Immediate effect of upright position on lumbar disc using multiposture MRI: Preliminary results

Gravity loading on lumbar intervertebral discs (IVDs) is affected by body position. Although the long-term effects of gravity on IVDs have been reported, the immediate effects of gravity on IVDs remain unclear. We considered that changes in IVD structure in the upright and supine positions provided new diagnostic information. Therefore, we compared the apparent diffusion coefficient (ADC), transverse relaxation time (T₂), and morphology of the lumbar spine between the quickly changing upright and supine positions using an original magnetic resonance imaging (MRI) system that can obtain images in any position (multiposture MRI).

On a 0.4-T multiposture MRI, diffusion-weighted images of the lumbar spine in seven healthy volunteers were obtained using single-shot diffusion echo-planar imaging (b = 0 and 600 s/mm²) in quickly changing upright and supine positions. Moreover, spin-echo images with multiple echo times (echo time = 30, 60, 90, and 120 ms) were obtained in each position. We calculated the ADC and T₂ of each IVD (L1 and S1) without any disc degeneration. In addition, the lumbar lordosis angle and length of the lumbar spine were measured to evaluate the morphology of the lumbar spine.

The T₂ of the IVD between L4 and L5 in the upright position was significantly lower than that in the supine position (P < 0.05). No significant differences were observed in the ADC. The morphology of the lumbar spine did not differ significantly between the two positions.

The T₂ of the IVD between L4 and L5 was likely decreased by the effect of gravity due to the postural change from supine to upright.