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Research Review By Dr. Joshua Plener©

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Date Posted:

March 2021

Study Title:

Disc Degeneration of Young Low Back Pain Patients: A prospective 30-year Follow-up MRI Study

Authors:

Saaksjarvi S, Kerttula L, Luoma K, et al.

Author's Affiliations:

University of Helsinki, Finland; Department of Hand Surgery, Töölö Hospital, Finland; HUS Medical Imaging Center, Radiology, Helsinki University Hospital, Finland

Publication Information:

Spine 2020; 45: 1341-47.

Background Information:

The impact of intervertebral disc degeneration (IDD), which can begin early in youth, has been the centre of much debate regarding its role in low back pain (1). Despite 80% of asymptomatic adults having disc abnormalities on lumbar MRI, some past research has demonstrated an association between degenerative disc changes and chronic low back pain symptoms (2-5).

MRI can be used to assess the phase of disc degeneration, as the decreased signal intensity of the nucleus pulposus correlates with its water content and grade of degeneration (6, 7). In a previous study assessing 20-year-old men using MRI, one or more lumbar discs were degenerated in 57% of individuals with chronic LBP, compared to only 35% in asymptomatic controls (8). This current study is a follow-up to the previous study, investigating the value of IDD detected in early adulthood as a predictor for progression of degenerative changes as well as low back pain symptoms and disability in middle age.

Pertinent Results:

In 2017, 96% of returning participants had more degenerated lumbar discs, defined as a decrease in signal intensity by > 20% compared to 1987. Out of the 107 normal discs from 1987 in the returning subjects, 73 degenerated during the 30-year follow-up. From 1987 to 2017, the average number of degenerated discs per person increased from 0.9 to 3.5. In addition, the distribution of degenerated discs was more evenly spread out in 2017 compared to 1987, where the majority was at L4/5.

The baseline signal intensity was found to be significantly associated with future degenerative changes at the same discs at follow-up. Furthermore, in a 1987 disc with just slight signal intensity decrease of > 20%, compared to a disc without a decrease in signal intensity, modic changes or severe endplate lesions were more common in 2017.

Of the 35 participants who replied to the questionnaire in 2017, 80% reported suffering from LBP. Subjects who had no decreased signal intensity in 1987 had an average VAS score of 3.3 and average ODI score of 20.1, and subjects who had one or more degenerated discs in 1987 had an average VAS score of 2.7 and ODI score of 15.1.

In the MRI studied individuals (n = 26), the average VAS and ODI of those with no discs with decreased signal intensity in 1987 compared to those with one or more degenerated discs was not significantly different.

The clinical test results in 2017 didn’t have an association with the subjects’ maximal grade of signal intensity decrease in 1987.

Clinical Application & Conclusions:

The results of this study demonstrate that decreased signal intensity of discs in 20-year-olds is associated with a further decrease of signal intensity and other degenerative changes at follow-up. Possibly, this can be a result of early lumbar degenerative changes predisposing oneself to accelerated degenerative processes in the specific disc space (5). As well, heritability could potentially explain this relationship.

However, the more important finding from this study is that the degree of degeneration at baseline doesn’t appear to have an impact on pain and disability. Therefore, signal intensity changes cannot be used as an accurate prognostic factor for the development of low back pain later in life. Future studies with larger cohorts, including genetic data and clinical information, could be assessed to further clarify the relationship between degenerative disc disease and LBP.

Reviewer’s Note: Even though some studies find greater degenerative discs in low back pain subjects, other studies have detected degenerative changes among asymptomatic individuals (2, 4). Research such as this study helps us understand the long-term impact of degenerative disc disease and its impact on patients’ lives. Conveying the results of this study can help empower patients and ensure they know that despite having degenerated discs at a young age, their long-term prognosis for low back pain and disability doesn’t appear to be impacted.

Study Methods:

Subjects:
In the original 1987 study, 75 white males suffering from LBP were recruited for an MRI study in a military hospital. LBP was classified as severe enough to hinder their participation in military service. In addition, 34 age matched asymptomatic controls were recruited.

In 2017, the study participants were invited for a follow-up MRI and clinical examination. Out of the original 69 subjects who completed the first study, 35 completed follow-up questionnaires and 26 had a subsequent MRI done.

MRI Interpretation:
The same methods were used to determine the signal intensity of the intervertebral discs in both studies. At each disc level from T12 to S1, a region of interest was determined in the nucleus pulposus in the sagittal T2-weighted images. In each subject, the highest signal intensity value was regarded as the healthiest disc and used as a reference for other discs to compare their signal intensity value. The degree of decreased signal intensity was graded as: normal (0-20% decreased signal intensity), moderately decreased (21%-60% signal intensity decreased), or severely decreased (> 60% decreased signal intensity). To assess intraobserver repeatability of the signal intensity measurements, 6 discs from five subjects were measured twice and the intraclass correlation was calculated which was found to be 0.98.

In addition to the original MRI assessment in 1987, additional degenerative changes in discs and adjacent subchondral bone were evaluated by two radiologists blinded to the 1987 MRI findings to assess the interobserver agreement. The assessments included:
  • The height of each disc was graded on a four grade scale as normal, decreased by 1-33%, decreased by 34-66%, or decreased by 67-100%.
  • Disc protrusions or bulging was graded as present or absent.
  • Signs of annular fissures were graded as absent, high intensity zone or large annular fissure present.
  • Modic changes, which are represented as M1 for edema, M2 for fat, and M3 for sclerosis, were divided into three grades (9). Grade 0 included disc spaces with no Modic changes, grade 1 included any disc space with M1 type changes with or without M2 or M3 types, grade 2 included those with M2 and/or M3 type changes without M1.
  • Lesions in adjacent bony endplates were graded as no lesion, minor lesion, Schmorl’s node type defect, an uneven or irregular border between the disc and vertebra, and a combination of Schmorl node and an irregular border.
The interobserver agreement for visual analyses ranged from 0.45 to 0.66.

In addition to the MRI assessment, a questionnaire including questions about health and lifestyle, employment status, history of spinal surgery, VAS (visual analogue scale) and ODI (Oswestry) were provided to subjects. VAS was interpreted as mild (0-3.4) moderate (3.5-6.4), or severe pain (6.5-10). The clinical examination provided included sensory, motor and jerk reflex tests, SLR and Schober’s test which were reported as positive or negative.

Statistical Analysis:
To determine the progress of IDD and assess whether early decrease in signal intensity predicted more severe degenerative changes in the same disc space, each disc from 1987 was categorized as either signal intensity of 0-20% or decreased > 20%. These values were used as predictors of the signal intensity decrease and degenerative changes in 2017. 2017 signal intensity decreases were categorized as 0-20%, 21-60%, or > 60%. Cross tabulation was used to demonstrate whether a disc with decreased signal intensity of > 20% in 1987 was more likely to have a higher grade of signal intensity decrease or changes in the adjacent subchondral bone at follow-up.

In addition, subjects were divided based on the presence or absence of decreased signal intensity at any disc level in 1987 and assessed to determine if this predicted VAS and/or ODI scores in 2017.

To determine if moderately or severely decreased signal intensity at any disc level in 1987 predicted clinical findings in 2017, each subject’s maximal decreased signal intensity grade in 1987 was used to assess its prediction of positive clinical findings in 2017.

Study Strengths / Weaknesses:

Strengths:
  • This study had a very long follow-up from the initial examination, which allows us to understand the long term effects of spinal degeneration.
Weaknesses:
  • The MRIs from the original study were not available, therefore an assessment of the morphological changes in 1987 was not possible. As a result, it was decided to only use the relative numerical value of measured signal intensity for grading of degenerated discs in 2017 to be consistent with measurements from 1987.
  • There was a lack of clinical data at baseline which prevented an analysis of the development of LBP symptoms at follow-up.
  • Less than half the original subjects had a follow-up assessment, and therefore it is uncertain if the MRI subgroup equally represents all subjects from 1987.

Additional References:

  1. Erkintalo MO, Salminen JJ, Alanen AM, et al. Development of degenerative changes in the lumbar intervertebral disk: Results of a prospective MR imaging study in adolescents with and without low-back pain. Radiology 1995; 196: 529–33.
  2. Luoma K, Riihima¨ ki H, Luukkonen R, et al. Low back pain in relation to lumbar disc degeneration. Spine 2000; 25: 487–92.
  3. Brinjikji W, Diehn FE, Jarvik JG, et al. MRI findings of disc degeneration are more prevalent in adults with low back pain than in asymptomatic controls: a systematic review and meta-analysis. AJNR Am J Neuroradiol 2015; 36: 2394–9.
  4. Jensen MC, Brant-Zawadzki MN, Obuchowski N, et al. Magnetic resonance imaging of the lumbar spine in people without back pain. N Engl J Med 1994; 331: 69–73.
  5. Boden SD, Davis DO, Dina TS, et al. Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. J Bone Joint Surg Am 1990; 72: 403–8.
  6. Tertti M, Paajanen H, Laato M, et al. Disc degeneration in magnetic resonance imaging. A comparative biochemical, histologic, and radiologic study in cadaver spines. Spine 1991; 16: 629–34.
  7. Modic MT, Steinberg PM, Ross JS, et al. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology 1988; 166 (1 pt 1):193–9.
  8. Paajanen H, Erkintalo M, Kuusela T, et al. Magnetic resonance study of disc degeneration in young low-back pain patients. Spine 1989; 14: 982–5.
  9. Kerttula L, Luoma K, Vehmas T, et al. Modic type I change may predict rapid progressive, deforming disc degeneration: a prospective 1-year follow-up study. Eur Spine J 2012; 21: 1135–42.

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