Lumbar MRI findings in the recumbent and the upright position: a prospective observational study on type and frequency of differences by direct comparison

Recumbent MRI is the most widely used image modality in people with low back pain; however, it has been proposed that upright (standing) MRI has advantages over recumbent MRI because of its ability to assess the effects of being weight-bearing and thus, potentially add clinically helpful information. Numerous studies, including a large scale study and a recent systematic review, including studies of 5.248 participants, have scientifically established and confirmed a systematic change in diagnostic findings in standing, upright MRI compared with standard recumbent MRI. The aim of this study was to investigate the types and frequencies of differences in lumbar MRI findings, between the recumbent and upright positions, both at the disc level as well as at the participant level. This prospective observational study included a total of 220 individuals, 69 low back pain patients without leg pain, 88 patients with low back pain and leg pain, and 63 controls. All participants were first scanned in the recumbent position using 0.5T, 1.5T or 3T MRI units, and then scanned in the upright position using an open 0.5T unit. For a series of 22 common MRI findings of the lumbar spine, differences between the two positions were assessed by direct comparison. Types of differences were classified as “ appeared ”, “ disappeared ”, “ worsened ”, or “ improved ” from the recumbent to the upright position, and separately at the disc levels L3/L4, L4/L5, L5/S1. Differences in at least one MRI finding could be observed in about half of all low back pain patients and in one-third of participants without back pain. At the participant level, upgrading of findings, involvement of other discs, or appearance of new findings could be observed rather frequently, whereas downgrading, narrowing or vanishing was rare. Differences were most frequently observed for disc contour (bulge, protrusion, extrusion), lateral recess stenosis, central canal stenosis and annular fissure, and for findings at the L4/L5 disc level. Direct comparison of a series of common lumbar MRI findings between the recumbent and the upright positions, shows a systematic increase in findings in the upright position. This gives a more detailed and nuanced overall picture of the lumbar spine than previously suggested by studies investigating only single or few findings. The clinical value of this additional information requires further investigation.