MRI findings of lumbar spine instability in degenerative spondylolisthesis

Purpose: To find out the factors suggesting lumbar segmental instability in patients with degenerative spondylolisthesis (DS) on conventional magnetic resonance imaging (MRI). Methods: Ninety-four patients with DS who underwent decompression surgery with or without fusion were selected. Patient demographics and findings on simple radiographs and MRI were analyzed. We divided patients into two groups by the presence of lumbar instability on simple standing plain radiographs and measured degeneration status of intervertebral discs and facet joints and distance of facet fluid signal on T2 axial MRI on each groups. The data were analyzed to find out the correlation between facet fluid signal and lumbar instability. Results: Sixty-three patients were confirmed to have lumbar instability (unstable group (UG), 67%), while 31 patients (stable group (SG), 33%) did not have instability on simple radiographs. The mean age was slightly older in SG (p < 0.05) and SG patients’ degeneration status of intervertebral discs and facet joints was advanced than UG patients. Fifty-five of 63 patients had high signal intensity on T2-weighted MR images in the UG, but only 4 of 31 patients had high signal intensity in the SG (p < 0.001) and UG patients have more larger facet joint distance than SG patients (p < 0.001). Conclusion: High signal in facet joints on T2 MR images can be a useful factor suggestive of lumbar instability. Thus, the identification of fluid signal in the facet joints on MRI should raise the suspicion for lumbar instability and prompt additional evaluations such as with stress radiographs.