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Cyclic Mechanical Tension and Intervertebral Disc Degeneration

intervertebral disc degeneration, model

Mechanobiology Research

Low back pain is a huge burden on our limited resources with limited knowledge of its pathophysiology. It is widely known that intervertebral disc degeneration (IDD) is intimately related, with the degree of degeneration associated with the severity of low back pain. The characteristics of intervertebral disc degeneration include disc height loss, proteoglycan loss, loss of water, annular fissures, and end plate calcification.

The degenerative process of the intervertebral disc has been seen as a phenotype change within the cells. This anabolic to catabolic shift seems to occur to the cells deep within the disc. One branch of research that studies the influence of mechanical forces on the biology is called Mechanobiology. In other words, can physical stressors on discs influence the process of degeneration? Can moving the disc is a certain way change the outcome of degeneration?

The Study

In this open access study, researchers were the first to investigate this kind of cyclical mechanical tension on the nucleus pulposus cells changing behaviour.  They extracted disc cells from caudal spines of (3-month-old) male Sprague-Dawley rats and conducted the mechanical testing using a device after the cells were cultured and prepared. They used this device to apply mechanical force on the cells of the nucleus pulposus (the centre of the disc) to see how the cells behaved under specific loading conditions.

Disc cell senescence involves telomere shortening,  free radical stress, DNA breakdown and cytokine proliferation. Mechanical loading conditions in the upright posture have been found to promote disc cell changes towards intervertebral disc degeneration in rats.  Studying the role of mechanical stress and the influence on disc health will benefit our understanding of disc pathogenesis. 

The results of this study showed a direct relationship of prolonged mechanical cyclic stress towards the catabolic shift of the cells in the nucleus pulposus. They concluded that unphysiological mechanical stress could push a disc into the degenerative cascade. They believe that eventually, too much mechanical stress can influence the cell’s behaviour and suggested that research continue on finding the optimal mechanical environment for the cells of the disc.

At Dynamic Disc Designs, we work to bring dynamic models to the practitioner to help in the discussions related to motion and the spine.


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Study Finds Annulus Fibrosus GAG Content Alters the Mechanics of Disc Torsion

Facet Joints, GAG, Annulus Fibrosus, Torsion

A recent study evaluated the role of facet joints in torsion using four different compressive preload conditions in healthy and degenerated lumbar discs—with, and without facet joints. The study also sought to develop a quantitative relationship between structure and function in tissue and torsion mechanics. The study found that annulus fibrosis GAG content substantially affects the mechanics of disc torsion.

Purpose of the Study

Because there is a large population of lower back pain (LBP) sufferers whose jobs involve excessive loading and rotating the lumbar spine, the authors of this study sought to quantify and understand how the facet joints in healthy and degenerated discs would behave under axial rotation scenarios. They did this by observing in vivo changes in spinal segments during torsional behavior. The intervertebral disc (IVD) is capable of stability and flexibility during most movement, receiving stresses and sharing them with the nearby facet joints and other surrounding structures. The facet joints should protect the disc from overload and degeneration by restricting motions that would cause damage to the spine, but some complex motions that involve axial rotation and bending during heavy loading can increase the chance of micro-damage and disc failure. How well the IVD and facet joints share loads is determined by the mode of loading and posture. Previous studies have demonstrated that up to 25 percent of axial compressive forces may be supported by the facet joints. Between 40 to 65 percent of healthy disc joint rotational and shear forces are also supported by the facet joints. Therefore, it is important to understand how the facet joints in healthy and degenerated discs react during torsion.

Study Design

Researchers obtained and imaged seven human cadaveric lumbar spine segments aged 43 to 80 years-old. The musculature and ligaments were then removed, and the intact facet joints near the discs were subdivided mid-vertebrae prior to the samples being potted in bone cement. The segments were then wrapped in gauze and stored in a phosphate solution until brought to room temperature just before testing. They were then mounted onto a testing machine and secured with screws.

The segments underwent a moderate-to-low preloaded axial compression, followed by axial rotation through the center of the disc. The cycles of compression and rotation were performed for two hours to allow the formation of creep. Ten cycles of cyclic rotation, and the samples were tested under four axial compressive preloads and allowed to recover between each test. The facet joints were then removed, and the samples were tested again, using the same loading configuration. For each round of testing, the researchers recorded the levels of force, rotation angle, displacement, and torque.

Isolating and Imaging Each Disc

Each disc was isolated and imaged after mechanical testing. Researchers measured the disc area, anterior-posterior and lateral width using a custom algorithm. Disc height was measured from the posterior, anterior, left, and right lateral sides, as well as the center. A mathematic formula determined the applied axial stress, and the images were graded and compared with radiographic-based grades.


The results of the tests indicated a strong correlation between creep and axial compressive preload and the loss of disc height. Removing the facet joint had no effect on this phenomenon. The presence of facet joints and an axial compressive preload did have a strong effect on torsional mechanical properties, with torsional stiffness and range decreased 50 to 60 percent for compressive loads after removing the facet joints. Energy absorption decreased about 70 percent during rotation after facetectomy, and disc-joint strain increased 74 percent, compared to only 62 percent in disc strain energy using the same axial compression.

Annulus Fibrosis GAG content in degenerated discs greatly reduced torsion mechanics, while the facet joints are integral in keeping the spine from rotating too far and helping to reduce shear stress and damage to the disc. The relationship between the biochemical-mechanical and compression-torsion levels noted in this study may help to provide for more effective and targeted biological repair methods for degenerating discs of various levels.


KEYWORDS: AF GAG Content Alters the Mechanics of Disc Torsion, role of facet joints in torsion, axial rotation scenarios, correlation between creep and axial compressive preload and the loss of disc height, targeted biological repair methods for degenerating discs

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Study Finds Strong Correlation Between LBP, Age-related Degeneration, and Spinal Instability


A study examined the relationship between lumbar disc degeneration and instability in spinal segments of three groups of volunteers and found that factors of spinal instability were closely related to disc height and the age of the study subjects and that disc height was intimately associated with age and spinal instability and was the most consistently affiliated parameter of those examined.

Patients with lower back pain (LBP) and/or sciatica often have evident disc degeneration in MRI their images, especially elderly patients. Because these patients may demonstrate no other neurological symptoms, it is commonly assumed specific evidence of LBP –aside from degeneration and the age of the patient—may not exist. Excessive motion surrounding the affected disc segment can cause LBP and spinal instability, and previous studies on the relationship between instability and LBP have been inconsistent in their findings—in part, because imaging of the subjects was performed while the patients were in the static supine position.

Study Design Utilized Flexion-Extension Standing Postured Imaging Reviews

The authors of the current study were building upon their previous research utilizing images that had been performed on patients during flexion-extension standing postures to examine the relationship between spinal instability and disc degeneration of the L4/L5 motion segment. Because disc degeneration may not be associated with LBP at all stages, the authors of the study devised a method of measurement to examine different types of segmental degeneration and any relationship it may have with spinal instability.

The subjects of the study were LBP or leg pain outpatients who had received radiologic and MRI imaging within a two-month interval during the past three years. Of the 447 patients included in the study, 268 were men, and 179 were women. Their ages ranged from 10 to 86 years, with an average age of roughly 54 years-old.

Instability was measured at the L4/L5 spinal segments during neutral, extension, and flexion postured images and was then analyzed and categorized into three variable types: Anterior slip at L4 onto L5 while in neutral position (SN), sagittal translation (ST), and segmental angulation (SA). Measurements were taken of each slip, and the results were evaluated and noted to determine the degree of apparent instability.

The disc segments were evaluated radiologically for degeneration by looking at and comparing disc height, spur formation of the anterior vertebral edges, endplate sclerosis, and evidence of vacuum phenomenon in the films taken during flexion-extension. Sixty-eight of the subjects had high disc height (HDH), 212 patients were considered to have medium disc height (MDH), and 67 patients were categorized as having low disc height (LDH). Bony spur measurements were taken, and the presence of endplate sclerosis and vacuum phenomenon were noted as either being present or not. The level of disc degeneration was evaluated by MRI and graded from 1 to 5, as “normal,” to “severe” degeneration. The patients were divided into eight groups based upon the severity of their spinal instability, and the relationship between disc height, spur size, endplate sclerosis, vacuum phenomenon, and degeneration in the MRI’s was noted in relation to the types of instability present.

The compared data indicated a link between instability, age, and a reduction in disc height. Though increased age and a loss of disc height have long been suspected to be linked to degeneration and instability of the spine, this study uses MRI to evaluate that relationship more closely, demonstrating that a lower disc height was associated at least a 3mm slippage and a higher disc height was associated with subjects who were younger in age, with larger angulation in the spinal segments. Instability was prevalent in older patients with prominent anterior spur formation and/or vacuum phenomenon.

Age and relative spinal stability were intimately related to disc height, and this instability was progressive in nature and occurred over decades.


KEYWORDS: Correlation Between LBP, Age-related Degeneration, and Spinal Instability, relationship between lumbar disc degeneration and instability, comparing disc height, spur formation of the anterior vertebral edges, endplate sclerosis, and evidence of vacuum phenomenon, link between instability, age, and a reduction in disc height, degeneration and instability of the spine

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Spinal Canal Spacing Predicts Better than Disc Degeneration for Low Back Pain

In a research paper published in Miltary Medicine, spinal canal spacing was found to be a better predictor in the development of chronic low back pain when compared to intervertebral disc degeneration. 1

These researchers used MRI to look at the role of spinal stenosis, disc degeneration, nerve root compression in low back pain among Finnish males ages 18-26. They looked at the intervertebral foramen (exiting nerve canals) and the midsagittal slice examining spacing of 108 of these subjects that had chronic low back pain comparing 90 asymptotic controls without chronic low back pain.

With the prevalence of degenerative disc disease in a reported 52% of Finnish 15-29yrs of age, the authors thought it would be good to determine if degeneration was related to chronic low back pain.

What they found was those who had reduced spinal canal spacing at the L1-L4 were more likely to exhibit chronic low back pain.

Disc degeneration is identified by disc height loss. And with disc height loss, there are spacing changes that take place in the intervertebral foramina and the spinal canal. Congenital spinal canal variations 2 can predispose a person to acquire low back pain but the maintenance of disc height, even in those people, should be priority number one. Disc height is diurnal and will vary with mechanical forces that people have complete control over.

At Dynamic Disc Designs, we have designed models to help convey these important low back pain topics, to help the patient understand clearly how spinal canal spacing, intervertebral disc narrowing, disc protrusion and intervertebral foraminal narrowing can impact function. Our dynamic disc models help the patient get to know their own back pain and how the postures, loads and motions can have a profound impact on their management of the pain.

Professional LxH Disc Model, spine models, lumbar model, professional LxH, disc herniation, model, spine models

A dynamic disc model showing flexible movements of the intervertebral disc with an annulus and nucleus.


lumbar spinal stenosis, spinal canal narrowing

A superior view of our Lumbar spinal stenosis model with a dynamic disc bulge and dynamic ligamentum flavum.

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Dynamic Disk Research – Disk Height and Fluid Flow

dynamic disk

The dynamic disk plays a significant role in the resistance to compression. It is known to physically compress over the course of the day by as much as 20 percent with recovery achieved during sleep or recumbency. Its implications intertwined with back pain. 1 One of the focused investigations into its essential function has been its intrinsic ability to maintain and absorb water. Negatively charged proteoglycans contain properties that attract water, and it is this hydraulic characteristic believed to be at the core.

However much still is to be discovered; especially in the higher understanding how best to draw in fluid and recover the expulsion of this water under axial compression. In a manuscript published in the Journal of Biomechanics 2, researchers worked to answer the questions regarding loading and unloading of the dynamic disk.

The researchers revealed a new personality of the annulus fibrosis as playing a significant in the ability to absorb water. The annulus demonstrated both properties of viscoelasticity as well as the binding capacity to retain water. This information is new in the better understanding of how disks maintain vertebral spacing with regards to recovery. Load and unloading cycles are natural, but it is the intrinsic ability of the dynamic disk to maintain spacing over time that is important to continue to study. Congratulations to the authors for choosing a worthy investigation.

At Dynamic Disk Designs, we work to model the dynamic nature of the spinal structures to improve communication of spine science. Our work facilitates patient education and student teaching of spine. Having a model dynamic disk allows the better understanding of disk height loss over time to explain back pain mechanics and the respective hydraulic solutions.

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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.


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.


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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Disc hydration – Unloading / Loading during the act of sitting.

posture, disc hydration

Disc hydration fluctuates naturally and diurnally. That is, over the course of the day/night cycle we (as humans) lose up to 20% of the water out of our spinal discs. 1 The intervertebral discs are sensitive to load and because of their visceo-elastic make-up they will deform under load. Most notable changes seem to occur under sustained or static loads. 2 3 4 5 6 Therefore, it is important to offload the spine, especially when one sits for an extended period of time.

Recently, a study published in the Lancet 7 looked at the 188 countries and followed them between 1990-2013 and revealed that the number one reason for disability was back pain. Yes, back pain! Not heart disease. Could we extract from this that it is perhaps the introduction of computers and more time sitting? There could be other factors but there little doubt that the human population is moving less and fixated in front of a computer….just like myself at the moment.

Lumbar Disc Changes Associated with Prolonged Sitting

Take a Break and Off-load

This 8 off-loading strategy is thought to relieve the compressive forces of the spine to allow it to refill slightly….interupting sustained compressive loads, which we know is harmful.

Interestingly, a paper published in the Journal of Human Evolution in 2000 9 looked at knuckle walkers and ‘compared to humans, all ape samples show dramatically less spinal disease, especially when considerng vertebral body involvement’ . The authors concluded that this significant difference was likely due to the gait mechanism. And obviously, they use their upper extremities to off-load their spines during the course of their gait cycle.

Therefore, it looks like if you behave more like an ape and use your upper extremities, your spine will benefit. Teach your patients to minimize compressive loads by integrating off-loading strategies in their day to decrease the creep and compressive responses in the spine…..keeping the discs hydrated to prevent disc height loss.


  1.  Urban,J.P., McMullin,J.F., 1988. Swelling pressure of the lumbar intervertebral discs: influence of age,spinal level, composition,and degeneration. Spine 13, 179–187.
  2.  Adams, M.A., Hutton,W.C., 1983. The effect of posture ont he fluid content of lumbar intervertebral discs. Spine (Philadelphia1976) 8, 665–671.
  3.  Kazarian, L.E., 1975. Creep characteristics of the human spinal column. Orthop. Clin. N. Am. 6, 3–18.
  4.  Keller,T.S., Spengler,D.M., Hansson,T.H. ,1987. Mechanical behavior of the human lumbar spine. Creep analysis during static compressive loading. J.Orthop.Res. 5, 467–478.
  5.  Koeller,W., Funke,F., Hartmann,F., 1984a. Biomechanical behavior of human intervertebral discs subjected to long lasting axial loading. Biorheology 21, 675–686.
  6.  Markolf, K.L.,1972. Deformation of the thoracolumbar intervertebral joints in response to external loads: a biomechanical study using autopsy material.J.Bone Jt. Surg.Am. 54,511–533.
  7. Lancet. 2015 Aug 22; 386(9995): 743–800. 
  8.  Fryer JC1, Quon JA, Smith FW. Magnetic resonance imaging and stadiometric assessment of the lumbar discs after sitting and chair-care decompression exercise: a pilot study. Spine J. 2010 Apr;10(4):297-305.
  9. Jurmain, R Degenerative joint disease in African great apes: an evolutionary perspective. Journal of Human Evolution (2000) 39, 185–203