Analysis of quantitative magnetic resonance imaging and biomechanical parameters on human discs with different grades of degeneration

Different Load-Induced Alterations in Intervertebral Discs Between Low Back Pain Patients and Controls: A T2-map Study

STUDY DESIGN

Prospective cohort study.

OBJECTIVE

Investigate load-induced effects in lumbar intervertebral discs (IVDs) and differences between low back pain (LBP) patients and controls.

SUMMARY OF BACKGROUND DATA

T2-map values, obtained from quantitative MRI sequences, reflect IVD tissue composition and integrity. Feasibility studies with T2-mapping indicate different load-induced effects in entire IVDs and posterior IVD parts between LBP patients and controls. Larger studies are required to confirm these findings and increase the understanding of specific characteristics distinguishing IVD changes in LBP patients compared with controls.

MATERIALS AND METHODS

Lumbar IVDs of 178 patients (mean age: 43.8 yr; range: 20-60 yr) with >3 months of LBP and 74 controls (mean age: 40.3 yr; range: 20-60 yr) were imaged with T2-map sequence in a 3T scanner in supine position without axial load, immediately followed by a repeated examination, using the same sequence, with axial load. On both examinations, mean T2-map values were obtained from entire IVDs and from central/posterior IVD parts on the three midsagittal slices in 855 patient IVDs and 366 control IVDs. Load-induced effect was compared with Fold-change ratio and adjusted for IVD-degeneration grade.

RESULTS

Loading induced an increase in T2-map values in both patients and controls. Excluding most extreme values, the ranges varied between -15% and +35% in patients and -11% and +36% in controls (first to 99th percentile). Compared with controls, the T2-map value increase in patients was 2% smaller in entire IVDs (Fold-change: 0.98, P =0.031), and for central and posterior IVD parts 3% (Fold-change: 0.98, P =0.005), respectively, 2% (Fold-change: 0.9, P =0.015) smaller.

CONCLUSIONS

This quantitative study confirmed diverse load-induced behaviors between LBP patients and controls, suggesting deviant biomechanical characteristics between IVDs in patients and controls not only attributed to the global grade of degeneration. These findings are an important step in the continuous work of identifying specific IVD phenotypes for LBP patients.

LEVEL OF EVIDENCE

Level II.

Nucleus pulposus structure and function assessed in shear using magnetic resonance elastography, quantitative MRI, and rheometry

Background

In vivo quantification of the structure-function relationship of the intervertebral disc (IVD) via quantitative MRI has the potential to aid objective stratification of disease and evaluation of restorative therapies. Magnetic resonance elastography (MRE) is an imaging technique that assesses tissue shear properties and combined with quantitative MRI metrics reflective of composition can inform structure-function of the IVD. The objectives of this study were to (1) compare MRE- and rheometry-derived shear modulus in agarose gels and nucleus pulposus (NP) tissue and (2) correlate MRE and rheological measures of NP tissue with composition and quantitative MRI.

Method

MRE and MRI assessment (i.e., T1ρ and T2 mapping) of agarose samples (2%, 3%, and 4% (w/v); n = 3-4/%) and of bovine caudal IVDs after equilibrium dialysis in 5% or 25% PEG (n = 13/PEG%) was conducted. Subsequently, agarose and NP tissue underwent torsional mechanical testing consisting of a frequency sweep from 1 to 100 Hz at a rotational strain of 0.05%. NP tissue was additionally evaluated under creep and stress relaxation conditions. Linear mixed-effects models and univariate regression analyses evaluated the effects of testing method, %agarose or %PEG, and frequency, as well as correlations between parameters.

Results

MRE- and rheometry-derived shear moduli were greater at 100 Hz than at 80 Hz in all agarose and NP tissue samples. Additionally, all samples with lower water content had higher complex shear moduli. There was a significant correlation between MRE- and rheometry-derived modulus values for homogenous agarose samples. T1ρ and T2 relaxation times for agarose and tissue were negatively correlated with complex shear modulus derived from both techniques. For NP tissue, shear modulus was positively correlated with GAG/wet-weight and negatively correlated with %water content.

Conclusion

This work demonstrates that MRE can assess hydration-induced changes in IVD shear properties and further highlights the structure-function relationship between composition and shear mechanical behaviors of NP tissue.

Variable flip angle T1 mapping and multi-echo T2 and T2* mapping magnetic resonance imaging sequences allow quantitative assessment of canine lumbar disc degeneration

Magnetic resonance imaging is the gold standard for diagnosing intervertebral disc (IVD) degeneration in dogs. However, published methods for quantifying severity or progression of IVD degeneration are currently limited. Mapping MRI sequences are used in humans for quantifying IVD degeneration but have rarely been applied in dogs. The objective of this prospective, method comparison study was to evaluate variable flip angle T1 mapping and multiecho T2 and T2* mapping as methods for quantifying canine lumbar IVD degeneration in twenty canine patients without clinical signs of spinal disease. Ventral and dorsal lumbar IVD widths were measured on radiographs, and lumbar IVDs were assigned a qualitative Pfirrmann grade based on standard T2-weighted sequences. T1, T2, and T2* relaxation times of the nucleus pulposus (NP) were measured on corresponding maps using manual-drawn ROIs. Strong intra- and interrater agreements were found (P < 0.01) for NP relaxation times. Radiographic IVD widths and T1, T2, and T2* mapping NP relaxation times were negatively correlated with Pfirrmann grading (P < 0.01). Significant differences in T1 NP relaxation times were found between Pfirrmann grade I and the other grades (P < 0.01). Significant differences in T2 and T2* NP relaxation times were found between grade I and the other grades and between grades II and III (P < 0.01). Findings indicated that T1, T2, and T2* MRI mapping sequences are feasible in dogs. Measured NP relaxation times were repeatable and decreased when Pfirrmann grades increased. These methods may be useful for quantifying the effects of regenerative treatment interventions in future longitudinal studies.

Magnetic Resonance Elastography of Intervertebral Discs: Spin-Echo Echo-Planar Imaging Sequence Validation

BACKGROUND

Magnetic resonance elastography (MRE) is an imaging technique that can noninvasively assess the shear properties of the intervertebral disc (IVD). Unlike the standard gradient recalled echo (GRE) MRE technique, a spin-echo echo-planar imaging (SE-EPI) sequence has the potential to improve imaging efficiency and patient compliance.

PURPOSE

To validate the use of an SE-EPI sequence for MRE of the IVD compared against the standard GRE sequence.

STUDY TYPE

Cross-over.

SUBJECTS

Twenty-eight healthy volunteers (15 males and 13 females, age range: 19-55).

FIELD STRENGTH/SEQUENCE

3 T; GRE, SE-EPI with breath holds (SE-EPI-BH) and SE-EPI with free breathing (SE-EPI-FB) MRE sequences.

ASSESSMENT

MRE-derived shear stiffnesses were calculated via principal frequency analysis. SE-EPI derived shear stiffness and octahedral shear strain signal-to-noise ratios (OSS-SNR) were compared against those derived using the GRE sequence. The reproducibility and repeatability of SE-EPI stiffness measurements were determined. Shear stiffness was evaluated in the nucleus pulposus (NP) and annulus fibrosus (AF) regions of the disc. Scan times between sequences were compared.

STATISTICAL TESTS

Linear mixed models, Bland-Altman plots, and Lin's concordance correlation coefficients (CCCs) were used with P < 0.05 considered statistically significant.

RESULTS

Good correlation was observed between shear stiffnesses derived from the SE-EPI sequences with those derived from the GRE sequence with CCC values greater than 0.73 and 0.78 for the NP and AF regions, respectively. OSS-SNR was not significantly different between GRE and SE-EPI sequences (P > 0.05). SE-EPI sequences generated highly reproducible and repeatable stiffness measurements with CCC values greater than 0.97 in the NP and AF regions and reduced scan time by at least 51% compared to GRE. SE-EPI-BH and SE-EPI-FB stiffness measurements were similar with CCC values greater than 0.98 for both regions.

DATA CONCLUSION

SE-EPI-based MRE-derived stiffnesses were highly reproducible and repeatable and correlated with current standard GRE MRE-derived stiffness estimates while reducing scan times.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 1.

Comparison of MRI T1, T2, and T2* mapping with histology for assessment of intervertebral disc degeneration in an ovine model

An easy, reliable, and time-efficient standardized approach for assessing lumbar intervertebral disc (IVD) degeneration with relaxation times measurements in pre-clinical and clinical studies is lacking. This prospective study aims to determine the most appropriate method for lumbar IVD degeneration (IDD) assessment in sheep by comparing three quantitative MRI sequences (variable-flip-angle T1 mapping, and multi-echo T2 and T2* mapping), correlating them with Pfirrmann grading and histology. Strong intra- and interrater agreements were found for Nucleus pulposus (NP) regions-of-interest (ROI). T1, T2, and T2* mapping correlated with Pfirrmann grading and histological scoring (p < 0.05) except for the most ventral rectangular ROI on T2 maps. Correlations were excellent for all of the T1 ROIs and the T2* NP ROIs. Highly significant differences in T1 values were found between all Pfirrmann grades except between grades I/II and between grades III/IV. Significant differences were identified in the T2 and the T2* values between all grades except between grades I/III. T1, T2, and T2* relaxation times measurements of the NP are an accurate and time-efficient tool to assess lumbar IDD in sheep. Variable-flip-angle T1 mapping may be further considered as a valuable method to investigate IDD and to assess the efficacy of regenerative treatments in longitudinal studies.

Biomechanical feasibility of semi-rigid stabilization and semi-rigid lumbar interbody fusion: a finite element study

BACKGROUND

Semi-rigid lumbar fusion offers a compromise between pedicle screw-based rigid fixation and non-instrumented lumbar fusion. However, the use of semi-rigid interspinous stabilization (SIS) with interspinous spacer and ligamentoplasty and semi-rigid posterior instrumentation (SPI) to assist interbody cage as fusion constructs remained controversial. The purpose of this study is to investigate the biomechanical properties of semi-rigidly stabilized lumbar fusion using SIS or SPI and their effect on adjacent levels using finite element (FE) method.

METHOD

Eight FE models were constructed to simulate the lumbosacral spine. In the non-fusion constructs, semi-rigid stabilization with (i) semi-rigid interspinous spacer and artificial ligaments (PD-SIS), and (ii) PI with semi-rigid rods were simulated (PD + SPI). For fusion constructs, the spinal models were implanted with (iii) PEEK cage only (Cage), (iv) PEEK cage and SIS (Cage+SIS), (v) PEEK cage and SPI (Cage+SPI), (vi) PEEK cage and rigid PI (Cage+PI).

RESULT

The comparison of flexion-extension range of motion (ROM) in the operated level showed the difference between Cage+SIS, Cage+SPI, and Cage+PI was less than 0.05 degree. In axial rotation, ROM of Cage+SIS were greater than Cage+PI by 0.81 degree. In the infrajacent level, while Cage+PI increased the ROM by 24.1, 27,7, 25.9, and 10.3% and Cage+SPI increased the ROM by 26.1, 30.0, 27.1, and 10.8% in flexion, extension, lateral bending and axial rotation respectively, Cage+SIS only increased the ROM by 3.6, 2.8, and 11.2% in flexion, extension, and lateral bending and reduced the ROM by 1.5% in axial rotation. The comparison of the von Mises stress showed that SIS reduced the adjacent IVD stress by 9.0%. The simulation of the strain energy showed a difference between constructs less than 7.9%, but all constructs increased the strain energy in the infradjacent level.

CONCLUSION

FE simulation showed semi-rigid fusion constructs including Cage+SIS and Cage+SPI can provide sufficient stabilization and flexion-extension ROM reduction at the fusion level. In addition, SIS-assisted fusion resulted in less hypermobility and less von Mises stress in the adjacent levels. However, SIS-assisted fusion had a disadvantage of less ROM reduction in lateral bending and axial rotation. Further clinical studies are warranted to investigate the clinical efficacy and safety of semi-rigid fusions.

Tenomodulin and Chondromodulin-1 Are Both Required to Maintain Biomechanical Function and Prevent Intervertebral Disc Degeneration

OBJECTIVE

The underlying mechanisms and molecular factors influencing intervertebral disc (IVD) homeostasis and degeneration remain clinically relevant. Tenomodulin (Tnmd) and chondromodulin (Chm1) are antiangiogenic transmembrane glycoproteins, with cleavable C-terminus, expressed by IVD cells that are implicated in the onset of degenerative processes. We evaluate the organ-level biomechanical impact of knocking out Tnmd alone, and Tnmd and Chm1, simultaneously.

DESIGN

Caudal (c5-8) and lumbar vertebrae (L1-4) of skeletally mature male and female 9-month-old wildtype (WT), Tnmd knockout (Tnmd^-/-), and Tnmd/Chm1 double knockout (Tnmd^-/-/Chm^-/-) mice were used (n = 9-13 per group). Disc height index (DHI), histomorphological changes, and axial, torsional, creep, and failure biomechanical properties were evaluated. Differences were assessed by one-way ANOVA with post hoc Bonferroni-corrected comparisons (P < 0.05).

RESULTS

Tnmd^-/-/Chm1^-/- IVDs displayed increased DHI and histomorphological scores that indicated increased IVD degeneration compared to the WT and Tnmd^-/- groups. Double knockout IVDs required significantly less torque and energy to initiate torsional failure. Creep parameters were comparable between all groups, except for the slow time constant, which indicated faster outward fluid flow. Tnmd^-/- IVDs lost fluid faster than the WT group, and this effect was amplified in the double knockout IVDs.

CONCLUSION

Knocking out Tnmd and Chm1 affects IVD fluid flow and organ-level biomechanical function and therefore may play a role in contributing to IVD degeneration. Larger effects of the Tnmd and Chm1 double knockout mice compared to the Tnmd single mutant suggest that Chm1 may play a compensatory role in the Tnmd single mutant IVDs.

Patient-specific apparent diffusion maps used to model nutrient availability in degenerated intervertebral discs

INTRODUCTION

In this study, magnetic resonance imaging data was used to (1) model IVD-specific gradients of glucose, oxygen, lactate, and pH; and (2) investigate possible effects of covariate factors (i.e., disc geometry, and mean apparent diffusion coefficient values) on the IVD's microenvironment. Mathematical modeling of the patient's specific IVD microenvironment could be important when selecting patients for stem cell therapy due to the increased nutrient demand created by that treatment.

MATERIALS AND METHODS

Disc geometry and water diffusion coefficients were extracted from MRIs of 37 patients using sagittal T1-weighted images, T2-weighted images, and ADC Maps. A 2-D steady state finite element mathematical model was developed in COMSOL Multiphysics® 5.4 to compute concentration maps of glucose, oxygen, lactate and pH.

RESULTS

Concentration of nutrients (i.e., glucose, and oxygen) dropped with increasing distance from the cartilaginous endplates (CEP), whereas acidity levels increased. Most discs experienced poor nutrient levels along with high acidity values in the inner annulus fibrosus (AF). The disc's physiological microenvironment became more deficient as degeneration progressed. For example, minimum glucose concentration in grade 4 dropped by 31.1% compared to grade 3 (p < 0.0001). The model further suggested a strong effect of the following parameters: disc size, AF and CEP diffusivities, metabolic reactions, and cell density on solute concentrations in the disc (p < 0.05).

CONCLUSION

The significance of this work implies that the individual morphology and physiological conditions of each disc, even among discs of the same Pfirrmann grade, should be evaluated when modeling IVD solute concentrations.

Lumbar intervertebral disc characterization through quantitative MRI analysis: An automatic voxel-based relaxometry approach

Purpose

To develop an automated pipeline based on convolutional neural networks to segment lumbar intervertebral discs and characterize their biochemical composition using voxel‐based relaxometry, and establish local associations with clinical measures of disability, muscle changes, and other symptoms of lower back pain.

Methods

This work proposes a new methodology using MRI (n = 31, across the spectrum of disc degeneration) that combines deep learning–based segmentation, atlas‐based registration, and statistical parametric mapping for voxel‐based analysis of T_1ρ and T₂ relaxation time maps to characterize disc degeneration and its associated disability.

Results

Across degenerative grades, the segmentation algorithm produced accurate, high‐confidence segmentations of the lumbar discs in two independent data sets. Manually and automatically extracted mean disc T_1ρ and T₂ relaxation times were in high agreement for all discs with minimal bias. On a voxel‐by‐voxel basis, imaging‐based degenerative grades were strongly negatively correlated with T_1ρ and T₂, particularly in the nucleus. Stratifying patients by disability grades revealed significant differences in the relaxation maps between minimal/moderate versus severe disability: The average T_1ρ relaxation maps from the minimal/moderate disability group showed clear annulus nucleus distinction with a visible midline, whereas the severe disability group had lower average T_1ρ values with a homogeneous distribution.

Conclusion

This work presented a scalable pipeline for fast, automated assessment of disc relaxation times, and voxel‐based relaxometry that overcomes limitations of current region of interest–based analysis methods and may enable greater insights and associations between disc degeneration, disability, and lower back pain.

Multiscale and multimodal structure-function analysis of intervertebral disc degeneration in a rabbit model

OBJECTIVES

The objective of this study was to perform a quantitative analysis of the structural and functional alterations in the intervertebral disc during in vivo degeneration, using emerging tools that enable rigorous assessment from the microscale to the macroscale, as well as to correlate these outcomes with noninvasive, clinically relevant imaging parameters.

DESIGN

Degeneration was induced in a rabbit model by puncturing the annulus fibrosus (AF) with a 16-gauge needle. 2, 4, 8, and 12 weeks following puncture, degenerative changes in the discs were evaluated via magnetic resonance imaging (MRI), whole motion segment biomechanics, atomic force microscopy, histology and polarized light microscopy, immunohistochemistry, biochemical content, and second harmonic generation imaging.

RESULTS

Following puncture, degeneration was evident through marked changes in whole disc structure and mechanics. Puncture acutely compromised disc macro and microscale mechanics, followed by progressive stiffening and remodeling. Histological analysis showed substantial anterior fibrotic remodeling and osteophyte formation, as well as an overall reduction in disc height, and disorganization and infolding of the AF lamellae into the NP space. Increases in NP collagen content and aggrecan breakdown products were also noted within 4 weeks. On MRI, NP T2 was reduced at all post-puncture time points and correlated significantly with microscale indentation modulus.

CONCLUSION

This study defined the time dependent changes in disc structure-function relationships during IVD degeneration in a rabbit annular injury model and correlated degeneration severity with clinical imaging parameters. Our findings identified AF infolding and occupancy of the space as a principle mechanism of disc degeneration in response to needle puncture, and provide new insights to direct the development of novel therapeutics.

The importance of level stratification for quantitative MR studies of lumbar intervertebral discs: a cross-sectional analysis in 101 healthy adults

PURPOSE

To investigate whether quantitative T2-times depend on lumbar intervertebral disc (IVD) level.

METHODS

The lumbar spine (Th12/L1-L5/S1) of 101 participants (53.5% female, 30.0[± 3.6]years, 173.5[± 9.6]cm and 69.9[± 13.4]kg), without history of back pain, was examined on a 3T scanner with sagittal T2-mapping. All IVDs were stratified according to Pfirrmann grade and lumbar level, with mean T2-time determined for the entire IVD volume and in five subregions of interests.

RESULTS

Significant level-dependent T2-time differences were detected, both for the entire IVD volume and its subregions. For the entire IVD volume, Pfirrmann grade 2 IVDs displayed 9-18% higher T2-times in Th12/L1 IVDs compared to L2/L3-L5/S1 IVDs (0.001 > p < 0.004) and significantly different T2-times in L1/L2-L2/L3 IVDs compared to most of the IVDs in the lower lumbar spine. In Pfirrmann grades 1, 3 and 4 IVDs, no significant level-dependent T2-time differences were observed for the entire IVD. More pronounced results were observed when comparing IVD subregions, with significant level-dependent differences also within Pfirrmann grade 1 and grade 3 IVDs. For example, in posterior IVD subregions mean T2-time was 80-82% higher in Th12/L1 compared to L3/L4-L4/L5 Pfirrmann grade 1 IVDs (p < 0.05) and 10-14% higher in L5/S1 compared to L3/L4-L4/L5 Pfirrmann grade 3 IVDs (0.02 > p < 0.001).

DISCUSSION

Significant level-dependent T2-time differences within several Pfirrmann grades, both for the entire IVD volume and for multiple IVD subregions, were shown in this large cohort study. The T2-time differences between levels existed in both non-degenerated and degenerated IVDs. These findings show the importance of stratifying for lumbar level when quantitative IVD studies are performed using T2-mapping. These slides can be retrieved under Electronic Supplementary Material.

Diffusion based MR measurements correlates with age-related changes in human intervertebral disks

BACKGROUND

Understanding the association between MR parameters and age related deterioration in human intervertebral disks forms an important step in the development of clinical diagnostic protocols for disk disease.

METHODS

Ten unfixed thoracic and lumbar cadaver disk joints, age 37-81 years were imaged at 9.4 T using T2 relaxation (CPMG) and ADC (DWI spin echo) MR protocols. For each MR parameter, spatial maps were computed from the axial images, with the AF and NP segmented based on the T2 maps. Linear regression tested for the correlation between mean and variance (COV) of T2 and ADC with age in the disk, nucleus and annulus, and the effect of thoracic vs. lumbar spine on these correlations.

FINDINGS

In the disk, age negatively correlated with mean ADC (P < 0.001) and positively with COV of ADC (P < 0.001) and T2 (P < 0.05). Age was negatively correlated with mean T2 (P < 0.01), mean ADC (P < 0.001) and positively with COV of ADC (P < 0.001) and T2 (P < 0.05) in the NP and positively correlated with mean T2 (P < 0.05), COV of ADC (P < 0.01) and T2 (P < 0.05) and negatively with mean ADC (P < 0.05) in the AF. Compared to thoracic disks, lumbar disks showed higher mean ADC (P < 0.05), lower mean T2 (P < 0.001) and higher COV of ADC (P < 0.01) and T2 (P < 0.05).

INTERPRETATION

Compared to T2, MR diffusion was a more sensitive measure of age mediated changes in disk tissues. Strong differences in the association of MR parameters with age between the lumbar and thoracic suggest that mechanical environment effects tissue specific MR parameters' association with age.

Advancing cell therapies for intervertebral disc regeneration from the lab to the clinic: Recommendations of the ORS spine section

Intervertebral disc degeneration is strongly associated with chronic low back pain, a leading cause of disability worldwide. Current back pain treatment approaches (both surgical and conservative) are limited to addressing symptoms, not necessarily the root cause. Not surprisingly therefore, long-term efficacy of most approaches is poor. Cell-based disc regeneration strategies have shown promise in preclinical studies, and represent a relatively low-risk, low-cost, and durable therapeutic approach suitable for a potentially large patient population, thus making them attractive from both clinical and commercial standpoints. Despite such promise, no such therapies have been broadly adopted clinically. In this perspective we highlight primary obstacles and provide recommendations to help accelerate successful clinical translation of cell-based disc regeneration therapies. The key areas addressed include: (a) Optimizing cell sources and delivery techniques; (b) Minimizing potential risks to patients; (c) Selecting physiologically and clinically relevant efficacy metrics; (d) Maximizing commercial potential; and (e) Recognizing the importance of multidisciplinary collaborations and engaging with clinicians from inception through to clinical trials.

Axial loading during MRI reveals deviant characteristics within posterior IVD regions between low back pain patients and controls

PURPOSE

To investigate differences in functional intervertebral disk (IVD) characteristics between low back pain (LBP) patients and controls using T2-mapping with axial loading during MRI (alMRI).

METHODS

In total, 120 IVDs in 24 LBP patients (mean age 39 years, range 25-69) were examined with T2-mapping without loading of the spine (uMRI) and with alMRI (DynaWell^® loading device) and compared with 60 IVDs in 12 controls (mean age 38 years, range 25-63). The IVD T2-value was acquired after 20-min loading in five regions of interests (ROI), ROI1-5 from anterior to posterior. T2-values were compared between loading states and cohorts with adjustment for Pfirrmann grade.

RESULTS

In LBP patients, mean T2-value of the entire IVD was 64 ms for uMRI and 66 ms for alMRI (p = 0.03) and, in controls, 65 ms and 65 ms (p = 0.5). Load-induced T2-differences (alMRI-uMRI) were seen in all ROIs in both patients (0.001 > p < 0.005) and controls (0.0001 > p < 0.03). In patients, alMRI induced an increase in T2-value for ROI1-3 (23%, 18% and 5%) and a decrease for ROI4 (3%) and ROI5 (24%). More pronounced load-induced decrease was detected in ROI4 in controls (9%/p = 0.03), while a higher absolute T2-value was found for ROI5 during alMRI in patients (38 ms) compared to controls (33 ms) (p = 0.04).

CONCLUSION

The alMRI-induced differences in T2-value in ROI4 and ROI5 between patients and controls most probably indicate biomechanical impairment in the posterior IVD regions. Hence, alMRI combined with T2-mapping offers an objective and clinical feasible tool for biomechanical IVD characterization that may deepen the knowledge regarding how LBP is related to altered IVD matrix composition. These slides can be retrieved under Electronic Supplementary Material.

Nature-Inspired Hydrogels with Soft and Stiff Zones that Exhibit a 100-Fold Difference in Elastic Modulus

Many biological materials, such as the squid beak and the spinal disc, have a combination of stiff and soft parts with very different mechanical properties, for example, the elastic modulus (stiffness) of the stiffest part of the squid beak is about 100 times that of the softest part. Researchers have attempted to mimic such structures using hydrogels but have not succeeded in synthesizing bulk gels with such large variations in moduli. Here, we present a general approach that can be used to form hydrogels with two or more zones having appreciably different mechanical characters. For this purpose, we use a technique developed in our lab for creating hybrid hydrogels with distinct zones. For the soft zone of the gel, we form a polymer network using a conventional acrylic monomer [ N, N'-dimethylacrylamide (DMAA)] and with laponite (LAP) nanoparticles as the cross-linkers. For the stiff zone, we combine DMAA, LAP, and a methacrylated silica precursor ([3-(methacryloyloxy)-propyl]trimethoxy-silane). When this mixture is polymerized, nanoscale silica particles (∼300 nm in diameter) are formed, and these serve as additional cross-links between the polymer chains, making this network very stiff. The unique character of each zone is preserved in the hybrid gel, and different zones are covalently linked to each other, thereby ensuring robust interfaces. Rheological measurements show that the elastic modulus of the stiff zone can be more than 100 times that of the soft zone. This ratio of moduli is the highest reported to date in a single, continuous gel and is comparable to the ratio in the squid beak. We present different variations of our soft-stiff hybrid gels, including multizone cylinders and core-shell discs. Such soft-stiff gels could have utility in bioengineering, such as in interfacing stiff medical implants with soft tissues.

Frequency-dependent shear properties of annulus fibrosus and nucleus pulposus by magnetic resonance elastography

Aging and degeneration are associated with changes in mechanical properties in the intervertebral disc, generating interest in the establishment of mechanical properties as early biomarkers for the degenerative cascade. Magnetic resonance elastography (MRE) of the intervertebral disc is usually limited to the nucleus pulposus, as the annulus fibrosus is stiffer and less hydrated. The objective of this work was to adapt high-frequency needle MRE to the characterization of the shear modulus of both the nucleus pulposus and annulus fibrosus. Bovine intervertebral discs were removed from fresh oxtails and characterized by needle MRE. The needle was inserted in the center of the disc and vibrations were generated by an amplified piezoelectric actuator. MRE acquisitions were performed on a 4.7-T small-animal MR scanner using a spin echo sequence with sinusoidal motion encoding gradients. Acquisitions were repeated over a frequency range of 1000-1800 Hz. The local frequency estimation inversion algorithm was used to compute the shear modulus. Stiffness maps allowed the visualization of the soft nucleus pulposus surrounded by the stiffer annulus fibrosus surrounded by the homogeneous gel. A significant difference in shear modulus between the nucleus pulposus and annulus fibrosus, and an increase in the shear modulus with excitation frequency, were observed, in agreement with the literature. This study demonstrates that global characterization of both the nucleus pulposus and annulus fibrosus of the intervertebral disc is possible with needle MRE using a preclinical magnetic resonance imaging (MRI) scanner. MRE can be a powerful method for the mapping of the complex properties of the intervertebral disc. The developed method could be adapted for in situ use by preserving adjacent vertebrae and puncturing the side of the intervertebral disc, thereby allowing an assessment of the contribution of osmotic pressure to the mechanical behavior of the intervertebral disc.

Short Link N promotes disc repair in a rabbit model of disc degeneration

Background

The degeneration of the intervertebral disc (IVD) is characterized by proteolytic degradation of the extracellular matrix, and its repair requires the production of an extracellular matrix with a high proteoglycan-to-collagen ratio characteristic of a nucleus pulposus (NP)-like phenotype in vivo. At the moment, there is no medical treatment to reverse or even retard disc degeneration. The purpose of the present study was to determine if a low dose of short link N (sLN), a recently discovered fragment of the link N peptide, could behave in a manner similar to that of link N in restoring the proteoglycan content and proteoglycan-to-collagen ratio of the disc in a rabbit model of IVD degeneration, as an indication of its potential therapeutic benefit in reversing disc degeneration.

Methods

Adolescent New Zealand white rabbits received an annular puncture with an 18-gauge needle into two noncontiguous discs to induce disc degeneration. Two weeks later, either saline (10 μL) or sLN (25 μg in 10 μL saline) was injected into the center of the NP. The sLN concentration was empirically chosen at a lower molar concentration equivalent to half that of link N (100 μg in 10 μL). The effect on radiographic, biochemical and histologic changes were evaluated.

Results

Following needle puncture, disc height decreased by about 25–30% within 2 weeks and maintained this loss for the duration of the 12-week study; a single 25-μg sLN injection at 2 weeks partially restored this loss in disc height. sLN injection led to an increase in glycosaminoglycans (GAG) content 12 weeks post-injection in both the NP and annulus fibrosus (AF). There was a trend towards maintaining control disc collagen-content with sLN supplementation and the GAG-to-collagen ratio in the NP was increased when compared to the saline group.

Conclusions

When administered to the degenerative disc in vivo, sLN injection leads to an increase in proteoglycan content and a trend towards maintaining control disc collagen content in both the NP and AF. This is similar to link N when it is administered to the degenerative disc. Thus, pharmacologically, sLN supplementation could be a novel therapeutic approach for treating disc degeneration.

Critical aspects and challenges for intervertebral disc repair and regeneration-Harnessing advances in tissue engineering

Low back pain represents the highest burden of musculoskeletal diseases worldwide and intervertebral disc degeneration is frequently associated with this painful condition. Even though it remains challenging to clearly recognize generators of discogenic pain, tissue regeneration has been accepted as an effective treatment option with significant potential. Tissue engineering and regenerative medicine offer a plethora of exploratory pathways for functional repair or prevention of tissue breakdown. However, the intervertebral disc has extraordinary biological and mechanical demands that must be met to assure sustained success. This concise perspective review highlights the role of the disc microenvironment, mechanical and clinical design considerations, function vs mimicry in biomaterial‐based and cell engineering strategies, and potential constraints for clinical translation of regenerative therapies for the intervertebral disc.

A Qualitative and Quantitative Correlation Study of Lumbar Intervertebral Disc Degeneration Using Glycosaminoglycan Chemical Exchange Saturation Transfer, Pfirrmann Grade, and T1-ρ

BACKGROUND AND PURPOSE

Glycosaminoglycan chemical exchange saturation transfer (gagCEST) imaging allows the direct measurement and mapping of glycosaminoglycans. In this study, we aimed to evaluate the usefulness of gagCEST imaging in the quantitative assessment of intervertebral disc degeneration in a comparison with Pfirrmann grade and T1-ρ measurements.

MATERIALS AND METHODS

Ninety-six lumbar intervertebral discs in 24 volunteers (36.0 ± 8.5 years of age, 21 men and 3 women) were examined with both gagCEST imaging and T1-ρ measurements. The gagCEST imaging was performed at 3T with a saturation pulse with 1.0-second duration and the B₁ amplitude of 0.8 μT followed by imaging by a 2D fast spin-echo sequence. The Z-spectra were obtained at 25 frequency offsets from -3 to +3 ppm (step, 0.25 ppm). A point-by-point B₀ correction was performed with a B₀ map. The gagCEST signal and T1-ρ values were measured in the nucleus pulposus in each intervertebral disc. The Pfirrmann grades were assessed on T2-weighted images.

RESULTS

The gagCEST signal at grade I (5.36% ± 2.79%) was significantly higher than those at Pfirrmann grade II (3.15% ± 1.40%, P = .0006), grade III (0.14% ± 1.03%, P < .0001), grade IV (-1.75% ± 2.82%, P < .0001), and grade V (-1.47% ± 0.36%, P < .0001). The gagCEST signal at grade II was significantly higher than those of grade III (P < .0001), grade IV (P < .0001), and grade V (P < .0001). The gagCEST signal was significantly correlated negatively with Pfirrmann grade (P < .0001) and positively correlated with T1-ρ (P < .0001).

CONCLUSIONS

GagCEST imaging could be a reliable and quantitative technique for assessing intervertebral disc degeneration.

Apparent Diffusion Coefficient of Diffusion-Weighted Imaging in Evaluation of Cervical Intervertebral Disc Degeneration: An Observational Study with 3.0 T Magnetic Resonance Imaging

Aims

To investigate the correlation between the apparent diffusion coefficient (ADC) value and cervical intervertebral disc degeneration in adult symptomatic patients.

Methods

A total of 52 symptomatic and 40 healthy volunteers were included. DWI and routine MRI examinations were performed to their cervical spines. The cervical discs (from C2-C3 to C6-C7) were graded according to the Pfirrmann grading system, and ADC values of the nucleus pulposus (NP) were measured. Differences of the ADC values between different genders and anatomic levels were analyzed; the correlation between the ADC value and the Pfirrmann grade was investigated. The cut-off ADC values of each Pfirrmann grade were calculated.

Results

The mean ADC value of the NP decreased with increasing Pfirrmann grade (I–V) upon both patients and asymptotic volunteers. The ADC value decreased descendingly from C2-C3 to C5-C6 (P < 0.05) and then increased at C6-C7 (P < 0.05). Additionally, the comparison of the ADC values between different genders achieved statistical significance at each anatomical level (P < 0.05), except at C6-C7 (P > 0.05). Significant negative correlations between the ADC value and either age or Pfirrmann grade were observed.

Conclusions

Our preliminary findings suggest that the ADC value obtained by DWI can provide a reliable indicator to evaluate the cervical disc degeneration.

Quantitative MRI in early intervertebral disc degeneration: T1rho correlates better than T2 and ADC with biomechanics, histology and matrix content

Introduction

Low-back pain (LBP) has been correlated to the presence of intervertebral disc (IVD) degeneration on T2-weighted (T2w) MRI. It remains challenging, however, to accurately stage degenerative disc disease (DDD) based on T2w MRI and measurements of IVD height, particularly for early DDD. Several quantitative MRI techniques have been introduced to detect changes in matrix composition signifying early DDD. In this study, we correlated quantitative T2, T1rho and Apparent Diffusion Coefficient (ADC) values to disc mechanical behavior and gold standard early DDD markers in a graded degenerated lumbar IVD caprine model, to assess their potential for early DDD detection.

Methods

Lumbar caprine IVDs were injected with either 0.25 U/ml or 0.5 U/ml Chondroïtinase ABC (Cabc) to trigger early DDD-like degeneration. Injection with phosphate-buffered saline (PBS) served as control. IVDs were cultured in a bioreactor for 20 days under axial physiological loading. High-resolution 9.4 T MR images were obtained prior to intervention and after culture. Quantitative MR results were correlated to recovery behavior, histological degeneration grading, and the content of glycosaminoglycans (GAGs) and water.

Results

Cabc-injected IVDs showed aberrancies in biomechanics and loss of GAGs without changes in water-content. All MR sequences detected changes in matrix composition, with T1rho showing largest changes pre-to-post in the nucleus, and significantly more than T2 and ADC. Histologically, degeneration due to Cabc injection was mild. T1rho nucleus values correlated strongest with altered biomechanics, histological degeneration score, and loss of GAGs.

Conclusions

T2- and T1rho quantitative MR-mapping detected early DDD changes. T1rho nucleus values correlated better than T2 and ADC with biomechanical, histological, and GAG changes. Clinical implementation of quantitative MRI, T1rho particularly, could aid in distinguishing DDD more reliably at an earlier stage in the degenerative process.

Diffusion-weighted 7.0T Magnetic Resonance Imaging in Assessment of Intervertebral Disc Degeneration in Rats

Background:

Intervertebral disc degeneration (IDD) is a major cause of disc protrusion, likely to be associated with decrease of water content. This research aimed to evaluate IDD by diffusion-weighted imaging (DWI) with a 7.0 Tesla (T) magnetic resonance imaging (MRI) machine.

Methods:

A total of 24 healthy Sprague-Dawley rats were randomly selected and divided into four groups (A, B, C, and D), each consisting of 3 male and 3 female rats (28, 42, 56, and 70 days old, respectively). All the rats were imaged with a 7.0T MRI, producing T2WI, T1WI, and functional DWI sequences. Data were collected and apparent diffusion coefficient (ADC) charts were constructed. Nucleus pulposus and annulus fibrosus regions were identified, several regions of interest were chosen, and their ADC values were obtained. After imaging, rats were sacrificed and their intervertebral discs (L1–L6) were dissected, yielding a total of 144 discs. Protein was extracted for the purpose of Western blotting. Comparison among multiple samples used one-way analysis of variance and least significant difference methods.

Results:

7.0T MRI revealed evident decrease in signal intensity within intervertebral discs of Sprague-Dawley rats with age. Intervertebral disc ADC values significantly decreased from Group A (0.00154 ± 0.00008) to Group D (0.00107 ± 0.00007; P < 0.01); nucleus pulposus ADC values significantly decreased from Group A (0.00164 ± 0.00005) to Group D (0.00140 ± 0.00007; P < 0.01) and annulus fibrosus ADC values significantly decreased from Group A (0.00129 ± 0.00014) to Group D (0.00082 ± 0.00012; P < 0.01). Meanwhile, it also revealed evident decrease from high spinal level to low spinal level: nucleus pulposus ADC values in Group A significantly decreased from L1/L2 (0.00163 ± 0.00006) to L6/S1 (0.00139 ± 0.00004; P < 0.01). While annulus fibrosus ADC values did not differ significantly between levels in Group A (P > 0.05). Western blotting showed that aggrecan content of intervertebral discs decreased from Group A (1.88 ± 0.16) to Group D (0.17 ± 0.04) with age (P < 0.01); Type II collagen content of intervertebral discs decreased from Group A (2.22 ± 0.04) to Group D (0.20 ± 0.01) with age (P < 0.01). No significant differences in aggrecan and Type II collagen content of L1–L6 intervertebral discs in Group A were noted (P > 0.05). Mean ADC values of different intervertebral regions were positively correlated with aggrecan and Type II collagen content (aggrecan: r = 0.631, P < 0.01; Type II collagen: r = 0.680, P < 0.01).

Conclusion:

7.0T MRI-DWI could be applied to effectively diagnose and research early IDD in tiny variations.

A Histopathological Scheme for the Quantitative Scoring of Intervertebral Disc Degeneration and the Therapeutic Utility of Adult Mesenchymal Stem Cells for Intervertebral Disc Regeneration

The purpose of this study was to develop a quantitative histopathological scoring scheme to evaluate disc degeneration and regeneration using an ovine annular lesion model of experimental disc degeneration. Toluidine blue and Haematoxylin and Eosin (H&E) staining were used to evaluate cellular morphology: (i) disc structure/lesion morphology; (ii) proteoglycan depletion; (iii) cellular morphology; (iv) blood vessel in-growth; (v) cell influx into lesion; and (vi) cystic degeneration/chondroid metaplasia. Three study groups were examined: 5 × 5 mm lesion; 6 × 20 mm lesion; and 6 × 20 mm lesion plus mesenchymal stem cell (MSC) treatment. Lumbar intervertebral discs (IVDs) were scored under categories (i-vi) to provide a cumulative score, which underwent statistical analysis using STATA software. Focal proteoglycan depletion was associated with 5 × 5 mm annular rim lesions, bifurcations, annular delamellation, concentric and radial annular tears and an early influx of blood vessels and cells around remodeling lesions but the inner lesion did not heal. Similar features in 6 × 20 mm lesions occurred over a 3-6-month post operative period. MSCs induced a strong recovery in discal pathology with a reduction in cumulative histopathology degeneracy score from 15.2 to 2.7 (p = 0.001) over a three-month recovery period but no recovery in carrier injected discs.

Hybrid Rigid-Deformable Model for Prediction of Neighboring Intervertebral Disk Loads During Flexion Movement After Lumbar Interbody Fusion at L3-4 Level

Knowledge of spinal loads in neighboring disks after interbody fusion plays an important role in the clinical decision of this treatment as well as in the elucidation of its effect. However, controversial findings are still noted in the literature. Moreover, there are no existing models for efficient prediction of intervertebral disk stresses within annulus fibrosus (AF) and nucleus pulposus (NP) regions. In this present study, a new hybrid rigid-deformable modeling workflow was established to quantify the mechanical stress behaviors within AF and NP regions of the L1-2, L2-3, and L4-5 disks after interbody fusion at L3-4 level. The changes in spinal loads were compared with results of the intact model without interbody fusion. The fusion outcomes revealed maximal stress changes (10%) in AF region of L1-2 disk and in NP region of L2-3 disk. The minimal stress change (1%) is noted at the NP region of the L1-2 disk. The validation of simulation outcomes of fused and intact lumbar spine models against those of other computational models and in vivo measurements showed good agreements. Thus, this present study may be used as a novel design guideline for a specific implant and surgical scenario of the lumbar spine disorders.

Cell-based therapies for intervertebral disc and cartilage regeneration- Current concepts, parallels, and perspectives

Lower back pain from degenerative disc disease represents a global health burden, and presents a prominent opportunity for regenerative therapeutics. While current regenerative therapies such as autologous disc chondrocyte transplantation (ADCT), allogeneic juvenile chondrocyte implantation (NuQu®), and immunoselected allogeneic adipose derived precursor cells (Mesoblast) show exciting clinical potential, limitations remain. The heterogeneity of preclinical approaches and the paucity of clinical guidance have limited translational outcomes in disc repair, lagging almost a decade behind cartilage repair. Advances in cartilage repair have evolved to single step approaches with improved orthopedic repair and regeneration. Elements from cartilage regeneration endeavors could be adopted and applied to harness translatable approaches and deliver a clinically and economically feasible regenerative surgery for back pain. In this article, we trace the developments behind the translational success of cartilage repair, examine elements to consider in achieving disc regeneration, and the need for surgical redesign. We further discuss clinical parameters, objectives, and coordination required to deliver improved regenerative surgery. Cell source, processing, and delivery modalities are key issues to be addressed in considering surgical redesign. Advances in biomanufacturing, tissue cryobanking, and point of care cell processing technology may enable intraoperative solutions for single step procedures. To maximize translational success a triad partnership between clinicians, industry, and researchers will be critical in providing instructive clinical guidelines for design as well as practical and economic considerations. This will allow a consensus in research ventures and add regenerative surgery into the algorithm in managing and treating a debilitating condition such as back pain. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:8-22, 2017.

AGEs induce ectopic endochondral ossification in intervertebral discs

Ectopic calcifications in intervertebral discs (IVDs) are known characteristics of IVD degeneration that are not commonly reported but may be implicated in structural failure and dysfunctional IVD cell metabolic responses. This study investigated the novel hypothesis that ectopic calcifications in the IVD are associated with advanced glycation end products (AGEs) via hypertrophy and osteogenic differentiation. Histological analyses of human IVDs from several degeneration stages revealed areas of ectopic calcification within the nucleus pulposus and at the cartilage endplate. These ectopic calcifications were associated with cells positive for the AGE methylglyoxal-hydroimidazolone-1 (MG-H1). MG-H1 was also co-localised with Collagen 10 (COL10) and Osteopontin (OPN) suggesting osteogenic differentiation. Bovine nucleus pulposus and cartilaginous endplate cells in cell culture demonstrated that 200 mg/mL AGEs in low-glucose media increased ectopic calcifications after 4 d in culture and significantly increased COL10 and OPN expression. The receptor for AGE (RAGE) was involved in this differentiation process since its inhibition reduced COL10 and OPN expression. We conclude that AGE accumulation is associated with endochondral ossification in IVDs and likely acts via the AGE/RAGE axis to induce hypertrophy and osteogenic differentiation in IVD cells. We postulate that this ectopic calcification may play an important role in accelerated IVD degeneration including the initiation of structural defects. Since orally administered AGE and RAGE inhibitors are available, future investigations on AGE/RAGE and endochondral ossification may be a promising direction for developing non-invasive treatment against progression of IVD degeneration.

Interobserver and Test-Retest Reproducibility of T1ρ and T2 Measurements of Lumbar Intervertebral Discs by 3T Magnetic Resonance Imaging

Objective

To investigate the interobserver and test-retest reproducibility of T1ρ and T2 measurements of lumbar intervertebral discs using 3T magnetic resonance imaging (MRI).

Materials and Methods

This study included a total of 51 volunteers (female, 26; male, 25; mean age, 54 ± 16.3 years) who underwent lumbar spine MRI with a 3.0 T scanner. Amongst these subjects, 40 underwent repeat T1ρ and T2 measurement acquisitions with identical image protocol. Two observers independently performed the region of interest measurements in the nuclei pulposi of the discs from L1–2 through L5–S1 levels. Statistical analysis was performed using intraclass correlation coefficient (ICC) with a two-way random model of absolute agreement. Comparison of the ICC values was done after acquisition of ICC values using Z test. Statistical significance was defined as p value < 0.05.

Results

The ICCs of interobserver reproducibility were 0.951 and 0.672 for T1ρ and T2 mapping, respectively. The ICCs of test-retest reproducibility (40 subjects) for T1ρ and T2 measurements were 0.922 and 0.617 for observer A and 0.914 and 0.628 for observer B, respectively. In the comparison of the aforementioned ICCs, ICCs of interobserver and test-retest reproducibility for T1ρ mapping were significantly higher than T2 mapping (p < 0.001).

Conclusion

The interobserver and test-retest reproducibility of T1ρ mapping were significantly higher than those of T2 mapping for the quantitative assessment of nuclei pulposi of lumbar intervertebral discs.

Design Requirements for Annulus Fibrosus Repair: Review of Forces, Displacements, and Material Properties of the Intervertebral Disk and a Summary of Candidate Hydrogels for Repair

There is currently a lack of clinically available solutions to restore functionality to the intervertebral disk (IVD) following herniation injury to the annulus fibrosus (AF). Microdiscectomy is a commonly performed surgical procedure to alleviate pain caused by herniation; however, AF defects remain and can lead to accelerated degeneration and painful conditions. Currently available AF closure techniques do not restore mechanical functionality or promote tissue regeneration, and have risk of reherniation. This review determined quantitative design requirements for AF repair materials and summarized currently available hydrogels capable of meeting these design requirements by using a series of systematic PubMed database searches to yield 1500+ papers that were screened and analyzed for relevance to human lumbar in vivo measurements, motion segment behaviors, and tissue level properties. We propose a testing paradigm involving screening tests as well as more involved in situ and in vivo validation tests to efficiently identify promising biomaterials for AF repair. We suggest that successful materials must have high adhesion strength (∼0.2 MPa), match as many AF material properties as possible (e.g., approximately 1 MPa, 0. 3 MPa, and 30 MPa for compressive, shear, and tensile moduli, respectively), and have high tensile failure strain (∼65%) to advance to in situ and in vivo validation tests. While many biomaterials exist for AF repair, few undergo extensive mechanical characterization. A few hydrogels show promise for AF repair since they can match at least one material property of the AF while also adhering to AF tissue and are capable of easy implantation during surgical procedures to warrant additional optimization and validation.

Effects of motion segment level, Pfirrmann intervertebral disc degeneration grade and gender on lumbar spine kinematics

MRI allows non-invasive assessment of intervertebral disc degeneration with the added clinical benefit of using non-ionizing radiation. What has remained unclear is the relationship between assessed disc degeneration and lumbar spine kinematics. Kinematic outcomes of 54 multi-segment (L1-Sacrum) lumbar spine specimens were calculated to discover if such an underlying relationship exists with degeneration assessed using the Pfirrmann grading system. Further analyses were also conducted to determine if kinematic outcomes were affected by motion segment level, gender or applied compressive preload. Range of motion, hysteresis, high flexibility zone size and rotational stiffness in flexion-extension, lateral bending and axial rotation were the kinematic outcomes. Caudal intervertebral discs in our study sample were more degenerative than cranial discs. L5-S1 discs had the largest flexion-extension range of motion (p < 0.005) and L1-L2 discs the lowest flexion high flexibility zone size (p < 0.013). No other strict cranial-caudal differences in kinematic outcomes were found. Low flexibility zone rotational stiffness increased with disc degeneration grade in extension, lateral bending and axial rotation (p < 0.001). Trends towards higher hysteresis and lower range of motion with increased degeneration were observed in flexion-extension and lateral bending. Applied compressive preload increased flexion-extension hysteresis and augmented the effect of degeneration on hysteresis (p < 0.0005). Female specimens had about one degree larger range of motion in all rotational modes, and higher flexion extension hysteresis (p = 0.016). These results suggest that gender differences exist in lumbar spine kinematics. Additionally high disc loads, applied compressive preload or applied moment, are needed to kinematically distinguish discs with different levels of degeneration. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1389-1398, 2016.

Correlations between quantitative T2 and T1ρ MRI, mechanical properties and biochemical composition in a rabbit lumbar intervertebral disc degeneration model

Improved diagnostic measures for intervertebral disc degeneration are necessary to facilitate early detection and treatment. The aim of this study was to correlate changes in mechanical and biochemical properties with the quantitative MRI parameters T2 and T1ρ in rabbit lumbar discs using an ex vivo chymopapain digestion model. Rabbit lumbar spinal motion segments from animals less than 6 months of age were injected with 100 μl of saline (control) or chymopapain at 3, 15, or 100 U/ml (n = 5 per group). T2 and T1ρ MRI series were obtained at 4.7T. Specimens were mechanically tested in tension-compression and creep. Normalized nucleus pulposus (NP) water and GAG contents were quantified. Stepwise multiple linear regression was performed to determine which parameters contributed significantly to changes in NP T2 and T1ρ. When all groups were included, multiple regression yielded a model with GAG, compressive modulus, and the creep time constants as variables significantly impacting T2 (multiple r(2)  = 0.64, p = 0.006). GAG and neutral zone (NZ) modulus were identified as variables contributing to T1ρ (multiple r(2)  = 0.28, p = 0.08). When specimens with advanced degeneration were excluded from the multiple regression analysis, T2 was significantly predicted by compressive modulus, τ1, and water content (multiple r(2)  = 0.71, p = 0.009), while no variables were significant predictors in the model for T1ρ. These results indicate that quantitative MRI can detect changes in the mechanical and biochemical properties of the degenerated disc. T2 may be more sensitive to early stage degenerative changes than T1ρ, while both quantitative MRI parameters are sensitive to advanced degeneration. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1382-1388, 2016.

Comparison of three approaches for defining nucleus pulposus and annulus fibrosus on sagittal magnetic resonance images of the lumbar spine

Objective

To compare three methods commonly used in the literature to define intervertebral disc nucleus pulposus (NP) and annulus fibrosus (AF) on magnetic resonance (MR) images.

Methods

Fifty-two patients (26 males and 26 females; age range, 23-76 years) were recruited for this study; they underwent standard T1/T2-weighted MR imaging, and T2 and T1rho mapping acquisitions. The corresponding midsagittal images were analysed and a total of 256 discs were evaluated, using three different region-of-interest (ROI) drawing methods: (1) radiologist-guided manual ROI (M-ROI); (2) five square ROIs where each measured 20% of the midline disc diameter (5-ROI); and (3) seven square ROIs placed horizontally from anterior to posterior (7-ROI) to define NP and AF. The agreement between the three ROI methods was assessed using intraclass correlation coefficient values and Bland-Altman plots.

Results

Inner AF and NP could not be differentiated on T1/T2-weighted MR imaging, T2 maps, or T1rho maps. The intraclass correlation coefficient values were all > 0.75 when comparing the 5-/7-ROI methods with the M-ROI methods for NP, and 0.167-0.488 for AF when comparing the 7-ROI method with the M-ROI method. The intraclass correlation coefficient values for AF increased to 0.378-0.582 for the M-ROI method compared with the 5-ROI method. Comparable results were obtained with Bland-Altman plots.

Conclusion

The 5-/7-ROI methods agreed with the M-ROI approach for NP selection, while the agreement with AF was moderate to poor, with the 5-ROI method showing slight advantage over the 7-ROI method. Cautions should be taken to interpret the MR relaxometry findings when 5-/7-ROI methods are used to select AF.

Sensitivity of MRI parameters within intervertebral discs to the severity of adolescent idiopathic scoliosis

PURPOSE

To measure magnetic resonance imaging (MRI) parameters including relaxation times (T₁ ρ, T₂ ), magnetization transfer (MT) and diffusion parameters (mean diffusivity [MD], fractional anisotropy [FA]) of intervertebral discs in adolescents with idiopathic scoliosis, and to investigate the sensitivity of these MR parameters to the severity of the spine deformities.

MATERIALS AND METHODS

Thirteen patients with adolescent idiopathic scoliosis and three control volunteers with no history of spine disease underwent an MRI acquisition at 3T including the mapping of T₁ ρ, T₂ , MT, MD, and FA. The apical zone included all discs within the scoliotic curve while the control zone was composed of other discs. The severity was analyzed through low (<32°) versus high (>40°) Cobb angles. One-way analysis of variance (ANOVA) and agglomerative hierarchical clustering (AHC) were performed.

RESULTS

Significant differences were found between the apical zone and the control zone for T₂ (P = 0.047), and between low and high Cobb angles for T₂ (P = 0.014) and MT (P = 0.002). AHC showed two distinct clusters, one with mainly low Cobb angles and one with mainly high Cobb angles, for the MRI parameters measured within the apical zone, with an accuracy of 0.9 and a Matthews correlation coefficient (MCC) of 0.8. Within the control zone, the AHC showed no clear classification (accuracy of 0.6 and MCC of 0.2).

CONCLUSION

We successfully performed an in vivo multiparametric MRI investigation of young patients with adolescent idiopathic scoliosis. The MRI parameters measured within the intervertebral discs were found to be sensitive to intervertebral disc degeneration occurring with scoliosis and to the severity of scoliosis. J. Magn. Reson. Imaging 2016;44:1123-1131.

Long-Term Results and Efficacy of Laminectomy with Fusion Versus Young Laminoplasty for the Treatment of Degenerative Spinal Stenosis

OBJECTIVE

In the treatment of degenerative lumbar stenosis, facet-sparing laminectomy with instrumented fusion (FSL) was recently almost totally replaced by less invasive, allegedly equally effective surgical techniques. We performed a long-term comparison between outcomes after Young laminoplasty (YL) as a representative of the less invasive technique and FSL.

METHODS

From December 4, 2000, to March 11, 2005, 56 patients with a history of neurogenic claudication and radiologically verified absolute lumbar stenosis were surgically treated. After applying inclusion and exclusion criteria, 44 patients were enrolled.

RESULTS

Using the Oswestry Disability Index scale, significant improvement on 1-year and 8-year follow-up examinations was noticed in the FSL and YL groups. The Oswestry Disability Index was significantly better in the FSL group compared with the YL group at the 8-year follow-up (27.82 ± 1.918 vs. 40.74 ± 2.163).

CONCLUSIONS

FSL is a more invasive and more expensive surgical technique than YL. In a short-term and long-term follow-up comparison, FSL is a more successful operative technique, and the difference increases over time in favor of FSL.

Identification of the potential molecular targets for human intervertebral disc degeneration based on bioinformatic methods

The present study aimed to explore potential molecular targets and gain further insights into the mechanism of intervertebral disc degeneration (IDD) progression. Microarray datasets of GSE19943, GSE15227 and GSE34095 were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) in 3 IDD specimens compared with 3 controls in GSE34095, DEGs in 7 grade III and 3 grade IV samples compared with 5 grade II samples in GSE19943, and differentially expressed miRNAs in 3 degenerated samples compared with 3 controls in GSE15227 were screened. Grade III‑ and IV‑specific networks were constructed and grade‑specific genes were extracted. The network features were analyzed, followed by Gene Ontology (GO) enrichment analysis and pathway enrichment analysis of grade‑specific genes and DEGs identified in GSE34095. Furthermore, miRNA‑pathway interactions were analyzed using Fisher's exact test. Tumor protein p53 (TP53) was a hub gene in the grade III‑specific network and ubiquitin C (UBC) was identified to be a hub gene in the grade IV‑specific network. Six significant features were identified by grade‑specific network topology analysis. Grade‑specific genes and DEGs were involved in different GO terms and pathways. Differentially expressed miRNAs were identified to participate in 35 pathways, among which 6 pathways were significantly enriched by DEGs, including apoptosis. The present study identified that key genes (TP53 and UBC) and miR‑129‑5p may participate in the mechanism of IDD progression. Thus, they may be potential therapeutic targets for IDD.

Quantitative T2 relaxation time and magnetic transfer ratio predict endplate biochemical content of intervertebral disc degeneration in a canine model

Background

Direct measurement of disc biochemical content is impossible in vivo. Therefore, magnetic resonance imaging (MRI) is used to evaluate disc health. Unfortunately, current clinical imaging techniques do not adequately assess degeneration, especially in the early stage of cartilage endplate, and subchondral bone zone (CEPZ). Therefore, this study aimed to investigate the sensitivity of quantitative MRI methods, namely T2 relaxation time and Magnetic Transfer Ratio (MTR), to identify early disc degeneration, especially for the CEPZ, using an experimental canine model of intervertebral disc injury and to investigate their sensitivity in depicting biochemically and histologically controlled degenerative changes in the disc.

Methods

Sixteen juvenile dogs underwent iatrogenic annular disruption via stab incisions. The animals underwent repeated 3.0 T MR imaging, and were sacrificed 4, 8, and 12 weeks post-operatively. A continuous rectangle drawing method was used to select regions of interest for the intervertebral disc from the cephalic to caudal CEPZ including the vertebrae, nucleus pulposus (NP) and annulus fibrosus (AF), which resembled pixel measurement for imaging analysis. Presence of degenerative changes was controlled by biochemical and histological analyses. The correlations between histological score, biochemical content, and quantitative MRI signal intensities were also analyzed.

Results

Both T2 relaxation time and MTR values changed for CEPZ, NP, and AF tissues within 12 weeks. T2 relaxation time values decreased significantly in the NP, AF, and CEPZ separately at pre-operation, 4, 8, and 12 weeks when compared each time (P < 0.05). MTR values showed no significant differences for the CEPZ between 8 and 4 weeks or 12 weeks, or compared to pre-operative values; there were significant differences for the AF. Biochemical and histological analysis showed changes consistent with quantitative MRI signal intensities for early stage degeneration.

Conclusions

Early traumatic or degenerative changes are detectable with both T2 and MTR. T2 changes were more sensitive to the differences in disc status, especially for the CEPZ. Since T2 and MTR reflect different disc properties, performing both imaging under the same conditions would be helpful in the evaluation of disc degeneration. The continuous rectangle drawing can be a sensitive method to detect the changes of CEPZ.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-015-0610-6) contains supplementary material, which is available to authorized users.

Developments in intervertebral disc disease research: pathophysiology, mechanobiology, and therapeutics

Low back pain is a leading cause of disability worldwide and the second most common cause of physician visits. There are many causes of back pain, and among them, disc herniation and intervertebral disc degeneration are the most common diagnoses and targets for intervention. Currently, clinical treatment outcomes are not strongly correlated with diagnoses, emphasizing the importance for characterizing more completely the mechanisms of degeneration and their relationships with symptoms. This review covers recent studies elucidating cellular and molecular changes associated with disc mechanobiology, as it relates to degeneration and regeneration. Specifically, we review findings on the biochemical changes in disc diseases, including cytokines, chemokines, and proteases; advancements in disc disease diagnostics using imaging modalities; updates on studies examining the response of the intervertebral disc to injury; and recent developments in repair strategies, including cell-based repair, biomaterials, and tissue engineering. Findings on the effects of the omega-6 fatty acid, linoleic acid, on nucleus pulposus tissue engineering are presented. Studies described in this review provide greater insights into the pathogenesis of disc degeneration and may define new paradigms for early or differential diagnostics of degeneration using new techniques such as systemic biomarkers. In addition, research on the mechanobiology of disease enriches the development of therapeutics for disc repair, with potential to diminish pain and disability associated with disc degeneration.

T1ρ and T2 mapping of the intervertebral disk: comparison of different methods of segmentation

BACKGROUND AND PURPOSE

Intervertebral disk biochemical composition could be accessed in vivo by T1ρ and T2 relaxometry. We found no studies in the literature comparing different segmentation methods for data extraction using these techniques. Our aim was to compare different manual segmentation methods used to extract T1ρ and T2 relaxation times of intervertebral disks from MR imaging. Seven different methods of partial-disk segmentation techniques were compared with whole-disk segmentation as the reference standard.

MATERIALS AND METHODS

Sagittal T1ρ and T2 maps were generated by using a 1.5T MR imaging scanner in 57 asymptomatic volunteers 20-40 years of age. Two hundred eighty-five lumbar disks were separated into 2 groups: nondegenerated disk (Pfirrmann I and II) and degenerated disk (Pfirrmann III and IV). In whole-disk segmentation, the disk was segmented in its entirety on all sections. Partial-disk segmentation methods included segmentation of the disk into 6, 5, 4, 3, and 1 sagittal sections. Circular ROIs positioned in the nucleus pulposus and annulus fibrosus were also used to extract T1ρ and T2, and data were compared with whole-disk segmentation

RESULTS

In the nondegenerated group, segmentation of ≥5 sagittal sections showed no statistical difference with whole-disk segmentation. All the remaining partial-disk segmentation methods and circular ROIs showed different results from whole-disk segmentation (P < .001). In the degenerated disk group, all methods were statistically similar to whole-disk segmentation. All partial-segmentation methods, including circular ROIs, showed strong linear correlation with whole-disk segmentation in both the degenerated and nondegenerated disk groups.

CONCLUSIONS

Manual segmentation showed strong reproducibility for T1ρ and T2 and strong linear correlation between partial- and whole-disk segmentation. Absolute T1ρ and T2 values extracted from different segmentation techniques were statistically different in disks with Pfirrmann grades I and II.

On the relative relevance of subject-specific geometries and degeneration-specific mechanical properties for the study of cell death in human intervertebral disk models

Capturing patient- or condition-specific intervertebral disk (IVD) properties in finite element models is outmost important in order to explore how biomechanical and biophysical processes may interact in spine diseases. However, disk degenerative changes are often modeled through equations similar to those employed for healthy organs, which might not be valid. As for the simulated effects of degenerative changes, they likely depend on specific disk geometries. Accordingly, we explored the ability of continuum tissue models to simulate disk degenerative changes. We further used the results in order to assess the interplay between these simulated changes and particular IVD morphologies, in relation to disk cell nutrition, a potentially important factor in disk tissue regulation. A protocol to derive patient-specific computational models from clinical images was applied to different spine specimens. In vitro, IVD creep tests were used to optimize poro-hyperelastic input material parameters in these models, in function of the IVD degeneration grade. The use of condition-specific tissue model parameters in the specimen-specific geometrical models was validated against independent kinematic measurements in vitro. Then, models were coupled to a transport-cell viability model in order to assess the respective effects of tissue degeneration and disk geometry on cell viability. While classic disk poro-mechanical models failed in representing known degenerative changes, additional simulation of tissue damage allowed model validation and gave degeneration-dependent material properties related to osmotic pressure and water loss, and to increased fibrosis. Surprisingly, nutrition-induced cell death was independent of the grade-dependent material properties, but was favored by increased diffusion distances in large IVDs. Our results suggest that in situ geometrical screening of IVD morphology might help to anticipate particular mechanisms of disk degeneration.

Population average T2 MRI maps reveal quantitative regional transformations in the degenerating rabbit intervertebral disc that vary by lumbar level

Magnetic resonance imaging (MRI) with T2-weighting is routinely performed to assess intervertebral disc degeneration. Standard clinical evaluations of MR images are qualitative, however, and do not focus on region-specific alterations in the disc. Utilizing a rabbit needle puncture model, T2 mapping was performed on injured discs to develop a quantitative description of the degenerative process following puncture. To do so, an 18G needle was inserted into four discs per rabbit (L3/L4 to L6/L7) and T2 maps were generated pre- and 4 weeks post-injury. Individual T2 maps were normalized to a disc-specific coordinate system and then averaged for pre- and post-injury population composite T2 maps. We also developed a method to automatically segment the nucleus pulposus by fitting the NP region of the T2 maps with modified 2-D and 3-D Gaussian distribution functions. Puncture injury produced alterations in MR signal intensity in a region-specific manner mirroring human degeneration. Population average T2 maps provided a quantitative representation of the injury response, and identified deviations of individual degenerate discs from the pre-injury population. We found that the response to standardized injury was modest at lower lumbar levels, likely as a result of increased disc dimensions. These tools will be valuable for the quantitative characterization of disc degeneration in future clinical and pre-clinical studies.

Finite element based nonlinear normalization of human lumbar intervertebral disc stiffness to account for its morphology

Disc degeneration, usually associated with low back pain and changes of intervertebral stiffness, represents a major health issue. As the intervertebral disc (IVD) morphology influences its stiffness, the link between mechanical properties and degenerative grade is partially lost without an efficient normalization of the stiffness with respect to the morphology. Moreover, although the behavior of soft tissues is highly nonlinear, only linear normalization protocols have been defined so far for the disc stiffness. Thus, the aim of this work is to propose a nonlinear normalization based on finite elements (FE) simulations and evaluate its impact on the stiffness of human anatomical specimens of lumbar IVD. First, a parameter study involving simulations of biomechanical tests (compression, flexion/extension, bilateral torsion and bending) on 20 FE models of IVDs with various dimensions was carried out to evaluate the effect of the disc's geometry on its compliance and establish stiffness/morphology relations necessary to the nonlinear normalization. The computed stiffness was then normalized by height (H), cross-sectional area (CSA), polar moment of inertia (J) or moments of inertia (Ixx, Iyy) to quantify the effect of both linear and nonlinear normalizations. In the second part of the study, T1-weighted MRI images were acquired to determine H, CSA, J, Ixx and Iyy of 14 human lumbar IVDs. Based on the measured morphology and pre-established relation with stiffness, linear and nonlinear normalization routines were then applied to the compliance of the specimens for each quasi-static biomechanical test. The variability of the stiffness prior to and after normalization was assessed via coefficient of variation (CV). The FE study confirmed that larger and thinner IVDs were stiffer while the normalization strongly attenuated the effect of the disc geometry on its stiffness. Yet, notwithstanding the results of the FE study, the experimental stiffness showed consistently higher CV after normalization. Assuming that geometry and material properties affect the mechanical response, they can also compensate for one another. Therefore, the larger CV after normalization can be interpreted as a strong variability of the material properties, previously hidden by the geometry's own influence. In conclusion, a new normalization protocol for the intervertebral disc stiffness in compression, flexion, extension, bilateral torsion and bending was proposed, with the possible use of MRI and FE to acquire the discs' anatomy and determine the nonlinear relations between stiffness and morphology. Such protocol may be useful to relate the disc's mechanical properties to its degree of degeneration.

In vivo multifrequency magnetic resonance elastography of the human intervertebral disk

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Screening of hyaluronic acid-poly(ethylene glycol) composite hydrogels to support intervertebral disc cell biosynthesis using artificial neural network analysis

Hyaluronic acid (HA)-poly(ethylene glycol) (PEG) composite hydrogels have been widely studied for both cell delivery and soft tissue regeneration applications. A very broad range of physical and biological properties have been engineered into HA-PEG hydrogels that may differentially affect cellular "outcomes" of survival, synthesis and metabolism. The objective of this study was to rapidly screen multiple HA-PEG composite hydrogel formulations for an effect on matrix synthesis and behaviors of nucleus pulposus (NP) and annulus fibrosus (AF) cells of the intervertebral disc (IVD). A secondary objective was to apply artificial neural network analysis to identify relationships between HA-PEG composite hydrogel formulation parameters and biological outcome measures for each cell type of the IVD. Eight different hydrogels were developed from preparations of thiolated HA (HA-SH) and PEG vinylsulfone (PEG-VS) macromers, and used as substrates for NP and AF cell culture in vitro. Hydrogel mechanical properties ranged from 70 to 489kPa depending on HA molecular weight, and measures of matrix synthesis, metabolite consumption and production and cell morphology were obtained to study relationships to hydrogel parameters. Results showed that NP and AF cell numbers were highest upon the HA-PEG hydrogels formed from the lower-molecular-weight HA, with evidence of higher sulfated glycosaminoglycan production also upon lower-HA-molecular-weight composite gels. All cells formed more multi-cell clusters upon any HA-PEG composite hydrogel as compared to gelatin substrates. Formulations were clustered into neurons based largely on their HA molecular weight, with few effects of PEG molecular weight observed on any measured parameters.

Link N and mesenchymal stem cells can induce regeneration of the early degenerate intervertebral disc

Link N is a naturally occurring peptide that can stimulate proteoglycan synthesis in intervertebral disc (IVD) cells. IVD repair can also potentially be enhanced by mesenchymal stem cell (MSC) supplementation to maximize extracellular matrix (ECM) production. In a previous study, we have shown that Link N can inhibit osteogenesis and increase the chondrogenesis of MSCs in vitro. The aim of the present study was to determine the potential of MSCs and Link N alone or in combination with regard to tissue repair in the degenerate disc. Bovine IVDs with trypsin-induced degeneration were treated with MSCs, Link N, or a combination of MSCs and Link N. Trypsin-treated discs were also injected with phosphate-buffered saline to serve as a degeneration control. The ECM proteins and proteoglycans were extracted from the inner nucleus pulposus (NP) of the discs, and sulfated glycosaminoglycans (GAGs) were analyzed by the dimethyl methylene blue dye-binding assay. The expression of type II collagen was analyzed by western blot. To track the MSCs after injection, MSCs were labeled with PKH67 and observed under confocal microscopy after the 2 week culture period. The GAG content significantly increased compared with the degeneration control when degenerate discs were treated with MSCs, Link N, or a combination of both Link N and MSCs. Histological analysis revealed that the newly synthesized proteoglycan was able to diffuse throughout the ECM and restore tissue content even in areas remote from the cells. The quantity of extractable type II collagen was also increased when the degenerate discs were treated with MSCs and Link N, either alone or together. MSCs survived, integrated in the tissue, and were found distributed throughout the NP after the 2 week culture period. MSCs and Link N can restore GAG content in degenerate discs, when administered separately or together. Treatment with MSCs and Link N can also increase the expression of type II collagen. The results support the concept that biological repair of disc degeneration is feasible, and that the administration of either MSCs or Link N has therapeutic potential in early stages of the disease.

Comparison of intervertebral disc displacements measured under applied loading with MRI at 3.0 T and 9.4 T

The purpose of this study was to compare displacement behavior of cyclically loaded cadaveric human intervertebral discs as measured noninvasively on a clinical 3.0 T and a research 9.4 T MRI system. Intervertebral discs were cyclically compressed at physiologically relevant levels with the same MRI-compatible loading device in the clinical and research systems. Displacement-encoded imaging was synchronized to cyclic loading to measure displacements under applied loading with MRI (dual MRI). Displacements from the two systems were compared individually using linear regression and, across all specimens, using Bland-Altman analysis. In-plane displacement patterns measured at 3.0 T and 9.4 T were qualitatively comparable and well correlated. Bland-Altman analyses showed that over 90% of displacement values within the intervertebral disc regions of interest lay within the limits of agreement. Measurement of displacement using dual MRI using a 3.0 T clinical system is comparable to that of a 9.4 T research system. Additional refinements of software, technique implementation, and image processing have potential to improve agreement between different MRI systems. Despite differences in MRI systems in this initial implementation, this work demonstrates that dual MRI can be reliably implemented at multiple magnetic field strengths, permitting translation of dual MRI for a variety of applications in the study of tissue and biomaterial biomechanics.

Mesenchymal stem cells: potential application in intervertebral disc regeneration

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