Magnetic resonance imaging (MRI) is often used to evaluate low back pain; however, MRI in the supine position does not always reveal degenerative spondylolisthesis. The existence of a linear correlation between increased fluid in the facet joints seen on the supine axial T2 MRI of the lumbosacral spine and lumbar instability seen on standing lateral flexion–extension lumbosacral radiographs has recently been reported. The objective of this prospective study was to determine the incidence of increased fluid in the lumbar facet joints seen on the supine axial T2 MRI, and to evaluate the correlation of this finding with radiographic evidence of lumbar instability.
We prospectively analyzed weight-bearing flexion–extension lumbosacral radiographs and lumbosacral MRI in the supine position for 52 patients (mean age 64.7 years) seen at our institution for low back pain and/or radiculopathy. The statistical analysis was performed with Fisher’s exact test. A difference was considered statistically significant if P < 0.05.
In all but 5 of the 52 patients, degenerative disc disease and facet joint disease were observed on the supine MRI of the lumbosacral spine. Fifteen patients had exaggerated fluid in the lumbar facets on the axial T2 MRI (28.8%). Radiographic signs of degenerative lumbar spondylolisthesis were observed in 12 patients (23.1%), and the degenerative spondylolisthesis was not evident on the supine sagittal MRI in 10 of these 12 patients (83.3%). Among these 12 patients, the axial T2 MRI showed exaggerated fluid in the facet joints at the corresponding level in 8 patients (66%). Increased fluid in the lumbar facet joints was present on the supine axial T2 MRI in 7 patients (13.4%), even though there were no radiographic signs of corresponding lumbar instability.
We observed a statistical correlation between increased fluid in the lumbar facet joints on the supine axial T2 MRI and degenerative spondylolisthesis seen on standing lateral flexion–extension lumbosacral radiographs.
