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

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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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.