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 and definitions

Background: The development in size and type of lumbar disc herniation (LDH) over time is not fully understood. Furthermore, the relationship between MRI defined LDH and clinical symptoms may not always confer with each other. This may be due to the lack of knowledge about the natural history of morphological changes in the related structures. In order to better understand the relationships, we investigated the following objectives. 1) the changes of LDH size through quantitative measures from MRI images taken at three time points over an eight-year period, 2) the cross-sectional associations between sizes of LDH and area of dural sac as well as disc height, and 3) LDH as a predictor of changes in dural sac areas and disc height after four and eight years.
Methods: The study sample was assembled using a population-based cohort study of 41 year olds called “Backs on Funen Cohort”. All individuals who had MRI confirmed LDH during the first four years period were included in the study. The individuals were followed for 8 years with MRIs taken at baseline, four years and eight years. Cross-sectional areas (mm2) of LDH, disc heights and dural sacs were calculated from measurements using sagittal T2 weighted images. Changes over time in LDH sizes were reported as “the same”, “increased “, “decreased”, or “fluctuating”. Beta-coefficients with 95% confidence intervals for cross-sectional and longitudinal analyses were obtained from linear regression adjusted for relevant covariates.
Results: In total, 65% of disc levels remained the same size, 17.5% decreased, 12.5% increased, and 5% had a fluctuating pattern. There was a negative association between LDH size and dural sac size (β-0.25[ -0.52;0.01]), and a positive association for disc height(β 0.35[0.14;0.56]). LDH size predicted statistical significant reductions in dural sac area (β -0.35 [-0.58;-0.13] and disc height (β -0.50[-0.81;-0.20].
Conclusions: This study provides detailed knowledge about changes in LDH size over time and its association with dural sac and disc height. Most LDHs did not change in size over time. However, the size of LDH predicted future reduction of cross-sectional area of dural sac as well, as loss of disc height.