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Increasing Gradients of Compressive Stress Can Lead to Annular Delamination, Collapse, and IVD Degeneration

delamination, annulus

A ISSLS Prize-winning study 1 examined how increasing gradients of compressive stress within the intervertebral disc (IVD) contributed to the progress of dis degeneration. The research findings suggest that an increased grade of disc degeneration created decreased nucleus pressure and compressive annulus stress, but anterior annular stress gradients increased by approximately 75 percent, and by 108 percent in the posterior annulus—findings that are clinically significant.

The neural arch may provide a stress-shield for the degenerating disc during mechanical loading, but delamination and collapse of the annulus are most likely caused not by loading, but by increasing gradients of compressive stress, leading to advanced disc degeneration, despite the stress-shield.

The Study

Using 191 motion segments from 42 cadavers of varied ages, researchers measured the intradiscal stresses under 1 kN of compression. A pressure transducer was pulled along the midsagittal diameter of the disc to measure the intradiscal stresses. Stress gradients in the annulus were quantified using a formula that averaged the rate of increase in compressive stress between the area of maximum stress in the anterior or posterior annuls, and the nucleus. Measurements were compared before and after applied creep-loading, as well as in flexed or erect postures. A scale of 1to 4 was used to describe the amount of macroscopic disc degeneration observed.

 

Results

An increase of disc degeneration from 2 to 4 decreased by 68 percent the amount of pressure in the nucleus, and compressive stress in the annulus was decreased by 48-64 percent, depending on the simulated posture of the segment and the location of the disc. However, anterior annular stress gradients showed an average 75 percent increase in the flexion position, and posterior annular stress gradients increased 108 percent in upright posture.

 

Conclusion

The neural-arch provides stress-shielding, but compressive stress gradients are significantly increased with an increasing grade of disc degeneration. Adjacent lamellae are sheared by the stress gradients, which may contribute to the delamination and collapse of the annulus.

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Low back pain and modic markers of cytokines

A L4-L5 Modic Model midsagittal cut demonstrating Type 1 Modic changes and the basivertebral nerve

Low back pain is very common and the markers to indicate why some people hurt and others do not, has been of a recent investigation. In The Spine Journal 1, just this month, researchers looked closer at modic changes and the chemicals that generate as a result. Modic changes were first identified by Michael Modic 2 in 1988 as unique findings on MR.

There is no doubt that disk degeneration appears to be related to low back pain, even if many asymptomatic people do have degenerative findings on MRI. 3 What seems to be the difference is the degree of inflammation in those that suffer with low back pain and those that don’t suffer.

Cytokines are inflammation markers, and in this study, these researchers found that Type 2 modic changes where associated with these markers and concluded:

“These results further strengthen the link between Modic Changes and low back pain”

 

The location of inflammation is something that is important to share with patients. Whether it is inflammation from the annulus within the disc itself, or whether MRI findings show intravertebral inflammation due to irritation to the basivertebral nerve, Dynamic Disc Designs develops models to help with spine education.

 

In a recent poll,

Do you know what patients really care about when choosing a spine surgeon?

Patients ranked Communicates well / Explains medical condition, symptoms, surgical, and non-surgical treatment options @ 17.7%.

3D discogenic pain model

modic, basivertebral

Modic and basivertebral nerve

 

 

  1.  Are modic changes associated with intervertebral disc cytokine profiles? Schroeder, Gregory D. et al. The Spine Journal IN PRINT ↩
  2. Modic MT, Steinberg PM, Ross JS, Masaryk TJ, Carter JR. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology. 1988;166(1 Pt 1):193-9 ↩
  3.  Boden SD, Davis DO, Dina TS, Patronas NJ, Wiesel SW. Abnormal magnetic- resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. The Journal of bone and joint surgery American volume. 26 1990;72(3):403-8 ↩
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Bending or twisting – Which predisposes low back pain?

bending or twisting

Bending or twisting?

In a recent bending study in Clinical Biomechanics, researchers looked at how the nucleus pulposus deformed as the vertebrae rotated at two lumbar levels: L1-2 and L4-5. They were curious about how the nucleus pulposus behaved as this hydraulic tissue has an important role in resisting compression with bending and twisting of the spine.

Rotation is often described as a body position to predispose low back injury but there is not much research on the topic to demonstrate this is actually the case.

There has also been mounting evidence that flexion bending is thought to be a mechanism for disc injury and this Flexion load is thought to be more important.

Coupling movements of both flexion AND rotation has historically been thought to be the worst.

These researchers led by Fazey, P. used MRI to look at 10 asymptomatic subjects of an average age of 29 yrs.

What these researchers determined was that side-ways bending demonstrated greater nuclear deformation compared to rotation. They also showed that the nucleus moves backwards when one bends forwards and moves forwards when one bends backwards. Opposite.

One of the take home messages from this study is that lateral flexion (or side-ways movement) of the spine causes the nucleus structure to deform more than twisting. Therefore, patients should be instructed to minimize sideways bending to help reduce the deformation of the nucleus pulposus.

This study is one example of why Dynamic Disc Designs has worked to showcase the anatomy and inner workings of human discs. Our latest is the Centralizer. Degeneration is as a result of annular fissures and understanding how to minimize annular stress will likely lead to better outcomes for pain practitioners.

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Degeneration vs. Disc Prolapse

Degeneration

Disc degeneration has been a topic of discussion in its mechanism of back pain for decades.

It is believed to be related but a causal link has been difficult to pin down. Researchers believe it to be related while others still question its role in back pain because of asymptomatic individuals with it as seen in MRI.

In order to continue to reveal the mechanisms related to back pain, a discernment between disc degeneration and prolapse was the topic of this outstanding runner up study in The Spine Journal.

Kanna et al. opened this research paper by stating that the pathogenesis, management, symptom presentation, etiology and prevention of lumbar disc degeneration has been elusive and how it is important to sub-classify and investigate degeneration and prolapse. These researchers wanted to analyze the patterns of degenerative disc disease with chronic low back pain and compare it to acute disc prolapse.

This study was conducted using a prospective MRI imaging approach.

In conclusion they found that back pain and degenerative disc disease (ddd) were radiologically and clinically different when compared to those with back pain and disc prolapse. These researchers found that in those with disc prolapse, there was less degeneration and more endplate disruption. This fits with other findings of endplate failure to be more common with disc herniation. Subjects in this study who had back pain were found to have more numbers of degenerative discs with primarily upper lumbar involvement.

Dynamic Disc Designs develops spine models to help patients understand more clearly their own pain generators….helping to reduce psychosocial factors involved with back pain.

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