Progression of lumbar disc herniations over an eight-year period in a group of adult Danes from the general population – a longitudinal MRI study using quantitative measures

BACKGROUND A lumbar disc herniation (LDH) is a localised displacement of disc material, which may initiate changes in the disc and adjacent structures such as the nerve root and the spinal canal. Knowledge about how morphological changes in the disc relate to changes in other spinal structures might give the clinician a better understanding of the natural history and consequences of lumbar disc herniations. However, few longitudinal studies have investigated this process using reliable measures from magnetic resonance imaging (MRI). The objectives of this study were to examine changes in and associations between the size of lumbar disc herniations, dural sac area and disc height over an eight-year period using MRI at three time-points. METHODS Individuals from a population-based cohort, the 'Backs on Funen Cohort', had MRIs taken at age 41 years and again at 45 and 49 years. Only disc levels with MRI-confirmed disc herniations at 41 or 45 years were included. Cross-sectional areas (mm(2)) of the LDH, dural sac and disc height were calculated from measurements performed on sagittal T2-weighted images using a previously validated method. Changes over time for the three MRI findings were defined as "unchanged", "increased ", "decreased", or "fluctuating". Only changes beyond 95% limits of agreement of the same measurements were regarded as valid. Associations between the three types of measures were examined cross-sectionally and longitudinally. RESULTS One hundred and forty disc levels, from 106 people (48 women and 58 men), were included. Over eight years, 65% of the herniations remained unchanged, 17.5% decreased, 12.5% increased, and 5% had a fluctuating pattern. Increased herniation size was associated with decreased dural sac area (β-0.25[-0.52;0.01]) and increased disc height (β 0.35[0.14;0.56]). Moreover, larger herniation size predicted a statistically significant reduction in both dural sac area (β-0.35[-0.58;-0.13]) and disc height (β-0.50[-0.81;-0.20]). CONCLUSIONS On average, most LDHs do not change over a four- to eight-year period. However, larger herniation size predicts a reduction in both dural sac area and disc height. Further research should be done to determine the correlations between the progression of LDH and resolution of patient symptoms.