Age changes in lumbar intervertebral discs

Biological principles of adult degenerative scoliosis

The global aging population has led to an increase in geriatric diseases, including adult degenerative scoliosis (ADS). ADS is a spinal deformity affecting adults, particularly females. It is characterized by asymmetric intervertebral disc and facet joint degeneration, leading to spinal imbalance that can result in severe pain and neurological deficits, thus significantly reducing the quality of life. Despite improved management, molecular mechanisms driving ADS remain unclear. Current literature primarily comprises epidemiological and clinical studies. Here, we investigate the molecular mechanisms underlying ADS, with a focus on angiogenesis, inflammation, extracellular matrix remodeling, osteoporosis, sarcopenia, and biomechanical stress. We discuss current limitations and challenges in the field and highlight potential translational applications that may arise with a better understanding of these mechanisms.

A Microstructure-Based Mechanistic Approach to Detect Degeneration Effects on Potential Damage Zones and Morphology of Young and Old Human Intervertebral Discs

There is an increasing demand to develop predictive medicine through the creation of predictive models and digital twins of the different body organs. To obtain accurate predictions, real local microstructure, morphology changes and their accompanying physiological degenerative effects must be taken into account. In this article, we present a numerical model to estimate the long-term aging effect on the human intervertebral disc response by means of a microstructure-based mechanistic approach. It allows to monitor in-silico the variations in disc geometry and local mechanical fields induced by age-dependent long-term microstructure changes. Both lamellar and interlamellar zones of the disc annulus fibrosus are constitutively represented by considering the main underlying microstructure features in terms of proteoglycans network viscoelasticity, collagen network elasticity (along with content and orientation) and chemical-induced fluid transfer. With age, a noticeable increase in shear strain is especially observed in the posterior and lateral posterior regions of the annulus which is in correlation with the high vulnerability of elderly people to back problems and posterior disc hernia. Important insights about the relation between age-dependent microstructure features, disc mechanics and disc damage are revealed using the present approach. These numerical observations are hardly obtainable using current experimental technologies which makes our numerical tool useful for patient-specific long-term predictions.

Recent Advances in Coupled MBS and FEM Models of the Spine—A Review

How back pain is related to intervertebral disc degeneration, spinal loading or sports-related overuse remains an unanswered question of biomechanics. Coupled MBS and FEM simulations can provide a holistic view of the spine by considering both the overall kinematics and kinetics of the spine and the inner stress distribution of flexible components. We reviewed studies that included MBS and FEM co-simulations of the spine. Thereby, we classified the studies into unidirectional and bidirectional co-simulation, according to their data exchange methods. Several studies have demonstrated that using unidirectional co-simulation models provides useful insights into spinal biomechanics, although synchronizing the two distinct models remains a key challenge, often requiring extensive manual intervention. The use of a bidirectional co-simulation features an iterative, automated process with a constant data exchange between integrated subsystems. It reduces manual corrections of vertebra positions or reaction forces and enables detailed modeling of dynamic load cases. Bidirectional co-simulations are thus a promising new research approach for improved spine modeling, as a main challenge in spinal biomechanics is the nonlinear deformation of the intervertebral discs. Future studies will likely include the automated implementation of patient-specific bidirectional co-simulation models using hyper- or poroelastic intervertebral disc FEM models and muscle forces examined by an optimization algorithm in MBS. Applications range from clinical diagnosis to biomechanical analysis of overload situations in sports and injury prediction.

Deep learning-based high-accuracy quantitation for lumbar intervertebral disc degeneration from MRI

To help doctors and patients evaluate lumbar intervertebral disc degeneration (IVDD) accurately and efficiently, we propose a segmentation network and a quantitation method for IVDD from T2MRI. A semantic segmentation network (BianqueNet) composed of three innovative modules achieves high-precision segmentation of IVDD-related regions. A quantitative method is used to calculate the signal intensity and geometric features of IVDD. Manual measurements have excellent agreement with automatic calculations, but the latter have better repeatability and efficiency. We investigate the relationship between IVDD parameters and demographic information (age, gender, position and IVDD grade) in a large population. Considering these parameters present strong correlation with IVDD grade, we establish a quantitative criterion for IVDD. This fully automated quantitation system for IVDD may provide more precise information for clinical practice, clinical trials, and mechanism investigation. It also would increase the number of patients that can be monitored.

Sex- and Age-related Differences in Spinal Degeneration: An Anatomical and Magnetic Resonance Imaging Study of the Human Spine

Objectives:

A precise anatomical understanding of the morphology of the spine is indispensable for neck and low back pain therapy including rehabilitation. However, few studies have directly addressed spinal morphology with a focus on the height of the vertebral body and discs. The aim of the current study was to analyze sex- and age-related changes in the spine by measuring the distance between adjacent centers of the intervertebral disc spaces from the posterior aspect in cadavers and by using magnetic resonance imaging (MRI) measurements at the cervical and lumbar vertebral levels.

Methods:

In the cadaveric study, the posterior distance between the adjacent centers of the disc spaces was measured for 58 spinal canals. The equivalent distances were examined using MRI in 370 and 660 subjects who presented with neck pain and back pain, respectively.

Results:

The distance between the adjacent centers of the intervertebral disc spaces in male cadavers was larger than that in female cadavers from C3 to L5/S1. The MRI results showed that the distance between the adjacent centers of the intervertebral disc spaces decreased with age in all spinal areas in men and women. Cadaveric values were significantly lower than the MRI values in men, whereas in women, no significant differences were observed.

Conclusions:

These results suggest that age-related changes in the cervical and lumbar spine are associated with differences between men and women in the degrees of progressive vertebral body and disc degeneration.

Evaluation of injectable nucleus augmentation materials for the treatment of intervertebral disc degeneration

Back pain affects a person's health and mobility as well as being associated with large health and social costs. Lower back pain is frequently caused by degeneration of the intervertebral disc. Current operative and non-operative treatments are often ineffective and expensive. Nucleus augmentation is designed to be a minimally invasive method of restoring the disc to its native healthy state by restoring the disc height, and mechanical and/or biological properties. The majority of the candidate materials for nucleus augmentation are injectable hydrogels. In this review, we examine the materials that are currently under investigation for nucleus augmentation, and compare their ability to meet the design requirements for this application. Specifically, the delivery of the material into the disc, the mechanical properties of the material and the biological compatibility are examined. Recommendations for future testing are also made.

Morphology and growth of the pediatric lumbar vertebrae

BACKGROUND CONTEXT

The majority of existing literature describing pediatric lumbar vertebral morphology are limited to characterization of the vertebral bodies, pedicles, and spinal canal and no study has described the rates of growth for any lumbar vertebral structure. While it is known that growth of the lumbar vertebrae results in changes in vertebral shape, the dimension ratios used to quantify these shape changes do not represent the 3D morphology of the vertebral structures. Additionally, many of the previous evaluations of growth and shape are purely descriptive and do not investigate sexual dimorphism or variations across vertebral levels.

PURPOSE

This study aims to establish a database of pediatric lumbar vertebra dimension, growth, and shape data for subjects between and ages of 1 and 19 years.

STUDY DESIGN

A retrospective study of computed tomography (CT) data.

METHODS

Retrospective, abdominal, CT scans of 102 skeletally normal pediatric subjects (54 males, 48 females) between the ages of 1 and 19 years were digitally reconstructed and manually segmented. Thirty surface landmark points (LMPs), 30 vertebral measurements, the centroid size, centroid location, and the local orientation were collected for each lumbar vertebra along with the centroid size of the LMPs comprising each subject's full lumbar spine and their intervertebral disc (IVD) heights. Nonparametric statistics were used to compare dimension values across vertebral levels and between sexes. Linear models with age as the independent variable were used to characterize dimension growth for each sex and vertebral level. Age-dependent quadratic equations were fit to LMP distributions resulting from a generalized Procrustes analysis (GPA) of the vertebrae and fixed effects models were used to investigate differences in model coefficients across levels and between sexes.

RESULTS

Intervertebral level dimension differences were observed across all vertebral structures in both sexes while pedicle widths and IVDs heights were the only measurements found to be sexually dimorphic. Dimension growth rates generally varied across vertebral levels and the growth rates of males were typically larger than those of females. Differences between male and female vertebral shapes were also found for all lumbar vertebral structures.

CONCLUSIONS

To the authors' knowledge, this is the first study to report growth rates for the majority of pediatric lumbar vertebral structures and the first to describe the 3D age-dependent shapes of the pediatric lumbar spine and vertebrae. In addition to providing a quantitative database, the dimension, growth, and shape data reported here would have applications in medical device design, surgical planning, surgical training, and biomechanical modeling.

Prediction of Lumbar Disc Bulging and Protrusion by Anthropometric Factors and Disc Morphology

The relationship between reduced disc height and disc bulging and/or protrusion has been controversial. The purposes of this study were to examine the relationship between disc morphology and disc bulging and protrusion and to establish a model for predicting disc bulging and protrusion. This is a retrospective study. A total of 452 MRI scans from a spine study were analysed, 210 (46.5%) were men. Logistic regression analysis was applied to identify the association between anthropometric factors, disc morphology factors, and outcome. Model 1 was constructed using anthropometric variables to investigate the capacity for predicting outcomes. Model 2 was constructed using anthropometric and disc morphology variables. Age, body weight, body height, disc height, and disc depth were significantly associated with outcome. The area under the curve (AUC) statistics of Model 2 were significantly better than those of Model 1 at the L3-L4 and L4-L5 levels but not at the L5-S1 level. The results showed an association between disc morphology and disc bulging and/or protrusion at the L3-L4, L4-L5, and L5-S1 levels. The model utilizing both anthropometric factors and disc morphology factors had a better capacity to predict disc bulging and/or protrusion compared with the model using only anthropometric factors.

Advances of Naturally Derived and Synthetic Hydrogels for Intervertebral Disk Regeneration

Intervertebral disk (IVD) degeneration is associated with most cases of cervical and lumbar spine pathologies, amongst which chronic low back pain has become the primary cause for loss of quality-adjusted life years. Biomaterials science and tissue engineering have made significant progress in the replacement, repair and regeneration of IVD tissue, wherein hydrogel has been recognized as an ideal biomaterial to promote IVD regeneration in recent years. Aspects such as ease of use, mechanical properties, regenerative capacity, and their applicability as carriers for regenerative and anti-degenerative factors determine their suitability for IVD regeneration. This current review provides an overview of naturally derived and synthetic hydrogels that are related to their clinical applications for IVD regeneration. Although each type has its own unique advantages, it rarely becomes a standard product in truly clinical practice, and a more rational design is proposed for future use of biomaterials for IVD regeneration. This review aims to provide a starting point and inspiration for future research work on development of novel biomaterials and biotechnology.

Effects of Glucose Deprivation on ATP and Proteoglycan Production of Intervertebral Disc Cells under Hypoxia

As the most common cause of low back pain, the cascade of intervertebral disc (IVD) degeneration is initiated by the disappearance of notochordal cells and progressive loss of proteoglycan (PG). Limited nutrient supply in the avascular disc environment restricts the production of ATP which is an essential energy source for cell survival and function such as PG biosynthesis. The objective of this study was to examine ATP level and PG production of porcine IVD cells under prolonged exposure to hypoxia with physiological glucose concentrations. The results showed notochordal NP and AF cells responded differently to changes of oxygen and glucose. Metabolic activities (including PG production) of IVD cells are restricted under the in-vivo nutrient conditions while NP notochordal cells are likely to be more vulnerable to reduced nutrition supply. Moreover, provision of energy, together or not with genetic regulation, may govern PG production in the IVD under restricted nutrient supply. Therefore, maintaining essential levels of nutrients may reduce the loss of notochordal cells and PG in the IVD. This study provides a new insight into the metabolism of IVD cells under nutrient deprivation and the information for developing treatment strategies for disc degeneration.

Multidimensional vertebral endplate defects are associated with disc degeneration, modic changes, facet joint abnormalities, and pain

The aim of the current study was to investigate the multi-dimensional characteristics of lumbar endplate defects in humans in relation to disc degeneration and other MRI phenotypes as well as their role with pain and disability. A total of 108 subjects were recruited and underwent 3T MRI of the lumbar spine. Structural endplate defects were identified and their dimensions were measured in terms of maximum width and depth, and were then standardized to the actual width of the endplate and depth of the vertebral body, respectively. Both width and depth of all endplate defects in each subject were added separately and scores were assigned on the basis of size from 1 to 3. Combining both scores provided "cumulative endplate defect scores." Disc degeneration scores, Modic changes, disc displacement, HIZ, and facet joint changes were assessed. Subject demographics, pain profile, and Oswestry Disability Index (ODI) were also obtained. Endplate defects were observed in 67.5% of the subjects and in 13.5% of the endplates. All dimensions of endplate defects showed significance with disc degenerative scores, Modic changes, and posterior disc displacement (p < 0.05). Maximum width (p = 0.009) and its standardized value (p = 0.02), and cumulative endplate defect scores (p = 0.004) increased with narrow facet joints. Cumulative endplate defect scores showed a strong positive association with ODI (p < 0.05) compared to disc degenerative scores. Large size endplate defects were strongly associated with degenerative spine changes and more back-related disability. Findings from this study stress the need to assess endplate findings from a multi-dimensional perspective, whose role may have clinical utility. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Biomechanics of the Lumbar Facet Joint

Zygapophyseal, or facet, joints are complicated biomechanical structures in the spine, with a complex three-dimensional (3D) anatomy, variable mechanical functions in different spinal movements, and effects on the overall spine mechanical behavior. The 3D morphology of the facet joint is linked to its biomechanical function. Failure of the biomechanical function of the facet joint leads to osteoarthritic changes in it and is implicated in other spinal disorders such as degenerative spondylolisthesis. Facet joints and intervertebral disk are part of an entity called the spinal motion segment, the three-joint complex, or the articular triad. Functioning together, the structures in the spinal motion segments provide physiological spinal motion, while protecting the spine by preventing activities that can be injurious. Loss of intervertebral disk height associated with disk degeneration affects the mechanical behavior of facet joints. Axial compressive load transmission through the tip of the inferior articular process can occur in the extended position, especially with reduced disk height, which may cause capsular impingement and low back pain. The 3D curvature of the articular surfaces and capsular ligaments play important roles in different spinal positions. In this review article, we will summarize the anatomy of the lumbar facet joint relevant to its biomechanical function and biomechanical behavior under different loading conditions.

Materials for the Spine: Anatomy, Problems, and Solutions

Disc degeneration affects 12% to 35% of a given population, based on genetics, age, gender, and other environmental factors, and usually occurs in the lumbar spine due to heavier loads and more strenuous motions. Degeneration of the extracellular matrix (ECM) within reduces mechanical integrity, shock absorption, and swelling capabilities of the intervertebral disc. When severe enough, the disc can bulge and eventually herniate, leading to pressure build up on the spinal cord. This can cause immense lower back pain in individuals, leading to total medical costs exceeding $100 billion. Current treatment options include both invasive and noninvasive methods, with spinal fusion surgery and total disc replacement (TDR) being the most common invasive procedures. Although these treatments cause pain relief for the majority of patients, multiple challenges arise for each. Therefore, newer tissue engineering methods are being researched to solve the ever-growing problem. This review spans the anatomy of the spine, with an emphasis on the functions and biological aspects of the intervertebral discs, as well as the problems, associated solutions, and future research in the field.

Morphometric Analysis of Lumbar Intervertebral Disc Height: An Imaging Study

BACKGROUND

Little published data exist regarding normal values of disc height. Current literature relies on plain radiographs making accurate measurements of individual lumbar disc height difficult.

OBJECTIVE

We seek to establish normal values for lumbar intervertebral discs in different age groups using computed tomography scans in healthy individuals.

METHODS

Two hundred forty anonymized abdominal computed tomography scans (131 women) were prospectively collected once institutional review board approval was obtained. Individuals with spinal pathologies were excluded. Disc height measurements were obtained at the anterior edge, center, and posterior edge of each vertebra in the midsagittal plane, averaged, and compared against age and sex.

RESULTS

Average age was 45 (14-83) years for women and 48 (14-89) years for men. Average lumbar disc height was 5.6 ± 1.1 mm for men and 4.8 ± 0.8 mm for women at T12/L1, 6.9 ± 1.3 mm for men and 5.8 ± 0.9 mm for women at L1/2, 8.1 ± 1.4 mm for men and 6.9 ± 1.1 mm for women at L2/3, 8.7 ± 1.5 mm for men and 7.6 ± 1.2 mm for women at L3/4, 9.2 ± 1.6 mm for men and 8.5 ± 1.6 mm for women at L4/5, and 8.8 ± 1.6 mm for men and 8.6 ± 1.8 mm for women at L5/S1. Disc height was significantly smaller for women than men (P < 0.001), except at L5/S1.

CONCLUSIONS

Variation in disc height is determined much more by sex than age. The maximum height of the interbody space in the adult lumbar spine was at the L4/5 level (8.9 ± 1.7 mm [men], 8.6 ± 1.8 mm [women]). Based on our findings, >10 mm cage height will result in supraphysiologic interbody space restoration and potentially predispose to complications.

Is it appropriate to measure age-related lumbar disc degeneration on the mid-sagittal MR image? A quantitative image study

PURPOSE

Even though phenotypes of disc degeneration vary on different sagittal magnetic resonance images (MRI), measurements typically are acquired on the mid-sagittal MRI. This study investigated the appropriateness of using the mid-sagittal MRI to measure various phenotypes of age-related disc degeneration.

METHODS

Lumbar spine MRIs of 66 subjects (mean age 50.3 years, standard deviation 16.5 years, range 22-84 years) were studied. An image analysis program Spine Explorer was used to obtain quantitative measurements for disc height, bulging, and signal on para- and mid-sagittal T2-weighted MRIs. Measurements on para- and mid-sagittal MRIs and their associations with age were compared.

RESULTS

Measurements of disc height, signal, and posterior disc bulging acquired on the mid-sagittal MRI were greater than those on the para-sagittal MRIs. Disc height measurements were not linearly associated with age. Greater age was correlated with greater anterior (r = 0.45, P < 0.001) and posterior (r = 0.33, P < 0.01) bulging on para-sagittal MRIs, but not posterior disc bulging on the mid-sagittal MRI (r = - 0.10, P > 0.05). Disc signal intensity measurements on the mid-sagittal MRI had stronger correlations with age than those on para-sagittal MRIs. Mean and standard deviation of disc signal intensity acquired on the mid-sagittal MRI had the strongest correlations with age among all measures of disc degeneration studied (r = - 0.50, - 0.67, respectively, P < 0.001 for both).

CONCLUSIONS

Disc signal measurements acquired on the mid-sagittal MRI were reliable and had strong correlations with age and thus can be used as an appropriate measure of disc degeneration. Disc bulging had better be measured on para-sagittal MRIs. Although severe disc narrowing clearly is a sign of severe disc degeneration, disc height was not linearly associated with age.

Disc Degeneration in the Thoracolumbar Junctional Region

Disc dimensions and lengths of spondylophytes in the thoracolumbar junctional region (T10-L1) of 37 male cadaveric spines were measured from conventional radiographs. The disc degeneration was assessed by discography. The surface areas of the spondylophytes at vertebral body margins were recorded directly from the bones of 24 of the spines. Disc degeneration and the largest spondylophytes at corresponding levels measured from radiographs were related at T10-11 and at T11-12 (r=0.41 and r=0.43; p<0.01), but not at T 12-L1 (r=−0.14). In the individual discs, however, only large spondylophytes in radiographs (actual length over 4 mm) were related to signs of disc degeneration. In addition, ‘traction spurs’ and Scheuermann's changes were more often associated with severe disc degeneration than ‘claw-type’ spondylophytes. The intervertebral disc space height correlated poorly with disc degeneration except, to some extent, at T11-12. Thus, the assessment of disc degeneration from conventional radiographs seems unreliable at this region of the spine.

Zygapophysial joint pain in selected patients

The zygapophysial joints (z-joints), together with the intervertebral disc, form a functional spine unit. The joints are typical synovial joints with an innervation from two medial branches of the dorsal rami. The joint capsule and the surrounding structures have an extensive nerve supply. The stretching of the capsule and loads being transmitted through the joint can cause pain. The importance of the z-joints as a pain generator is often underestimated because the prevalence of z-joint pain (10%-80%) is difficult to specify. Z-joint pain is a somatic referred pain. Morning stiffness and pain when moving from a sitting to a standing position are typical. No historic or physical examination variables exist to identify z-joint pain. Also, radiologic findings do not have a diagnostic value for pain from z-joints. The method with the best acceptance for diagnosing z-joint pain is controlled medial branch blocks (MBBs). They are the most validated of all spinal interventions, although false-positive and false-negative results exist and the degree of pain relief after MBBs remains contentious. The prevalence of z-joint pain increases with age, and it often comes along with other pain sources. Degenerative changes are commonly found. Z-joints are often affected by osteoarthritis and inflammatory processes. Often additional factors including synovial cysts, spondylolisthesis, spinal canal stenosis, and injuries are present. The only truly validated treatment is medial branch neurotomy. The available technique vindicates the use of radiofrequency neurotomy provided that the correct technique is used and patients are selected rigorously using controlled blocks.

The ancestral shape hypothesis: an evolutionary explanation for the occurrence of intervertebral disc herniation in humans

Background

Recent studies suggest there is a relationship between intervertebral disc herniation and vertebral shape. The nature of this relationship is unclear, however. Humans are more commonly afflicted with spinal disease than are non-human primates and one suggested explanation for this is the stress placed on the spine by bipedalism. With this in mind, we carried out a study of human, chimpanzee, and orangutan vertebrae to examine the links between vertebral shape, locomotion, and Schmorl’s nodes, which are bony indicators of vertical intervertebral disc herniation. We tested the hypothesis that vertical disc herniation preferentially affects individuals with vertebrae that are towards the ancestral end of the range of shape variation within Homo sapiens and therefore are less well adapted for bipedalism.

Results

The study employed geometric morphometric techniques. Two-dimensional landmarks were used to capture the shapes of the superior aspect of the body and posterior elements of the last thoracic and first lumbar vertebrae of chimpanzees, orangutans, and humans with and without Schmorl’s nodes. These data were subjected to multivariate statistical analyses.

Canonical Variates Analysis indicated that the last thoracic and first lumbar vertebrae of healthy humans, chimpanzees, and orangutans can be distinguished from each other (p<0.028), but vertebrae of pathological humans and chimpanzees cannot (p>0.4590). The Procrustes distance between pathological humans and chimpanzees was found to be smaller than the one between pathological and healthy humans. This was the case for both vertebrae. Pair-wise MANOVAs of Principal Component scores for both the thoracic and lumbar vertebrae found significant differences between all pairs of taxa (p<0.029), except pathological humans vs chimpanzees (p>0.367). Together, these results suggest that human vertebrae with Schmorl’s nodes are closer in shape to chimpanzee vertebrae than are healthy human vertebrae.

Conclusions

The results support the hypothesis that intervertebral disc herniation preferentially affects individuals with vertebrae that are towards the ancestral end of the range of shape variation within H. sapiens and therefore are less well adapted for bipedalism. This finding not only has clinical implications but also illustrates the benefits of bringing the tools of evolutionary biology to bear on problems in medicine and public health.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0336-y) contains supplementary material, which is available to authorized users.

CT morphometry of adult thoracic intervertebral discs

PURPOSE

Despite being commonly affected by degenerative disorders, there are few data on normal thoracic intervertebral disc dimensions. A morphometric analysis of adult thoracic intervertebral discs was, therefore, undertaken.

METHODS

Archival computed tomography scans of 128 recently deceased individuals (70 males, 58 females, 20-79 years) with no known spinal pathology were analysed to determine thoracic disc morphometry and variations with disc level, sex and age. Reliability was assessed by intraclass correlation coefficients (ICCs).

RESULTS

Anterior and posterior intervertebral disc heights and axial dimensions were significantly greater in men (anterior disc height 4.0±1.4 vs 3.6±1.3 mm; posterior disc height 3.6±0.90 vs 3.4±0.93 mm; p<0.01). Disc heights and axial dimensions at T4-5 were similar or smaller than at T2-3, but thereafter increased caudally (mean anterior disc height T4-5 and T10-11, 2.7±0.7 and 5.4±1.2 mm, respectively, in men; 2.6±0.8 and 5.1±1.3 mm, respectively, in women; p<0.05). Except at T2-3, anterior disc height decreased with advancing age and anteroposterior and transverse disc dimensions increased; posterior and middle disc heights and indices of disc shape showed no consistent statistically significant changes. Most parameters showed substantial to almost perfect agreement for intra- and inter-rater reliability.

CONCLUSIONS

Thoracic disc morphometry varies significantly and consistently with disc level, sex and age. This study provides unique reference data on adult thoracic intervertebral disc morphometry, which may be useful when interpreting pathological changes and for future biomechanical and functional studies.

Lumbar disc nomenclature: version 2.0: recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology, and the American Society of Neuroradiology

STUDY DESIGN

This article comprises a review of the literature pertaining to the normal and pathological lumbar disc and the compilation of a standardized nomenclature.

OBJECTIVE

To provide a resource that promotes a clear understanding of lumbar disc terminology among clinicians, radiologists, and researchers.

SUMMARY OF BACKGROUND DATA

The article "Nomenclature and Classification of Lumbar Disc Pathology. Recommendations of the Combined Task Forces of the North American Spine Society, American Society of Spine Radiology and American Society of Neuroradiology" was published in 2001 in Spine © Lippincott, Williams and Wilkins and formally endorsed by the 3 boards. Its purpose, which it served for well over a decade, was to promote greater clarity and consistency of usage of spine terminology. Since 2001, there has been sufficient evolution in our understanding of the lumbar disc to suggest the need for revision and updating. The document represents the consensus recommendations of the current combined task forces and reflects changes consistent with current concepts in radiological and clinical care.

METHODS

A PubMed search was performed for literature pertaining to the lumbar disc. The task force members individually and collectively reviewed the literature and revised the 2001 document. It was then reviewed by the governing boards of the American Society of Spine Radiology, the American Society of Neuroradiology, and the North American Spine Society. After further revision based on their feedback, the paper was approved for publication.

RESULTS

The article provides a discussion of the recommended diagnostic categories and a glossary of terms pertaining to the lumbar disc, a detailed discussion of the terms and their recommended usage, as well as updated illustrations and literature references.

CONCLUSION

We have revised and updated a document that, since 2001, has provided a widely accepted nomenclature that helps maintain consistency and accuracy in the description of the properties of the normal and abnormal lumbar discs and that serves as a system for classification and reporting built upon that nomenclature.

Lumbar disc nomenclature: version 2.0: Recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology

BACKGROUND CONTEXT

The paper ''Nomenclature and classification of lumbar disc pathology, recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology,'' was published in 2001 in Spine (© Lippincott, Williams & Wilkins). It was authored by David Fardon, MD, and Pierre Milette, MD, and formally endorsed by the American Society of Spine Radiology (ASSR), American Society of Neuroradiology (ASNR), and North American Spine Society (NASS). Its purpose was to promote greater clarity and consistency of usage of spinal terminology, and it has served this purpose well for over a decade. Since 2001, there has been sufficient evolution in our understanding of the lumbar disc to suggest the need for revision and updating of the original document. The revised document is presented here, and it represents the consensus recommendations of contemporary combined task forces of the ASSR, ASNR, and NASS. This article reflects changes consistent with current concepts in radiologic and clinical care.

PURPOSE

To provide a resource that promotes a clear understanding of lumbar disc terminology amongst clinicians, radiologists, and researchers. All the concerned need standard terms for the normal and pathologic conditions of lumbar discs that can be used accurately and consistently and thus best serve patients with disc disorders.

STUDY DESIGN

This article comprises a review of the literature.

METHODS

A PubMed search was performed for literature pertaining to the lumbar disc. The task force members individually and collectively reviewed the literature and revised the 2001 document. The revised document was then submitted for review to the governing boards of the ASSR, ASNR, and NASS. After further revision based on the feedback from the governing boards, the article was approved for publication by the governing boards of the three societies, as representative of the consensus recommendations of the societies.

RESULTS

The article provides a discussion of the recommended diagnostic categories pertaining to the lumbar disc: normal; congenital/developmental variation; degeneration; trauma; infection/inflammation; neoplasia; and/or morphologic variant of uncertain significance. The article provides a glossary of terms pertaining to the lumbar disc, a detailed discussion of these terms, and their recommended usage. Terms are described as preferred, nonpreferred, nonstandard, and colloquial. Updated illustrations pictorially portray certain key terms. Literature references that provided the basis for the task force recommendations are included.

CONCLUSIONS

We have revised and updated a document that, since 2001, has provided a widely acceptable nomenclature that helps maintain consistency and accuracy in the description of the anatomic and physiologic properties of the normal and abnormal lumbar disc and that serves as a system for classification and reporting built upon that nomenclature.

Growth guidance system for early-onset scoliosis: comparison of experimental and retrieval wear

STUDY DESIGN

Laboratory study conducted using an in vitro wear simulator with a growth guidance system. Analysis of variance performed to compare in vitro specimens (n = 6) with in vivo retrieval components (n = 5).

OBJECTIVE

To characterize the stainless steel, wear debris potential of a spinal growth guidance system by developing an in vitro model and validating tested implants with retrospectively obtained retrievals.

SUMMARY OF BACKGROUND DATA

Growth enabling, surgical treatments have been developed to provide fusionless options for patients with early-onset scoliosis. There exist few data regarding the wear debris associated with such spinal systems.

METHODS

In this study, we determined in vitro wear from the stainless steel components of the SHILLA™ Growth Guidance System. An analogue lumbar spine model was adapted from ISO 12189:2008 to assess the growth guidance system. In a multistation wear simulator, 6 assembled constructs were tested under displacement control for 5 million cycles (Mc) with diluted bovine serum, and the wear was measured gravimetrically at end of the test. The components were compared quantitatively for wear scar depth with retrieved growth guidance implants (n = 5), and qualitatively for wear, corrosion, and other surface damage.

RESULTS

The average total wear rate over 5 Mc was 0.39 ± 0.13 mm/Mc (3.12 ± 1.01 mg/Mc) with an average particle size of 1.3 μm in equivalent circular diameter. Prominent wear scars were noticed on both the tested and retrieved specimens with no statistical difference in the wear scar depths of the tested and retrieved components when set and multiaxial screws when compared collectively.

CONCLUSION

An in vitro wear analysis for a spinal growth guidance system was conducted using a novel protocol and validated against retrieved implants. This is the first study establishing a baseline value for the wear of "growth enabling" devices for the treatment of early-onset scoliosis.

Morphological changes of lumbar vertebral bodies and intervertebral discs associated with decrease in bone mineral density of the spine: a cross-sectional study in elderly subjects

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

To investigate changes in the morphology of the lumbar vertebrae and intervertebral discs associated with osteoporosis of the spine in elderly subjects.

SUMMARY OF BACKGROUND DATA

Osteoporosis is a common condition that primarily affects the elderly with significant impact on quality of life. How exactly osteopenia and osteoporosis influence vertebral and intervertebral disc morphology remains unknown and needs exploration.

METHODS

A total of 395 community-dwelling ambulatory adults from 67 to 89 years of age were studied. The lumbar bone mineral density (BMD) was measured by dual-energy x-ray absorptiometry. T2-weighted sagittal images of the lumbar spine were obtained using a 1.5-T magnet. For each subject, the anterior height (Ha), middle height (Hm), posterior height (Hp), and anterior-posterior (AP) dimension of the 5 lumbar vertebrae (L1-L5) and 6 intervertebral discs (T12-L1 to L5-S1) were measured. To minimize the age effect, volume of these vertebrae and discs was measured in subgroups of 47 men (mean age = 74 yr, range: 73-75 yr) and 67 women (mean age = 72 yr, range: 71-73 yr). Continuous variables were examined by analysis of covariance after adjustment of height and age.

RESULTS

There was no significant age difference between the groups of normal BMD, osteopenia, and osteoporosis. For the vertebral bodies, lower BMD was associated with a decrease of Ha, Hm, and Hp but not AP in both sexes, leading to an increased biconcavity index. For the discs, lower BMD was associated with a decrease of Ha and Hp, as well as AP, and an increase in Hm in both men and women. The disc biconvexity index was increased. Lower BMD is associated with an overall decrease in both vertebral volume and disc volume.

CONCLUSION

Lower BMD is associated with a decreasing trend in both lumbar vertebral and disc volumes in elderly subjects but an increase in the Hm of the intervertebral discs.

Intervertebral disc degeneration: evidence for two distinct phenotypes

We review the evidence that there are two types of disc degeneration. 'Endplate-driven' disc degeneration involves endplate defects and inwards collapse of the annulus, has a high heritability, mostly affects discs in the upper lumbar and thoracic spine, often starts to develop before age 30 years, usually leads to moderate back pain, and is associated with compressive injuries such as a fall on the buttocks. 'Annulus-driven' disc degeneration involves a radial fissure and/or a disc prolapse, has a low heritability, mostly affects discs in the lower lumbar spine, develops progressively after age 30 years, usually leads to severe back pain and sciatica, and is associated with repetitive bending and lifting. The structural defects which initiate the two processes both act to decompress the disc nucleus, making it less likely that the other defect could occur subsequently, and in this sense the two disc degeneration phenotypes can be viewed as distinct.

Prevalence of non-fracture short vertebral height is similar in premenopausal and postmenopausal women: the osteoporosis and ultrasound study

We observed similar prevalence of short vertebral height without endplate depression (SVH) in young women aged 20-39 years and older women aged 55-79 years. There was no association between SVH and low bone density. In older women, therefore, SVH may be largely long standing and not indicative of osteoporotic fracture.

INTRODUCTION

Algorithm-based qualitative (ABQ) definition of osteoporotic vertebral fracture (VF) requires evidence of endplate fracture, and there is no minimum threshold for apparent 'reduction' in vertebral height. In older women, SVH without endplate fracture identified on baseline assessment may be long standing and unrelated to VF. If this is so, we would expect to see a similar prevalence of SVH in younger women. We aimed to compare the prevalence of pre- and postmenopausal women with SVH and the characteristics of women with and without SVH.

METHODS

We used the ABQ method to classify baseline vertebral images (DXA-based imaging) from 257 premenopausal and 1,361 postmenopausal women participating in the population-based Osteoporosis and Ultrasound Study. Images were classified as follows: normal (no VF, no SVH), SVH (no VF) or VF (with/without SVH in unfractured vertebrae). We compared proportions of women with SVH (chi-squared test) and compared age, height, weight and bone mineral density (BMD) by ABQ classification (two-sample t test/analysis of variance).

RESULTS

The prevalence of pre- and postmenopausal women with SVH was 37% and 33%, respectively (P>0.05). Compared to women without SVH, premenopausal women with SVH were older (P<0.001) and heavier (P=0.05), and postmenopausal women with SVH were taller (P<0.05), with higher spine BMD (P<0.01). Postmenopausal women with VF were older (P<0.001) and shorter (P<0.01) with lower BMD (P<0.001) than women without VF.

CONCLUSIONS

Short vertebral height without endplate fracture is equally prevalent in pre- and postmenopausal women and not associated with low bone density.

Biomechanics of vertebral compression fractures and clinical application

Local biomechanical factors in the etiology of vertebral compression fractures are reviewed. The vertebral body is particularly vulnerable to compression fracture when its bone mineral density (BMD) falls with age. However, the risk of fracture, and the type of fracture produced, does not depend simply on BMD. Equally important is the state of degeneration of the adjacent intervertebral discs, which largely determines how compressive forces are distributed over the vertebral body. Disc height also influences load-sharing between the vertebral body and neural arch, and hence by Wolff's Law can influence regional variations in trabecular density within the vertebral body. Vertebral deformity is not entirely attributable to trauma: it can result from the gradual accumulation of fatigue damage, and can progress by a quasi-continuous process of "creep". Cement injection techniques such as vertebroplasty and kyphoplasty are valuable in the treatment of these fractures. Both techniques can stiffen a fractured vertebral body, and kyphoplasty may contribute towards restoring its height. The presence of cement can limit endplate deformation, and thereby partially reverse the adverse changes in load-sharing which follow vertebral fracture. Cement also reduces time-dependent "creep" deformation of damaged vertebrae.

Hydrogels in acellular and cellular strategies for intervertebral disc regeneration

Low back pain is an extremely common illness syndrome that causes patient suffering and disability and requires urgent solutions to improve the quality of life of these patients. Treatment options aimed to regenerate the intervertebral disc (IVD) are still under development. The cellular complexity of IVD, and consequently its fine regulatory system, makes it a challenge to the scientific community. Biomaterials-based therapies are the most interesting solutions to date, whereby tissue engineering and regenerative medicine (TE&RM) strategies are included. By using such strategies, i.e., combining biomaterials, cells, and biomolecules, the ultimate goal of reaching a complete integration between native and neo-tissue can be achieved. Hydrogels are promising materials for restoring IVD, mainly nucleus pulposus (NP). This study presents an overview of the use of hydrogels in acellular and cellular strategies for intervertebral disc regeneration. To better understand IVD and its functioning, this study will focus on several aspects: anatomy, pathophysiology, cellular and biomolecular performance, intrinsic healing processes, and current therapies. In addition, the application of hydrogels as NP substitutes will be addressed due to their similarities to NP mechanical properties and extracellular matrix. These hydrogels can be used in cellular strategies when combined with cells from different sources, or in acellular strategies by performing the functionalization of the hydrogels with biomolecules. In addition, a brief summary of therapies based on simple injection for primary biological repair will be examined. Finally, special emphasis will focus on reviewing original studies reporting on the use of autologous cells and biomolecules such as platelet-rich plasma and their potential clinical applications.

Previous vertebral compression fractures add to the deterioration of the disability and quality of life after an acute compression fracture

Prevalent vertebral compression fracture(s) have been reported as having a negative impact on pain, disability, and quality of life. But no study has evaluated the effect of previous fracture on the course of acute compression fractures. The aim of the present study was to compare the natural course of the acute compression fracture in patients with (n = 51) and without (n = 56) previous vertebral compression fracture(s). The study is a retrospective analysis of a prospective cohort followed with postal questionnaires during a 12-month period after an acute fracture event. Eligible patients were those over 40 years of age, who were admitted to the emergency unit because of back pain and had an X-ray confirmed acute vertebral body fracture. A total of 107 patients were included in the study. The pain, disability (von Korff pain and disability scores), ADL (Hannover ADL score), and quality of life (QoL) (EQ-5D) were measured after 3 weeks, and 3, 6, and 12 months. The X-rays from the first visit to the emergency unit were evaluated. The difference of the scores between the groups with and without previous fracture was statistically significant (P < 0.05) at 3 weeks, 6 and 12 months for von Korff disability score, at all occasions for EQ-5D and at 3-12 months for Hannover ADL score, but only at 12 months for the von Korff pain intensity score. In both the groups all scores had improved in a statistically significant way at 3 months. The number of previous fractures was related to all the outcome scores in a statistically significant way (P < 0.05) except von Korff pain intensity score at 3 weeks and 3 months and von Korff disability score at 3 months. In conclusion, disability, ADL, and QoL scores, but not pain intensity score, were significantly worse in the patients with previous fracture from the fracture episode through the first 12 months. However, the improvements during the follow-up year seen in both groups were of a similar magnitude. The presence or absence of a previous fracture in an acutely fractured patient will influence the prognosis and thus possibly also the indications for treatments.

Osteoporosis and back pain among the elderly

Questionnaire responses from 120 men and 337 women over the age of 50 years were studied to determine the prevalence of back pain among the elderly. In order to gain a rough indication of the back pain among elderly women which might be due to osteoporosis, the prevalence was compared in the two sexes. The prevalence of back pain without radiation to the legs and concomitant morbidity was found to be similar among men and women up to the 70-79-year age-group. After this age the prevalence was higher in women. Those with exceptional loss of body height or kyphosis had a high prevalence of back pain, while those who had sustained previous hip or radius fractures did not. There was increasing prevalence of back pain among women with increasing number of previous fractures. The study gives little indication of serious morbidity of osteoporosis in the form of back pain before very old age.

Prevalence and pattern of lumbar magnetic resonance imaging changes in a population study of one thousand forty-three individuals

STUDY DESIGN

A cross-sectional population study of magnetic resonance imaging (MRI) changes. OBJECTIVE.: To examine the pattern and prevalence of lumbar spine MRI changes within a southern Chinese population and their relationship with back pain.

SUMMARY OF BACKGROUND DATA

Previous studies on MRI changes and back pain have used populations of asymptomatic individuals or patients presenting with back pain and sciatica. Thus, the prevalence and pattern of intervertebral disc degeneration within the population is not known.

METHODS

Lumbar spine MRIs were obtained in 1043 volunteers between 18 to 55 years of age. MRI changes including disc degeneration, herniation, anular tears (HIZ), and Schmorl's nodes were noted by 2 independent observers. Differences were settled by consensus. Disc degeneration was graded using Schneiderman's classification, and a total score (DDD score) was calculated by the summation of the Schneiderman's score for each lumbar level. A K-mean clustering program was used to group individuals into different patterns of degeneration.

RESULTS

Forty percent of individuals under 30 years of age had lumbar intervertebral disc degeneration (LDD), the prevalence of LDD increasing progressively to over 90% by 50 to 55 years of age. There was a positive correlation between the DDD score and low back pain. L5-S1 and L4-L5 were the most commonly affected levels. Apart from the usual patterns of degeneration, some uncommon patterns of degeneration were identified, comprising of subjects with skip level lesions (intervening normal levels) and isolated upper or mid lumbar degeneration.

CONCLUSION

LDD is common, and its incidence increases with age. In a population setting, there is a significant association of LDD on MRI with back pain.

Effect of osteoporosis on morphology and mobility of the lumbar spine

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

The purpose of this study was to examine disc morphology and spinal mobility in subjects with varying degrees of osteoporosis.

SUMMARY OF BACKGROUND DATA

There was limited information on the effect of osteoporosis on lumbar morphology and spinal mobility. It was also unclear how osteoporosis affects the nonosseous tissues such as the intervertebral disc.

METHODS

Ninety elderly subjects with varying bone mineral densities (22 normal, 28 osteopenia, 40 osteoporosis) were recruited from an osteoporosis clinic. Lateral radiographs and magnetic resonance images of their lumbar spines were obtained. An electromagnetic tracking device was employed to measure the ranges of motion of the whole lumbar spine.

RESULTS

Although the thoracic spine had been shown to have decreased anterior vertebral body height in subjects with osteoporosis, this study revealed that the anterior height was increased in the lumbar region. Osteoporosis was associated with expansion of the middle of the disc with corresponding collapse of vertebral bodies, but osteoporosis was found not to be related to either disc preservation or degeneration. No significant change in spinal mobility was observed in patients with osteoporosis.

CONCLUSION

Osteoporosis does not only affect the bone but also the nonosseous tissues. It was found to be associated with expansion of the intervertebral disc, which was likely to be secondary to changes in the vertebral endplate.

Effects of an adapted physical activity program in a group of elderly subjects with flexed posture: clinical and instrumental assessment

BACKGROUND

Flexed posture commonly increases with age and is related to musculoskeletal impairment and reduced physical performance. The purpose of this clinical study was to systematically compare the effects of a physical activity program that specifically address the flexed posture that marks a certain percentage of elderly individuals with a non specific exercise program for 3 months.

METHODS

Participants were randomly divided into two groups: one followed an Adapted Physical Activity program for flexed posture and the other one completed a non-specific physical activity protocol for the elderly. A multidimensional clinical assessment was performed at baseline and at 3 months including anthropometric data, clinical profile, measures of musculoskeletal impairment and disability. The instrumental assessment of posture was realized using a stereophotogrammetric system and a specific biomechanical model designed to describe the reciprocal position of the body segments on the sagittal plane in a upright posture.

RESULTS

The Adapted Physical Activity program determined a significant improvement in several key parameters of the multidimensional assessment in comparison to the non-specific protocol: decreased occiput-to-wall distance, greater lower limb range of motion, better flexibility of pectoralis, hamstrings and hip flexor muscles, increased spine extensor muscles strength. Stereophotogrammetric analysis confirmed a reduced protrusion of the head and revealed a reduction in compensative postural adaptations to flexed posture characterized by knee flexion and ankle dorsiflexion in the participants of the specific program.

CONCLUSION

The Adapted Physical Activity program for flexed posture significantly improved postural alignment and musculoskeletal impairment of the elderly. The stereophotogrammetric evaluation of posture was useful to measure the global postural alignment and especially to analyse the possible compensatory strategies at lower limbs in flexed posture.

Biomechanical and radiographic evaluation of an ovine model for the human lumbar spine

While various species of animal models have been used in preclinical investigations of spinal implant devices to assess their biological adaptation and biomechanical performance, few studies have made comprehensive comparisons to validate their suitability of modelling the human spine. The purpose of this study was to assess essential biomechanical behaviours and disc morphology of the ovine lumbar model. Flexibility testing was conducted on the spines (L3—L4 and L4—L5) of nine skeletally matured sheep. Segmental rotation and intradiscal pressure were measured and load sharing between the intervertebral disc and posterior elements were calculated on the basis of a simplified parallel spring model. Following the tests, the spinal segments were sectioned into a series of sagittal slabs, and transverse radiographs of these slabs were taken to evaluate the variation in the disc height and end-plate curvature. Comparing the biomechanical and radiographic results with published data on the human lumbar spine, good comparability between the ovine and cadaveric lumbar spines was found in terms of the general disc shape and in most of the biomechanical parameters including the range of motion, neutral zone, and load sharing between the intervertebral disc and posterior elements. A few distinctive differences were also found between the two, including flatter sagittal alignment, smaller disc dimensions, and greater lateral bending motion in the ovine model.

The natural history of age-related disc degeneration: the pathology and sequelae of tears

STUDY DESIGN

A quasi 3-dimensional pathologic survey of tears in the L4-L5 disc.

OBJECTIVE

To seek accurate information on the pathogenesis and outcomes of tears to facilitate correlation with radiologic imaging and biomechanical testing; and to improve laboratory models for testing hypotheses of disc function and failure.

SUMMARY OF BACKGROUND DATA

Tears are evidence of structural failure involving the anulus. There are substantial differences in the structure and function of the anterior and posterior anulus and the nonlamellar "nucleus" is much smaller than generally conceptualized and modeled.

METHOD

Microscopy of sections prepared from 5-mm-thick parallel sagittal slices of 70 L4-L5 discs was used to construct maps of tears in each slice and record other features of interest. A template was used to classify data for analysis.

RESULTS

Multiple-level analysis detected 20% more tears than in a single disc section. Concentric, perinuclear, and radiating tears often appeared first in the posterior disc and were numerous throughout life. However, rim lesions, transdiscal tears, endplate separations, and Schmorl's nodes were infrequent in young discs. Rim lesions and transdiscal tears markedly increased in the older discs while the other tears showed modest growth. In elderly discs, many tears acquired blood vessels accompanied by nerves capable of transmitting pain. Apart from about 15% of rim lesions, healing of tears by scar tissue was absent. Links between various types of tears result in complex discographic images from older discs and the cavitation of transdiscal tears lead to segmental instability.

CONCLUSION

Tears in the L4-L5 disc show different patterns of incidence with aging, which can be explained by current biomechanical concepts. Tears may not only perturb disc function and cause segmental instability, but the frequency of neovascularization accompanied by neoinnervation indicates that pain originating within the degenerate disc should not be dismissed as the frequent evidence of bleeding into the tear lumen indicates the susceptibility of the vessels to trauma.

Lumbar degenerative disk disease

The sequelae of disk degeneration are among the leading causes of functional incapacity in both sexes and are a common source of chronic disability in the working years. Disk degeneration involves structural disruption and cell-mediated changes in composition. Mechanical, traumatic, nutritional, and genetic factors all may play a role in the cascade of disk degeneration, albeit to variable degree in different individuals. The presence of degenerative change is by no means an indicator of symptoms, and there is a very high prevalence in asymptomatic individuals. The etiology of pain as the symptom of degenerative disease is complex and appears to be a combination of mechanical deformation and the presence of inflammatory mediators. The role of imaging is to provide accurate morphologic information and influence therapeutic decision making. A necessary component, which connects these two purposes, is accurate natural history data. Understanding the relationship of etiologic factors, the morphologic alterations, which can be characterized with imaging, and the mechanisms of pain production and their interactions in the production of symptoms will require more accurate and reproducible stratification of patient cohorts.

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.

The course of macroscopic degeneration in the human lumbar intervertebral disc

STUDY DESIGN

Assessment of age-related macroscopic changes in human lumbar intervertebral discs (IVD) and vertebral bodies.

OBJECTIVES

To determine the sequence of macroscopic changes during aging/degeneration.

SUMMARY OF BACKGROUND DATA

Descriptive studies on macroscopic alterations of the IVD during aging/degeneration are readily available, but quantitative analyses are sparse.

METHODS

A total of 248 mid-/parasagittal sections of lumbar IVD and vertebral bodies from 41 routine autopsies (range, 7 months to 88 years) were semiquantitatively assessed for macroscopic parameters and correlated with age.

RESULTS

Nuclear fibrous transformation, anular disorganization, endplate, and vertebral body alterations progress predominantly in the first two and in the fifth to seventh decades. In the third and fourth decade, little progression occurs. Nuclear clefts and anular tears appear later, mostly starting in the second decade, with clefts preceding tear formation. Radial and concentric tears develop similarly over time, whereas rim lesions mostly develop after the sixth decade. Significant differences are observed between upper and lower lumbar spine.

CONCLUSION

Our data show that fibrous nuclear transformation during aging/degeneration precedes cleft formation. The temporal sequence suggests a strong correlation of cleft and tears formation starting with clefts in the second decade. Our results support the hypothesis that disc degeneration starts in the nucleus. Extensive macroscopic alterations already apparent in the second life decade present a challenge to any tissue engineering and repair attempt.

Effect of aging and degeneration on disc volume and shape: A quantitative study in asymptomatic volunteers

Debate continues on the effect of disc degeneration and aging on disc volume and shape. So far, no quantitative in vivo MRI data is available on the factors influencing disc volume and shape. The objective of this MRI study was to quantitatively investigate changes in disc height, volume, and shape as a result of aging and/or degeneration omitting pathologic (i.e., painful) disc alterations. Seventy asymptomatic volunteers (20-78 years) were investigated with sagittal T1- and T2-weighted MR-images encompassing the whole lumbar spine. Disc height was determined by the Dabbs method and the Farfan index. Disc volume was calculated by the Cavalieri method. For the disc shape the "disc convexity index" was calculated by the ratio of central disc height and mean anterior/posterior disc height. Disc height, disc volume, and the disc convexity index measurements were corrected for disc level and the individuals age, weight, height, and sex in a multilevel regression analysis. Multilevel regression analysis showed that disc volume was negatively influenced by disc degeneration (p < 0.001) and positively correlated with body height (p < 0.001) and age (p < 0.01). Mean disc height and the disc convexity index were negatively influenced by disc degeneration but not by gender, weight, and height. Disc height was positively correlated with age (p < 0.01). From the results of this study, it can be concluded that disc degeneration generally results in a decrease of disc height and volume as well as a less convex disc shape. In the absence of disc degeneration, however, age tends to result in an inverse relationship on disc height, volume, and shape.

Histology and pathology of the human intervertebral disc

The intervertebral disc is a highly organized matrix laid down by relatively few cells in a specific manner. The central gelatinous nucleus pulposus is contained within the more collagenous anulus fibrosus laterally and the cartilage end plates inferiorly and superiorly. The anulus consists of concentric rings or lamellae, with fibers in the outer lamellae continuing into the longitudinal ligaments and vertebral bodies. This arrangement allows the discs to facilitate movement and flexibility within what would be an otherwise rigid spine. At birth, the human disc has some vascular supply within both the cartilage end plates and the anulus fibrosus, but these vessels soon recede, leaving the disc with little direct blood supply in the healthy adult. With increasing age, water is lost from the matrix, and the proteoglycan content also changes and diminishes. The disc-particularly the nucleus-becomes less gelatinous and more fibrous, and cracks and fissures eventually form. More blood vessels begin to grow into the disc from the outer areas of the anulus. There is an increase in cell proliferation and formation of cell clusters as well as an increase in cell death. The cartilage end plate undergoes thinning, altered cell density, formation of fissures, and sclerosis of the subchondral bone. These changes are similar to those seen in degenerative disc disease, causing discussion as to whether aging and degeneration are separate processes or the same process occurring over a different timescale. Additional disorders involving the intervertebral disc can demonstrate other changes in morphology. Discs from patients with spinal deformities such as scoliosis have ectopic calcification in the cartilage end plate and sometimes in the disc itself. Cells in these discs and cells from patients with spondylolisthesis have been found to have very long cell processes. Cells in herniated discs appear to have a higher degree of cellular senescence than cells in nonherniated discs and produce a greater abundance of matrix metalloproteinases. The role that abnormalities play in the etiopathogenesis of different disorders is not always clear. Disorders may be caused by a genetic predisposition or a tissue response to an insult or altered mechanical environment. Whatever the initial cause, a change in the morphology of the tissue is likely to alter the physiologic and mechanical functioning of the tissue.

Spine biomechanics

Current trends in spine research are reviewed in order to suggest future opportunities for biomechanics. Recent studies show that psychosocial factors influence back pain behaviour but are not important causes of pain itself. Severe back pain most often arises from intervertebral discs, apophyseal joints and sacroiliac joints, and physical disruption of these structures is strongly but variably linked to pain. Typical forms of structural disruption can be reproduced by severe mechanical loading in-vitro, with genetic and age-related weakening sometimes leading to injury under moderate loading. Biomechanics can be used to quantify spinal loading and movements, to analyse load distributions and injury mechanisms, and to develop therapeutic interventions. The authors suggest that techniques for quantifying spinal loading should be capable of measurement "in the field" so that they can be used in epidemiological surveys and ergonomic interventions. Great accuracy is not required for this task, because injury risk depends on tissue weakness as much as peak loading. Biomechanical tissue testing and finite-element modelling should complement each other, with experiments establishing proof of concept, and models supplying detail and optimising designs. Suggested priority areas for future research include: understanding interactions between intervertebral discs and adjacent vertebrae; developing prosthetic and tissue-engineered discs; and quantifying spinal function during rehabilitation. "Mechanobiology" has perhaps the greatest future potential, because spinal degeneration and healing are both mediated by the activity of cells which are acutely sensitive to their local mechanical environment. Precise characterisation and manipulation of this environment will be a major challenge for spine biomechanics.

Degeneration and height of cervical discs classified from MRI compared with precise height measurements from radiographs

STUDY DESIGN

Descriptive study comparing MRI classifications with measurements from radiographs.

OBJECTIVES

1. Define the relationship between MRI classified cervical disc degeneration and objectively measured disc height. 2. Assess the level of inter- and intra-observer errors using MRI in defining cervical disc degeneration.

SUMMARY OF BACKGROUND DATA

Cervical spine degeneration has been defined radiologically by loss of disc height, decreased disc and bone marrow signal intensity and disc protrusion/herniation on MRI. The intra- and inter-observer error using MRI in defining cervical degeneration influences data interpretation. Few previous studies have addressed this source of error. The relation and time sequence between cervical disc degeneration classified by MRI and cervical disc height decrease measured from radiographs is unclear.

METHODS

The MRI classification of degeneration was based on nucleus signal, prolaps identification and bone marrow signal. Two neuro-radiologists evaluated the MR-images independently in a blinded fashion. The radiographic disc height measurements were done by a new computer-assisted method compensating for image distortion and permitting comparison with normal level-, age- and gender-appropriate disc height.

RESULTS/CONCLUSIONS

1. Progressing disc degeneration classified from MRI is on average significantly associated with a decrease of disc height as measured from radiographs. Within each MRI defined category of degeneration measured disc heights, however, scatter in a wide range. 2. The inter-observer agreement between two neuro-radiologists in both defining degeneration and disc height by MRI was only moderate. Studies addressing questions related to cervical disc degeneration should take this into consideration.

Effects of intervertebral disc infection on the developing ovine spine

STUDY DESIGN

A prospective in vivo animal study.

OBJECTIVES

To determine whether infection in the juvenile spine influences spinal development.

SUMMARY OF BACKGROUND DATA

Discitis is thought to occur in children when blood-borne infection penetrates the highly vascular immature disc. The condition generally resolves without apparent complication, but little is known about the long-term effects on the growing spine.

METHODS

Twenty-nine 6-week-old lambs underwent discography at multiple lumbar levels using radiographic contrast deliberately inoculated with Staphylococcus epidermidis. No antibiotics were given. Plain radiographs were taken at intervals up to 52 weeks after inoculation for morphometric analysis of the vertebral bodies and discs, and the lumbar spines were prepared for histology.

RESULTS

Sixteen of 44 inoculated discs showed radiological evidence of discitis between 2 and 6 weeks after inoculation. Disc height and disc area were significantly reduced from 2 weeks, and did not recover during the study period. Vertebral body dimensions and overall lumbar spine length were not significantly affected.

CONCLUSION

Infection of juvenile ovine discs impedes disc development but has no significant effect on vertebral body growth.