction was associated with an increase in diffusion of water within the L5-S1 IVDs of middle-age individuals, but not in young adults, suggesting age-related differences in the diffusion response. Further study is needed to assess the relationship between these findings and the symptoms of back pain.

LEVEL OF EVIDENCE

4.

Structural vertebral endplate nomenclature and etiology: a study by the ISSLS Spinal Phenotype Focus Group

PURPOSE

Vertebral endplate abnormalities may be associated with disc degeneration and, perhaps, pain generation. However, consensus definitions for endplate findings on spine MRI do not exist, posing a challenge to compare findings between studies and ethnic groups. The following survey was created to characterize the variability among the global spine community regarding endplate structural findings with respect to nomenclature and etiology.

METHODS

A working group within the International Society for the Study of the Lumbar Spine (ISSLS) Spinal Phenotype Focus Group was established to assess the endplate phenotype. A survey which consisted of 13 T2-weighted sagittal MRIs of the human lumbar spine illustrating the superior and inferior endplates was constructed based on discussion and agreement by the working group. A list of nomenclature and etiological terms with historical precedence was generated. Participants were asked to describe the endplates of each image and select from 14 possible nomenclatures and 10 etiological terms along with the option of free text response. The survey was entered into RedCap and was circulated throughout the ISSLS membership for data capture. Participants' demographics were also noted.

RESULTS

The survey was completed by 55 participants (87% males; 85% above 45 years of age, 39 clinicians, and 16 researchers). Sixty-eight percent of researchers and seventy-four percent of clinicians reported more than 16 and 20 years of research and clinical experience. Considerable variation existed in selection of nomenclature, etiology, and degree of severity of the endplate structural findings (reliability coefficients for single measures in each case were 0.3, 0.08, and 0.2, respectively). Sixty-seven percent regarded Modic changes as being a structural endplate finding. Approximately 84 and 80% of clinicians and researchers, respectively, agreed that a standardized endplate nomenclature and understanding the etiology is clinically important and needed.

CONCLUSIONS

This study found that variations exist with respect to endplate nomenclature and etiology between clinicians and basic scientists, and paves the way for a consensus process to formalize the definitions.

Whole Transcriptome Analysis of Notochord-Derived Cells during Embryonic Formation of the Nucleus Pulposus

Recapitulation of developmental signals represents a promising strategy for treating intervertebral disc degeneration. During development, embryonic notochord-derived cells (NDCs) are the direct progenitors of cells that populate the adult nucleus pulposus (NP) and are an important source of secreted signaling molecules. The objective of this study was to define global gene expression profiles of NDCs at key stages of embryonic disc formation. NDCs were isolated from Shh-cre;ROSA:YFP mice at embryonic day 12.5 and postnatal day 0, representing opposite ends of the notochord to NP transformation. Differences in global mRNA abundance across this developmental window were established using RNA-Seq. Protein expression of selected molecules was confirmed using immunohistochemistry. Principal component analysis revealed clustering of gene expression at each developmental stage with more than 5000 genes significantly differentially expressed between E12.5 and P0. There was significantly lower mRNA abundance of sonic hedgehog pathway elements at P0 vs E12.5, while abundance of elements of the transforming growth factor-beta and insulin-like growth factors pathways, and extracellular matrix components including collagen 6 and aggrecan, were significantly higher at P0. This study represents the first transcriptome-wide analysis of embryonic NDCs. Results suggest signaling and biosynthesis of NDCs change dramatically as a function of developmental stage.

Hypoxia suppresses serum deprivation-induced degradation of the nucleus pulposus cell extracellular matrix through the JNK and NF-κB pathways

Intervertebral disc (IVD) degeneration is associated with the imbalance between anabolism and catabolism of the nucleus pulposus (NP) extracellular matrix (ECM). Serum deprivation (SD) has been reported to exacerbate IVD degeneration; however, the effect of SD on ECM metabolism is not fully understood. Hypoxia plays important roles in maintaining the physiological functions of IVD cells; however, whether hypoxia has any effect on NP ECM production under conditions of SD is still unclear. In the current study, we established an in vitro SD model by exposing NP cells to serum-free medium. SD decreased the expression of aggrecan and collagen II, as well as the production of sulfated glycosaminoglycan (sGAG) in a time-dependent manner. However, hypoxia abolished SD-mediated down-regulation of aggrecan and collagen II expression via JNK1/2 activation. Moreover, hypoxia abolished SD-induced MMP-3 and MMP-13 expression by inhibiting NF-κB activation, p65 translocation, and MMP-3 and MMP-13 promoter activity. These results indicated that, hypoxia maintained ECM production under conditions of SD. This effect was elicited in part through JNK1/2-mediated up-regulation of matrix gene expression and down-regulation of MMP expression, through the inhibition of NF-κB. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2059-2066, 2017.

Semi-quantitative evaluation of signal intensity and contrast-enhancement in Modic changes

Background

Semi-quantitative evaluation of Modic changes (MCs) has recently been proposed as a way to standardise and increase repeatability of clinical studies. This study is aimed at developing semi-quantitative measures of enhancement, given by contrast agent injection, on T1-weighted images in MCs, and to investigate their reliability and relation with MC types.

Methods

Thirty-seven subjects suffering from low back pain underwent T1-weighted and T2-weighted turbo spin-echo sequences. Five minutes after the injection of a paramagnetic contrast agent, a second T1-weighted sequence was acquired. Regions of interest (ROIs) corresponding to MCs were selected manually on the unenhanced image; control ROIs in the “healthy” bone marrow were selected. For each ROI, the mean signal intensity (SI) of unenhanced pixels and the mean absolute and normalised difference in SI between unenhanced and contrast-enhanced pixels values were calculated.

Results

A total of 103 MCs were recognised and 61 were semi-quantitatively analysed: 16 type I, 34 type II and 11 type I/II. Regarding controls, MCs I showed a lower SI on the unenhanced T1-weighted images and a marked contrast enhancement (CE); MCs II showed a higher SI than controls on unenhanced images and a lower or comparable CE; and MCs I/II presented an intermediate SI on the unenhanced images and a marked CE. Inter-rater and intra-rater agreements were found to be excellent or substantial.

Conclusions

Semi-quantitative measurements could differentiate MC types in terms of unenhanced SI and of CE with respect to “healthy” bone marrow.

ISSLS PRIZE IN BASIC SCIENCE 2017: Intervertebral disc/bone marrow cross-talk with Modic changes

STUDY DESIGN

Cross-sectional cohort analysis of patients with Modic Changes (MC).

OBJECTIVE

Our goal was to characterize the molecular and cellular features of MC bone marrow and adjacent discs. We hypothesized that MC associate with biologic cross-talk between discs and bone marrow, the presence of which may have both diagnostic and therapeutic implications.

BACKGROUND DATA

MC are vertebral bone marrow lesions that can be a diagnostic indicator for discogenic low back pain. Yet, the pathobiology of MC is largely unknown.

METHODS

Patients with Modic type 1 or 2 changes (MC1, MC2) undergoing at least 2-level lumbar interbody fusion with one surgical level having MC and one without MC (control level). Two discs (MC, control) and two bone marrow aspirates (MC, control) were collected per patient. Marrow cellularity was analyzed using flow cytometry. Myelopoietic differentiation potential of bone marrow cells was quantified to gauge marrow function, as was the relative gene expression profiles of the marrow and disc cells. Disc/bone marrow cross-talk was assessed by comparing MC disc/bone marrow features relative to unaffected levels.

RESULTS

Thirteen MC1 and eleven MC2 patients were included. We observed pro-osteoclastic changes in MC2 discs, an inflammatory dysmyelopoiesis with fibrogenic changes in MC1 and MC2 marrow, and up-regulation of neurotrophic receptors in MC1 and MC2 bone marrow and discs.

CONCLUSION

Our data reveal a fibrogenic and pro-inflammatory cross-talk between MC bone marrow and adjacent discs. This provides insight into the pain generator at MC levels and informs novel therapeutic targets for treatment of MC-associated LBP.

Notochordal cell-derived conditioned medium protects human nucleus pulposus cells from stress-induced apoptosis

BACKGROUND CONTEXT

Degenerative disc disease (DDD) remains without an effective therapy and presents a costly burden to society.

PURPOSE

Based upon prior reports concerning the effects of notochordal cell-conditioned medium (NCCM) on disc cells, we performed a proof of principle study to determine whether NCCM could reduce cytotoxic stress-induced apoptosis in human disc nucleus pulposus (NP) cells.

STUDY DESIGN/SETTING

This is an "in vitro" fundamental or basic science study.

METHODS

Nucleus pulpous cells derived from 15 patients undergoing spinal surgery were treated with interleukin (IL)-1β and Fas ligand or etoposide in the presence of NCCM. We determined pro- or antiapoptotic events using activated caspase assays and determined genomic regulation of apoptosis using polymerase chain reaction arrays validated using Western blotting methods. We interrogated cellular apoptotic regulation using JC-1 dye and flow cytometry and performed enzyme-linked immunosorbent assays to evaluate NP inflammatory cytokine secretion.

RESULTS

Notochordal cell-conditioned medium inhibits cytotoxic stress-induced caspase-9 and -3/7 activities and maintains the mitochondrial membrane potential in human NP cells, thereby suppressing the intrinsic apoptotic pathway. Gene expression analysis revealed the X-linked inhibitor of apoptosis protein as a key player responsible for evading etoposide-induced apoptosis in the presence of NCCM, and we verified these data using Western blotting. Enzyme-linked immunosorbent assay results revealed distinct differences in IL-6 and IL-8 secretions by NP cells in response to etoposide in the presence of NCCM.

CONCLUSIONS

Here we demonstrate for the first time that NCCM reduces cytotoxic stress-induced apoptosis in human NP cells. Soluble factors present in NCCM could be harnessed for the development of novel therapeutics for the treatment of DDD.

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.

ISSLS PRIZE IN CLINICAL SCIENCE 2017: Is infection the possible initiator of disc disease? An insight from proteomic analysis

STUDY DESIGN

Proteomic and 16S rDNA analysis of disc tissues obtained in vivo.

OBJECTIVE

To address the controversy of infection as an aetiology for disc disorders through protein profiling. There is raging controversy over the presence of bacteria in human lumbar discs in vivo, and if they represent contamination or infection. Proteomics can provide valuable insight by identifying proteins signifying bacterial presence and, also host defence response proteins (HDRPs), which will confirm infection.

METHODS

22 discs (15-disc herniations (DH), 5-degenerate (DD), 2-normal in MRI (NM) were harvested intraoperatively and immediately snap frozen. Samples were pooled into three groups and proteins extracted were analysed with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Post identification, data analysis was performed using Uniprotdb, Pantherdb, Proteome discoverer and STRING network. Authentication for bacterial presence was performed by PCR amplification of 16S rDNA.

RESULTS

LC-MS/MS analysis using Orbitrap showed 1103 proteins in DH group, compared to 394 in NM and 564 in DD. 73 bacterial specific proteins were identified (56 specific for Propionibacterium acnes; 17 for Staphylococcus epidermidis). In addition, 67 infection-specific HDRPs, unique or upregulated, such as Defensin, Lysozyme, Dermcidin, Cathepsin-G, Prolactin-Induced Protein, and Phospholipase-A2, were identified confirming presence of infection. Species-specific primers for P. acnes exhibited amplicons at 946 bp (16S rDNA) and 515 bp (Lipase) confirming presence of P. acnes in both NM discs, 11 of 15 DH discs, and all five DD discs. Bioinformatic search for protein-protein interactions (STRING) documented 169 proteins with close interactions (protein clustering co-efficient 0.7) between host response and degenerative proteins implying that infection may initiate degradation through Ubiquitin C.

CONCLUSION

Our study demonstrates bacterial specific proteins and host defence proteins to infection which strengthen the hypothesis of infection as a possible initiator of disc disease. These results can lead to a paradigm shift in our understanding and management of disc disorders.

Simulation of water content distributions in degenerated human intervertebral discs

The objective of this study was to investigate the spatial and temporal variations of water content in intervertebral discs during degeneration and repair processes. We hypothesized that the patterns of water content distribution in the discs are related to the intensity patterns observed in T2-weighted MRI images. Water content distributions in the mildly (e.g., 80% viable cells in the disc, 2.3% decrease in disc height) and moderately (e.g., 40% viable cells in the disc, 9.3% decrease in disc height) degenerated discs were predicted using a finite element model. The variation of water content in the degenerated discs treated with three biological therapies (i.e., increasing the cell density in the nucleus pulposus [Case I], increasing glycosaminoglycan synthesis rate in the nucleus pulposus [Case II], and decreasing glycosaminoglycan degradation rate in the nucleus pulposus [Case III]) were also predicted. It was found that two patterns of water content distributions, a horizontal region with lower water content at the mid-axial plane of nucleus pulposus and a spot with higher water content at the posterior region, were shown during the degeneration progress for the disc simulated in this study. These two patterns disappeared after treatment in Case I, but in Case II and Case III. The implication of these patterns for the horizontal gray band and high intensity zone in T2-weighted MRI images was discussed. This study provided new guidance to develop a novel method for diagnosing disc degeneration and assessing outcomes of biological therapies with MRI techniques. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:147-153, 2017.

Can Exercise Positively Influence the Intervertebral Disc?

To better understand what kinds of sports and exercise could be beneficial for the intervertebral disc (IVD), we performed a review to synthesise the literature on IVD adaptation with loading and exercise. The state of the literature did not permit a systematic review; therefore, we performed a narrative review. The majority of the available data come from cell or whole-disc loading models and animal exercise models. However, some studies have examined the impact of specific sports on IVD degeneration in humans and acute exercise on disc size. Based on the data available in the literature, loading types that are likely beneficial to the IVD are dynamic, axial, at slow to moderate movement speeds, and of a magnitude experienced in walking and jogging. Static loading, torsional loading, flexion with compression, rapid loading, high-impact loading and explosive tasks are likely detrimental for the IVD. Reduced physical activity and disuse appear to be detrimental for the IVD. We also consider the impact of genetics and the likelihood of a 'critical period' for the effect of exercise in IVD development. The current review summarises the literature to increase awareness amongst exercise, rehabilitation and ergonomic professionals regarding IVD health and provides recommendations on future directions in research.

Pathobiology of Modic changes

PURPOSE

Low back pain (LBP) is the most disabling condition worldwide. Although LBP relates to different spinal pathologies, vertebral bone marrow lesions visualized as Modic changes on MRI have a high specificity for discogenic LBP. This review summarizes the pathobiology of Modic changes and suggests a disease model.

METHODS

Non-systematic literature review.

RESULTS

Chemical and mechanical stimulation of nociceptors adjacent to damaged endplates are likely a source of pain. Modic changes are adjacent to a degenerated intervertebral disc and have three generally interconvertible types suggesting that the different Modic change types represent different stages of the same pathological process, which is characterized by inflammation, high bone turnover, and fibrosis. A disease model is suggested where disc/endplate damage and the persistence of an inflammatory stimulus (i.e., occult discitis or autoimmune response against disc material) create predisposing conditions. The risk to develop Modic changes likely depends on the inflammatory potential of the disc and the capacity of the bone marrow to respond to it. Bone marrow lesions in osteoarthritic knee joints share many characteristics with Modic changes adjacent to degenerated discs and suggest that damage-associated molecular patterns and marrow fat metabolism are important pathogenetic factors. There is no consensus on the ideal therapy. Non-surgical treatment approaches including intradiscal steroid injections, anti-TNF-α antibody, antibiotics, and bisphosphonates have some demonstrated efficacy in mostly non-replicated clinical studies in reducing Modic changes in the short term, but with unknown long-term benefits. New diagnostic tools and animal models are required to improve painful Modic change identification and classification, and to clarify the pathogenesis.

CONCLUSION

Modic changes are likely to be more than just a coincidental imaging finding in LBP patients and rather represent an underlying pathology that should be a target for therapy.

Lumbar disc degeneration is associated with modic change and high paraspinal fat content - a 3.0T magnetic resonance imaging study

Background

Degenerative disc disease of the lumbar spine is common, with severe disease increasing the risk for chronic low back pain. This cross-sectional study examined whether disc degeneration is representative of a ‘whole-organ’ pathology, by examining its association with bone (vertebral endplate) and soft tissue (paraspinal muscle fat) abnormalities.

Methods

Seventy-two community-based individuals unselected for low back pain, had Magnetic Resonance Imaging (MRI). Lumbosacral disc degeneration was determined via the Pfirrmann grading system, a validated method to assess the intervertebral disc, distinguishing the nucleus and annulus, the signal intensity and the height of the intervertebral disc. Modic change and high paraspinal muscle fat content was also measured from MRI.

Results

Severe disc degeneration was associated, or tended to be associated with type 2 Modic change from L2 to L5 (OR range 3.5 to 25.3, p ≤ 0.06). Moreover, severe disc degeneration at all intervertebral levels was associated with or tended to be associated with high fat content of the paraspinal muscles (OR range 3.7 to 14.3, p ≤ 0.09).

Conclusion

These data demonstrate that disc degeneration of the lumbar spine is commonly accompanied by Modic change and high fat content of paraspinal muscles, thus representing a ‘whole-organ’ pathology. Longitudinal studies are required to determine the temporal relationship between these structural abnormalities. Understanding this may have the potential to identify novel targets for the treatment and prevention of lumbosacral disc degeneration.

Randomized sham-controlled, double-blind, multicenter clinical trial on the effect of percutaneous radiofrequency at the ramus communicans for lumbar disc pain

Background

Investigate the effect of percutaneous radiofrequency compared to a sham procedure, applied to the ramus communicans for treatment of lumbar disc pain.

Methods

Randomized sham‐controlled, double‐blind, crossover, multicenter clinical trial. Multidisciplinary pain centres of two general hospitals. Sixty patients aged 18 or more with medical history and physical examination suggestive for lumbar disc pain and a reduction of two or more on a numerical rating scale (0–10) after a diagnostic ramus communicans test block. Treatment group: percutaneous radiofrequency treatment applied to the ramus communicans; sham: same procedure except radiofrequency treatment. Primary outcome measure: pain reduction. Secondary outcome measure: Global Perceived Effect.

Results

No statistically significant difference in pain level over time between the groups, as well as in the group was found; however, the factor period yielded a statistically significant result. In the crossover group, 11 out of 16 patients experienced a reduction in NRS of 2 or more at 1 month (no significant deviation from chance). No statistically significant difference in satisfaction over time between the groups was found. The independent factors group and period also showed no statistically significant effects. The same applies to recovery: no statistically significant effects were found.

Conclusions

The null hypothesis of no difference in pain reduction and in Global Perceived Effect between the treatment and sham group cannot be rejected. Post hoc analysis revealed that none of the investigated parameters contributed to the prediction of a significant pain reduction.

Significance

Interrupting signalling through the ramus communicans may interfere with the transition of painful information from the discs to the central nervous system. Methodological differences exist in studies evaluating the efficacy of radiofrequency treatment for lumbar disc pain. A randomized, sham‐controlled, double‐blind, multicenter clinical trial on the effect of radiofrequency at the ramus communicans for lumbar disc pain was conducted. The null hypothesis of no difference in pain reduction and in Global Perceived Effect between the treatment and sham group cannot be rejected.

Diffusion characteristics of human annulus fibrosus-a study documenting the dependence of annulus fibrosus on end plate for diffusion

BACKGROUND

Intervertebral disc being avascular depends on nutrition from either the end plate or the annulus fibrosus (AF). The role of the end plate on disc diffusion had been extensively studied. However, diffusion of human AF remains poorly understood because of the lack of reliable techniques to study AF in vivo and non-invasively. The present study for the first time evaluates the 24-hour diffusion characteristics of AF in radial, axial, and circumferential directions.

PURPOSE

The study aimed to document the 24-hour diffusion characteristics of human AF.

STUDY DESIGN

This is an in vivo human serial post-contrast magnetic resonance image study.

METHODS

Twenty-five discs from five healthy volunteers (age <20 years) were studied. Diffusion over 24 hours following intravenous gadodiamide injection (0.3 mmol/kg) was studied at 10 minutes, and at 2, 4, 6, 12, and 24 hours. Axial images of the cranial, middle, and caudal zones of the discs were obtained. The vertebral body and end plate signal intensities were measured in sagittal sections. Thirty-nine regions of interest (24 in AF, 15 in nucleus pulposus) in each disc were analyzed. The peak enhancement percentage (EPmax) and the time to attain EPmax (Tmax) were calculated. Radial (outer vs. inner AF), axial (cranial vs. caudal vs. middle zone), and circumferential diffusions were analyzed. (The study received research grant from AOSpine India for US$6,000).

RESULTS

Annulus fibrosus showed a biphasic pattern of diffusion with a characteristic "double peak." Early peak was seen at 10 minutes (coinciding with Tmax of the vertebral body) and delayed peak was seen at 6 hours (coinciding with Tmax of the nucleus pulposus), and characteristically noted after Tmax of the end plate (2 hours). The inner AF showed significant regional differences both at the early and delayed peaks, but the outer AF had no regional differences in the early peak. In axial direction, both outer and inner AF showed maximum enhancement percentage in the middle zone, followed by the caudal zone and least in the cranial zone.

CONCLUSIONS

Annulus fibrosus characteristically showed a "double-peak" pattern of diffusion. Both the peaks had different characteristics, confirming two different sources of nutrition. The initial peak was contributed by periannular vascularity and the delayed one via the end plate from the vertebral body. The fact that even AF depends on the end plate for nutrition helps us better understand the complex nutritional pathways of intervertebral discs.

MRI quantification of human spine cartilage endplate geometry: Comparison with age, degeneration, level, and disc geometry

Geometry is an important indicator of disc mechanical function and degeneration. While the geometry and associated degenerative changes in the nucleus pulposus and the annulus fibrosus are well-defined, the geometry of the cartilage endplate (CEP) and its relationship to disc degeneration are unknown. The objectives of this study were to quantify CEP geometry in three dimensions using an MRI FLASH imaging sequence and evaluate relationships between CEP geometry and age, degeneration, spinal level, and overall disc geometry. To do so, we assessed the MRI-based measurements for accuracy and repeatability. Next, we measured CEP geometry across a larger sample set and correlated CEP geometric parameters to age, disc degeneration, level, and disc geometry. The MRI-based measures resulted in thicknesses (0.3-1 mm) that are comparable to prior measurements of CEP thickness. CEP thickness was greatest at the anterior/posterior (A/P) margins and smallest in the center. The CEP A/P thickness, axial area, and lateral width decreased with age but were not related to disc degeneration. Age-related, but not degeneration-related, changes in geometry suggest that the CEP may not follow the progression of disc degeneration. Ultimately, if the CEP undergoes significant geometric changes with aging and if these can be related to low back pain, a clinically feasible translation of the FLASH MRI-based measurement of CEP geometry presented in this study may prove a useful diagnostic tool. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1410-1417, 2016.

Region and strain-dependent diffusivities of glucose and lactate in healthy human cartilage endplate

The cartilage endplate (CEP) is implicated as the main pathway of nutrient supply to the healthy human intervertebral disc (IVD). In this study, the diffusivities of nutrient/metabolite solutes in healthy CEP were assessed, and further correlated with tissue biochemical composition and structure. The CEPs from non-degenerated human IVD were divided into four regions: central, lateral, anterior, and posterior. The diffusivities of glucose and lactate were measured with a custom diffusion cell apparatus under 0%, 10%, and 20% compressive strains. Biochemical assays were conducted to quantify the water and glycosaminoglycan (GAG) contents. The Safranin-O and Ehrlich׳s hematoxylin and eosin staining and scanning electron microscopy (SEM) were performed to reveal the tissue structure of the CEP. Average diffusivities of glucose and lactate in healthy CEP were 2.68±0.93×10^-7cm²/s and 4.52±1.47×10^-7cm²/s, respectively. Solute diffusivities were region-dependent (p<0.0001) with the highest values in the central region, and mechanical strains impeded solute diffusion in the CEP (p<0.0001). The solute diffusivities were significantly correlated with the tissue porosities (glucose: p<0.0001, r=0.581; lactate: p<0.0001, r=0.534). Histological and SEM studies further revealed that the collagen fibers in healthy CEP are more compacted than those in the nucleus pulposus (NP) and annulus fibrosus (AF) and show no clear orientation. Compared to human AF and NP, much smaller solute diffusivities in human CEP suggested that it acts as a gateway for solute diffusion through the disc, maintaining the balance of nutritional environment in healthy human disc under mechanical loading and preventing the progression of disc degeneration.

Oestrogen and parathyroid hormone alleviate lumbar intervertebral disc degeneration in ovariectomized rats and enhance Wnt/β-catenin pathway activity

To investigate the mitigation effect and mechanism of oestrogen and PTH on disc degeneration in rats after ovariectomy, as well as on Wnt/β-catenin pathway activity, thirty 3-month-old rats were ovariectomized and divided into three groups. Ten additional rats were used as controls. Eight weeks later, the rats were administered oestrogen or PTH for 12 weeks, and then discs were collected for tests. Results showed that nucleus pulposus cells in the Sham group were mostly notochord cells, while in the OVX group, cells gradually developed into chondrocyte-like cells. Oestrogen or PTH could partly recover the notochord cell number. After ovariectomy, the endplate roughened and endplate porosity decreased. After oestrogen or PTH treatment, the smoothness and porosity of endplate recovered. Compared with the Sham group, Aggrecan, Col2a and Wnt/β-catenin pathway expression in OVX group decreased, and either oestrogen or PTH treatment improved their expression. The biomechanical properties of intervertebral disc significantly changed after ovariectomy, and oestrogen or PTH treatment partly recovered them. Disc degeneration occurred with low oestrogen, and the underlying mechanisms involve nutrition supply disorders, cell type changes and decreased Wnt/β-catenin pathway activity. Oestrogen and PTH can retard disc degeneration in OVX rats and enhance Wnt/β-catenin pathway activity in nucleus pulposus.

Influences of Nutrition Supply and Pathways on the Degenerative Patterns in Human Intervertebral Disc

STUDY DESIGN

Investigation of the effects of the impairment of different nutritional pathways on the intervertebral disc degeneration patterns in terms of spatial distributions of cell density, glycosaminoglycan content, and water content.

OBJECTIVE

The aim of this study was to test the hypothesis that impairment of different nutritional pathways would result in different degenerative patterns in human discs.

SUMMARY OF BACKGROUND DATA

Impairment of nutritional pathways has been found to affect cell viability in the disc. However, details on how impairment of different nutritional pathways affects the disc degeneration patterns are unknown.

METHODS

A 3D finite element model was used for this study. This finite element method was based on the cell-activity coupled mechano-electrochemical theory for cartilaginous tissues. Impairment of the nutritional pathways was simulated by lowering the nutrition level at the disc boundaries. Effects of the impartment of cartilaginous endplate-nucleus pulposus (CEP-NP) pathway only (Case 1), annulus fibrosus (AF) pathway only (Case 2), and both pathways (Case 3) on disc degeneration patterns were studied.

RESULTS

The predicted critical levels of nutrition for Case 1, Case 2, and Case 3 were around 30%, 20%, and 50% of the reference values, respectively. Below this critical level, the disc degeneration would occur. Disc degeneration appeared mainly in the NP for Case 1, in the outer AF for Case 2, and in both the NP and inner to middle AF for Case 3. For Cases 1 and 3, the loss of water content was primarily located in the mid-axial plane, which is consistent with the horizontal gray band seen in some T2-weighted magnetic resonance imaging (MRI). For the disc geometry used in this study, it was predicted that there existed a high-intensity zone (for Case 3), as seen in some T2-weighted MRI images.

CONCLUSION

Impairment of different nutrition pathways results in different degenerative patterns.

LEVEL OF EVIDENCE

N/A.

Aging and age related stresses: a senescence mechanism of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is a complicated process that involves both age-related change and tissue damage caused by multiple stresses. In a degenerative IVD, cellular senescence accumulates and is associated with reduced proliferation, compromised self-repair, increased inflammatory response, and enhanced catabolic metabolism. In this review, we decipher the senescence mechanism of IVD degeneration (IVDD) by interpreting how aging coordinates with age-related, microenvironment-derived stresses in promoting disc cell senescence and accelerating IVDD. After chronic and prolonged replication, cell senescence may occur as a natural part of the disc aging process, but can potentially be accelerated by growth factor deficiency, oxidative accumulation, and inflammatory irritation. While acute disc injury, excessive mechanical overloading, diabetes, and chronic tobacco smoking contribute to the amplification of senescence-inducing stresses, the avascular nature of IVD impairs the immune-clearance of the senescent disc cells, which accumulate in cell clusters, demonstrate inflammatory and catabolic phenotypes, deteriorate disc microenvironment, and accelerate IVDD. Anti-senescence strategies, including telomerase transduction, supply of growth factors, and blocking cell cycle inhibitors, have been shown to be feasible in rescuing disc cells from early senescence, but their efficiency for disc regeneration requires more in vivo validations. Guidelines dedicated to avoiding or alleviating senescence-inducing stresses might decelerate cellular senescence and benefit patients with IVD degenerative diseases.

Human cartilage endplate permeability varies with degeneration and intervertebral disc site

Despite the critical functions the human cartilage endplate (CEP) plays in the intervertebral disc, little is known about its structural and mechanical properties and their changes with degeneration. Quantifying these changes with degeneration is important for understanding how the CEP contributes to the function and pathology of the disc. Therefore the objectives of this study were to quantify the effect of disc degeneration on human CEP mechanical properties, determine the influence of superior and inferior disc site on mechanics and composition, and simulate the role of collagen fibers in CEP and disc mechanics using a validated finite element model. Confined compression data and biochemical composition data were used in a biphasic-swelling model to calculate compressive extrafibrillar elastic and permeability properties. Tensile properties were obtained by applying published tensile test data to an ellipsoidal fiber distribution. Results showed that with degeneration CEP permeability decreased 50-60% suggesting that transport is inhibited in the degenerate disc. CEP fibers are organized parallel to the vertebrae and nucleus pulposus and may contribute to large shear strains (0.1-0.2) and delamination failure of the CEP commonly seen in herniated disc tissue. Fiber-reinforcement also reduces CEP axial strains thereby enhancing fluid flux by a factor of 1.8. Collectively, these results suggest that the structure and mechanics of the CEP may play critical roles in the solute transport and disc mechanics.

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

BACKGROUND

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Diffusion-weighted imaging in musculoskeletal radiology-clinical applications and future directions

Diffusion-weighted imaging (DWI) is an established diagnostic tool with regards to the central nervous system (CNS) and research into its application in the musculoskeletal system has been growing. It has been shown that DWI has utility in differentiating vertebral compression fractures from malignant ones, assessing partial and complete tears of the anterior cruciate ligament (ACL), monitoring tumor response to therapy, and characterization of soft-tissue and bone tumors. DWI is however less useful in differentiating malignant vs. infectious processes. As of yet, no definitive qualitative or quantitative properties have been established due to reasons ranging from variability in acquisition protocols to overlapping imaging characteristics. Even with these limitations, DWI can still provide clinically useful information, increasing diagnostic accuracy and improving patient management when magnetic resonance imaging (MRI) findings are inconclusive. The purpose of this article is to summarize recent research into DWI applications in the musculoskeletal system.

Fundamental biomechanics of the spine--What we have learned in the past 25 years and future directions

Since the publication of the 2nd edition of White and Panjabi׳s textbook, Clinical Biomechanics of the Spine in 1990, there has been considerable research on the biomechanics of the spine. The focus of this manuscript will be to review what we have learned in regards to the fundamentals of spine biomechanics. Topics addressed include the whole spine, the functional spinal unit, and the individual components of the spine (e.g. vertebra, intervertebral disc, spinal ligaments). In these broad categories, our understanding in 1990 is reviewed and the important knowledge or understanding gained through the subsequent 25 years of research is highlighted. Areas where our knowledge is lacking helps to identify promising topics for future research. In this manuscript, as in the White and Panjabi textbook, the emphasis is on experimental research using human material, either in vivo or in vitro. The insights gained from mathematical models and animal experimentation are included where other data are not available. This review is intended to celebrate the substantial gains that have been made in the field over these past 25 years and also to identify future research directions.

The poro-elastic behaviour of the intervertebral disc: A new perspective on diurnal fluid flow

Diurnal disc height changes, due to fluid in- and outflow, are in equilibrium while daytime spinal loading is twice as long as night time rest. A direction-dependent permeability of the endplates, favouring inflow over outflow, reportedly explains this; however, fluid flow through the annulus fibrosus should be considered. This study investigates the fluid flow of entire intervertebral discs. Caprine discs were preloaded in saline for 24h under four levels of static load. Under sustained load, we modulated the disc׳s swelling pressure by exchanging saline for demineralised water (inflow) and back to saline (outflow), both for 24h. We measured disc height creep and used stretched exponential models to determine time-constants. During inflow disc height increased in relation to applied load, and during outflow disc height decreased to preload levels. When comparing in- and outflow phases, there was no difference in creep, and time-constants were similar indicating no direction-dependent resistance to fluid flow in the entire intervertebral disc. Results provoked a new hypothesis for diurnal fluid flow: in vitro time-constants for loading are shorter than for unloading and in vivo daytime loading is twice as long as night time unloading, i.e. in diurnal loading the intervertebral disc is closer to loading equilibrium than to unloading equilibrium. Per definition, fluid flow is slower close to equilibrium than far from equilibrium; therefore, as diurnal loading occurs closer to loading equilibrium, fluid inflow during night time unloading can balance fluid outflow during daytime loading, despite a longer time-constant.

The relationship between cervical and lumbar spine lesions in rheumatoid arthritis with a focus on endplate erosion

STUDY DESIGN

A cross-sectional imaging study.

OBJECTIVE

To investigate the relationship between cervical and lumbar spine lesions in patients with rheumatoid arthritis (RA), and to analyze associated factors in those with concurrent cervical and lumbar endplate erosion (EE).

SUMMARY OF BACKGROUND DATA

Both the lumbar and cervical spines are often involved in RA, but little is known about the relationship between cervical and lumbar lesions. EE is often found in the spine of RA patients, but its prevalence and associated factors have not been well studied.

METHODS

We enrolled 201 RA patients in this study. Cervical lesions (horizontal and vertical atlantoaxial dislocation, subaxial subluxation) and lumbar lesions (vertebral fracture, scoliosis, spondylolisthesis) were evaluated on plain radiographs. EE was evaluated on sagittal T1-weighted magnetic resonance images, and graded into 4 categories. The prevalence of each lesion was calculated, and correlations between general cervical and lumbar lesions and between cervical and lumbar EE were analyzed. To assess the clinical condition of RA, we evaluated disease duration, Steinbrocker stage, modified Stanford Health Assessment Questionnaire results, and Disease Activity Score for 28 joints with the erythrocyte sedimentation rate. Factors associated with concurrent lumbar and cervical EE were analyzed using multiple logistic regression analysis.

RESULTS

Cervical lesions were found in 42.3% of patients and lumbar lesions in 56.2%. There was no significant correlation between the presence of cervical and the presence of lumbar lesions, but patients with cervical subaxial subluxation were significantly more likely to have lumbar spondylolisthesis. Cervical EE (≥1 points) was found in 61.2% of patients and lumbar EE in 39.3%. Total cervical EE score was significantly correlated with lumbar EE score. Moderate/high disease activity, Steinbrocker stage IV, and severe cervical or lumbar disk degeneration were associated with concurrent cervical and lumbar EE.

CONCLUSIONS

Some cervical lesions are significantly associated with lumbar spinal lesions. Concurrent cervical and lumbar EE are related to RA disease activity and peripheral joint deterioration, suggesting that RA activity may play an important role in total spinal involvement.

Does evaluator experience have an impact on the diagnosis of lumbar spine instability in dynamic MRI? Interobserver agreement study

OBJECTIVES

We aimed to evaluate interobserver agreement in the definition of spine instability among spine neuroradiologists with or without experience in dynamic magnetic resonance imaging (MRI).

MATERIAL AND METHODS

Two expert neuroradiologists and two residents retrospectively evaluated the pre-operative dynamic MRI examinations of patients with vertebral instability. Segmental motion, defined as excessive (more than 3 mm) translational motion from supine to upright, was investigated in 103 subjects (309 segments) using kinetic MRI. Radiographic parameters which can help indicate segmental instability include disc degeneration, facet joint osteoarthritis, and ligament flavum hypertrophy. These three radiographic parameters were simultaneously evaluated, and the combinations corresponding to significant segmental instability at each level were determined. The agreement among the neuroradiologists was calculated using the kappa coefficient. All patients had neurosurgical intervention to stabilize the spine.

RESULTS

Agreement was high among experienced and non-experienced neuroradiologists. Agreement was nearly perfect for spinal location of spinal instability.

CONCLUSIONS

This study demonstrates that the experience of the evaluator has a low impact on the assessment of spinal instability if correct classification is used. The interobserver agreement confirms the usefulness and safety of kinetic MRI in the correct diagnosis of spinal instability even by less experienced evaluators.

Circulatory dynamics of the cauda equina in lumbar canal stenosis using dynamic contrast-enhanced magnetic resonance imaging

BACKGROUND CONTEXT

There has been no study regarding the cauda equina circulation of patients with neurogenic intermittent claudication (NIC) in lumbar spinal canal stenosis (LSCS) using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

PURPOSE

The mechanism responsible for the onset of NIC was investigated using DCE-MRI to examine changes in cauda equina blood flow in patients with LSCS.

STUDY DESIGN

This was a retrospective longitudinal registry and magnetic resonance imaging study.

PATIENT SAMPLE

The subjects consisted of 23 patients who had LSCS associated with NIC (stenosis group). Ten asymptomatic volunteers who did not have NIC served as controls (control group). In the LSCS group, the cross-sectional area of the dural sac was <75 mm2 at the site of most severe stenosis. These patients were further divided into single and double stenosis subgroups.

OUTCOME MEASURES

The main measures we used were the signal intensity (S-I) ratio and the shape and size of the time intensity (T-I) curves. We compared these between the stenosis and control groups.

METHODS

At first, plain T1-weighted MR images were obtained and the lumbar dural sac cross-sectional area was measured using a digitizer. For DCE-MRI, sagittal T1-weighted images of the same slice were acquired continuously for 10 minutes after administration of gadolinium as an intravenous bolus to observe the distribution of contrast medium (gadolinium) in the cauda equina. To objectively evaluate changes in contrast enhancement of the cauda equina at the site of canal stenosis, regions of interest were established. The signal intensity (SI) ratio was calculated to compare the signal intensities before and after contrast enhancement, and time-intensity curves were prepared to investigate changes over time.

RESULTS

The static imaging findings and the changes of gadolinium uptake showed striking differences between the study and control patients. In the stenosis group, abnormal intrathecal enhancement showed around the site of stenosis on enhanced MR imaging. The SI ratio at the site of canal stenosis had a slower increase in the arterial phase when compared with that in the control group and remained high in the venous phase for up to 10 minutes. Finally, abnormal intrathecal enhancement was visible around the site of stenosis on enhanced MR imaging in all patients.

CONCLUSIONS

These clinical data indicate that cauda equina nerve roots in the LSCS patients are pathologic even when symptoms are not elicited in the supine position, suggesting that intraradicular venous congestion and edema themselves do not influence the existence of radicular symptoms.

The biological basis of degenerative disc disease: proteomic and biomechanical analysis of the canine intervertebral disc

INTRODUCTION

In the present study, we sought to quantify and contrast the secretome and biomechanical properties of the non-chondrodystrophic (NCD) and chondrodystrophic (CD) canine intervertebral disc (IVD) nucleus pulposus (NP).

METHODS

We used iTRAQ proteomic methods to quantify the secretome of both CD and NCD NP. Differential levels of proteins detected were further verified using immunohistochemistry, Western blotting, and proteoglycan extraction in order to evaluate the integrity of the small leucine-rich proteoglycans (SLRPs) decorin and biglycan. Additionally, we used robotic biomechanical testing to evaluate the biomechanical properties of spinal motion segments from both CD and NCD canines.

RESULTS

We detected differential levels of decorin, biglycan, and fibronectin, as well as of other important extracellular matrix (ECM)-related proteins, such as fibromodulin and HAPLN1 in the IVD NP obtained from CD canines compared with NCD canines. The core proteins of the vital SLRPs decorin and biglycan were fragmented in CD NP but were intact in the NP of the NCD animals. CD and NCD vertebral motion segments demonstrated significant differences, with the CD segments having less stiffness and a more varied range of motion.

CONCLUSIONS

The CD NP recapitulates key elements of human degenerative disc disease. Our data suggest that at least some of the compromised biomechanical properties of the degenerative disc arise from fibrocartilaginous metaplasia of the NP secondary to fragmentation of SLRP core proteins and associated degenerative changes affecting the ECM. This study demonstrates that the degenerative changes that naturally occur within the CD NP make this animal a valuable animal model with which to study IVD degeneration and potential biological therapeutics.

Stem Cell Approaches to Intervertebral Disc Regeneration: Obstacles from the Disc Microenvironment

Intervertebral disc (IVD) degeneration results in segmental instability and irritates neural compressive symptoms, such as low back pain and motor deficiency. The transplanting of stem cell into degenerative discs has attracted increasing clinical attention, as a new and proven approach to alleviating disc degeneration and to relieving discogenic pains. Aside from supplementation with stem cells, the IVD itself already contains a pool of stem and progenitor cells. Since the resident disc stem cells are incapable of reversing the pathologic changes that occur during aging and disc degeneration, it has been debated as to whether transplanted stem cells are capable of providing an efficient and durable therapeutic effect, even though there have been positive outcomes in both animal models and in clinical trials. This review aims to decipher the interactions between the stem cell and the disc microenvironment. Within their new niches in the IVD, the exogenous stem cell shows metabolic adaptation to the low-glucose supply, hypoxia, and compressive loadings, but demonstrates little tolerance to the disc-like acidity and hypertonicity. Similarly, the survival of endogenous stem cells is threatened as well by the harsh disc microenvironment, which may exhaust the stem cell resources and restrict the self-repair capacity of a degenerating IVD. To eliminate the intrinsic obstacles within the stressful disc niches, stem cells should be delivered with an injectable scaffold that provides both survival and mechanical support. Quick healing or concretion of the injection injuries, which minimizes stem cell leakage and disturbance to disc homeostasis, is of equal importance toward achieving efficient stem cell-based disc regeneration.

Changes in perfusion and diffusion in the endplate regions of degenerating intervertebral discs: a DCE-MRI study

PURPOSE

Dynamic contrast-enhanced MRI (DCE-MRI) was used to investigate the associations between intervertebral disc degeneration and changes in perfusion and diffusion in the disc endplates.

METHODS

56 participants underwent MRI scans. Changes in DCE-MRI signal enhancement in the endplate regions were analyzed. Also, a group template was generated for the endplates and enhancement maps were registered to this template for group analysis.

RESULTS

DCE-MRI enhancement changed significantly in cranial endplates with increased degeneration. A similar trend was observed for caudal endplates, but it was not significant. Group-averaged enhancement maps revealed major changes in spatial distribution of endplate perfusion and diffusion with increasing disc degeneration especially in peripheral endplate regions.

CONCLUSIONS

Increased enhancement in the endplate regions of degenerating discs might be an indication of ongoing damage in these tissues. Therefore, DCE-MRI could aid in understanding the pathophysiology of disc degeneration. Moreover, it could be used in the planning of novel treatments such as stem cell therapy.

Porosity and Thickness of the Vertebral Endplate Depend on Local Mechanical Loading

STUDY DESIGN

Mechanical and microcomputed tomography (micro-CT) study of cadaver spines.

OBJECTIVE

To compare porosity and thickness of vertebral endplates with (1) compressive stresses measured in adjacent intervertebral discs and (2) grade of disc degeneration.

SUMMARY OF BACKGROUND DATA

Endplate porosity is important for disc metabolite transport, and yet porosity increases with age and disc degeneration. We hypothesize that porosity is largely determined by mechanical loading from adjacent discs.

METHODS

Forty motion segments (T8-9 to L4-5) were dissected from 23 cadavers aged 48 to 98 years. Each was subjected to 1 kN compression during which time intradiscal stresses were measured by pulling a pressure transducer along the disc's midsagittal diameter. "Stress profiles" revealed the average pressure in the nucleus, and the maximum stress in the anterior and posterior annulus. Specimens were further dissected to obtain discs with endplates (and 5 mm of bone) on either side. Microcomputed tomography scans (resolution 35 μm) were analyzed to calculate thickness and porosity in the midsagittal regions of all 80 endplates. Average values for the anterior, central, and posterior regions of each endplate were obtained. Disc degeneration was assessed macroscopically and microscopically.

RESULTS

Endplate porosity was inversely related to its thickness, being greatest in the central region opposite the nucleus, and least near the periphery. Superior endplates (relative to the disc) were 14% thicker (P < 0.001) and 4% less porous (P = 0.008) than inferior. In each of the 3 endplate regions (anterior, central, and posterior), porosity was inversely and significantly related to mechanical loading (pressure or maximum stress) in the adjacent disc region (P < 0.01 in all cases). Disc degeneration was best predicted by (reduced) nucleus pressure (R = 0.46, P < 0.001) and (reduced) maximum stress in the anterior annulus (R = 0.31, P < 0.001).

CONCLUSION

Mechanical loading is a major determinant of endplate thickness and porosity. Disc degeneration is more closely related to reduced disc stresses than to endplate thickness or porosity.

LEVEL OF EVIDENCE

N/A.

ISSLS Prize Winner: Dynamic Loading-Induced Convective Transport Enhances Intervertebral Disc Nutrition

STUDY DESIGN

Experimental animal study of convective transport in the intervertebral disc.

OBJECTIVE

To quantify the effects of mechanical loading rate on net transport into the healthy and degenerative intervertebral disc in vivo.

SUMMARY OF BACKGROUND DATA

Intervertebral disc degeneration is linked with a reduction in transport to the avascular disc. Enhancing disc nutrition is, therefore, a potential strategy to slow or reverse the degenerative cascade. Convection induced by mechanical loading is a potential mechanism to augment diffusion of small molecules into the disc.

METHODS

Skeletally mature New Zealand white rabbits with healthy discs and discs degenerated via needle puncture were subjected to low rate axial compression and distraction loading for 2.5, 5, 10, 15, or 20 minutes after a bolus administration of gadodiamide. Additional animals with healthy discs were subjected to high-rate loading for 10 minutes or no loading for 10 minutes. Transport into the disc for each loading regimen was quantified using post-contrast-enhanced magnetic resonance imaging.

RESULTS

Low-rate loading resulted in the rapid uptake and clearance of gadodiamide in the disc. Low-rate loading increased net transport into the nucleus by a mean 16.8% and 12.6% in healthy and degenerative discs, respectively. The kinetics of small molecule uptake and clearance were accelerated in both healthy and degenerative discs with low-rate loading. In contrast, high-rate loading reduced transport into nucleus by a mean 16.8%.

CONCLUSION

These results illustrate that trans-endplate diffusion can be enhanced by forced convection in both healthy and degenerative discs in vivo. Mechanical loading-induced convection could offer therapeutic benefit for degenerated discs by enhancing uptake of nutrients and clearance of by-products.

LEVEL OF EVIDENCE

4.

The region-dependent biomechanical and biochemical properties of bovine cartilaginous endplate

Regional biomechanical and biochemical properties of bovine cartilaginous endplate (CEP) and its role in disc mechanics and nutrition were determined. The equilibrium aggregate modulus and hydraulic permeability between the central and lateral regions were examined by confined compression testing. Biochemical assays were conducted to quantify the amount of water, collagen, and glycosaminoglycan (GAG). The equilibrium aggregate modulus of the CEP in the central region (0.23 ± 0.15 MPa) was significantly lower than for the lateral region (0.83 ± 0. 26 MPa). No significant regional difference was found for the permeability of the CEP (central region: 0.13 ± 0.07×10(-15)m(4)/Ns and lateral region: 0.09 ± 0.03 × 10(-15)m(4)/Ns). CEPs were an average of 75.6% water by wet weight, 41.1% collagen, and 20.4% GAG by dry weight in the central region, as well as an average of 70.2% water by wet weight, 73.8% collagen, and 11.7% GAG by dry weight in the lateral region. Regional differences observed for the equilibrium aggregate modulus were likely due to the regional variation in biochemical composition. The lateral bovine endplate is much stiffer and may share a greater portion of the load. Compared with the nucleus pulposus (NP) and annulus fibrosus (AF), a smaller hydraulic permeability was found for the CEP in both the central and lateral regions, which could be due to its lower water content and higher collagen content. Our results suggest that the CEP may block rapid fluid exchange and solute convection, allow pressurization of the interstitial fluid, and play a significant role in nutrient supply in response to loading.