Disc height and signal intensity of the nucleus pulposus on magnetic resonance imaging as indicators of lumbar disc degeneration

Study Design. A cross-sectional magnetic resonance imaging (MRI) study of degeneration of the lumbar spine. Objectives. To compare the usefulness of disc height and that of T2-weighted signal intensity as indicators of disc degeneration. Summary of Background Data. Disc height and signal intensity have been used as indicators for disc degeneration. Their relation to each other and to early degeneration has not been well documented. There is evidence that physical load can affect disc height. Methods. Forty-one machine operators, 41 construction carpenters, and 46 office workers, aged 40-45 years, and 22 students aged 18-20 years were examined with sagittal magnetic resonance imaging. All study participants were men. The mean value of the anterior and posterior disc height and the relative T2-weighted signal intensity of the nucleus pulposus of discs L2-L3 to L5-S1 were measured. Results. Young men showed the lowest disc height but the highest relative signal intensity. Disc height showed an increasing trend from the office workers (sedentary) to blue-collar workers (more physical work) at all disc levels but L5-S1. Relative signal intensity showed a decreasing trend for these same worker types at all levels. In generalized linear modeling, signal intensity and the occupations, in reference to the young students, showed a significant effect on disc height. Conclusions. Relative signal intensity was lower in the middle-aged men than in the young men, indicating agerelated disc degeneration. Despite the general positive association between disc narrowing and decreased relative signal intensity, disc narrowing may behave unexpectedly in relation to signal intensity and age. Signal intensity may be a more sensitive measure of disc degeneration. The validity of disc height as an indicator of early degeneration seems questionable.