Routine Upright Imaging for Evaluating Degenerative Lumbar Stenosis: Incidence of Degenerative Spondylolisthesis Missed on Supine MRI
Restrospective Cohort.
Degenerative spondylolisthesis with lumbar stenosis is a well-studied pathology and diagnosis is most commonly determined by a combination of magnetic resonance imaging (MRI) and standing radiographs. However, routine upright imaging is not universally accepted as standard in all practices. To our knowledge, there has been no study investigating the incidence of missed diagnosis of degenerative spondylolisthesis evident only on standing lateral or dynamic radiographs when compared to sagittal alignment on MRI.
The authors hypothesize that supine MRI evaluation alone in lumbar degenerative disease will significantly underestimate the incidence of degenerative spondylolisthesis. Secondary hypothesis is that there will be no significant difference in detecting spondylolisthesis when comparing dynamic flexion-extension radiographs to standing lateral radiographs.
We retrospectively evaluated all patients presenting to spine clinic for degenerative lumbar conditions from July 2004 to July 2006 who had an MRI, upright lateral, as well as flexion-extension radiographs at our institution. The incidence of degenerative spondylolisthesis found on dynamic flexion-extension radiographs but not on MRI was determined. We then reviewed each and compared flexion-extension versus standing lateral views to determine if there was any significant difference in detecting anterolisthesis.
Of 416 patients with eligible studies, 109 were found to have degenerative spondylolisthesis at levels L4-5, L5-S1, or L3-4 based on flexion-extension radiographs. Of these, only 78 were found to have a corresponding spondylolisthesis on MRI, leaving 31/109 (28%) of degenerative spondylolisthesis levels undiagnosed on MRI. No additional anterolisthesis cases were detected on standing flexion-extension verses standing lateral radiographs.
Routine standing lateral radiographs should be standard practice in order to identify degenerative spondylolisthesis, as nearly 1/3 of cases will be missed on supine MRI. This may have implications on whether or not an arthrodesis is performed on those patients requiring lumbar decompression. Flexion-extension radiographs demonstrated no added value compared to standing lateral xrays for the purposes of diagnosing degenerative spondylolisthesis.
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