Imaging characteristics of "dynamic" versus "static" spondylolisthesis: analysis using magnetic resonance imaging and flexion/extension films

BACKGROUND CONTEXT

Traditionally, the "dynamic" and "static" types of spondylolisthesis have been lumped into a single group in the literature. The goal of this study was to define the radiographic characteristics of "dynamic" and "static" spondylolisthesis with the use of magnetic resonance imaging (MRI) and flexion/extension radiographs.

PURPOSE

Describe the characteristic findings present on MRI and flexion/extension radiographs that are associated with dynamic versus static spondylolisthesis.

STUDY DESIGN

Retrospective radiographic/imaging study.

METHODS

From 2009 to 2011, patients who underwent elective primary posterior spinal fusion for the diagnosis of spondylolisthesis had their plain films assessed for the degree of spondylolisthesis and were designated "dynamic" or "static," as defined by historical measures. Axial and sagittal T2 MRIs were evaluated for associated facet fluid (FF), facet cysts, interspinous fluid (ISF), and facet hypertrophy. These finding were then statistically evaluated for associations between dynamic and static spondylolisthesis on flexion/extension radiographs and characteristic MRI findings.

RESULTS

Ninety patients were included in the study with 114 levels examined for spondylolisthesis. Patients with greater than 3 mm of instability on flexion/extension films were more likely to have FF (p=.018) and ISF (p<.001). Of the patients who had a greater than 3 mm of instability, 39.5% did not demonstrate spondylolisthesis on the sagittal MRI reconstruction. If ISF was present on MRI, there was a positive predictive value of 69.0% that there would be greater than 3 mm instability on flexion/extension films. Absence of FF on MRI had a positive predictive value of 75.6% for instability less than 3 mm on flexion/extension films. In the presence of ISF on MRI, the likelihood ratio of finding more than 3 mm of instability on flexion/extension films was 3.68. The presence of FF on MRI had a likelihood ratio of 1.43 for instability. A total of 36.8% of all spondylolisthesis reduced when supine on MRI.

CONCLUSIONS

The presence of FF and/or ISF is associated with instability greater than 3 mm in flexion/extension radiographs.

Lumbar Facet Fluid-Does It Correlate with Dynamic Instability in Degenerative Spondylolisthesis? A Systematic Review and Meta-Analysis

BACKGROUND

Lumbar degenerative spondylolisthesis (LDS) is a common spinal disease. LDS has been differentiated into dynamic (unstable) and static (stable) spondylolisthesis. Standing flexion/extension lumbar spine radiographs are the best investigation to detect presence of dynamic spondylolisthesis. Magnetic resonance imaging is the investigation of choice to show lumbar canal stenosis and disc prolapse but it can miss dynamic LDS. Studies have shown good association between presence of facet fluid (FF) and dynamic spondylolisthesis.

METHODS

A systematic review and meta-analysis were performed. All studies describing the relationship between FF and degenerative spondylolisthesis as measured on dynamic radiographs or kinematic magnetic resonance imaging were included.

RESULTS

Fourteen articles met the inclusion criteria. A total of 1065 patients were included in the meta-analysis. Of the patients with unstable spondylolisthesis, 71% had FF, whereas only 22% of the patients with stable spondylolisthesis had FF. The combined pooled odds ratio for unstable spondylolisthesis in the presence of FF was 7.55 (3.61-15.08; P <0.00001). The pooled standard mean difference in the FF size in the patients with unstable and stable spondylolisthesis was 0.97 mm (0.38-1.57; P = 0.001).

CONCLUSIONS

FF has positive correlation with the presence of dynamic LDS and the probability of dynamic LDS increases as the size of FF increases. The probability of having a dynamic spondylolisthesis in patients with FF >1 mm is 8 times that of patients with no FF. Standing flexion extension radiographs should be performed in patients with FF >1 mm.

Significance of Facet Fluid Index in Anterior Cervical Degenerative Spondylolisthesis

STUDY DESIGN

Retrospective cohort study.

PURPOSE

To correlate cervical facet fluid characteristics to radiographic spondylolisthesis, determine if facet fluid is associated with instability in cervical degenerative spondylolisthesis, and examine whether vertebral levels with certain facet fluid characteristics and spondylolisthesis are more likely to be operated on.

OVERVIEW OF LITERATURE

The relationship between facet fluid and lumbar spondylolisthesis is well-documented; however, there is a paucity of literature investigating facet fluid in degenerative cervical spondylolisthesis.

METHODS

Patients diagnosed with cervical degenerative spondylolisthesis were identified from a hospital's medical records. Demographic and surgical characteristics were collected through a structured query language search and manual chart review. Radiographic measurements were made on preoperative MRIs for all vertebral levels diagnosed with spondylolisthesis and adjacent undiagnosed levels between C3 and C6. The facet fluid index was calculated by dividing the facet fluid measurement by the width of the facet. Bivariate analysis was conducted to compare facet characteristics based on radiographic spondylolisthesis and spondylolisthesis stability.

RESULTS

We included 154 patients, for whom 149 levels were classified as having spondylolisthesis and 206 levels did not. The average facet fluid index was significantly higher in patients with spondylolisthesis (0.26±0.07 vs. 0.23±0.08, p <0.001). In addition, both fluid width and facet width were significantly larger in patients with spondylolisthesis (p <0.001 each). Cervical levels in the fusion construct demonstrated a greater facet fluid index and were more likely to have unstable spondylolisthesis than stable spondylolisthesis (p <0.001 each).

CONCLUSIONS

Facet fluid index is associated with cervical spondylolisthesis and an increased facet size and fluid width are associated with unstable spondylolisthesis. While cervical spondylolisthesis continues to be an inconclusive finding, vertebral levels with spondylolisthesis, especially the unstable ones, were more likely to be included in the fusion procedure than those without spondylolisthesis.

Utility of Flexion-Extension Radiographs with Brackets and Magnetic Resonance Facet Fluid for the Assessment of Lumbar Instability in Degenerative Lumbar Spondylolisthesis

OBJECTIVE

To propose a new standardized technique for evaluating lumbar stability in degenerative lumbar spondylolisthesis using lumbar lateral flexion-extension radiographs with brackets and magnetic resonance facet fluid.

METHODS

A retrospective analysis of 57 patients diagnosed with lumbar (L4-5) spondylolisthesis was performed. We analyzed lateral flexion-extension radiographs obtained with a bracket (LFEB) and without a bracket (LFE). Sagittal translation, segmental angulation, posterior opening, lumbar instability, and changes in lumbar lordosis were compared using functional radiographs. The mean width and maximum width of the facet fluid, mean facet joint length, and facet fluid index (FFI) of the 2 groups were compared using sagittal translation.

RESULTS

The average value of sagittal translation was 1.68 ± 0.96 mm in LFE and 3.07 ± 1.29 mm in LFEB, and the difference was significant (P < 0.05). Segmental angulation, posterior opening, and changes in lumbar lordosis were significantly greater in LFEB than in LFE. The instability detection rate was 14.0% in LFE and 35.1% in LFEB. The FFI, maximum width, and mean width were significantly increased in the unstable lumbar spondylolisthesis group compared with the stable group in LFEB. The FFI and maximum width of the facet fluid were significantly increased in the unstable lumbar spondylolisthesis group compared with the stable group in LFE.

CONCLUSIONS

Lumbar lateral flexion-extension radiographs with brackets can standardize the operation process and provide sufficient hyperflexion and hyperextension images. The width of the facet fluid and FFI are significant factors in the evaluation of lumbar stability in patients with lumbar spondylolisthesis.