The distended facet sign: an indicator of position-dependent spinal stenosis and degenerative spondylolisthesis.

BACKGROUND CONTEXT: Symptoms of spinal stenosis are position-dependent. Stand up magnetic resonance imaging (MRI) and myelography can demonstrate further dynamic components of spinal stenosis that may go unrecognized on supine MRI.

PURPOSE: To describe a radiographic finding seen on standard supine MRI that is an indicator for dynamic spinal stenosis and degenerative spondylolisthesis.

STUDY DESIGN/SETTING: Case series.

PATIENT SAMPLE: Six patients.

OUTCOMES MEASURES: Radiographic observation.

METHODS: Six patients with classic neurogenic claudication but equivocal supine MRI findings were evaluated with myelography. The imaging findings were reviewed and compared.

RESULTS: All patients had severe position-dependent spinal stenosis upon upright myelographic imaging with grade I or II spondylolisthesis. The MRI showed very minimal to no spondylolisthesis. These dynamic slips reduced when supine, causing the vertebral bodies to appear aligned with adequate canal space, whereas the irregular facet joints became distended. Hypertrophic and fluid-filled facets at the dynamic slip level were seen in all patients, giving the appearance of a distended joint.

CONCLUSIONS: MRI may not demonstrate significant stenosis in patients with neurogenic claudication caused by dynamic degenerative spondylolisthesis. However, the presence of large fluid-filled facet joints indicates the likelihood of positional translation at that level which could be further confirmed by upright imaging.