Is it appropriate to measure age-related lumbar disc degeneration on the mid-sagittal MR image? A quantitative image study.

Abstract

Even though phenotypes of disc degeneration vary on different sagittal magnetic resonance images (MRI), measurements typically are acquired on the mid-sagittal MRI. This study investigated the appropriateness of using the mid-sagittal MRI to measure various phenotypes of age-related disc degeneration. Lumbar spine MRIs of 66 subjects (mean age 50.3years, standard deviation 16.5years, range 22-84years) were studied. An image analysis program Spine Explorer was used to obtain quantitative measurements for disc height, bulging, and signal on para- and mid-sagittal T2-weighted MRIs. Measurements on para- and mid-sagittal MRIs and their associations with age were compared. Measurements of disc height, signal, and posterior disc bulging acquired on the mid-sagittal MRI were greater than those on the para-sagittal MRIs. Disc height measurements were not linearly associated with age. Greater age was correlated with greater anterior (r=0.45, P<0.001) and posterior (r=0.33, P<0.01) bulging on para-sagittal MRIs, but not posterior disc bulging on the mid-sagittal MRI (r=-0.10, P>0.05). Disc signal intensity measurements on the mid-sagittal MRI had stronger correlations with age than those on para-sagittal MRIs. Mean and standard deviation of disc signal intensity acquired on the mid-sagittal MRI had the strongest correlations with age among all measures of disc degeneration studied (r=-0.50, -0.67, respectively, P<0.001 for both). Disc signal measurements acquired on the mid-sagittal MRI were reliable and had strong correlations with age and thus can be used as an appropriate measure of disc degeneration. Disc bulging had better be measured on para-sagittal MRIs. Although severe disc narrowing clearly is a sign of severe disc degeneration, disc height was not linearly associated with age.