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Study of Human Lumbar Foramen Dimensions During Activity Show Changes are Segment-Dependent

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

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Diurnal Disc Shape and Height Changes – Basic Science and Natural Variations to Understand Back Pain

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.

 

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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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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
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Disc height loss under constant compression – time-dependent response.

The intervertebral disc is home to visceoelastic material than deforms under constant load. Its role is to keep vertebrae separated to avoid the bones to approximate one another. Many researchers have seen how the disc gets squashed more under a constant and sustained load. 1 2 3 4 5

compression of spine with prolonged sitting

disc height loss and sitting – spine education with dynamic model

Sustained load, as seen in sitting patients with low back pain, is a common clinical complaint that is difficult to describe for the attending doctor without an appropriate model. Why a patient experiences low back pain as a result of not doing anything can be difficult for the patient to understand but using a visceoelastic model that deforms under compression can be helpful in the compliance of improving posture strategies or in the simple drive to get up out of the chair.

Dynamic Disc Designs has just made life a lot easier for doctors to explain this compression phenomenon. Using only the finest materials, these patient education models for spine can be easily accessed to demonstrate how compression of sitting will reduce disc height loss–sending a clear message that the patient should do something to move and help recover the disc hydration.

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Intervertebral Disc – Stress Shielded by Facets – Dynamic Education

intervertebral disc, model, facets, stress shielded, dynamic, spine, patient education

The intervertebral disc annulus can be shielded by the facets. This is important for the patient to understand to help motivate exercise strategies to relieve their back pain.

Researchers have seen in studies that bending the spine backwards (extension) helps resist compression of the spine discs 1 especially when the disc has already lost some height. 2 3 When crafting exercises, and if the facets are not considered a pain generator, bending backwards, especially in the unloaded position, can be an effective strategy to help heal discogenic pain.

Several mechanisms have been proposed on why extension-based exercises aid in the reduction of back pain. One likely path is the direction the nucleus moves as the spine is bent backwards. It has been shown in several studies that the nucleus moves away from the posterior annulus in spinal extension 4 5 6 7 8 9

Dynamic Disc Designs Corp. is the only spine modeling company that demonstrates these findings in a dynamic spine education platform. The Professional and Academic LxH models allows clear visualization of the nucleus as the model moves through 6 degrees of freedom. Patient education that motivates and drives compliance through knowledge to improve clinic outcomes for spine.

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Back pain and radiculopathy – upright mri research

Radiculopathy, upright mri

Back pain and radiculopathy is common….very common. Furthermore, it is very common for patients to explain that it ‘hurts’ more when they are vertical. Then why are we mainly looking at supine MRI for findings? Supine MRI is helpful in ruling out pathology and does offer higher resolution with the 1.5 and 3.0 Tesla…but this magnet power is not necessary to investigate biomechanical problems.

In a recent research paper published in The Journal of Craniovertebral Junction and Spine [full text], these group of researchers looked at seventeen adults (10 asymptomatic and 7 symptomatic) and used the .6 Tesla MRI to evaluate the lumbar spine and pelvis in the seated position.

They looked at the “foramen area, height, mid-disc width, width, thickness of ligamentum flavum, disc (bulge, height, width), vertebral body (height and width), and alignment (lordosis angle, wedge angle, lumbosacral angle).” 1

Some of the important results showed significant foramen narrowing and disc bulge was 48% greater in symptomatic volunteers compared to asymptomatic volunteers. Thickness of ligamentum flavum increased as well.

Overall, the researchers were cautious in their conclusive remarks…like all great researchers. But the bottom line is that we all know that symptoms related to spine are often worse being vertical. It is a bit of a no-brainer to continue to investigate the tissue in its load bearing state.

Yet another reason why Dynamic Disc Designs knew it was inevitable that a dynamic model would be to market. They were the first to pioneer this patient education movement. Be sure you are equipped.

flexible spine model nerves

 

  1.  Nguyen HS, Doan N, Shabani S, Baisden J, Wolfl a C, Paskoff G, et al. Upright magnetic resonance imaging of the lumbar spine: Back pain and radiculopathy. J Craniovert Jun Spine 2016;7:31-7.