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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. [ABSTRACT FROM AUTHOR]

Background: There is a shortage of agreement studies relevant for measuring changes over time in lumbar intervertebral disc structures. The objectives of this study were: 1) to develop a method for measurement of intervertebral disc height, anterior and posterior disc material and dural sac diameter using MRI, 2) to evaluate intra- and inter-rater agreement and reliability for the measurements included, and 3) to identify factors compromising agreement. Methods: Measurements were performed on MRIs from 16 people with and 16 without lumbar disc herniation, purposefully chosen to represent all possible disc contours among participants in a general population study cohort. Using the new method, MRIs were measured twice by one rater and once by a second rater. Agreement on the sagittal start- and end-slice was evaluated using weighted Kappa. Length and volume measurements were conducted on available slices between intervertebral foramens, and cross-sectional areas (CSA) were calculated from length measurements and slice thickness. Results were reported as Bland and Altman’s limits of agreement (LOA) and intraclass correlation coefficients (ICC). Results: Weighted Kappa (Kw (95% CI)) for start- and end-slice were: intra-: 0.82(0.60;0.97) & 0.71(0.43;0.93); inter-rater: 0.56 (0.29;0.78) & 0.60(0.35;0.81). For length measurements, LOA ranged from [−1.0;1.0] mm to [−2.0;2.3] mm for intra-; and from [−1.1; 1.4] mm to [−2.6;2.0] mm for inter-rater. For volume measurements, LOA ranged from [−293;199] mm3 to [−582;382] mm3 for intra-, and from [−17;801] mm3 to [−450;713] mm3 for inter-rater. For CSAs, LOA ranged between [−21.3; 18.8] mm2 and [−31.2; 43.7] mm2 for intra-, and between [−10.8; 16.4] mm2 and [−64.6; 27.1] mm2 for inter-rater. In general, LOA as a proportion of mean values gradually decreased with increasing size of the measured structures. Agreement was compromised by difficulties in identifying the vertebral corners, the anterior and posterior boundaries of the intervertebral disc and the dural sac posterior boundary. With two exceptions, ICCs were above 0.81. Conclusions: Length measurements and calculated CSAs of disc morphology and dural sac diameter from MRIs showed acceptable intra- and inter-rater agreement and reliability. However, caution should be taken when measuring very small structures and defining anatomical landmarks. [ABSTRACT FROM AUTHOR]