Are "patterns" of lumbar disc degeneration associated with low back pain?: new insights based on skipped level disc pathology

Changes in vertebral strain energy correlate with increased presence of Schmorl's nodes in multi-level lumbar disk degeneration

Patients with skipped-level disk degeneration (SLDD) were recently reported as having a higher prevalence of Schmorl's nodes than patients with contiguous multi-level disk degeneration (CMDD). Fourteen versions of a nonlinear finite element model of a lumbar spine, representing different patterns of single and multi-level disk degeneration, were simulated under physiological loading. Results show that vertebral strain energy is a possible predictor in the development of Schmorl's nodes. The analysis also shows evidence that the development of Schmorl's nodes may be highly dependent on the location of the degeneration disk, with a higher prevalence at superior levels of the lumbar spine.

Defining clinically relevant values for developmental spinal stenosis: a large-scale magnetic resonance imaging study

STUDY DESIGN

Case-control study.

OBJECTIVE

The aim of this study was to define clinically relevant relative and critical (absolute) magnetic resonance imaging values of lumbar spinal stenosis in a cohort of 100 surgical cases and 100 asymptomatic controls.

SUMMARY OF BACKGROUND DATA

Developmental spinal stenosis is a precipitating factor in patients presenting with lumbar canal stenosis. Yet, due to a lack of agreement on definitions and methods of assessment, as well as ethnic-specific normative values, its prevalence and significance is not known.

METHODS

This was a case-control study comparing 100 age and sex-matched asymptomatic, volunteers with that of 100 patients who underwent surgery for spinal stenosis. All patients were of Chinese ethnicity and their details were blinded to 2 observers. Spinal stenosis parameters were measured on the basis of axial (pedicle level) and sagittal (midsagittal) magnetic resonance images.

RESULTS

Anteroposterior spinal canal diameters change with levels. At each level, patients were found to have significantly narrower anteroposterior canal diameters than controls. By use of receiver operating characteristic curve, we defined developmental spinal stenosis if the anteroposterior canal diameter was at L1 <20 mm, L2 <19 mm, L3 <19 mm, L4 <17 mm, L5 <16 mm, and at S1 <16 mm on the basis of a value including 50% of controls and demonstrated best sensitivity and specificity. Furthermore, for L4, L5, and S1, critical stenosis values could be defined, below which almost all subjects needed surgery, these were L4 <14 mm, L5 <14 mm, and S1 <12 mm.

CONCLUSION

This is the largest magnetic resonance imaging-based study with standardized measurements and comparable groups to determine clinically relevant magnetic resonance imaging criteria for lumbar spinal stenosis. The findings strongly suggest that developmental stenosis plays an important role in the pathogenesis of symptomatic spinal stenosis. Critical values of stenosis below which symptoms were highly likely were defined. These will need to be validated by longitudinal studies in future. However, they may possess clinical utility in determining the appropriate levels requiring canal-widening surgery.

LEVEL OF EVIDENCE

3.

Investigating the role of DNA damage in tobacco smoking-induced spine degeneration

BACKGROUND CONTEXT

Tobacco smoking is a key risk factor for spine degeneration. However, the underlying mechanism by which smoking induces degeneration is not known. Recent studies implicate DNA damage as a cause of spine and intervertebral disc degeneration. Because tobacco smoke contains many genotoxins, we hypothesized that tobacco smoking promotes spine degeneration by inducing cellular DNA damage.

PURPOSE

To determine if DNA damage plays a causal role in smoking-induced spine degeneration.

STUDY DESIGN

To compare the effect of chronic tobacco smoke inhalation on intervertebral disc and vertebral bone in normal and DNA repair-deficient mice to determine the contribution of DNA damage to degenerative changes.

METHODS

Two-month-old wild-type (C57BL/6) and DNA repair-deficient Ercc1(-/Δ) mice were exposed to tobacco smoke by direct inhalation (4 cigarettes/day, 5 days/week for 7 weeks) to model first-hand smoking in humans. Total disc proteoglycan (PG) content (1,9-dimethylmethylene blue assay), PG synthesis ((35)S-sulfate incorporation assay), aggrecan proteolysis (immunoblotting analysis), and vertebral bone morphology (microcomputed tomography) were measured.

RESULTS

Exposure of wild-type mice to tobacco smoke led to a 19% increase in vertebral porosity and a 61% decrease in trabecular bone volume. Intervertebral discs of smoke-exposed animals also showed a 2.6-fold decrease in GAG content and an 8.1-fold decrease in new PG synthesis. These smoking-induced degenerative changes were similar but not worse in Ercc1(-/Δ) mice.

CONCLUSIONS

Short-term exposure to high levels of primary tobacco smoke inhalation promotes degeneration of vertebral bone and discs. Disc degeneration is primarily driven by reduced synthesis of proteoglycans needed for vertebral cushioning. Degeneration was not exacerbated in congenic DNA repair-deficient mice, indicating that DNA damage per se does not have a significant causal role in driving smoke-induced spine degeneration.

The role of the vertebral end plate in low back pain

End plates serve as the interface between rigid vertebral bodies and pliant intervertebral disks. Because the lumbar spine carries significant forces and disks don't have a dedicated blood supply, end plates must balance conflicting requirements of being strong to prevent vertebral fracture and porous to facilitate transport between disk cells and vertebral capillaries. Consequently, end plates are particularly susceptible to damage, which can increase communication between proinflammatory disk constituents and vascularized vertebral bone marrow. Damaged end plate regions can be sites of reactive bone marrow lesions that include proliferating nerves, which are susceptible to chemical sensitization and mechanical stimulation. Although several lines of evidence indicate that innervated end plate damage can be a source of chronic low back pain, its role in patients is likely underappreciated because innervated damage is poorly visualized with diagnostic imaging. This literature review summarizes end plate biophysical function and aspects of pathologic degeneration that can lead to vertebrogenic pain. Areas of future research are identified in the context of unmet clinical needs for patients with chronic low back pain.

Genetic association studies in lumbar disc degeneration: a systematic review

Objective

Low back pain is associated with lumbar disc degeneration, which is mainly due to genetic predisposition. The objective of this study was to perform a systematic review to evaluate genetic association studies in lumbar disc degeneration as defined on magnetic resonance imaging (MRI) in humans.

Methods

A systematic literature search was conducted in MEDLINE, MEDLINE In-Process, SCOPUS, ISI Web of Science, The Genetic Association Database and The Human Genome Epidemiology Network for information published between 1990–2011 addressing genes and lumbar disc degeneration. Two investigators independently identified studies to determine inclusion, after which they performed data extraction and analysis. The level of cumulative genetic association evidence was analyzed according to The HuGENet Working Group guidelines.

Results

Fifty-two studies were included for review. Forty-eight studies reported at least one positive association between a genetic marker and lumbar disc degeneration. The phenotype definition of lumbar disc degeneration was highly variable between the studies and replications were inconsistent. Most of the associations presented with a weak level of evidence. The level of evidence was moderate for ASPN (D-repeat), COL11A1 (rs1676486), GDF5 (rs143383), SKT (rs16924573), THBS2 (rs9406328) and MMP9 (rs17576).

Conclusions

Based on this first extensive systematic review on the topic, the credibility of reported genetic associations is mostly weak. Clear definition of lumbar disc degeneration phenotypes and large population-based cohorts are needed. An international consortium is needed to standardize genetic association studies in relation to disc degeneration.