In Vivo Diurnal Variation in Intervertebral Disc Volume and Morphology

STUDY DESIGN: Three-dimensional reconstructions of MRI scans measured volume, height, and diameter of intervertebral discs. These measurements were made in vivo. OBJECTIVES: This study documented diurnal change in lumbar disc volume and morphology. The authors studied the pattern of this change over the disc levels that were examined and documented individual differences. SUMMARY OF BACKGROUND DATA: There is a diurnal pattern of standing heights. The majority of this diurnal height change can be accounted for by height loss within the intervertebral disc, which bulges radially with loading. These studies have been performed in vivo. METHODS: Eight normal males were studied using two protocols. In one, the volunteers were in the supine position for 6 hours before MRI scanning. In the other, volunteers spent 4 hours standing and 3 hours sitting before MRI scanning. Three-dimensional MRI scanning was carried out on the L3-4, L4-5, and L5-S1 discs. RESULTS: Volume height and AP diameter of the lumbar intervertebral discs decreased significantly after the protocol of a day's activity. The mean decrease in disc volume at the L3-4 level after standing was 21.1%. At the L4-5 level, it decreased a mean of 18.7%, whereas at the L5-S1 level, there was a 21.6% mean decrease. CONCLUSIONS: The mean simulated diurnal volume decrease in the lower three lumbar discs is 16.2%. Most of the diurnal loss in disc height is due to volume loss. The effect of radial bulging is minimal.