Date of Award

6-3-2009

Document Type

Thesis

Degree Name

Medical Doctor (MD)

First Advisor

Jonathan Grauer

Abstract

The purpose of this study was to determine the incidence of exaggerated fluid signal in lumbar facet joints on Magnetic Resonance Imaging (MRI) and evaluate the correlation of this finding with radiographic evidence of instability. One hundred and thirty-four consecutive lumbar MRIs obtained by a single surgeon over a 2-year period were selected for review. Studies were evaluated for exaggerated fluid (defined as greater than one millimeter) between the articular surfaces of the facets on axial views. Standing plain films of all patients were then evaluated to determine the incidence of spondylolisthesis for patients with and without exaggerated fluid in the facets on MRI. Of 134 consecutive MRIs, 118 were available for review. Sixteen (13.6%) had exaggerated fluid in the facets on axial images. Only 2 of these 16 (12.5%) had spondylolisthesis appreciable on MRI at that level. In contrast, 8 of the 16 (50.0%) had spondylolisthesis at the level of exaggerated fluid when the corresponding radiographs were reviewed. Thus, spondylolisthesis was suggested in 6 of 14 cases (42.9%) when the exaggerated fluid sign was present but spondylolisthesis was not evident on the supineMRI. In comparison, in the population without exaggerated fluid, only 1 in 102 (0.9%) showed a slip on plain film that was not observed on MRI. This difference was statistically significant (P<0.001). The sensitivity and specificity for this finding in detecting spondylolisthesis were 57% and 92%, respectively. The positive predictive value was 50%, and the negative predictive value was 94% when using the presence of fluid in the facets on MRI as an indicator of radiographic lumbar instability. The positive diagnostic likelihood ratio was 7.43, and the negative diagnostic likelihood ratio was 0.46. Given a patient with fluid in the facets, the post-test probability of having spondylolisthesis was 93.0%. In conclusion, patients with exaggerated fluid in the facets on axial MRI had a far greater likelihood of having spondylolisthesis on standing plain films than those without (odds ratio = 16.0, 95% CI, 4.44-57.60), even if this was not appreciated on the supine sagittal MRI sequences.

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