Positional MR imaging of the lumbar spine: Does it demonstrate nerve root compromise not visible at conventional MR imaging?

PURPOSE: To evaluate whether positional magnetic resonance (MR) images of t he lumbar spine demonstrate nerve root compromise not visible on MR images obtained with the patient in a supine position (conventional MR images). MATERIALS AND METHODS: Thirty patients with chronic low back pain unrespons ive to nonsurgical treatment and with disk abnormalities but without compre ssion of neural structures were included. Positional MR images were obtaine d by using an open-configuration, 0.5-T MR imager with the patients seated and with flexion and extension of their backs. The disk and nerve root were related to the body position. Nerve root compression and foraminal size we re correlated with the patient's symptoms, as assessed with a visual analog ue scale. RESULTS: Nerve root contact without deviation was present in 34 of 152 inst ances in the supine position, in 62 instances in the seated flexion positio n, and in 45 instances in the seated extension position. As compared with t he supine position, in the seated flexion position nerve root deviation dec reased from 10 to eight instances; in the seated extension position, it inc reased from 10 to 13 instances. Nerve root compression was seen in one pati ent in the seated extension position. Positional pain score differences wer e significantly related to changes in foraminal size (P = .046) but not to differences in nerve root compromise. CONCLUSION: Positional MR imaging more frequently demonstrates minor neural compromise than does conventional MR imaging. Positional pain differences are related to position-dependent changes in foraminal size.