Dynamic spine models designed by chiropractors. Our spine models are scientifically accurate, showing details in the discs, lumbar, pelvis and cervical spine. They can be used to demonstrate a range of clinical conditions which contribute to back pain or discomfort. Our models use an elastomeric two-part intervertebral disc design to show important anatomical features so are perfect for chiropractors, osteopaths, spine surgeons, physiotherapists and medicine students. See the back under compression and conditions such as disc herniation, epidural punctures and more.

properties of the annulus, disc model

Researchers examined the effects of endplate fractures  1 on the mechanical properties of the annulus fibrosis (AF) in porcine spinal segments and found that laminate adhesion strength was significantly compromised in the fractured spines. The findings suggest that microdamage may occur beyond the vertebra, into the interlamellar matrix of the AF—information that could be helpful in the diagnosis and treatment of adolescent spinal growth-plate fractures.

The Study

The authors of this study wished to examine the effects of high-intensity pressurization on the intervertebral discs (IVD) to see how it effected the mechanical and physiological properties of the posterior AF. They used 28 fresh, recently-thawed functional porcine spinal units from 14 porcine specimens that were approximately six months old.  Control units were also used as a comparative measure against the units subjected to pressure.

A hydraulic pump and high-pressure inflation needle were used to pump hydraulic fluid into the IVD of specimens. The researchers were careful not to pierce the AF in the samples. Pressure in the needle was measured by a pressure transducer and converted from analogue to digital at 2048 Hz. The needle was subsequently removed, and the vertebral bodies were assessed for damage. Although fractured endplates created an audible ‘pop,’ the condition was only confirmed after dissection of the IVD. The control-group segments were not tested for fractures. Measurements were taken following the dissection, and the end-plate area was quantified. Bilayer AF samples were then dissected and tested for tensile endurance in the circumferential direction. A second multi-layered sample was then dissected and subjected to delamination and a peel test. Mathematical ratios were then plotted to mark the variable results for each sample.


End-plate size measurements remained consistent across the control and fracture group samples. Bilayer stiffness, toe-region stretch ratio and stress, and stress at 30% stretch were consistent in the control and fracture group samples. However, there was a clinically-significant variance in peel strength—but not peel strength variability— between the two groups. In the fracture group, the peel strength was 31 percent lower than in the control group. Dissection and manual delamination were significantly easier in the fracture group of samples, as well.


The results of this study indicate that growth-plate fracture damage may not be limited to the vertebra and may cause microdamage in the nearby AF. This was indicated by the reduction of laminate adhesion strength in the posterior AF of the fracture IVD samples subjected to pressure in the tests. This information should be taken into account when practitioners are examining and treating adolescent or childhood vertebral fractures involving the endplates.


KEYWORDS: damage during spinal growth-plate fractures, effects of endplate fractures on the mechanical properties of the annulus fibrosis, effects of high-intensity pressurization on the intervertebral discs, mechanical and physiological properties of the posterior AF, delamination and a peel test, Bilayer stiffness, toe-region stretch ratio and stress


A new study 1 sought to create an etiology-based system of classification by identifying and characterizing typical endplate irregularities and found that tidemark avulsions were a predominant pathology in the cadaveric spine sample images. This represents a previously unidentified observation and, along with the histologic classification system developed in the study, should assist practitioners in organizing their patients into categories that will help to diagnose, research, and treat their spine symptoms.


The Study

Researchers used magnetic resonance imaging (MRI) to analyze and categorize 15 donated human cadaveric spines from 11 males and four females between the ages of 49 to 67 years old. Each of the spine samples showed evidence of moderate to severe disc degeneration. Motion segments were excluded if they appeared with imaging to have experienced pre-mortem surgery, deformity, or fracture. No medical history about the donors was obtained.

Histological Observation

Spinal segments were extracted using a band saw, and their various features were stained with different colors for observation. Each of the sections were imaged with polarized lights under a microscope, and two raters developed a classification system to identify and record various focal tissue-scale endplate irregularities and their anatomical location.

Researchers noticed a novel histological phenomenon wherein there appeared to be a separation of the annulus from the vertebra at the tidemark (the insertion point of outer annular fibers into the calcified layer of cartilage). They immune-stained the “tidemark avulsions” to search for the 9.5 neuronal marker protein gene using a polymer detection system. Each of the slides was then analyzed to identify the presence or absence of nerves in the bone nearest the endplate irregularity.

endplate irregulariities, models

Models to help explain back pain as it relates to endplate irregularities.

MRI Analysis

Each spine was studied via MRI to identify the presence of absence of tidemark avulsions, and their location was noted. Two orthopedic specialist clinicians were used to assess the findings. These researchers—neither of whom was previously used as a rater— were blinded to the histologic findings.


The endplate irregularities were grouped into three categories based upon their features and location. They were then subcategorized to further classify their pathologies.

The categories and subcategories identified were:

  • Avulsions: There was a separation of the tissue at the place where the disc joined the vertebra. Two types of avulsions were observed—tidemark (separation occurring at the tidemark location, where outer annulus fibers join the layer of calcified cartilage, and CEP-bone avulsion—occurring where the bone meets the cartilage endplate (CEP).
  • Nodes: Traumatic nodes occurred when there was a herniation of the nuclear materials reaching through the endplate. When abnormal fibrocartilage ingrowth or bony erosions were found, the were classified as Erosive.
  • Rim degeneration: This classification was reserved for samples that showed loss of organization in the annular fiber, bone marrow alterations, or degradation of the bone-marrow interface.

Endplate Irregularity Observations

The most common irregularities noted were rim degeneration (50 %) and avulsions (35%). Nodes were less common (15%) and found mostly in the thoracic spine, where the avulsions and rim degenerations were found in the lumbar spine samples. Eighty-seven percent of the noted avulsions were found in the anterior discs.

Though linear regression showed little association between endplate irregularities and age, the largest number of tidemark avulsions (90%) were found in the oldest spine samples. Interestingly, the annular fibers in the tidemark avulsions appeared to change their direction after crossing the tidemark. Of the 35 discs that showed tidemark avulsions, 14 of them contained multiple avulsions. Marrow changes and increased innervation was noted along vertebral bones beside endplate irregularities. An increase of nerve density was observed even in bones adjacent to very small tidemark avulsions.


The ability to identify tidemark avulsions on MRI may help practitioners identify and treat disc-vertebra injuries in a targeted way. High density images in the study showed that fluid can collect around avulsion irregularities, potentially creating gas in the extra-cellular spaces surrounding thee separation. High-intensity regions in MRI may indicate disc delamination or potentially painful lesions.  It is possible that tidemark avulsions may create anterior widening and create a scenario wherein the disc may detach from the vertebra. Overall, the findings of this study should contribute to a beneficial system of classification, allowing clinicians to more effectively diagnose and treat their lower back pain patients.

KEYWORDS: endplate irregularities, tidemark avulsions, endplate pathologies, histologic classification system, separation of the annulus from the vertebra at the tidemark, CEP-bone avulsion, traumatic nodes, rim degeneration


spine pain, models

Ed Cambridge: “Our colleague Jerome Fryer created some models for us, and this is some of the work that has come out of our lab with you and Christian Balkovec about the dynamic changes we see after herniation. Where we have disc height loss at one level, creating hypermobility at the adjacent level. So here you can see, when you move the spine around there is a stiffening effect down in the lower joint and in the upper joint hypermobility. That’s what we see when an injury propagates from one joint to the next. The patient says, “Well, the pain used to be lower but now its starting to creep up my back a little bit.” “

Stuart McGill: “Fabulous. Another little take on that … By the way, these are all cast from real human specimens. So this is the real deal. Once again, Dynamic Disc Designs has been so clever in representing the biofidelity. We start to see how this disc has been damaged, and it’s quite lax as we move it around. So those micro-movements now are triggering pain just at that level. And this joint has normal stiffness, but then look what happens. Over time, the join changes because of the change in mechanics. The lax disc now cases a bit more arthritis in those facet joints, because they are now responsible for much more motion. So then, look what happens to the cascade. As the person now extends, look what happens. The joint that was hypermobile has now bound up, has no mobility because the facets have bound up and all the motion is now left at the previously stiffened joint. The polar opposite. And then you need some kind of mobility to pop those facet joints open again after they’ve been jammed.”

inflammatory mediators

The changing spine and the anatomy. Professional LxH Dynamic Disc Model

Stuart McGill:  “So, when you understand the cascade of change that happens at a joint, it might be kicked off with a little bit of a flattened disc, which puts more load in the facet joints, which causes a little bit of arthritic growth. In two years, the joint has changed and so have the pain patterns and the mechanics. So, it really does lend insight to allow us to understand the cascade of how the patient reports those changes and their pain changes over the years. And it better allows us to show them what to do to wind down the pain sensitivity. “


A cross-sectional study 1of the multifidus muscles (MM) and erector spinae muscles of 68 women and 42 men found significantly higher levels of muscles in subjects without disc herniation than in the disc herniation group, indicating that chronic pressure on the root of the spinal nerve may cause degeneration and atrophy of the MM and erector spinae muscles groups.


Single-Level Disc Herniation

Model of Single-Level Disc Herniation.


The Study

110 LBP patients with an average age of 40 were analyzed and divided into two groups—those with single-level disc degeneration, and those without disc degeneration. Subjects with multilevel degeneration were excluded, as were those with deformities of the spine or a history of spinal surgeries. Both groups were radiographed via MRI at the lumbar levels, and the imaging results were compared to examine the paravertebral muscles, disc heights, and perpendicular distances between the laminae and MM. Statistical analysis using software compared the variables using the Kolmogorov-Smirnov test to investigate data distribution.


The LBP patients without lumbar disc herniation had clinically-significant greater MM and erector spinae muscles than those with radiographically-confirmed disc degeneration. No significant differences existed, however, in the disc heights, perpendicular distances between the MM and the laminae, or the psoas major cross-sectional areas of the two study groups.


The MM stabilizes the lumbar spine and, when negatively impacted, contributes to LBP. The muscle group create more force over a smaller range than the longer spine muscle groups, which helps to stabilize movement. The dorsal rami of the spinal nerves stimulates the MM and erector spinae, but the psoas major is stimulated by ventral rami lumbar spinal branches, prior to their joining the lumbar plexus. The medial paraspinal muscles are stimulated from one nerve root, but the iliocostalis and longissimus muscles receives stimulation from many roots. Indications of muscle degeneration include decreased muscle size and increased fat deposits in the area.

Because the MM and erector spinae are stimulated by the dorsal root stemming from a singular level, the chronic and long-lasting pressure on the root due to disc herniation contributes to the degeneration and atrophy of these muscles. This atrophy is not evident in the psoas muscle because it is stimulated by the nerves of many different levels, rather than a singular source. In order for muscle atrophy to occur, there must be at least six weeks of compression, according to this study’s authors.


Evidence of increased fatty deposits and decreased muscle in a cross-sectional lumbar image indicates the existence of muscle degeneration in LBP patients, assuming there has been at least six weeks of compression on the MM or erector spinae muscle groups, which are stimulated by a single nerve root.


KEYWORDS: Muscle Degeneration in LBP Patients with Single-Level Disc Herniation, single-level disc degeneration, paravertebral muscles, disc heights, and perpendicular distances between the laminae and MM, pressure on the root due to disc herniation contributes to the degeneration and atrophy of these muscles

  1. Volumetric Muscle Measurements Indicate Significant Muscle Degeneration in Single-Level Disc Herniation Patients
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 cell’s 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 a cell’s behaviour and suggested that research continue searching the optimal mechanical environment for intervertebral disc cells.

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


fissures in the annulus fibrosis, model

A recent study found that fissures in the annulus fibrosis can create a biomechanical and chemical environment that is conducive to the ingrowth and formation of blood vessels and nerves, which may contribute to back pain in patients with disc degeneration—particularly of the lumbar segments. An examination and analysis of cadaveric discs used safranin staining to examine the proteoglycan loss and measure the water concentration in the 25 surgically-removed discs and compared the data from intact and disrupted annular region to quantify the extent to which a reduction in compressive stress might allow blood vessels to grow and thrive within annular fissures. Results indicated 54 percent less proteoglycan content in the fissured annulus than in the intact samples, with only a slight reduction in water content.


Examining the Link between Fissures and Nerve Growth

Persistent lower back pain—particularly of the lumbar intervertebral discs—often presents with severe symptoms that can lead to long-term disability and loss of earnings. Chronic pain may be the result of posterior annulus fibrosis and the stimulation of the sinuvertebral nerve. Previous studies have demonstrated that the injection of neurotoxins into the compromised discs can curtail this nerve pain for up to two years. While studies have shown that disc degeneration increases the risk of lower back pain, much of the focus of previous research has been on the association between structural defects, such as endplate defects and a loss of annular height, rather than biochemical changes.

Radial fissures in the annulus, with, or without disc herniation, are considered a strong indicator of LBP. The subsequent in-growth of blood vessels and nerves into these fissures can sensitize the disc area and cause inflammation, which may cause pain in some—but not all—with disc degeneration. Researchers involved in this study supposed a possible causal link between annulus fissures and nerve ingrowth.

lumbar models

A professional lumbar spine model with a demonstration of in-growth of nerves and blood vessels from fissures in the annulus fibrosis.

Three Comparative Studies of Thoracolumbar Spine Segments

Three consecutive studies of surgically-removed cadaveric thoracolumbar spine segments from subjects who had experienced no spinal injury or extensive bed rest prior to death were compared with 25 samples taken from 18 cadavers of patients who had suffered from LBP, disc herniation, scoliosis, or spondylolisthesis prior to being deceased. The first study used die to identify annular fissures in 35 discs and radiographs to assess disc degeneration and height. Stress profiles were then performed on the segments in flexion and extension postures and then repeated following two hours of “creep” loading to simulate the rate of disc dehydration that might occur after a day’s activity. The discs were then dissected and photographed, then graded to determine the scale of degeneration.

The second study measured focal loss of proteoglycans from annular fissures in 25 samples using a custom-made software program, and a third study measured the loss of sulphated glycosamineoglycans in the fissured annulus.


Results—Higher Levels of Stress Reduction and Proteoglycan Loss in DD Samples

The analysis of the three studies indicated a compressive stress reduction of between 36 and 46 percent within the annulus fissures. The level was higher in degenerated discs. The fissured annulus regions had between 36 and 54 percent less proteoglycans than intact areas of the same discs, though the water content was only slightly reduced.

Pressure Reduction Contributes to Loss of Proteoglycans and Nerve Growth

The reduction of pressure inside the annulus fissures creates a biochemical environment that is conducive to the loss of focal proteoglycans. This allows for the in-growth of blood vessels and nerves within the fissured areas. These findings suggest that the injections of therapeutic neurotoxic dyes into the affected fissures could disable the in-grown nerves and help alleviate LBP in some patients.

KEYWORDS: Link Between Annular Fissures and In-growth of Blood Vessels and Nerves; fissures in the annulus fibrosis can create a biomechanical and chemical environment that is conducive to the ingrowth and formation of blood vessels and nerves; reduction in compressive stress might allow blood vessels to grow and thrive within annular fissures; possible causal link between annulus fissures and nerve ingrowth; reduction of pressure inside the annulus fissures creates a biochemical environment that is conducive to the loss of focal proteoglycans; posterior annulus fibrosis; persistent lower back pain