Observations on morphologic changes in the aging and degenerating human disc: secondary collagen alterations

How to spot the recurring lumbar disc? Risk factors for recurrent lumbar disc herniation (rLDH) in adult patients with lumbar disc prolapse: a systematic review and meta-analysis

Despite a fast-growing evidence-base examining the relationship of certain clinical and radiological factors such as smoking, BMI and herniation-type with rLDH, there remains much debate around which factors are clinically important. We conducted a systematic review and meta-analysis to identify risk factors for recurrent lumbar disc herniation (rLDH) in adults after primary discectomy. A systematic literature search was carried out using Ovid-Medline, EMBASE, Cochrane library and Web of Science databases from inception to 23rd June-2022. Observational studies of adult patients with radiologically-confirmed rLDH after ≥3 months of the initial surgery were included, and their quality assessed using the Quality-In-Prognostic-Studies (QUIPS) appraisal tool. Meta-analyses of univariate and multivariate data and a sensitivity-analysis for rLDH post-microdiscectomy were performed. Twelve studies (n=4497, mean age:47.3; 34.5% female) were included, and 11 studies (n=4235) meta-analysed. The mean follow-up was 38.4 months. Mean recurrence rate was 13.1% and mean time-to-recurrence was 24.1 months (range: 6-90 months). Clinically, older age (OR:1.04, 95%CI:1.00-1.08, n=1014), diabetes mellitus (OR:3.82, 95%CI:1.58-9.26, n=2330) and smoking (OR:1.80, 95%CI:1.03- 3.14, n=3425) increased likelihood of recurrence. Radiologically, Modic-change type-2 (OR:7.93, 95%CI:5.70-11.05, n=1706) and disc extrusion (OR:12.23, 95%CI:8.60-17.38, n=1706) increased likelihood of recurrence. The evidence did not support an association between rLDH and sex; BMI; occupational labour/driving; alcohol-consumption; Pfirmann- grade, or herniation-level. Older patients, smokers, patients with diabetes, those with type-2 Modic-changes or disc extrusion are more likely to experience rLDH. Higher quality studies with robust adjustment of confounders are required to determine the clinical bearing of all other potential risk factors for rLDH.

Factors associated with incomplete clinical improvement in patients undergoing transforaminal endoscopic lumbar discectomy for lumbar disc herniation

PURPOSES

To analyze the clinical and radiographic risk factors that might predict incomplete clinical improvement after transforaminal endoscopic lumbar discectomy (TELD).

METHODS

A retrospective analysis was conducted from 194 consecutive patients who underwent TELD due to lumbar disc herniation (LDH). Patients with incomplete clinical improvement were defined from patient-reported outcomes of poor improvement in pain or disability after surgery and patient dissatisfaction. Clinical and radiographic characteristics were evaluated to identify predicting factors of poor outcomes.

RESULTS

Of 194 patients who underwent TELD procedures, 32 patients (16.5%) had incomplete clinical improvement and 12 patients (6.1%) required revision surgery. The mean ages were 46.4 years and most of the patients suffered from predominant leg pain (48.9%). The most common surgical level was L4-5 (63.9%). Overall, the Oswestry Disability Index (44.3-15), visual analog scores of back pain (4.9-1.8) and leg pain (7.3-1.6) were significantly improved after surgery. Multivariate logistic regression analysis demonstrated that high body mass index, history of previous surgery, preoperative disability, weakness, and disc degeneration were related to incomplete clinical improvement. There were 15 recurrent LDH (7.7%) with a total of 12 revision surgeries (6.2%).

CONCLUSIONS

We identified independent risk factors associated with incomplete clinical improvement following TELD, including overweight, significant preoperative disability or weakness and history of previous surgery. Advanced age, disc degeneration, vacuum phenomenon, and spondylolisthesis were also possible risk factors. Recognizing these risk factors would help decide whether patients are good candidates for TELD, and optimize the surgical planning preoperatively to achieve good surgical results.

Risk Factors Involved in the Early and Medium-Term Poor Outcomes of Percutaneous Endoscopic Transforaminal Discectomy: A Single-Center Experience

Objective

To investigate the risk factors involved in the early and medium-term poor outcomes of percutaneous endoscopic transforaminal discectomy (PETD) treatment of lumbar disc herniation (LDH) at the L4-5 level.

Methods

Between January 2015 and May 2020, we recruited 148 LDH patients at the L4-5 level who underwent PETD surgery. The patients were divided into Groups A and B, according to the surgical outcomes. Good and excellent outcomes were categorized into Group A, and generally good and poor outcomes were categorized into Group B. Clinical parameters (age, gender, symptom duration, hospital stay, operation time, blood loss, straight-leg raising (SLR), visual analog scale (VAS), Oswestry Disability Index (ODI) score and modified MacNab criteria) and radiologic parameters (foraminal height (FH), intervertebral height index (IHI), intervertebral angle (IVA), sagittal range of motion (sROM), and lumbar lordosis (LL)) were collected and analyzed using univariate and multiple logistic regression analyses.

Results

At the 6-month follow-up post operation, univariate analysis revealed that the symptom duration, SLR, IHI, and sROM were strongly associated with poor outcomes. However, multiple logistic regression analysis demonstrated that prolonged symptom duration, large SLR angel, and large sROM were independent risk factors for poor outcomes. At the 2-year follow-up post operation, univariate analysis suggested that advanced age, prolonged symptom duration, large preoperative VAS score, small FH, small IHI, and large sROM were potential risk factors for poor outcomes. However, multiple logistic regression analysis demonstrated that prolonged symptom duration, small IHI, and large sROM were independent risk factors for poor outcomes.

Conclusion

Our study demonstrated that prolonged symptom duration, large SLR angel, and large sROM were independent risk factors for poor outcomes immediately following PETD at the L4-5 level. However, prolonged symptom duration, small IHI, and large sROM were independent risk factors for poor outcomes at medium-term post PETD at the L4-5 level.

Endoplasmic reticulum stress associates with the development of intervertebral disc degeneration

Endoplasmic reticulum (ER) is an important player in various intracellular signaling pathways that regulate cellular functions in many diseases. Intervertebral disc degeneration (IDD), an age-related degenerative disease, is one of the main clinical causes of low back pain. Although the pathological development of IDD is far from being fully elucidated, many studies have been shown that ER stress (ERS) is involved in IDD development and regulates various processes, such as inflammation, cellular senescence and apoptosis, excessive mechanical loading, metabolic disturbances, oxidative stress, calcium homeostasis imbalance, and extracellular matrix (ECM) dysregulation. This review summarizes the formation of ERS and the potential link between ERS and IDD development. ERS can be a promising new therapeutic target for the clinical management of IDD.

Peptide Location Fingerprinting Reveals Tissue Region-Specific Differences in Protein Structures in an Ageing Human Organ

In ageing tissues, long-lived extracellular matrix (ECM) proteins are susceptible to the accumulation of structural damage due to diverse mechanisms including glycation, oxidation and protease cleavage. Peptide location fingerprinting (PLF) is a new mass spectrometry (MS) analysis technique capable of identifying proteins exhibiting structural differences in complex proteomes. PLF applied to published young and aged intervertebral disc (IVD) MS datasets (posterior, lateral and anterior regions of the annulus fibrosus) identified 268 proteins with age-associated structural differences. For several ECM assemblies (collagens I, II and V and aggrecan), these differences were markedly conserved between degeneration-prone (posterior and lateral) and -resistant (anterior) regions. Significant differences in peptide yields, observed within collagen I α2, collagen II α1 and collagen V α1, were located within their triple-helical regions and/or cleaved C-terminal propeptides, indicating potential accumulation of damage and impaired maintenance. Several proteins (collagen V α1, collagen II α1 and aggrecan) also exhibited tissue region (lateral)-specific differences in structure between aged and young samples, suggesting that some ageing mechanisms may act locally within tissues. This study not only reveals possible age-associated differences in ECM protein structures which are tissue-region specific, but also highlights the ability of PLF as a proteomic tool to aid in biomarker discovery.

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

Intervertebral disc (IVD) degeneration is a major risk factor of low back pain. It is defined by a progressive loss of the IVD structure and functionality, leading to severe impairments with restricted treatment options due to the highly demanding mechanical exposure of the IVD. Degenerative changes in the IVD usually increase with age but at an accelerated rate in some individuals. To understand the initiation and progression of this disease, it is crucial to identify key top-down and bottom-up regulations' processes, across the cell, tissue, and organ levels, in health and disease. Owing to unremitting investigation of experimental research, the comprehension of detailed cell signaling pathways and their effect on matrix turnover significantly rose. Likewise, in silico research substantially contributed to a holistic understanding of spatiotemporal effects and complex, multifactorial interactions within the IVD. Together with important achievements in the research of biomaterials, manifold promising approaches for regenerative treatment options were presented over the last years. This review provides an integrative analysis of the current knowledge about (1) the multiscale function and regulation of the IVD in health and disease, (2) the possible regenerative strategies, and (3) the in silico models that shall eventually support the development of advanced therapies.

Risk Factors for Recurrent L4-5 Disc Herniation After Percutaneous Endoscopic Transforaminal Discectomy: A Retrospective Analysis of 654 Cases

Background

Percutaneous endoscopic lumbar discectomy (PELD) is an increasingly applied minimally invasive procedure that has several advantages in the treatment of lumbar disc herniation (LDH). However, recurrent LDH (rLDH) has become a concerning postoperative complication. It remains difficult to establish a consensus and draw reliable conclusions regarding the risk factors for rLDH.

Purpose

This retrospective study aimed to investigate the risk factors associated with rLDH at the L4-5 level after percutaneous endoscopic transforaminal discectomy (PETD).

Methods

A total of 654 patients who underwent the PETD procedure at the L4-5 level from October 2013 to January 2020 were divided into a recurrence (R) group (n=46) and a nonrecurrence (N) group (n=608). Demographic and clinical data and imaging parameters were collected and analyzed using univariate and multiple regression analyses.

Results

The current study found a 7% rate of rLDH at the L4/5 level after successful PETD. Univariate analysis showed that older age, high BMI, diabetes mellitus history, smoking, large physical load intensity, moderate disc degeneration, small muscle-disc ratio (M/D), more fat infiltration, large sagittal range of motion (sROM), scoliosis, small disc height index (DHI), small intervertebral space angle (ISA), and small lumbar lordosis (LL) were potential risk factors (P < 0.10) for LDH recurrence after PETD at the L4-5 level. Multivariate analysis suggested that high BMI, large physical load intensity, moderate disc degeneration, small M/D, more fat infiltration, large sROM, small ISA, and small LL were independent significant risk factors for recurrence of LDH after PETD.

Conclusion

Consideration of disc degeneration, M/D, fat infiltration of the paravertebral muscles, sROM, ISA, LL, BMI, and physical load intensity prior to surgical intervention may contribute to the prevention of rLDH following PETD and lead to a more satisfactory operative outcome and the development of a reasonable rehabilitation program after discharge.

Spatial mapping of collagen content and structure in human intervertebral disk degeneration

Collagen plays a key structural role in both the annulus fibrosus (AF) and nucleus pulposus (NP) of intervertebral disks (IVDs). Changes in collagen content with degeneration suggest a shift from collagen type II to type I within the NP, and the activation of pro-inflammatory factors is indicative of fibrosis throughout. While IVD degeneration is considered a fibrotic process, an increase in collagen content with degeneration, reflective of fibrosis, has not been demonstrated. Additionally, changes in collagen content and structure in human IVDs with degeneration have not been characterized with high spatial resolution. The collagen content of 23 human lumbar L2/3 or L3/4 IVDs was quantified using second harmonic generation imaging (SHG) and multiple image processing algorithms, and these parameters were correlated with the Rutges histological degeneration grade. In the NP, SHG intensity increased with degeneration grade, suggesting fibrotic collagen deposition. In the AF, the entropy of SHG intensity was reduced with degeneration indicating increased collagen uniformity and suggesting less-organized lamellar structure. Collagen orientation entropy decreased throughout most IVD regions with increasing degeneration grade, further supporting a loss in collagen structural complexity. Overall, SHG imaging enabled visualization and quantification of IVD collagen content and organization with degeneration. There was an observed shift from an initially complex structure to more uniform structure with loss of microstructural elements and increased NP collagen polarity, suggesting fibrotic remodeling.

Microstructural characterization of annulus fibrosus by ultrasonography: a feasibility study with an in vivo and in vitro approach

The main function of the intervertebral disc is biomechanical function, since it must resist repetitive high loadings, while giving the spine its flexibility and protecting the spinal cord from over-straining. It partially owes its mechanical characteristics to the lamellar architecture of its outer layer, the annulus fibrosus. Today, no non-invasive means exist to characterize annulus lamellar structure in vivo. The aim of this work was to test the feasibility of imaging annulus fibrosus microstructure in vivo with ultrasonography. Twenty-nine healthy adolescents were included. Ultrasonographies of L3-L4 disc were acquired with a frontal approach. Annulus fibrosus was segmented in the images to measure the thickness of the lamellae. To validate lamellar appearance in ultrasonographies, multimodality images of two cow tail discs were compared: ultrasonography, magnetic resonance and optical microscopy. In vivo average lamellar thickness was 229.7 ± 91.5 μm, and it correlated with patient body mass index and age. Lamellar appearance in the three imaging modalities in vitro was consistent. Lamellar measurement uncertainty was 7%, with good agreement between two operators. Feasibility of ultrasonography for the analysis of lumbar annulus fibrosus structure was confirmed. Further work should aim at validating measurement reliability, and to assess the relevance of the method to characterize annulus alterations, for instance in disc degeneration or scoliosis.

Fibroblast Transplantation Results to the Degenerated Rabbit Lumbar Intervertebral Discs

Background:

Our study is an analysis of the histological and radiological changes in degenerated lumbar intervertebral discs, after transplantation of fibroblasts in rabbits. With that study we aimed to show the viability of the fibroblasts injected to the degenerated discs, and observe their potential for further studies.

Method:

The apoptosis of the cell is one of the factors at the disc degeneration process. Fibroblasts may act as mesenchymal stem cells at the tissue to which they are injected and they may replace the apoptotic cells. The nucleus pulposus of the discs from eight rabbits were aspirated under scopic guidance to induce disc degeneration.

Results:

One month later, cultured fibroblasts, which had been taken from the skin, were injected into the disc. The viability and the potential of the injected cells for reproduction were studied histologically and radiologically. Cellular formations and organizations indicating to the histological recovery were observed at the discs to which fibroblasts were transplanted. The histological findings of the discs to which no fibroblasts were transplanted, did not show any histological recovery. Radiologically, no finding of the improvement was found in both groups. The fibroblasts injected to the degenerated discs are viable.

Conclusion:

The findings of improvement, observed in this study, suggest that fibroblast transplantation could be an effective method of therapy for the prevention or for the retardation of the degenerative disease of the discs.

Bovine and degenerated human annulus fibrosus: a microstructural and micromechanical comparison

The complex structure of the annulus fibrosus is strongly related to its mechanical properties. Recent work showed that it is possible to observe the relative movement of fibre bundles in loaded cow tail annulus; the aim of this work was to describe and quantify annulus fibrosus micromechanics in degenerated human disc, and compare it with cow tail annulus, an animal model often used in the literature. Second harmonic generation was used to image the collagen matrix in twenty strips of annulus fibrosus harvested from intervertebral disc of seven patients undergoing surgery. Samples were loaded to 6% tensile strain in 1% steps. Elastic modulus was calculated from loading curves, and micromechanical strains were calculated from the images using custom software. The same protocol was applied to twenty strips of annulus harvested from cow tail discs. Significant morphological differences were found between human and cow tail samples, the most striking being the lack of collagen fibre crimp in the former. Fibres were also observed bending and running from one lamella to the other, forming a strong flexible interface. Interdigitation of fibre bundles was also present at this interface. Quantitative results show complex patterns of inter-bundle and inter-lamellar behaviour, with inter-bundle sliding being the main strain mechanism. Elastic modulus was similar between species, and it was not affected by the degree of degeneration. This work gives an insight into the complex structure and mechanical function of the annulus fibrosus, which should be accounted for in disc numerical modelling.

Intra-discal injection of autologous, hypoxic cultured bone marrow-derived mesenchymal stem cells in five patients with chronic lower back pain: a long-term safety and feasibility study

Background

Chronic low back pain due to disc degeneration represents a major social and economic burden worldwide. The current standard of care is limited to symptomatic relief and no current approved therapy promotes disc regeneration. Bone marrow-derived mesenchymal stem cells (MSCs) are easily accessible and well characterized. These MSCs are multipotent and exhibit great tissue regenerative potential including bone, cartilage, and fibrous tissue regeneration. The use of this cell-based biologic for treating protruding disc herniation and/or intervertebral disc degeneration is a promising therapeutic strategy, due to their known regenerative, immuno-modulatory and anti-inflammatory properties.

Methods

Five patients diagnosed with degenerative disc disease received an intra-discal injection of autologous, hypoxic cultured, bone marrow-derived mesenchymal stem cells (15.1–51.6 million cells) as part of a previous study. These patients were re-consented to participate in this study in order to assess long-term safety and feasibility of intra-discal injection of autologous, hypoxic cultured, bone marrow-derived mesenchymal stem cells 4–6 years post mesenchymal stem cell infusion. The follow-up study consisted of a physical examination, a low back MRI, and a quality of life questionnaire.

Results

Patients’ lower back MRI showed absence of neoplasms or abnormalities surrounding the treated region. Based on the physical examination and the quality of life questionnaire, no adverse events were reported due to the procedure or to the stem cell treatment 4–6 years post autologous, hypoxic cultured mesenchymal stem cell infusion. All patients self-reported overall improvement, as well as improvement in strength, post stem cell treatment, and four out of five patients reported improvement in mobility.

Conclusion

This early human clinical data suggests the safety and feasibility of the clinical use of hypoxic cultured bone marrow-derived mesenchymal stem cells for the treatment of lower back pain due to degenerative disc disorders and support further studies utilizing hypoxic cultured bone marrow-derived stem cells. The overall improvements reported are encouraging, but a larger double-blind, controlled, randomized clinical study with significant number of patients and implementation of validated endpoint measurements are next steps in order to demonstrate efficacy of this cell-based biologic.

Mesenchymal stem cell tracking in the intervertebral disc

Low back pain is a common clinical problem, which leads to significant social, economic and public health costs. Intervertebral disc (IVD) degeneration is accepted as a common cause of low back pain. Initially, this is characterized by a loss of proteoglycans from the nucleus pulposus resulting in loss of tissue hydration and hydrostatic pressure. Conservative management, including analgesia and physiotherapy often fails and surgical treatment, such as spinal fusion, is required. Stem cells offer an exciting possible regenerative approach to IVD disease. Preclinical research has demonstrated promising biochemical, histological and radiological results in restoring degenerate IVDs. Cell tracking provides an opportunity to develop an in-depth understanding of stem cell survival, differentiation and migration, enabling optimization of stem cell treatment. Magnetic Resonance Imaging (MRI) is a non-invasive, non-ionizing imaging modality with high spatial resolution, ideally suited for stem cell tracking. Furthermore, novel MRI sequences have the potential to quantitatively assess IVD disease, providing an improved method to review response to biological treatment. Superparamagnetic iron oxide nanoparticles have been extensively researched for the purpose of cell tracking. These particles are biocompatible, non-toxic and act as excellent MRI contrast agents. This review will explore recent advances and issues in stem cell tracking and molecular imaging in relation to the IVD.

Annulus fissures are mechanically and chemically conducive to the ingrowth of nerves and blood vessels

STUDY DESIGN

Mechanical and biochemical analyses of cadaveric and surgically removed discs.

OBJECTIVE

To test the hypothesis that fissures in the annulus of degenerated human discs are mechanically and chemically conducive to the ingrowth of nerves and blood vessels.

SUMMARY OF BACKGROUND DATA

Discogenic back pain is closely associated with fissures in the annulus fibrosus, and with the ingrowth of nerves and blood vessels.

METHODS

Three complementary studies were performed. First, 15 cadaveric discs that contained a major annulus fissure were subjected to 1 kN compression, while a miniature pressure transducer was pulled through the disc to obtain distributions of matrix compressive stress perpendicular to the fissure axis. Second, Safranin O staining was used to evaluate focal loss of proteoglycans from within annulus fissures in 25 surgically removed disc samples. Third, in 21 cadaveric discs, proteoglycans (sulfated glycosaminoglycans [sGAGs]) and water concentration were measured biochemically in disrupted regions of annulus containing 1 or more fissures, and in adjacent intact regions.

RESULTS

Reductions in compressive stress within annulus fissures averaged 36% to 46%, and could have been greater at the fissure axis. Stress reductions were greater in degenerated discs, and were inversely related to nucleus pressure (R(2) = 47%; P = 0.005). Safranin O stain intensity indicated that proteoglycan concentration was typically reduced by 40% at a distance of 600 μm from the fissure axis, and the width of the proteoglycan-depleted zone increased with age (P < 0.006; R(2) = 0.29) and with general proteoglycan loss (P < 0.001; R(2) = 0.32). Disrupted regions of annulus contained 36% to 54% less proteoglycans than adjacent intact regions from the same discs, although water content was reduced only slightly.

CONCLUSION

Annulus fissures provide a low-pressure microenvironment that allows focal proteoglycan loss, leaving a matrix that is conducive to nerve and blood vessel ingrowth.

Temporal interactions of degenerative changes in individual components of the lumbar intervertebral discs: a sequential magnetic resonance imaging study in patients less than 40 years of age

STUDY DESIGN

A retrospective longitudinal observational study using baseline and follow-up magnetic resonance imaging (MRI).

OBJECTIVE

To study the natural history of disc degeneration, focusing on the significance of changes affecting the individual components of the intervertebral disc.

SUMMARY OF BACKGROUND DATA

The natural history of the degenerative disc disease is poorly understood. Focusing on the relative prevalence, temporal evolution, and interactions of pathology in the anulus fibrosus, nucleus pulposus, and the end plates can help in better understanding of this process.

METHODS

MRIs of the lumbar spine in 63 patients, obtained at a mean interval of 30 months, were evaluated independently by two neuroradiologists to assess the temporal evolution of degeneration changes in 378 discs between T12 through S1 segments. In addition, a direct side-by-side comparison of two studies was also performed. Statistical analysis was performed to assess the association between the degeneration of individual disc components and to find the predictors of future degeneration.

RESULTS

Radial anular tears and end plate defects were associated with worse nuclear degeneration at the time of the initial study. Both end plate defects and nuclear degeneration were rare in the absence of radial tears. Multiple nominal logistic regression analysis showed that radial tears and herniation at the time of the initial study, along with the duration between the two imaging studies were the significant predictors of worsening nuclear degeneration. Age, sex, and the segmental disc level did not show any significant association with temporal progression of nuclear degeneration.

CONCLUSION

Radial tears and herniation are significant predictors of progressive nuclear degeneration, which was not seen in the absence of radial tears. End plate defects also frequently occur before nuclear degeneration but rarely in the absence of anular tears.

Disc height and segmental motion as risk factors for recurrent lumbar disc herniation

STUDY DESIGN

Retrospective review and multivariate analysis.

OBJECTIVES

Recurrent lumbar disc herniation (rLDH) is a repeated disc herniation at a previously operated disc level in patients who experienced a pain-free interval of at least 6 months after surgery. We investigated whether the preoperative radiologic biomechanical factors (disc height index [DHI] and sagittal range of motion [sROM]) have any effect on rLDH.

SUMMARY OF BACKGROUND DATA

rLDH has been reported in 5% to 15% of patients. There have been many studies suggesting various risk factors for rLDH, such as disc degeneration, trauma, age, smoking, gender, and obesity. However, these factors did not reflect a biomechanical effect on the affected joint directly. Investigation of DHI and sROM would be helpful to understand the biomechanical impact on the occurrence of rLDH.

METHODS

This study enrolled 157 patients who underwent surgery for L4-L5 LDH. We divided the patients into the recurrent and the nonrecurrent group and compared their clinical parameters (age, sex, body-mass index, symptom duration, diabetes, smoking, herniation type, preoperative visual analogue scale) and preoperative radiologic parameters (disc degeneration, DHI, sROM).

RESULTS

rLDH occurred at 40.8+/-15.5 months (7-70 months) after primary surgery. Mean DHI was 0.37+/-0.09 and 0.29+/-0.09 in the recurrent and the nonrecurrent group, respectively (P<0.05). Mean sROM was 11.3 degrees+/-2.9 degrees and 5.9 degrees+/-3.7 degrees in the recurrent and the nonrecurrent group, respectively (P<0.05). Both smoking and disc degeneration were related with the development of rLDH (P<0.05).

CONCLUSION

Together with our data, DHI and sROM showed a significant correlation with the incidence of recurrent lumbar disc herniation, suggesting that preoperative biomechanical conditions of the spine can be an important pathogenic factor in the site of lumbar disc surgery.

In vivo remodeling of intervertebral discs in response to short- and long-term dynamic compression

This study evaluated how dynamic compression induced changes in gene expression, tissue composition, and structural properties of the intervertebral disc using a rat tail model. We hypothesized that daily exposure to dynamic compression for short durations would result in anabolic remodeling with increased matrix protein expression and proteoglycan content, and that increased daily load exposure time and experiment duration would retain these changes but also accumulate changes representative of mild degeneration. Sprague-Dawley rats (n = 100) were instrumented with an Ilizarov-type device and divided into three dynamic compression (2 week-1.5 h/day, 2 week-8 h/day, 8 week-8 h/day at 1 MPa and 1 Hz) and two sham (2 week, 8 week) groups. Dynamic compression resulted in anabolic remodeling with increased matrix mRNA expression, minimal changes in catabolic genes or disc structure and stiffness, and increased glysosaminoglycans (GAG) content in the nucleus pulposus. Some accumulation of mild degeneration with 8 week-8 h included loss of annulus fibrosus GAG and disc height although 8-week shams also had loss of disc height, water content, and minor structural alterations. We conclude that dynamic compression is consistent with a notion of "healthy" loading that is able to maintain or promote matrix biosynthesis without substantially disrupting disc structural integrity. A slow accumulation of changes similar to human disc degeneration occurred when dynamic compression was applied for excessive durations, but this degenerative shift was mild when compared to static compression, bending, or other interventions that create greater structural disruption.

The effects of recombinant human bone morphogenetic protein-2, recombinant human bone morphogenetic protein-12, and adenoviral bone morphogenetic protein-12 on matrix synthesis in human annulus fibrosis and nucleus pulposus cells

BACKGROUND CONTEXT

Bone morphogenetic proteins (BMPs) are potential therapeutic factors for degenerative discs, and BMP-12 does not have the osteogenic potential of BMP-2, making it better suited for intradiscal injection. However, no reports have compared the actions of BMP-2 and -12 on human annulus fibrosus (AF) and nucleus pulposus (NP) cells nor evaluated adenoviral-mediated gene therapy in human AF cells.

PURPOSE

To evaluate and compare the effects of recombinant human (rh) BMP-2, rhBMP-12, and adenoviral BMP-12 (Ad-BMP-12) on nucleus pulposus and annulus fibrosis cell matrix protein synthesis.

STUDY DESIGN

In vitro study using rhBMP-2 and -12 and adenoviral BMP-12 with human intervertebral disc (IVD) cells.

METHODS

Human NP and AF IVD cells were isolated, maintained in monolayer, and incubated with BMP-2 or -12 for 2 days. AF and NP cells were transduced with Ad-BMP-12, pellets formed, and incubated for 6 days. Growth factor-treated cells were labelled with either 35-S or 3H-proline to assay matrix protein synthesis.

RESULTS

rhBMP-2 increased NP proteoglycan, collagen, and noncollagen protein synthesis to 355%, 388%, and 234% of control. RhBMP-12 increased the same NP matrix proteins' synthesis to 140%, 143%, and 160% of control. Effects on AF matrix protein synthesis were minimal. Ad-BMP-12 significantly increased matrix protein synthesis and DNA content of AF and NP cells in pellet culture. NP synthesis of all matrix proteins and AF synthesis of proteoglycans was increased when the data were normalized to pellet DNA. AF synthesis of noncollagen protein and collagen was not modulated by Ad-BMP-12 if the data are normalized to pellet DNA content.

CONCLUSIONS

Both rhBMP-2 and -12 increase human NP cell matrix protein synthesis while having minimal effects on AF cells. However, Ad-BMP-12 did increase matrix protein synthesis in both NP and AF cells, making it a potential therapy for enhancing matrix production in the IVD. These responses plus the proliferative action of Ad-BMP-12 seen in the current studies, and the lack of an osteogenic action noted in other studies justifies future studies to determine if gene therapy with BMP-12 could provide protective and/or reparative actions in degenerating discs.

Measurements of proteoglycan and water content distribution in human lumbar intervertebral discs

STUDY DESIGN

Study of regional variations in composition in a sample of 9 mildly to moderately degenerated human intervertebral discs.

OBJECTIVE

The aim of this study was to obtain proteoglycan distribution in human lumbar discs with high position resolution in the: 1) sagittal, 2) coronal, and 3) axial directions.

SUMMARY OF BACKGROUND DATA

Regional variation in disc proteoglycan content has only been reported in coronal sections in a small number of discs and with low spatial resolution in the sagittal direction, and has not been reported in the axial direction.

METHODS

Each of 9 human L2-L3 or L3-L4 lumbar discs (age, 53-56 years) were dissected into 36 to 41 specimens using a rectangular cutting die, measured for water content and analyzed for glycosaminoglycan content using the dimethylmethylene blue dye binding assay.

RESULTS

The intervertebral discs were mildly to moderately degenerated. They had glycosaminoglycan content ranging approximately 40 to 600 microg/mg dry tissue, with largest values in the nucleus and lowest in the outer anulus. In general, posterior regions had greater glycosaminoglycan content than anterior regions, although values were not as high as in the nucleus. Small variations in glycosaminoglycan content in the axial direction were observed with the largest values in the center, although this variation was small compared with radial variations. Water content results followed similar trends as glycosaminoglycan content with average values ranging from approximately 66% to 86%.

CONCLUSIONS

A refined map of proteoglycan content is presented with 3 important findings. First, sagittal variations were distinct from coronal variations. Second, the proteoglycan content was not uniform across the nucleus regions. Third, some specimens had localized variations in proteoglycan and water contents suggestive of focal damage and degeneration.

Senescence in cells of the aging and degenerating intervertebral disc: immunolocalization of senescence-associated beta-galactosidase in human and sand rat discs

STUDY DESIGN

Human intervertebral disc anulus tissue was obtained in a prospective study of cell senescence. Localization of the senescence biomarker beta-galactosidase (senescence associated beta-galactosidase, SA-beta-gal) was used for quantitative determination of the % senescent cells. Discs were obtained from surgical specimens or control donors. Discs were also studied from the lumbar spine of the sand rat. Experimental studies were approved by the authors' Human Subjects Institutional Review Board and animal use committee.

OBJECTIVES

To determine the incidence of cell senescence in human discs with Thompson Grades I through V using immunocytochemistry to quantify the percentage of cells positive for the senescence biomarker SA-beta-gal.

SUMMARY OF BACKGROUND DATA

Cell senescence has been recognized as a potential factor playing a role age-related disc degeneration. Senescent cells are viable but have lost the ability to divide. Senescence cells, however, are metabolically active.

METHODS

Fifty-seven discs specimens from 54 subjects were examined with immunocytochemistry for anti-SA-beta-gal immunocytochemical localization to identify senescent cells. The fraction of positive cells was determined with quantitative histomorphometry.

RESULTS

Quantitative histomorphometry of human discs show an overall incidence of SA-beta-gal-positive cells of 29.9% (+/-24.8, SD), with a range from 0 to 92.01%. Analysis by ANOVA of the % senescent cells grouped by Thompson grade showed significant increases in senescence with increasing disc degeneration (P < 0.0001). Further analysis with Tukey's test showed significant differences between the % senescent cells in Grades I/II versus IV, and versus V. SA-beta-gal-positive cells were also present in discs of the aging sand rat spine.

CONCLUSIONS

Quantitative analysis of immunohistochemical localization of SA-beta-gal identified a sizeable population of senescent cells in the aging/degenerating disc. It is important to discover more about the senescent disc cell population because these cells persist and accumulate over time within the disc. Since senescent cells cannot divide, senescence may reduce the disc's ability to generate new cells to replace existing ones lost to necrosis or apoptosis.

Value and limitations of using the bovine tail as a model for the human lumbar spine

STUDY DESIGN

The contents of DNA, proteoglycan, type II collagen, and denatured type II collagen in the bovine coccygeal intervertebral discs were examined in situ in relation to disc level, age, and tissue region.

OBJECTIVE

To determine whether bovine coccygeal discs are a suitable model to study human lumbar discs.

SUMMARY OF BACKGROUND DATA

Bovine coccygeal discs have been suggested as a suitable alternative model because they are readily available, in contrast to human discs, and represent a common source of tissue in the disc field. However, it is not known whether the changes in matrix contents in bovine coccygeal discs are similar to those found in the human lumbar spine.

METHODS

Intervertebral discs from bovine tails were dissected into the nucleus pulposus (NP) and anulus fibrosus (AF). Tissues were weighed and analyzed for matrix contents using specific assays.

RESULTS

Similar to water content, the proteoglycan content was higher in the NP than in the AF. Water content of the bovine NP did not change with age, unlike the proteoglycan content, which decreased. type II collagen content was higher in the NP than in the AF, and both did not change overall significantly with age. The percent of denatured type II collagen decreased with age only in the NP. The DNA content did not vary with age in the AF and in the NP.

CONCLUSION

Differences in matrix contents exist between the bovine coccygeal discs and the human lumbar spine. Thus, caution must be exercised when using the bovine tail as a model for the human lumbar spine in biochemical studies.

Prolonged spinal loading induces matrix metalloproteinase-2 activation in intervertebral discs

STUDY DESIGN

An established in vivo mouse model of compression-induced disc degeneration was used to investigate the effects of load on matrix catabolism.

OBJECTIVES

To determine whether matrix metalloproteinase-2 expression in discs is modulated by mechanical load and to characterize the regulation of matrix metalloproteinase-2 activity.

SUMMARY OF BACKGROUND DATA

We have previously shown that static compression of discs elicits changes in tissue architecture consistent with those seen with degeneration. Evidence in the literature demonstrates the existence of matrix metalloproteinases in both healthy and pathologic discs and suggests that mechanical load may influence matrix metalloproteinase expression and activity.

METHODS

Static compression was applied to mouse coccygeal discs in vivo for 1, 4, or 7 days, with adjacent discs serving as sham control. An activity assay was used to measure concentrations of active and total matrix metalloproteinase-2, and changes in matrix metalloproteinase-2 gene expression relative to beta-actin were assessed by reverse transcriptase-polymerase chain reaction.

RESULTS

Although no change was seen relative to sham after 1 day of load, the proportion of total matrix metalloproteinase-2 that was active increased after 4 days. This elevation was sustained through 7 days of compression, with no significant differences in total matrix metalloproteinase-2 concentrations among discs throughout the range of time points examined. Semiquantitative reverse transcriptase-polymerase chain reaction demonstrated no significant changes in matrix metalloproteinase-2 gene expression at 1 day or 4 days.

CONCLUSIONS

In this model, regulation of matrix metalloproteinase-2 activity occurs primarily through enhanced molecular activation of the proenzyme rather than through elevated gene expression or translation. Our results suggest that matrix metalloproteinase-2 may have a role in load-induced changes in disc architecture.