Lumbar disc degeneration: epidemiology and genetic influences

Characterization of intervertebral disc aging: longitudinal analysis of a rabbit model by magnetic resonance imaging, histology, and gene expression

STUDY DESIGN

A cohort of young, healthy New Zealand White rabbits was followed longitudinally with serial magnetic resonance imaging (MRI) analysis and terminal analysis of histologic changes and gene expression.

OBJECTIVE

To examine the changes observed during normal aging in the intervertebral disc.

SUMMARY OF BACKGROUND DATA

Although there is a correlation between aging and the onset of intervertebral disc degeneration (IDD), evidence suggests that distinct pathways are involved in these processes. Our group has characterized a reproducible rabbit model of IDD by MRI, radiograph, histology, and mRNA expression. However, no similar analysis has been performed longitudinally for intervertebral disc aging to allow comparison of these 2 important processes.

METHODS

Four skeletally mature female NZW rabbits were housed for 122 weeks, and lumbar spine MRIs were characterized serially. Histologic and quantitative gene expression analysis of the nucleus pulposus of these aging animals was performed, and compared with adult and young rabbits.

RESULTS

Mean MRI index decreased by <25% through 120 weeks. The histologic analysis showed changes in cell composition, with abundant notochordal cells in the young, chondrocyte-like cells and notochordal cells in the adult, and clusters of hypertrophic chondrocytes in the aging discs. The PCR analysis of the nucleus pulposus showed that gene expression of collagen decreased, whereas that for proteoglycans increased with aging. BMP-2, TIMP-1, and SOX-9 expression was significantly lower in the young compared with adult discs and TGF-beta1 demonstrated lower gene expression in young and aging animals.

CONCLUSION

Although dramatic cellular changes were observed, age-related MRI changes occurred in this rabbit model of normal aging at a much slower rate than in a previous injury model of degeneration. In addition, the gene expression analysis of the nucleus pulposus demonstrated remarkable differences between aging and injury induced degeneration. These results suggest that aging and injury contribute uniquely to the process of IDD.

Magnetic resonance imaging showed no signs of overuse or permanent injury to the lumbar sacral spine during a Special Forces training course

BACKGROUND CONTEXT

Special Forces training is even more demanding than that of elite athletes. The training includes grueling physical activity and periods of sleep deprivation. The soldiers routinely carry heavy loads up to 40% of their body weight on their backs while running and marching for distances up to 90 km.

PURPOSE

Our purpose was to find out if Special Forces recruits are able to complete the preparatory Navy Seals training program without sustaining magnetic resonance imaging (MRI) signs of overuse or irreversible injury to their backs.

STUDY DESIGN/SETTING

Prospective cohort study. We performed MRI scans before and after 14 weeks of Navy Seals preparatory training course.

PATIENT SAMPLE

Ten soldiers underwent MRI of their lumbar sacral spines and right knees before and after the completion of Navy Seals preparatory training.

OUTCOME MEASURES

Physiologic measures. Lumbar sacral spine and knee MRI tests were performed before and after the training to identify changes in the spinal discs, facet joints, pars interarticularis, vertebral bodies, knee articular cartilage, ligaments, knee menisci, and the presence or absence of soft tissue and/or bone edema.

METHODS

We investigated the difference in spine and knee pathology before and after a 14-week Navy Seals preparatory training course by using MRI criteria. The recruits participating in the study were monitored for acute and overuse injuries every 3 to 4 weeks.

RESULTS

Before the training, seven out of ten spine MRI scans were normal. Two showed small L5-S1 disc bulges, one of them with concomitant Scheuermann's disease. Another soldier's MRI showed L1-L4 mild Scheuermann's disease. Follow-up MRI showed no spinal changes. Before the training, one knee had a small lateral femoral condyle cartilage lesion. Nine of ten knees had prepatellar swelling, five had increased joint fluid, and two bone edema. Follow-up magnetic resonance imaging showed improvement in the prepatellar swelling in eight soldiers, no change in one soldier, and increased knee effusion and a new medial femoral condyle bone edema in another. The lateral femoral condyle lesion remained unchanged.

CONCLUSIONS

According to MRI criteria, the soldiers in this study completed the 14-week training, which involved loading of their spines far beyond the levels recommended by the US National Institute for Occupational Safety and Health without sustaining irreversible damage to their spines or knees. Although the subjects' knees showed signs of overuse injury, their backs did not.

Associations of low back pain with neck pain: a study of industrial employees with 5-, 10-, and 28-year follow-ups

Low back pain (LBP) and neck pain (NP) are common among the adult population but relatively few reports exist on the associations between these. We examined cross-sectional and prospective relationships of LBP with NP in an employee cohort studied repeatedly over 28 years. Locally perceived pain was studied separately from pain with a radiating component. At baseline, adjusted for age, gender, and occupational class, the prevalence ratio (PR) of local NP for those with local LBP was 1.93 (95% CI 1.47-2.54), and for those with radiating LBP 2.16 (1.59-2.94), while the PR of radiating NP for those with local LBP was 1.51 (0.97-2.35) and for those with radiating LBP 3.24 (2.25-4.65). These associations remained stable at the 5-, 10-, and 28-year follow-ups. Both local and radiating LBP at baseline predicted new cases of radiating NP at the 5- and 10-year follow-ups, but not at the 28-year follow-up. In analyses stratified by gender, both the cross-sectional and prospective associations were more pronounced in men. In conclusion, the study showed a clear association of LBP with NP that persisted on a similar level irrespective of the aging of the cohort. Particularly, radiating LBP was associated with radiating NP. The prospective associations of LBP at baseline with new reports of radiating NP decreased as the length of follow-up increased.

Current understanding of lumbar intervertebral disc degeneration: a review with emphasis upon etiology, pathophysiology, and lumbar magnetic resonance imaging findings

Degeneration of the lumbar intervertebral discs (IVDs) is highly prevalent in adults and is nearly universal in the elderly population. Degenerative changes within, and adjacent to, the IVDs are likely to contribute to a variety of pain syndromes; however, the exact association between these findings and symptoms remains speculative. Recent research has provided new information regarding the etiology, pathophysiology, and clinical relevance of degeneration of the IVD. This information will assist clinicians and researchers in understanding the development and clinical course of lumbar disc degeneration, as well as its potential impact upon patients seeking physical therapy care for back pain. The purposes of this clinical commentary are to review the structure and metabolic capacity of the normal and degenerative lumbar IVD, and to discuss factors that influence the onset and progression of disc degeneration. Lumbar magnetic resonance images will be used to illustrate the common findings associated with this condition.

In vivo intervertebral disc remodeling: kinetics of mRNA expression in response to a single loading event

Kinetics of mRNA expression following a single loading event was measured using an in vivo rat tail model. Animals were instrumented and loaded in compression for 1.5 h at 1 MPa and 1 Hz. Real-time RT-PCR was used to measure mRNA levels 0, 8, 24 and 72 h after mechanical stimulation for genes associated with matrix proteins (aggrecan, collagen-I, collagen-II), proteases (MMP-2, MMP-3, MMP-13, ADAMTS-4), and their inhibitors (TIMP-1, TIMP-3) in anulus fibrosus and nucleus pulposus regions. Baseline mRNA levels were of greatest abundance for matrix proteins and lowest for proteases. The mRNA levels reached maximum levels 24 h following mechanical stimulation for the majority of genes evaluated, but some had maximum levels 8 and 72 h following loading. The mRNA levels returned to baseline levels for all genes in the nucleus 72 h following loading, but the majority of genes in the anulus remained upregulated. Results support a coordinated strategy of relative mRNA expression that varied over time beginning with inhibition of tissue breakdown, followed by synthesis of aggrecan and matrix degrading enzymes, and eventually collagen metabolism days following loading. Consequently, optimal time for tissue harvest for mRNA measurements depends on genes of interest. Results suggest attempts at anabolic remodeling must be given adequate time for metabolic processes and protein synthesis to occur, and that changes in TIMP and MMP levels may have greater potency in affecting structural protein abundance than direct changes in the structural protein messages. Results have important implications for disc remodeling and tissue engineering.

Early-onset degeneration of the intervertebral disc and vertebral end plate in mice deficient in type IX collagen

OBJECTIVE

Type IX collagen is an important component of the intervertebral disc extracellular matrix. Mutations in type IX collagen are associated with premature disc degeneration in mice and a predisposition to disc disorders in humans. The aim of this study was to assess the prevalence and timeline of intervertebral disc degeneration in mice homozygous for an inactivated Col9a1 gene.

METHODS

Intact spine segments were harvested from wild-type (WT) and type IX collagen-knockout (Col9a1(-/-)) mice at 3, 6, and 12 months of age. Sagittal spine sections were evaluated for evidence of histologic changes, by 2 blinded graders, using a semiquantitative grading method.

RESULTS

There was evidence of more degeneration of the disc and end plate in the spines of Col9a1(-/-) mice compared with those of WT controls, at most time points. These findings were significant for the disc region at 3 and 6 months (P<0.01) and at 12 months (P<0.10) and for the end plate region only at 6 months (P<0.10). Degenerative changes in the disc consisted of cellular changes and mucous degeneration. Degeneration in the end plates was associated with more cell proliferation, cartilage disorganization, and new bone formation.

CONCLUSION

A deletion mutation for type IX collagen is associated with connective tissue changes characteristic of musculoskeletal degeneration in bony and cartilaginous tissue regions. Some of the observed changes were similar to cartilage changes in osteoarthritis, while others were more similar to disc degenerative changes in humans. The finding of premature onset of intervertebral disc degeneration in this mouse model may be useful in studies of the pathology and treatment of human disc degeneration.

Self-reported hard physical work combined with heavy smoking or overweight may result in so-called Modic changes

Background

Recently, the MRI finding of "Modic changes" has been identified as pathologic spinal condition that probably reflects a vertebral inflammatory process (VIP), which coincides with spinal pain in most. We hypothesized that heavy smoking in combination with macro- or repeated microtrauma could lead to VIP. The objectives were to investigate if combinations of self-reported heavy smoking, hard physical work, and overweight would be more strongly linked with VIP than with other spinal conditions, such as degenerated discs and non-specific low back pain (LBP).

Methods

Secondary analysis was made of a data base pertaining to a population-based cross-sectional study. A population-generated cohort of 412 40-yr old Danes provided questionnaire information on smoking, weight, height, type of work, and LBP. MRI was used to determine the presence/absence of disc degeneration and of VIP. Associations were tested between three explanatory variables (type of work, smoking, and body mass index) and four outcome variables (LBP in the past year, more persistent LBP in the past year, disc degeneration, and VIP). Associations with these four outcome variables were studied for each single explanatory variable and for combinations of two at a time, and, finally, in a multivariable analysis including all three explanatory variables.

Results

There were no significant associations between the single explanatory variables and the two pain variables or with disc degeneration. However, VIP was found in 15% of non-smokers vs. 26% of heavy smokers. Similarly, VIP was noted in 11% of those in sedentary jobs vs. 31% of those with hard physical work. Further, the prevalence of VIP in those, who neither smoked heavily nor had a hard physical job was 13%, 25% in those who either smoked heavily or had a hard physical job, and 41% in those who both smoked heavily and worked hard. The odds ratio was 4.9 (1.6–13.0) for those who were both heavy smokers and had a hard physical job as compared to those who were classified as "neither". Similar but weaker findings were noted for the combination of overweight and hard physical work but not for the combination of smoking and overweight.

Conclusion

Hard physical work in combination with either heavy smoking or overweight is strongly associated with VIP. If this finding can be reproduced in other studies, it may have consequences in relation to both primary and secondary prevention of LBP, because blue collar workers, who are most likely to experience the consequences of LBP, also are those who are most likely to smoke.

Absence of the mutated Trp2 allele but a common polymorphism of the COL9A2 collagen gene is associated with early recurrence after lumbar discectomy in a German population

Genetic factors seem to play a role in symptomatic lumbar disc disease (LDD). It has been shown previously that a tryptophan mutation of the COL9A2 gene is a major risk factor for LDD in a Finish population. The impact of collagen gene variations on the relapse rate after lumbar discectomy, however, has not been studied so far. Here, we conducted a cross-sectional genotyping study of patients who underwent lumbar discectomy to determine the influence of a COL9A2 mutation on the recurrence rates. Biopsy samples from 288 patients suffering from LDD with and without relapse were analyzed by PCR restriction fragment analysis and direct sequencing. The mutated Trp2 allele was not detected in the patients' samples of the present study. However, nine patients with recurrent LDD, but only two without recurrence were homozygous for the Arg allele. Homozygosity for the Arg allele of Col9A2 seems to be more frequent in the patient group with early recurrence although the differences in the allele frequencies were statistically not significant. In contrast, the Trp2 mutation seems not to be a major susceptibility factor for LDD in a German population.

Invasive and minimally invasive surgical techniques for back pain conditions

This article summarizes current issues related to invasive and minimally invasive surgical techniques for back pain conditions. It describes pain generators and explains theories about how discs fail. The article discusses techniques for treating painful sciatica, painful motion segments, and spinal stenosis. Problems related to current imaging are also presented. The article concludes with a discussion about physical therapy.

Expression of the Trp2 allele of COL9A2 is associated with alterations in the mechanical properties of human intervertebral discs

STUDY DESIGN

Biomechanical study into the association between genetic polymorphism in COL9A2 and mechanical properties of human nucleus pulposus.

OBJECTIVE

To examine whether there is an association between genetic polymorphism in a structural gene, and alterations in the mechanical properties of the intervertebral discs that may predispose to disc degeneration.

SUMMARY OF BACKGROUND DATA

Genetic studies have demonstrated that a polymorphism (Trp2 allele) in COL9A2 coding for alpha2 chain of collagen IX predisposes the individual to disc degeneration. The mechanism of this predisposition is not known.

METHODS

Blood and whole disc samples were retrieved from adolescents and young adults during scoliosis surgery, degenerated discs were retrieved from patients with back pain during anterior spinal fusion. Anulus fibrosus and nucleus pulposus from a set of the scoliosis discs were used to perform immunohistochemistry to demonstrate the presence of collagen IX in the scoliosis discs. For the remaining samples, DNA was extracted from blood to determine the Trp2 status by sequencing. Nondegenerated (Trp2-), nondegenerated (Trp2+), and degenerated (Trp2-) nucleus pulposus samples were tested in confined compression. Swelling pressure and compressive modulus were measured and compared between groups.

RESULTS

Positive staining of collagen IX was detected in both anulus fibrosus and nucleus pulposus sections confirming its presence in the scoliosis discs. The mean swelling pressure and compressive modulus values of 6 nondegenerated (Trp2+) samples (swelling pressure = 0.0019 MPa, compressive modulus = 0.97 MPa) were significantly lower (P < 0.05) than those of the 6 nondegenerated (Trp2-) samples (swelling pressure = 0.015 MPa; compressive modulus = 1.89 MPa).

CONCLUSION

This is the first study to demonstrate an association between the Trp2 allele and disc mechanics, thus relating genetic variations and debilitating mechanical alterations that may ultimately result in intervertebral disc degeneration.

Aggrecanases and aggrecanase-generated fragments in the human intervertebral disc at early and advanced stages of disc degeneration

STUDY DESIGN

A comparative study of aggrecanases and aggrecan fragmentation profile in the human intervertebral disc at early and advanced stages of disc degeneration.

OBJECTIVE

To determine differences in the content of the aggrecanases and the profile of aggrecan fragmentation in early and advanced stages of disc degeneration using cadaveric human intervertebral discs.

SUMMARY OF BACKGROUND DATA

Aggrecanases and aggrecanase-generated aggrecan fragments have been found in human degenerated discs. However, the association between the grade of disc degeneration and the content of the aggrecanases and the profile of aggrecan fragments has not been well studied.

METHODS

A total of 108 cadaveric donor spines were assessed by MRI T2 imaging and graded based on the Thompson scale. Twelve donor spines (average age, 63 years), each specifically exhibiting 2 different stages (Grade 2 and Grade 4) of disc degeneration at different disc levels, were included in this study. After harvesting the preselected discs, tissue samples were obtained from the center of the nucleus pulposus (NP) and the middle zone of the anulus fibrosus (AF). The amount of the aggrecanases, specifically ADAMTS-4 and ADAMTS-5, and the pattern of aggrecan fragmentation in the isolated tissues were assessed by western blot using specific antibodies.

RESULTS

In both NP and the AF tissues, the amount of ADAMTS-4 detected was higher in disc tissues with a higher level of degeneration (Grade 4) than in Grade 2 disc tissues with a lower level of degeneration. However, the amount of ADAMTS-5 detected did not differ between the 2 disc tissue grades. The aggrecan fragmentation analysis of these samples demonstrated the presence of aggrecanase-mediated fragmentation in both groups; however, there was no apparent difference in the aggrecan fragmentation profile between discs at early and advanced stages of disc degeneration.

CONCLUSION

Aggrecanases are involved in aggrecanolysis at both the early and advanced stages of disc degeneration. The aggrecan fragmentation profile analysis demonstrates the involvement of aggrecanases, as well as that of matrix metalloproteinases and/or cathepsins, during disc degeneration.

Pain and disability correlated with disc degeneration via magnetic resonance imaging in scoliosis patients

Prior imaging studies of scoliosis patients attempted to demonstrate a relationship between plain radiographic curve patterns and curve progression and pain, or used magnetic resonance imaging (MRI) to focus on spinal cord abnormalities. Pain in scoliosis patients may differ from nondeformity patients, yet may still be discogenic. The purpose of this study was to assess the possible relationship of degenerative disc findings on MRI to scoliosis patients' pain. This prospective study enrolled scoliosis and control patients, all of whom had assessment for back pain (visual analog scale) and disability (Oswestry Index) and spinal MRI to identify prevalence and distribution of degenerative disc findings. Specifically, we assessed 60 consecutive pediatric and adult idiopathic scoliosis patients who had progressed to surgical treatment, 60 age- and gender-matched asymptomatic controls, and 172 nondeformity symptomatic degenerative disc disease patients who had progressed to surgical treatment. All subjects had independent analysis of their preoperative MRI for disc degeneration, disc herniation, Schmorl's nodes, and inflammatory end plate changes. Imaging findings of the scoliosis patients were compared to those from asymptomatic and symptomatic control groups. Our results found that both pediatric and adult scoliosis patients had significantly more pain and disability than did asymptomatic controls (P < 0.001). The adult idiopathic scoliosis patients had pain and disability similar to those of surgical degenerative disc disease control groups. Disc degeneration and herniation (contained) were not related to pain. However, in the pediatric scoliosis patients, those with Schmorl's nodes often had greater pain than those without (P = 0.01). Adults with painful scoliosis, typically occurring at the apex of the scoliosis or at the lumbosacral junction, had a significantly higher frequency of inflammatory end plate changes on MRI than did controls (P < 0.001). Prior studies have demonstrated a correlation of inflammatory end plate changes to lumbar discogenic pain. In conclusions, scoliosis patients who have progressed to surgical intervention, pediatric patients have varying degrees of pain, and those with Schmorl's nodes may be at greater risk for pain. Adult scoliosis patients have multifactorial pain of which one component may be related to degeneration of the lower lumbar discs similar to that in nondeformity patients. Additionally, adult scoliosis patients may have MRI findings consistent with discogenic pain at the apex of their curvature, most commonly at the proximal lumbar levels.

Inhibition of vertebral endplate perfusion results in decreased intervertebral disc intranuclear diffusive transport

Impaired nutrition of the intervertebral disc has been hypothesized to be one of the causes of disc degeneration. However, no causal relationship between decreased endplate perfusion and limited nutrient transport has been demonstrated to support this pathogenic mechanism. To determine the importance of endplate perfusion on solute diffusion into the nucleus pulposus and to show causality of endplate perfusion on intranuclear diffusion in large animal lumbar intervertebral discs, diffusive transport into ovine lumbar intervertebral discs was evaluated after inhibiting adjacent vertebral endplate perfusion. Partial perfusion blocks were created in vertebrae close and parallel to both endplates of lumbar discs of anaesthetized sheep. To assess diffusivity of small molecules through the endplate, N2O was introduced into the inhalation gas mixture and concentrations of intranuclear N2O were measured for 35 min thereafter. Post mortem, procion red was infused through the spinal vasculature and perfusion through the endplate was assessed by quantifying the density of dye-perfused endplate vascular buds in histology sections. Perfusion of the endplates overlying the nucleus pulposus was inhibited by almost 50% in the partially blocked discs relative to the control discs. There was also a nine-fold decreased transport rate of intranuclear N2O in partially blocked discs compared with control discs. The density of perfused endplate vascular buds correlated significantly to the amount of transported intranuclear N2O (r2 = 0.52, P = 0.008). The vertebral endplate was demonstrated to be the main route of intravascular solute transport into the nucleus pulposus of intervertebral discs, and inhibition of endplate perfusion can cause inhibited solute transport into the disc intranuclear tissue.

Imaging the degenerative diseases of the lumbar spine

Degenerative changes of the spine may involve the disc space, the facet joints, or the supportive and surrounding soft tissues. MR imaging is ideally suited for delineating the presence, extent, and complications of degenerative spinal disease. Other imaging modalities such as radiography, myelography, and CT may provide complimentary information in selected cases. Percutaneous procedures may be used to confirm that a morphologic abnormality is the source of symptoms. Correlation with clinical and electrophysiologic data is also helpful for accurate diagnosis. Combining the information obtained from imaging studies with the patient's clinical presentation is mandatory for determining the appropriate patient management strategy, especially true in patients afflicted with any condition directly attributed to the degenerative processes of the spine.

Lumbar intervertebral disk degeneration in elite competitive swimmers: a case control study

BACKGROUND

The majority of orthopaedic problems experienced by competitive swimmers are related to pain in the shoulder, low back, and knee. Three of 39 national swim team members were hampered in their performance due to lumbar disk herniation at an international competition in 2001. There has been no previous research into lumbar disk degeneration in elite competitive swimmers.

HYPOTHESIS

Excessive competitive swimming activities accelerate lumbar disk degeneration.

STUDY DESIGN

Case control study; Level of evidence, 3.

METHODS

Fifty-six elite swimmers (high-load group, 35 men and 21 women; mean age, 19.6 years) and a control group of 38 university recreational level swimmers (low-load group, 24 men and 14 women; mean age, 21.1 years) were evaluated for lumbar disk degeneration using magnetic resonance imaging. We compared the prevalence of disk degeneration and the disk level between the 2 groups and further investigated the relationship among their symptoms, swimming styles, and disk degeneration.

RESULTS

Thirty-eight (68%) elite swimmers and 11 (29%) controls had degenerated disks at various disk levels, and the prevalence was significantly greater in the elite swimmers (P = .0002). Comparison between the 2 groups of the prevalence of disk degeneration at each level revealed that the disk level of L5-S1 was significantly more frequently degenerated in the high-load group (P = .026). There was no significant relationship observed among the variables of low back pain symptoms, swimming strokes, and disk degeneration.

CONCLUSION

Excessive competitive swimming activities might exaggerate lumbar intervertebral disk degeneration, especially in the L5-S1 intervertebral segment.

Are animal models useful for studying human disc disorders/degeneration?

Intervertebral disc (IVD) degeneration is an often investigated pathophysiological condition because of its implication in causing low back pain. As human material for such studies is difficult to obtain because of ethical and government regulatory restriction, animal tissue, organs and in vivo models have often been used for this purpose. However, there are many differences in cell population, tissue composition, disc and spine anatomy, development, physiology and mechanical properties, between animal species and human. Both naturally occurring and induced degenerative changes may differ significantly from those seen in humans. This paper reviews the many animal models developed for the study of IVD degeneration aetiopathogenesis and treatments thereof. In particular, the limitations and relevance of these models to the human condition are examined, and some general consensus guidelines are presented. Although animal models are invaluable to increase our understanding of disc biology, because of the differences between species, care must be taken when used to study human disc degeneration and much more effort is needed to facilitate research on human disc material.

Gene therapy for disc degeneration

Recent advances in our understanding of the biology of the intervertebral disc have led to increased interest in the development of novel treatments of intervertebral disc degeneration. With the ability to provide sustained delivery of a potentially therapeutic agent, gene therapy has shown much promise in regard to the treatment of disc degeneration. Many new targets for gene therapy have been identified and new vectors are being investigated for use in intervertebral disc applications. Multiple studies have demonstrated the feasibility of intradiscal gene therapy, and recent studies have shown proof of efficacy of vector-mediated gene transfer in the reproducible animal model, as well as the potential to control transgene expression, improving safety. With continued efforts, gene therapy may prove to be an extremely powerful tool in the future treatment of intervertebral disc degeneration.

The effects of anthropometrics, lifting strength, and physical activities in disc degeneration

STUDY DESIGN

A cross-sectional study design was used.

OBJECTIVE

The objective was to examine the influences of body anthropometrics, axial disc area, and lifting strength on disc degeneration and to compare these with the effects of lifetime physical demands and age.

SUMMARY OF BACKGROUND DATA

Although recent studies have shown that heredity is a dominant factor in disc degeneration, the common notion that occupational physical loading is the major risk factor persists. However, substantial variations in disc degeneration, particularly at the lowest lumbar levels, remain unexplained by heredity or occupational physical demands.

METHODS

Univariate methods and stepwise multiple regression modeling were used to estimate associations of body height, weight, fat content, axial disc area, isokinetic lifting performance, and lifetime routine physical activities at work and leisure with disc height narrowing and disc signal (in T2 images) based on lumbar MRIs. These data were available from a population sample of 600 men, 35 to 70 years of age.

RESULTS

Lower disc signal, representing disc desiccation, was associated with higher age, lower body mass and lifting strength, and larger axial disc area. Of the variance in disc signal, age explained 8.0% (P < 0.001) and body weight/axial disc area, isokinetic lifting strength, and occupational lifting history added 3.9%, 2.3%, and 1.3%, respectively. Greater disc narrowing was associated with higher age, larger axial disc area, and higher occupational physical loading. Of the variance in disc narrowing, age accounted for 3.8% (P < 0.001); axial disc area and occupational loading added 1.9% (P < 0.004) and 1.3% (P < 0.007), respectively.

CONCLUSIONS

Body weight, lifting strength, and axial disc area were more highly associated with disc degeneration than occupational and leisure physical activity histories, although all had modest influences. Furthermore, higher body mass, greater lifting strength, and heavier work were all associated with more disc height narrowing but less disc desiccation contrary to current views. Smaller discs appeared to have beneficial effects.

Identical twins with cervical myelopathy: a case for hereditary cervical spondylosis? Report of two cases and review of the literature

Although degenerative cervical spondylosis is a common neurosurgical problem, not much has been published about the hereditary factors responsible for it. The authors report on a set of identical twins who presented to their service at a relatively young age with myelopathy due to degenerative cervical disc prolapse and who needed surgery. The early age of presentation and the fact that the patients were identical twins suggest a genetic element. The authors also review the available literature on the genetic factors in the causation of degenerative cervical spondylosis. To the best of their knowledge this is the first reported instance of identical twins with cervical myelopathy at a young age needing curative surgery.

Juvenile degenerative disc disease: a report of 76 cases identified by magnetic resonance imaging

BACKGROUND

Persistent low back pain in the young remains a significant diagnostic and treatment challenge for clinicians. Traditionally, chronic low back pain in this population has been attributed to either serious undetected pathology or psychosocial etiologies. This assumption may be incorrect because patients in this population may have underlying juvenile degenerative disc disease (JDDD), an important pathological diagnosis in the adult population.

PURPOSE

The purpose of this study is to report the presentation, radiographic findings, diagnosis, and treatment modalities of juvenile patients presenting with persistent low back pain for greater then 6 months.

STUDY DESIGN

This is a retrospective review of patients less than 21 years old referred to a spine specialty practice with persistent low back pain.

PATIENT SAMPLE

The charts of 1,877 patients less than 21 years old referred to a spine specialty practice for the evaluation of spinal problems.

OUTCOME MEASURES

Magnetic resonance images (MRI) were obtained and reviewed by a neuroradiologist and two orthopedic surgeons.

METHODS

Patients younger than 21 years old with persistent low back pain for greater that 6 months were identified. Patients with scoliosis, Scheuermann's kyphosis, spondylolisthesis, fracture, tumor, and metabolic bone disease were excluded. Standard demographic information, relevant medical history and physical examination findings were collected. Patients were evaluated with an MRI of their spines to detect any potential underlying pathology. The success of various treatment modalities used was reviewed. The findings of this study were correlated to those of the available literature following a thorough review.

RESULTS

Seventy-six patients (34 males, 42 females) with degenerative disc disease were identified on MRI. The mean age was 17.1 years (range 11.5-21.0) with a mean body mass index (BMI) of 24.5 (range 17.7-35.4). Thirty-one had associated radiculopathy. There was 11 smokers, 20 involved in athletics, 17 with co-morbidities, and 9 with a BMI greater than 30. A distinct subgroup of 13 patients with multilevel concurrent spinal stenosis was documented. Four of this subgroup required surgical intervention for severe radicular or claudication symptoms. The majority of JDDD patients were successfully treated with nonoperative modalities.

CONCLUSION

The findings of this study question whether lumbosacral degenerative disc disease, commonly thought to exist only in an older population, in fact begins earlier in selected patients. Our study confirms the findings of others that there is a definite population of juveniles that present with chronic low back pain who have degenerative disc disease identified on MRI. Within this population is a subgroup of patients with concurrent congenital spinal stenosis. Most patients with JDDD appear to be well managed by traditional nonoperative treatment modalities.

Long-term actuarial survivorship analysis of an interspinous stabilization system

In 1986, an interspinous dynamic stabilization system (the prototype of the current Wallis implant) was designed to stiffen unstable operated degenerate lumbar segments with a hard interspinous blocker to limit extension and a tension band around the spinous processes to secure the implant and limit flexion. Restoring physiological mechanical conditions to the treated level(s) while preserving some intervertebral mobility was intended to treat low-back pain related to degenerative instability without increasing stress forces in the adjacent segments. The procedure was easily reversible. If low back pain persisted or recurred, the device was removed and stability was achieved using fusion. The intermediate-term results were promising, but the long-term safety and efficacy of this dynamic interspinous stabilization device has not been previously documented. We retrospectively reviewed the hospital files of all the patients (n = 241) who had this dynamic stabilization system implanted between 1987 and 1995, contacting as many as possible to determine the actuarial survivorship of the system. In this manner, 142 of the 241 patients (58.9%) were contacted by telephone. The endpoints used for the survivorship analysis were 'any subsequent lumbar operation' and 'implant removal'. At 14 years follow-up, values of actuarial survivorship with 95% confidence interval were 75.9 +/- 8.3 and 81.3 +/- 6.8% for the endpoints 'any subsequent lumbar operation' and 'implant removal', respectively. There was no difference in survivorship of multiple-level implants with respect to single-level devices. Although the conclusions of the present study must be tempered by the 41% attrition rate, these findings support the long-term safety of this system, and possibly long-term protective action against adjacent-level degeneration by motion preservation. Outcomes at least equivalent to those of fusion were observed without the primary drawbacks of fusion.

Disc degeneration in low back pain: a 17-year follow-up study using magnetic resonance imaging

STUDY DESIGN

A prospective, cohort clinical and magnetic resonance imaging (MRI) study of patients with low back pain.

OBJECTIVE

To study if lumbar disc degeneration (DD), diagnosed in young patients with low back pain by using MRI will predict chronic pain, disc herniation, or functional disability after a 17-year follow-up.

SUMMARY OF BACKGROUND DATA

In 1987, 75 male Finnish conscripts aged 20 years, with low back pain hindering their military service, were studied using MRI at 0.02 T.

METHODS

In 2003, 32 patients were reexamined with MRI at 1.0 T. The history of low back illness during the follow-up and current functional outcome were recorded.

RESULTS

In 1987, 69% of the 32-patient cohort had DD in one or more lumbar discs. In 2003, all subjects had DD in MRI. The mean number of degenerated discs in each subject increased from 1.1 to 3.0. A total of 76% of discs degenerated in 1987 were herniated in 2003, whereas only 29% of well-hydrated discs in 1987 were herniated at the time of follow-up (P = 0.0002). During 17 years of follow-up, 3 patients had undergone spinal surgery.

CONCLUSIONS

Early DD in adolescent patients with low back pain predicted the evolution of enhanced DD and herniation in adulthood, but it was not associated with severe low back pain or increased frequency of spinal surgery.

Radiologic assessment of all unfused lumbar segments 7.5 years after instrumented posterior spinal fusion

STUDY DESIGN

Prospective observational single-cohort study.

OBJECTIVE

To analyze long-term radiographic changes in all unfused lumbar segments after instrumented posterolateral lumbar fusion.

SUMMARY OF BACKGROUND DATA

Adjacent segment degeneration (ASD) after lumbar fusion may be a consequence of biomechanical stress or result from constitutional factors. Most studies analyzing ASD only investigate the motion segments immediately above and below the fusion. None compares adjacent segments to all the other unfused segments after instrumented posterior fusion.

METHODS

Using the distortion-compensated roentgen analysis method, disc height, dorsoventral displacement, and lordosis were measured in 212 unfused segments from 62 patients, on digitized standing radiographs taken before fusion surgery and after a mean follow-up of 7.5 years (range, 4-11 years). The effect of covariables, such as age, length of follow-up, fusion level, number of fused segments, and sagittal and spinopelvic parameters on the preoperative to follow-up changes, were analyzed using a repeated-measurement model.

RESULTS

No changes were observed at the segments located below the fusion. All the unfused segments above the fusion showed the same significant loss of disc height. Loss of disc height did not depend on fusion parameters, correlated weakly with age and length of follow-up, and correlated highly across adjacent unfused segments.

CONCLUSIONS

After posterior lumbar instrumented fusion, radiographic changes suggesting disc degeneration appear homogeneously at several levels cephalad to fusion and seem to be determined by individual characteristics.

Invasive and minimally invasive surgical techniques for back pain conditions

Back pain is a ubiquitous problem for developed countries. It is a source of disability for society and is a financial drain through lost wages and productivity. The treatment of spine-related pain has changed over the years: minimally invasive approaches are now favored. Despite this trend, surgeons still rely on decompressions of compressed neurological structures and the fusion of painful motion segments. The history of treatments of spine-related pain as well as modern and minimally invasive techniques are reviewed.

Fatores genéticos e ambientais envolvidos na degeneração do disco intervertebral

A etiologia da degeneração do disco intervertebral (DDI) ainda não está totalmente esclarecida. O gene do receptor da vitamina D (VDR) tem sido apontado como um dos possíveis envolvidos no surgimento das discopatias. Por outro lado, este estudo relaciona pela primeira vez, a participação dos genes das glutatião transferases M1 e T1 (GSTT1 e GSTM1), responsáveis pela inativação dos componentes do cigarro, na DDI. Foi extraído DNA de leucócitos de 66 pacientes e 88 controles, pareados por gênero e idade. O polimorfismo VDR-FokI foi amplificado por reação em cadeia da polimerase (PCR) seguido de restrição com a enzima FokI. Os polimorfismos das GSTT1/M1 foram determinados por meio da PCR multiplex. A história familial e a gravidade da doença se destacaram nos pacientes portadores do alelo f do gene VDR-FokI (P=0,000 e 0,0012, respectivamente). A idade de surgimento da doença mostrou-se precoce nos indivíduos com genótipo _/f (média de 26 anos). Foi encontrada associação do polimorfismo FokI com a degeneração precoce e gravidade da DDI, sendo que o hábito de fumar também interferiu nesse processo, independente da presença ou não do genótipo favorável para GSTT1/M1.

Schmorl's nodes: Common, highly heritable, and related to lumbar disc disease

OBJECTIVE

Schmorl's nodes (SN) are common, but little is known of their relationship with degenerative change and back pain or genetic and environmental factors influencing their expression. We studied healthy female twin volunteers to determine the prevalence and clinical features associated with SN.

METHODS

Serial sagittal T1- and T2-weighted magnetic resonance images of the lower thoracic and lumbar spine were analyzed in 516 healthy female twins (150 monozygotic and 366 dizygotic). The images were scored for lumbar degenerative change. Presence of SN was noted at cranial and caudal vertebral levels T9 to L5. Data on physical activity and back pain were collected by questionnaire. Heritability of SN was calculated using variance components modeling.

RESULTS

SN were found in 30% of subjects. Of the 374 SN, 153 (41%) were in the lumbar spine and 221 (59%) were in the thoracic spine. SN heritability was >70%. There was a positive association between SN and lumbar disc disease (LDD). SN were more frequent in subjects with back pain (for >/=2 SN: odds ratio [OR] 2.68, 95% confidence interval [95% CI] 1.11-6.47, P = 0.03), but this was largely accounted for by the association of SN with LDD (OR 1.97, 95% CI 0.78-5.0, P = 0.15 adjusted for LDD). No independent association of SN with back pain was identified.

CONCLUSION

SN are common in middle-aged women and are strongly genetically determined. They are associated with lumbar degenerative change, which is a risk factor for back pain, but are not themselves an independent risk factor for back pain.

Does minor trauma cause serious low back illness?

STUDY DESIGN

Prospective, 5-year, cohort study of working subjects.

OBJECTIVES

To assess whether the occurrence of common minor trauma events affects the risk of developing serious low back pain (LBP) and LBP disability in subjects with and without degenerative changes to the lumbar spine.

SUMMARY OF BACKGROUND DATA

Although some theories suggest that minor traumatic events in combination with preexisting degenerative changes commonly cause significant structural injury to spinal segments and serious LBP illness, no prospective data exist on the relationship of minor trauma, detailed structural changes, and outcome measures of serious LBP episodes and occupational disability.

METHODS

Two hundred subjects without clinical LBP problems were recruited, and underwent baseline clinical and imaging studies. Every 6 months, subjects completed a scripted, algorithm-based interview assessing interval back pain episodes, severity, medical treatment, occupational disability, and the subject's perceived relation of this LBP episode to any preceding event. If a serious LBP episode clinically required a new magnetic resonance examination, the follow-up imaging was obtained and compared to baseline for interval changes.

RESULTS

There was no association of minor trauma to adverse LBP events. For each 6-month study interval, the risk of developing a serious LBP episode was 2.1% unassociated with minor trauma and 2.4% following minor trauma (P = 0.59). Neither the frequency of minor trauma events nor the reported severity of the event correlated with adverse outcomes. Subjects with advanced structural findings were not more likely to become symptomatic with minor trauma events than with spontaneously evolving LBP episodes. Follow-up magnetic resonance imaging evaluating new serious LBP illness rarely revealed new clinically significant findings. Age and sex-adjusted prediction models, including abnormal psychometric testing, smoking, and compensation issues, accurately identified 80% of serious LBP events and 93% of LBP disability events.

CONCLUSIONS

In this study cohort, minor trauma does not appear to increase the risk of serious LBP episodes or disability. The vast majority of incident-adverse LBP events may be predicted not by structural findings or minor trauma but by a small set of demographic and behavioral variables.

Are first-time episodes of serious LBP associated with new MRI findings?

BACKGROUND

Magnetic resonance (MR) imaging is frequently used to evaluate first-time episodes of serious low back pain (LBP). Common degenerative findings are often interpreted as recent developments and the probable anatomic cause of the new symptoms. To date no prospective study has established a baseline MR status of the lumbar spine in subjects without significant LBP problems and prospectively surveyed these subjects for acute changes shortly after new and serious LBP episodes. This method can identify new versus old MR findings possibly associated with the acute symptomatic episode.

PURPOSE

To determine if new and serious episodes of LBP are associated with new and relevant findings on MRI.

STUDY DESIGN

Prospective observational study with baseline and post-LBP MRI monitoring of 200 subjects over 5 years.

OUTCOME MEASURES

Clinical outcomes: LBP intensity (visual analogue scale), Oswestry Disability Index, and work loss. MRI outcomes: disc degeneration, herniation, annular fissures, end plate changes, facet arthrosis, canal stenosis, spondylolisthesis, and root impingement.

METHODS

200 subjects with a lifetime history of no significant LBP problems, and a high risk for new LBP episodes were studied at baseline with physical examination, plain radiographs, and MR imaging. Subjects were followed every 6 months for 5 years with a detailed telephone interview. Subjects with a new severe LBP episode (LBP>or=6/10,>1 week) were assessed for new diagnostic tests. New MR imaging, taken within 6 to 12 weeks of the start of a new LBP episode, was compared with baseline (asymptomatic) images. Two independent and blinded readers evaluated each baseline and follow-up study.

RESULTS

During the 5-year observation period of 200 subjects, 51 (25%) subjects were evaluated with a lumbar MRI for clinically serious LBP episodes, and 3/51 (6%) had a primary radicular complaint. These 51 subjects had 67 MR scans. Of 51 subjects, 43 (84%) had either unchanged MR or showed regression of baseline changes. The most common progressive findings were disc signal loss (10%), progressive facet arthrosis (10%), or increased end plate changes (4%). Only two subjects, both with primary radicular complaints, had new findings of probable clinical significance (4%). Subjects having another MR were more likely to have had chronic pain at baseline (odds ratio [OR]=3.19; 95% confidence interval [CI] 1.61-6.32), to smoke (OR=5.81; 95% CI 1.99-16.45), have baseline psychological distress (OR 2.27; 95% CI 1.15-4.49), and have previous disputed compensation claims (OR=2.35; 95% CI 0.97-5.69). Subjects involved in current compensation claims were also more likely to have an MR scan to evaluate the LBP episode (risk ratio=4.75, p<.001), but were unlikely to have significant new findings. New findings were not more frequent in subjects with LBP episodes developing after minor trauma than when LBP developed spontaneously.

CONCLUSION

Findings on MR imaging within 12 weeks of serious LBP inception are highly unlikely to represent any new structural change. Most new changes (loss of disc signal, facet arthrosis, and end plate signal changes) represent progressive age changes not associated with acute events. Primary radicular syndromes may have new root compression findings associated with root irritation.

Influence of diurnal hyperosmotic loading on the metabolism and matrix gene expression of a whole-organ intervertebral disc model

It is generally agreed that the mechanical environment of intervertebral disc cells plays an important role in maintaining a balanced matrix metabolism. The precise mechanism by which the signals are transduced into the cells is poorly understood. Osmotic changes in the extracellular matrix (ECM) are thought to be involved. Current in-vitro studies on this topic are mostly short-term and show conflicting data on the reaction of disc cells subjected to osmotic changes which is partially due to the heterogenous and often substantially-reduced culture systems. The aim of the study was therefore to investigate the effects of cyclic osmotic loading for 4 weeks on metabolism and matrix gene expression in a full-organ intervertebral disc culture system. Intervertebral disc/endplate units were isolated from New Zealand White Rabbits and cultured either in iso-osmotic media (335 mosmol/kg) or were diurnally exposed for 8 hours to hyper-osmotic conditions (485 mosmol/kg). Cell viability, metabolic activity, matrix composition and matrix gene expression profile (collagen types I/II and aggrecan) were monitored using Live/Dead cell viability assay, tetrazolium reduction test (WST 8), proteoglycan and DNA quantification assays and quantitative PCR. The results show that diurnal osmotic stimulation did not have significant effects on proteoglycan content, cellularity and disc cell viability after 28 days in culture. However, hyperosmolarity caused increased cell death in the early culture phase and counteracted up-regulation of type I collagen gene expression in nucleus and annulus cells. Moreover, the initially decreased cellular dehydrogenase activity recovered with osmotic stimulation after 4 weeks and aggrecan gene down-regulation was delayed, although the latter was not significant according to our statistical criteria. In contrast, collagen type II did not respond to the osmotic changes and was down-regulated in both groups. In conclusion, diurnal hyper-osmotic stimulation of a whole-organ disc/endplate culture partially inhibits a matrix gene expression profile as encountered in degenerative disc disease and counteracts cellular metabolic hypo-activity.

Advanced glycation end-products downregulating intervertebral disc cell production of proteoglycans in vitro

Object

The authors sought to clarify the role, if any, of advanced glycation end-products (AGEs) in disc degeneration.

Methods

Intervertebral discs were analyzed for the presence of AGEs and of their receptor (RAGE) by immunohistochemical analysis. Reverse transcriptase polymerase chain reaction (RT-PCR) was performed to detect any RAGE gene expression, and real-time PCR was used to quantify messenger RNA (mRNA) levels of aggrecan and collagen types I and II in nucleus pulposus cells treated with AGEs. Aggrecan protein concentration was determined by enzyme-linked immunosorbent assay.

Immunohistochemical analysis revealed that AGEs and RAGE were localized in the nucleus pulposus of the intervertebral disc. Advanced glycation end-products were found to significantly suppress the expression of aggrecan at both mRNA and protein levels in a dose- and time-dependent manner. The levels of collagen types I and II remained unchanged after treatments with AGEs.

Conclusions

These results suggest that the accumulation of AGEs and their interaction with their receptor in the nucleus pulposus might result in the downregulation of aggrecan production responsible for disc degeneration.

Improvement of lower extremity electrodiagnostic findings following a trial of spinal manipulation and motion-based therapy

BACKGROUND

Lumbar disc herniation is a problem frequently encountered in manual medicine. While manual therapy has shown reasonable success in symptomatic management of these cases, little information is known how manual therapy may affect the structure and function of the lumbar disc itself. In cases where lumbar disc herniation is accompanied by radicular symptoms, electrodiagnostic testing has been used to provide objective clinical information on nerve function. This report examines the treatment rendered for a patient with lower extremity neurological deficit, as diagnosed on electrodiagnostic testing. Patient was treated using spinal manipulation and exercises performed on a Pettibon Wobble Chair, using electrodiagnostic testing as the primary outcome assessment.

CASE PRESENTATION

An elderly male patient presented to a private spine clinic with right-sided foot drop. He had been prescribed an ankle-foot orthosis for this condition. All sensory, motor, and reflex findings in the right leg and foot were absent. This was validated on prior electromyography and nerve conduction velocity testing, performed by a board certified neurologist. Patient was treated using spinal manipulation twice-weekly and wobble chair exercises three times daily for 90 days total. Following this treatment, the patient was referred for follow-up electrodiagnostic studies. Significant improvements were made in these studies as well as self-rated daily function.

CONCLUSION

Motion-based therapies, as part of a comprehensive rehabilitation program, may contribute to the restoration of daily function and the reversal of neurological insult as detected by electrodiagnostic testing. Electrodiagnostic testing may be a useful clinical tool to evaluate the progress of chiropractic patients with lumbar disc herniation and radicular pain syndromes.

What is intervertebral disc degeneration, and what causes it?

STUDY DESIGN

Review and reinterpretation of existing literature.

OBJECTIVE

To suggest how intervertebral disc degeneration might be distinguished from the physiologic processes of growth, aging, healing, and adaptive remodeling.

SUMMARY OF BACKGROUND DATA

The research literature concerning disc degeneration is particularly diverse, and there are no accepted definitions to guide biomedical research, or medicolegal practice.

DEFINITIONS

The process of disc degeneration is an aberrant, cell-mediated response to progressive structural failure. A degenerate disc is one with structural failure combined with accelerated or advanced signs of aging. Early degenerative changes should refer to accelerated age-related changes in a structurally intact disc. Degenerative disc disease should be applied to a degenerate disc that is also painful.

JUSTIFICATION

Structural defects such as endplate fracture, radial fissures, and herniation are easily detected, unambiguous markers of impaired disc function. They are not inevitable with age and are more closely related to pain than any other feature of aging discs. Structural failure is irreversible because adult discs have limited healing potential. It also progresses by physical and biologic mechanisms, and, therefore, is a suitable marker for a degenerative process. Biologic progression occurs because structural failure uncouples the local mechanical environment of disc cells from the overall loading of the disc, so that disc cell responses can be inappropriate or "aberrant." Animal models confirm that cell-mediated changes always follow structural failure caused by trauma. This definition of disc degeneration simplifies the issue of causality: excessive mechanical loading disrupts a disc's structure and precipitates a cascade of cell-mediated responses, leading to further disruption. Underlying causes of disc degeneration include genetic inheritance, age, inadequate metabolite transport, and loading history, all of which can weaken discs to such an extent that structural failure occurs during the activities of daily living. The other closely related definitions help to distinguish between degenerate and injured discs, and between discs that are and are not painful.

Influence of osmotic pressure changes on the opening of existing cracks in 2 intervertebral disc models

STUDY DESIGN

An experimental hydrogel model and a numerical mixture model were used to investigate why the disc herniates while osmotic pressure is decreasing.

OBJECTIVE

To investigate the influence of decreasing osmotic pressure on the opening of cracks in the disc.

SUMMARY OF BACKGROUND DATA

In the degeneration process, the disc changes structure (i.e., cracks occur, and osmotic pressure decreases). Disc herniation typically develops when hydration declines, but, on the other hand, it is said that the anulus of a highly hydrated disc has a high risk of rupture. We hypothesized that disc herniation is preceded by the opening of cracks as a result of decreasing osmotic pressure.

METHODS

The osmotic pressure was changed in hydrogel samples with a crack, which was visualized with a confocal laser scanning microscope (Zeiss, Göttingen, Germany). A 2-dimensional finite element mixture model simulated a decrease in osmotic pressure around a crack in a swelling material.

RESULTS

Experiments and simulations show that a decrease in osmotic pressure results in the opening of cracks. The simulations show high effective stress concentrations around the crack tip, while the overall stress level decreases, indicating an increased risk of crack growth.

CONCLUSIONS

Decreasing osmotic pressure in a degenerating intervertebral disc enhances the opening of existing cracks, despite the concomitant decrease in anular stresses.

Mechanical concepts for disc regeneration

Different strategies exist to treat intervertebral disc degeneration. Biological attempts to regenerate the disc are promising. However, degeneration of the disc is always accompanied by alterations of disc height, intradiscal pressure, load distribution, and motion patterns, respectively. Since those preconditions are independent factors for disc degeneration, it is unlikely that regeneration may occur without firstly restoring the physiological status of the affected spinal segment. In vitro and in vivo animal studies demonstrate that disc distraction normalizes intradiscal height and pressure. Furthermore, histological and radiological examinations provided some evidence for regenerative processes in the disc. Only dynamic stabilization systems currently offer the potential of a mechanical approach to intervertebral disc regeneration. Dynamic stabilization systems either using pedicle screws or with an interspinous device, demonstrate restabilization of spinal segments and reduction of intradiscal pressure. Clinical reports of patients with degenerative disc disease who underwent dynamic stabilization are promising. However, there is no evidence that those implants will lead to disc regeneration. Future treatment concepts should combine intradiscal cell based therapy together with dynamic restoration of the affected spinal segment.

Disc distraction shows evidence of regenerative potential in degenerated intervertebral discs as evaluated by protein expression, magnetic resonance imaging, and messenger ribonucleic acid expression analysis

STUDY DESIGN

An animal model of degeneration was used to determine the effects of disc distraction, and was evaluated with magnetic resonance imaging (MRI) as well as gene and protein expression levels.

OBJECTIVE

To investigate gene expression and MRI effects of distraction.

SUMMARY OF BACKGROUND DATA

Disc degeneration can result from hyper-physiologic loading. Distracted discs with degeneration showed histologic signs of tissue recovery.

METHODS

There were 18 rabbits that underwent 28 days of compression (200 N) to induce moderate disc degeneration followed by 28 days of distraction (120 N; attached and loaded distraction device) or sham distraction (attached but unloaded distraction device). Comparison was performed with 56 days of compressed discs without distraction. Quantitative outcome measures were MRI signal intensity and gene expression analysis to determine: messenger ribonucleic acid levels for extracellular matrix genes, including collagen 1, collagen 2, biglycan, decorin, aggrecan, fibromodulin, and osteonectin; and matrix-regulative genes, including matrix metalloproteinase-13, tissue-inhibitor of matrix metalloproteinase-1, and bone morphogenetic protein (BMP)-2. Immunohistology was performed for collagen 2 and BMP-2 to label cells semiquantitatively by staining of the cell-surrounding matrix.

RESULTS

A total of 28 days of compression decreased signal intensity. Distraction over the same period reestablished physiologic signal intensity, however, a persistent reduction was found in sham distraction. Distraction resulted in gene expression up-regulation of collagen 1 (5.4-fold), collagen 2 (5.5-fold), biglycan (7.7-fold), and decorin (3.4-fold), while expression of fibromodulin (0.16-fold), tissue-inhibitor of matrix metalloproteinase-1 (0.05-fold), and BMP-2 (0.15-fold) was decreased, as compared with 56 days compression. Distracted discs showed more BMP-2 (19.67 vs. 3.67 in 56 days compression) and collagen 2 (18.67 vs. 11.33 in 56 days compression) positive cells per field.

CONCLUSIONS

Distraction results in disc rehydration, stimulated extracellular matrix gene expression, and increased numbers of protein-expressing cells.

Disc space narrowing as a new risk factor for vertebral fracture: the OFELY study

OBJECTIVE

In a previous cross-sectional analysis, we found a positive association between disc space narrowing (DSN) and vertebral fracture. The aim of the present study was to analyze prospectively the risk of vertebral and nonvertebral fractures in women with spine osteoarthritis (OA).

METHODS

Using radiographs, spine OA was evaluated in 634 postmenopausal women from the OFELY (Os des Femmes de Lyon) cohort (mean+/-SD age 61.2+/-9 years). Prevalence and severity of spine OA were assessed by scoring osteophytes and DSN. Incidental clinical fractures were prospectively registered during annual followup, and vertebral fractures were evaluated by radiography every 4 years.

RESULTS

During an 11-year followup, fractures occurred in 121 women, including 42 with vertebral fractures. No association was found between osteophytes and the risk of fracture. In contrast, DSN was associated with an increased risk of vertebral fractures but not of nonvertebral fractures. After adjusting for confounding variables, the presence of DSN was associated with a marked increased risk of vertebral fractures, with an odds ratio of 6.59 (95% confidence interval 1.36-31.9). In addition, 95% of incident vertebral fractures were located above the disc with the most severe narrowing.

CONCLUSION

This longitudinal study shows that, despite a higher bone mineral density (BMD), women with spine OA do not have a reduced risk of fracture and that DSN is significantly associated with vertebral fracture risk. The location of DSN and of incident vertebral fractures suggests that disc degeneration impairs the biomechanics of the above spine, which leads to the increased risk of vertebral fractures, independent of BMD. We suggest that DSN is a newly identified risk factor for vertebral fracture that should be taken into consideration when assessing vertebral fracture risk in postmenopausal women.

Rat spinal motion segment in organ culture: a cell viability study

STUDY DESIGN

This study investigated tissue integrity and viability of cells in an organ culture system of intervertebral disc (IVD) with adjoining vertebral bodies.

OBJECTIVE

The goal of this study was to design a methodology to maintain an IVD motion segment in organ culture, thereby preserving viability and tissue architecture.

SUMMARY OF BACKGROUND DATA

Study of IVD mechanobiology in vitro necessitates availability of vertebral bodies for controlled application of complex loads.

METHODS

IVD motion segments were dissected from rat lumbar segments and maintained in organ culture and cell viability was evaluated histochemically using NitroBlue Tetrazolium. Tissue integrity and morphology were evaluated using conventional histologic techniques.

RESULTS

The in vitro organ culture of motion segments maintained the viability and tissue integrity for 14 days. More than 95% viability in all three regions of interest (anulus fibrosus, nucleus pulposus, end plates) was maintained for 14 days in culture.

CONCLUSION

Our initial results suggest that long-term motion segment culture is practical, and the inclusion of vertebral bodies will facilitate anchoring during biomechanical stimulation. Thus, we expect the culture system to provide us with an excellent model for studying the pathomechanics of IVD degeneration and the effects of mechanical stimulation on the biology of IVD cells.

The alpha2 type IX collagen tryptophan polymorphism is associated with the severity of disc degeneration in younger patients with herniated nucleus pulposus of the lumbar spine

Tryptophan alleles in COL9A2 (Trp2) and COL9A3 (Trp3) have been linked to lumbar disc diseases in the Finnish population. Although such diseases consist of various pathogenetically different conditions, detailed analysis of each has not been well documented. The aim of this study was to clarify whether the collagen IX tryptophan alleles influence the symptomatic degeneration of the lumbar disc in Japanese patients with herniated nucleus pulposus. We performed a prospective study of 84 patients who underwent lumbar discectomy. The degree of disc degeneration was evaluated by magnetic resonance images in relation to the collagen IX genotype. Twenty patients (21.4%) had the Trp2 allele and no patients had the Trp3 allele. Patients under 40 years with the Trp2 allele showed more severe disc degeneration at the surgical level than did those without the Trp2 allele (odds ratio 6.00, P=0.043). In contrast, patients aged 40 years or over did not show significant association between disc degeneration and collagen IX genotype. Our results suggest that the Trp2 allele is an age-dependent risk factor for the severity of disc degeneration in younger patients with symptomatic herniated nucleus pulposus of the lumbar spine.

Lumbar disc degeneration: epidemiology and genetics

Research conducted over the past decade has led to a dramatic shift in the understanding of disc degeneration and its etiology. Previously, heavy physical loading-often associated with occupation-was the main suspected risk factor for disc degeneration, which was commonly viewed as a wear-and-tear phenomenon exacerbated by the precarious nutritional status of the disc. However, results of studies on twins suggest that physical loading specific to occupation and sport plays a relatively minor role in disc degeneration. Recent research indicates that heredity has a dominant role in disc degeneration, which would explain the variance of up to 74% seen in adult populations that have been studied to date. Since 1998, genetic influences have been confirmed by the identification of several gene forms associated with disc degeneration. This research is paving the way for a better understanding of the biologic mechanisms through which disc degeneration occurs, including specific interactions between genes and environment. Research into disc degeneration and genetics has become more limited by phenotypes or definitions and measures of disc degeneration than by DNA analysis. Standardized, universally accepted definitions of disc degeneration are lacking, in part due to limited knowledge of the process. The measurements that are selected depend on the method used to evaluate the disc and are often qualitative ordinal rating scales, lacking in precision. Although it is generally agreed that disc degeneration is common, the prevalence of specific findings is unclear. A review of the epidemiology of disc degeneration reveals wide-ranging prevalence estimates for various signs of disc degeneration in samples of the general population and in patients with back symptoms. The extreme variations in prevalence rates are likely largely due to inconsistencies in the definitions and measurements of disc degeneration. Such inconsistencies and inaccuracies impede epidemiologic research on disc degeneration.

Cell deformation and micromechanical environment in the intervertebral disc

The purpose of this research was to explore the in situ anatomic and mechanical environment of disc cells. Laser scanning confocal microscopy was used to characterize three-dimensional morphology of intervertebral disc cells, micromechanical deformation and interaction with extracellular matrix, and functional intercellular communication. Bovine coccygeal discs were used for both the anatomic and micromechanical investigations. Anulus fibrosus cells had a complex morphology with sinuous processes woven into the extracellular matrix, particularly in the outer aspect of the anulus where they were also interconnected via functional gap junctions. They were also found in an extensive pericellular matrix of type-VI collagen, joining as many as ten cells into linear cell arrays that could be extracted from the matrix as functional units. Mechanically, collagen fibril sliding was demonstrated to govern cell mechanics and strain transfer in the anulus fibrosus during loading activities. Lamellar cells were largely protected from direct tensile strains in the matrix, with minimal intercellular strains. However, intercellular strains between lamellar cells in adjacent arrays were large, illustrating shearing between linear cell arrays. Appreciable shear was observed across the lamellar cell bodies as well as to the cellular processes woven into the matrix. These findings demonstrated the morphologic and micromechanical complexity of anulus fibrosus cells. The knowledge of the in situ environment of disc cells will provide a base to investigate the mechanical implications of disc degeneration on the cellular environment and to better understand how mechanical and genetic risk factors can impact the cells that are essential to maintaining the intervertebral disc.

Lumbar disc disorders and low-back pain: socioeconomic factors and consequences

Socioeconomic factors are important risk factors for lumbar pain and disability. The total costs of low-back pain in the United States exceed $100 billion per year. Two-thirds of these costs are indirect, due to lost wages and reduced productivity. Each year, the fewer than 5% of the patients who have an episode of low-back pain account for 75% of the total costs. Because indirect costs rely heavily on changes in work status, total costs are difficult to calculate for many women and students as well as elderly and disabled patients. These methodologic challenges notwithstanding, the toll of lumbar disc disorders is enormous, underscoring the critical importance of identifying strategies to prevent these disorders and their consequences.

Effects of mechanical loading on intervertebral disc metabolism in vivo

The overall goal of this work is to define more clearly which mechanical loading conditions are associated with accelerated disc degeneration. This article briefly reviews recent studies describing the effects of mechanical loading on the metabolism of intervertebral disc cells and defines hypothetical models that provide a framework for quantitative relationships between mechanical loading and disc-cell metabolism. Disc cells respond to mechanical loading in a manner that depends on loading magnitude, frequency, and duration. On the basis of the current data, four models have been proposed to describe the effects of continuous loading on cellular metabolism: (1) on/off response, in which messenger ribonucleic acid (mRNA) transcription remains altered for the duration of loading; (2) maintenance, characterized by an initial change in mRNA levels with return to baseline levels; (3) adaptation, in which mRNA transcription is altered and remains at a new steady state; and (4) no response. In addition, five hypothetical mechanisms that describe the long-term consequences of these metabolic changes on disc-remodeling are presented. The transient nature of gene expression along with enzyme activation/inhibition is associated with changes at the protein level. The hypothetical models presented provide a framework for obtaining quantitative relationships between mechanical loading, gene expression, and changes at the compositional level; however, additional factors, such as regulatory mechanisms, must also be considered when describing disc-remodeling. A more quantitative relationship between mechanical loading effects and the metabolic response of the disc will contribute to injury prevention, facilitate more effective rehabilitation treatments, and help realize the potential of biologic and tissue engineering approaches toward disc repair.

Changes in gene expression and protein distribution at different stages of mechanically induced disc degeneration--an in vivo study on the New Zealand white rabbit

The objective of the study was to improve the biological understanding of degenerative disc disease using a rabbit model in which different stages of disc degeneration are induced by variation of the duration of loading with an external compression-device applying 2.4 MPa. Gene expression and protein distribution were analyzed in controls and after 1, 28, and 56 days of hyperphysiologic loading. To evaluate extracellular matrix genes, quantitative real-time reverse-transcriptase polymerase chain reaction was applied for collagen I, collagen II, biglycan, decorin, fibromodulin, fibronectin, aggrecan, and osteonectin. As representatives of catabolic, anticatabolic, and anabolic factors, matrix metalloproteinase-13 (MMP-13), tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), and bone morphogenetic protein-2 (BMP-2) were chosen. To evaluate protein distribution, immunohistochemistry was performed for collagen I, collagen II, and BMP-2/4. Matrix gene expression was characterized by two major developments: collagen I and II, biglycan, and decorin showed early elevation followed by later downregulation to control levels, whereas fibromodulin, fibronectin, aggrecan, and osteonectin showed continuous upregulation or remained at similar levels. Induction of MMP-13 gene expression was found in degenerated discs. TIMP-1 and BMP-2 were elevated immediately after hyperphysiologic loading and presented highest levels in the 56-day group. Immunohistochemistry showed less collagen II and BMP-2/4 positive cells after compression. In conclusion, elevated matrix gene expression represents an early cellular response to hyperphysiologic loading. As degeneration progresses, some matrix genes increase upregulation, whereas others start downregulation. Continuous upregulation of catabolic, anticatabolic, and anabolic factors indicates their important role in the degeneration process.

In vitro organ culture of the bovine intervertebral disc: effects of vertebral endplate and potential for mechanobiology studies

STUDY DESIGN

Whole bovine coccygeal discs were cultured under static load, with or without vertebral endplates (VEPs), and assessed for cell viability, biochemical stability, biosynthetic activity, and biosynthetic responsiveness to changes in mechanical load.

OBJECTIVES

To assess the effects of VEPs on biochemical and cellular stability of disc cells during in vitro culture of large disc explants. To determine whether cultured discs could respond to mechanical perturbation.

SUMMARY OF BACKGROUND DATA

Previous methods for culturing the intervertebral disc have focused on rabbit and rat discs, but the small size of these discs limits the relevance of these culture systems to the human condition. Bovine coccygeal discs have similar dimensions to the human lumbar disc (i.e., similar size and nominal stresses), but long-term culture of these discs has not been reported.

METHODS

Bovine coccygeal discs were harvested with or without VEPs, cultured under static load (5 kg, approximately 0.25 MPa, in situ swelling pressure) for up to 1 week, and evaluated for changes in hydration, glycosaminoglycan content, cell viability, and biosynthetic activity. Additionally, the biochemical and biosynthetic response of discs cultured without VEP to increasing the load to a 20-kg (approximately 1 MPa, the estimated stress in human lumbar disc during heavy lifting) static load for 6 hours was assessed.

RESULTS

During the first 24 hours, culturing discs with endplates was moderately better with regards to maintaining in situ anulus hydration and nucleus glycosaminoglycan levels. The endplates, however, obstructed media flow to the disc, resulting in a marked decrease in cell viability after 1 week of culture. Nucleus pulposus cell viability was maintained in discs cultured without endplates, but there was a significant drop in biosynthetic activity within 2 days of culture. Despite this drop, the disc cells in the discs without VEP remained biosynthetically responsive to changes in mechanical loading.

CONCLUSIONS

It is possible to maintain cell viability and the biosynthetic responsiveness of large discs for up to 1 week in vitro when the discs are cultured under static load and without VEP.