Vacuum Facet Phenomenon in Computed Tomography Imaging: A Sign of Instability in Degenerative Spondylolisthesis?

OBJECTIVE

The aim of the present study was to investigate the relationship between vacuum facet phenomena and lumbar instability in patients with degenerative spondylolisthesis (DS) in L4-L5.

METHODS

Patients with L4-L5 DS who had both lumbosacral flexion-extension radiographs and computed tomography (CT) scans available for review from January 2016 to December 2017 were eligible for the present study. The dynamic motion index (DMI) of each patient was used to represent the percentage of slippage of L-L4 on the L5 vertebral disks on the flexion radiographs minus the percentage on the extension radiographs. The facet vacuum index refers to the average width of the facet vacuum on the left and right sides.

RESULTS

A total of 67 patients with L4-L5 DS were included in the present study. Of the 67 patients, 35 had a vacuum facet phenomenon on their CT scan and 32 patients did not. The incidence of lumbar instability in the patients with a vacuum facet phenomenon was significantly greater than that in the patients without a vacuum facet phenomenon (P = 0.015). The mean DMI for the patients with a vacuum facet phenomenon was significantly greater than that for the patients without a vacuum facet phenomenon (P < 0.001). A positive linear correlation was found between the facet vacuum index and DMI for patients with a vacuum facet phenomenon (Pearson correlation coefficient, 0.597; P < 0.001).

CONCLUSIONS

A linear correlation was found between the degree of segmental motion and the width of the vacuum facet phenomenon in patients with DS at L4-L5. Our study has shown that vacuum facet phenomena detected on the CT images of patients with DS are highly predictive of segmental instability.