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.

Results

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.

Discussion

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

 

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. “

 

Lumbar Foramen

 An in vivo study of cross-sectional lumbar foramen dimensions during a weight-lifting activity showed that all levels of the lumbar intervertebral foramen (LIVF) area decreased, except for the L5-S1 segment during lumbar extension, which had consistent measurements of the foramen, height, and width throughout the activity. The results of the study could provide insight into ways to improve the diagnosis or treatment of lumbar foramen stenosis.

Purpose of the Study

Radiculopathy caused by nerve root compression is a common symptom of LIVF stenosis and is often treated surgically, through the implantation of an interspinous device or decompression. Because the LIVF is surrounded by mobile facet joints, its shape undergoes changes during typical daily movement. As it changes shape, it may put pressure on nerve roots or other structures that may cause pain. Complications arising from the changing dynamic anatomy of the LIVF during activity can lead to failed back surgery syndrome, so understanding how movement and weight-bearing affects the LIVF is important to effective treatment and maintenance of back pain.

The Study

An MRI study of 10 healthy subjects (five male, five female) in supine, relaxed positions was conducted, and 3D spine models were constructed based upon the results of the scans. The lumbar spines of the subjects were then imaged during lumbar extension postures of 45 degrees to a maximally-extended position, while the subjects were holding an 8-pound dumbbell in both hands. These scans were also used to create 3D vertebral models of the in-vivo dimensions during activity, and a data analytic design was created to determine the area, height, and width of the L2-S1 vertebral levels during the activity for 45-degree flexion, upright position, and maximal extension.

Results

Researchers found that the LIVF area in L2-L3, L3-L4, and L4-L5 decreased during weight-lifting activity. The LIVF widths also showed a similar decrease, but the heights remained throughout the extension activity. However, the foramen area, height, and width at L5-S1 did not change during the weight-lifting. Overall, the data for all other areas demonstrated a change of approximately 10 percent from 45 degrees flexion to an upright standing posture, and again from upright standing to maximal extension. This information underscores how patients with LIVF stenosis may experience nerve root impingement pain during extension postures and feel relief from that pain during flexion. Understanding the in vivo dynamics of the functioning lumbar spine may help practitioners in the treatment and diagnosis of lumbar foramen stenosis.

 

lumbar spinal stenosis, spinal canal narrowing

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

KEYWORDS: Lumbar Foramen Dimensions During Activity, in vivo study of cross-sectional lumbar foramen dimensions during a weight-lifting activity, insight into ways to improve the diagnosis or treatment of lumbar foramen stenosis, Radiculopathy caused by nerve root compression, Complications arising from the changing dynamic anatomy of the LIVF during activity, nerve root impingement pain during extension postures

Diurnal Disc Shape

The spine undergoes natural shape and fluid changes over the course of 24 hours. Often, back pain symptoms vary as well over the day and night cycle.  But the small changes and the links to pain have not been researched thoroughly. Here, a group of researchers from Duke University looked at the reliability of measuring intervertebral disc shape with recumbent MRI. This large avascular structure is linked to back pain and has significant diurnal variation in the human body. It would seem wise to further understand its diurnal disc shape changes.

Some people feel pain in the mornings and others feel things more so at the end of the day. Yet others feel pain more so when they lie down.

The intervertebral disc hydraulically keeps vertebrae separated. Water is squeezed out throughout the day as the human frame is vertical, and this water gets resorbed when an individual lays down. During the process, the disc changes shape and height. And when pain is involved, these shape and height changes can bear increased ( or decreased ) physical stress on structures that may be inflammatory. These can include annular fissures, disc bulges, disc herniations, disc protrusions, encroaching nerve or rootlets of nerves and the shingling of facet joints, just to name a few.

The purpose of this study was to determine intra and inter-rater reliability using MRI to measure diurnal changes of the intervertebral discs.

They did find excellent reliability, and interestingly they saw the most significant change in the posterior annulus region of L5-1. The diurnal variations were in line with what others had seen in previous work. Boos at al. in 1996 saw a 1-2mm change over the course of an 8h workday while Hutton et al. in 2003 saw a volume change of 1-2 cm3.

This research is essential if we are to fully understand back pain origins. Often pain syndromes related to the lower back present with symptoms that are diurnal. At Dynamic Disc Designs, we have models to help explain these subtle but significant changes to the discs, assisting patients to understand the onset of their pains and the diurnal disc shape and the natural variations.

 

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.

3D discogenic pain model

Nuclear tracking as a result of vibration for spine has been revealed in an ISSLS price winning study in Spine. In a microanatomical investigation titled : ” Vibration Really Does Disrupt the Disc ” 1 researchers looked at motion segments and the influence of vibration as it relates to intervertebral disc damage.

There has been background knowledge stating that whole body vibration can lead to back pain but no-one had studied the micro structure of the disc. Looking carefully how nuclear tracking disrupts the annulus and endplate, this study looked at sheep discs, with controls, and vibrated motion segments under 7 degrees of flexion. The forces used were 1300 plus or minus 500N and the frequency applied was 5hz. This equates to 5 vibration movements per second. They conducted the movement for 20,00 to 120,000 cycles to mimic lose does and high dose variation.

Nuclear Tracking in a Spine Model

nuclear tracking, flexion, motion segment, model, modeling

Flexion load causes posterior nuclear tracking.

They found there was no sharp significant drop in displacement revealing there was not one moment of catastophic failure. What they found was nuclear tracking and internal disruption of the inner and mid layers of the annulus fibrosus. They also saw delamination of the annular fibres where they attach to the endplate (aka, Sharpey’s Fibres)

In conclusion, these researchers revealed that vibration in a flexed spinal motion segment leads to inner and mid layer annular disruption rather than outer annular disruption that is seen with disc herniation. They believe this mechanism could lead to a better understanding of the initiation of the degenerative cascade of spine.

Dynamic Disc Designs tries to highlight important research and model the respective findings for spine professionals working with patients of back problems. Educating patients about the mechanisms  of back pain can be an empowering tool for both doctors and patients.

spine patient education, patient education, spine, models, lumbar, cervical

Improving compliance through spine patient education.

Communication is very important. We all know that. In any relationship, communication seems to be the key element in making sure a common goal is delivered. This is especially important when doctors connect with patients about spinal problems. Spine patient education is imperative in a patient centered model. It also seems helpful in reducing fear avoidance behaviours. 1

Spine Patient Education, Patient Centered, Education

Patient Centered

Doctor-patient communication is critical when relaying information about what the spinal diagnosis is.  Effective communication is also important when relaying the best options for treatment. Doctors and therapists will use their skills to connect with patients. Making reference to the experience they have had with the condition with some offering of favourable outcomes.

What is important is that the patient feels ‘listened to’ and that the doctor can relate their symptoms with the spinal movements that seem to aggravate or miminize the problem.

For example, if a patient exhibits pain bending forward, it can be very helpful to have a dynamic spine model that bulges under flexion load. If a patient can physically see and understand that bending forward can compress the discs (or squeeze on the nerves), this can be very effective in communicating the disc is the likely culprit in the case of sciatica.

spine, education, patient, doctor

Bending forward can cause pain.

Conversely, if a patient demonstrates pain while bending backwards, a dynamic model can show how the facets rub together into extension.

A doctor unequipped for spine patient education is like a mechanic without its tools. Patients are usually very curious about the internal workings of their own bodies. When a doctor or therapist can clearly demonstrate where and why it hurts, often they will be a patient for life.

Spinal pain frequently relates to the spacing of the vertebrae, or lack thereof. Dynamic disc height loss, for example, can now be shown with a model both a doctor and patient can hold and manipulate.