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Physical Inactivity and Spinal Compression

Dynamic Disc Designs

Physical inactivity relates to many poor musculoskeletal conditions but has not been carefully looked at with regards to disc height loss.

In Arthritis and Research Therapy, a manuscript published May 7, 2015, researchers looked at seventy-two community based volunteer’s lumbar spine during 2011-2012. They used MRI to evaluate their spines after obtaining information of the level of activity by questionnaire between 2005 and 2008. At the time of MRI, they  a chronic pain scale to evaluate low back pain. Intervertebral disc height, muscle area of two spinal muscles and fat content of the multifidus muscle were measured.

The results showed that physical inactivity was related to disc height loss. There was no association seen between the size of the muscles in the spine but there was a relationship to fat within the multifidus.

It is very likely that the disc height loss seen, relates to the static load of the spinal tissues. Previous research has demonstrated static compression shows disc height loss. This was seen in a publication in Effects of static compression with different loading magnitudes and durations on the intervertebral disc: an in vivo rat-tail study.

Interestingly, too much activity, like seen with moderate-intensity running, has also shown significant disc height loss.

While research continues to expose the balance between physical inactivity and activity, too much of either looks to be deleterious to spinal discs. Spine educators have a job to teach patients about the important balance between too much or too little motion. Dynamic Disc models help doctors convey important load examples in the drive to improve spinal outcomes.

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Lumbar Disc Assessment – Research Update

Lumbar Disc Research - Intervertebral Disc

Lumbar Disc Assessment of Bedrest using MRI

Lumbar disc assessment of glycoaminoglycan content by MRI was investigated using gadolinium to look at the changes that took place after 21 days of bedrest. This research published in PLOS One investigated the effects of recumbancy on the lumbar discs to get a better understanding of whether the discs imbibe water or increase proteoglycan content with unloading. Spaceflight has effects of disc swelling and associated back pain.

Using bedrest as an analog to spaceflight, five volunteers, healthy, non-smoking males were subjected to 24hr bed rest with a 6 degree head down tilt for 21 days. Magnetic Resonance Imaging (MRI) scans were taken according to the delayed gadolinium-enhanced magnetic resonance imaging (dGEMRIC) protocol before and after bedrest.

Results showed significant changes in T1 which indicated that insufficient sleep can be a risk factor for low back pain. These researchers concluded that sufficient recumbency (unloading, decompression) is necessary for the intervertebral discs to recover from mechanical load and strain of daily activities. Interestingly, they not only showed how water increases to the discs with bedrest but also glycosaminoglycan content.

Clinical Tips

Clinically, patients often complain of symptoms related to sleep or lack thereof. They also complain of back pain related to the diurnal timing of load and respective disc height loss. That is, some complain of symptoms early in the morning after a period of recumbency (indicative if a degenerative disc) and others complain of symptoms later in their day, likely due to the progressive and hydraulic disc height loss of vertebral approximation irritating intradiscal tissue and/or facets with the associated articular capsule/synovial folds.

A careful dissection of the timing of patients symptoms will help point the investigator to the anatomy in question. Our models can assist in the patient education of the diurnal timing of symptoms and the importance of bedrest and unloading of interverterbal discs.

Explaining the timing of pain onset helps in the management of back pain. When patients understand that symptoms are related to hydraulic height loss, lying down or taking a nap mid-day may be a viable therapeutic strategy to increase disc height.

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Disc Height Loss and Preclinical Instability

annulus angle and disc height loss

Disc height loss is the common theme in back pain.

And with early disc height loss, hypermobility is related. But how are they associated to one another? Barr in 1948 (1) was the first to describe instability. His description of low back pain related to disc height and the passive stabilizers. A nice review of lumbar instability as an evolving concept was written by Beazell et al. These authors discussed the evolution through Farfan and his model, to Kirkadly-Willis and the three phases of degeneration as well Panjabi’s added concepts of neurological control. To understand the relationship between disc height loss and the development of hypermobility, it may be helpful to highlight the anatomy. In Panjabi’s and Adams “Biomechanics of the Spine”, there is a description of the annulus angles in alternating lemellae at 35 degrees from the horizontal explaining the tensile resistance with movement. What appears to not be described is the relationship of the annulus fibres when a disc loses its height. Below are a series of images, developed by Dr. Jerome Fryer, to help explain the displacement factor.

Annulus Fibrosus

Annulus Orientation

Each disc consists of concentric, alternating in orientation, fibrous sheets that encompass a hydraulic centre core named the nucleus pulposus. Once the disc height is reduced, the annulus angles change. If the length of the annulus fibres do not change, a displacement factor of hypermobility can occur.

annulus angle

Annulus angle change with disc height loss

 

disc height loss

Disc height loss leads to displacement

As it is often a therapeutic goal to increase spinal stability, increasing disc heights should be at the forefront.

The common theme seen in back or neck pain is intervertebral disc height loss. It is the earliest radiological finding in the degenerative cascade. This height loss leads to many geometrical and morphological changes that results, initially, in hypermobility which often leads to pain. This has been discussed thoroughly in the literature.

The three important changes related to disc height loss include:

  1. increased annular and endplate stress
  2. development of hypermobility
  3. facet approximation with reduced joint space width

These anatomical areas are important because this is where the innervation exists that contributes to pain.

Generally, spinal pain generators can be categorized into three distinct areas…all affected by disc height loss:

  1. discogenic and associated sinuvertebral nerve
  2. vertebral endplate disruption and associated basivertebral nerve
  3. facetogenic with medial branch and subchondrial innervation

A better understanding of the relationship between disc height loss and hypermobility will help us move toward developing models–as this relationship is thought to be the beginning stage of degeneration. A focus on the related biorheology to maintain disc height will be of paramount importance in the decades to come in the prevention of reduced joint space width of the opposing endplates and facet hyaline cartilaginous surfaces.

  1. Barr JS. Low-back and sciatic pain: results of treatment. J Bone Joint Surg Am 1951;33-A: 633–49.
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Intradiscal pressure and height

Disc Height Model

Intradiscal pressure depends on the understanding disc height loss and its relationship to load.

In a recent publication titled: Intradiscal pressure depends on recent loading and correlates with disc height and compressive stiffness, these authors tackled an important topic to help reveal the deformation an intervertebral disc will experience when subjected to prolonged and oscillatory loads. Often in clinical settings patients will experience low back pain as a result of cumulative and repetitive loads on the spine. It is therefore important to educate the patient on the reasons why pain may generate as the vertebrae begin to approximate. In their methods they tested 15 lumbar goat discs and found that as the pressures decreased over time, the heights of the discs were reduced significantly.  Past ideas around intradiscal pressure and height loss did not think that recent loading events played as much of a role as seen in this publication. Over the course of 4.5 hours of varying high and low dynamic loading, the disc heights reduced significantly. In human discs it is well known that spine pain is more likely to generate from a disc that is compressed vs. one that has normal height. Dynamic Disc Designs construct dynamic disc models to help the educator explain the pain sites in an interactive and research supported way. Explore.