P42. Facet fluid is indicative of cervical degenerative spondylolisthesis

BACKGROUND CONTEXT Given the well-reported relationship between facet fluid and lumbar spondylolisthesis, intuitively, a similar relationship may exist in the cervical spine. However, there is a lack of literature investigating facet fluid in degenerative cervical spondylolisthesis. Therefore, an investigation of facet fluid association with spondylolisthesis is needed in the cervical spine. PURPOSE To identify cervical facet characteristics associated with (1) radiographic spondylolisthesis and (2) spondylolisthesis instability. STUDY DESIGN/SETTING Single institution retrospective cohort. PATIENT SAMPLE One hundred and fifty-four patients >18 years old with preoperative MRIs available who underwent ACDF for primary degenerative spondylolisthesis below C3 during 2015-2021. OUTCOME MEASURES Spondylolisthesis was defined as >3.0 millimeters (mm) of anterior translation of a vertebral body and vertebral instability was defined as translational difference of >3.5 mm between flexion and extension radiographs. METHODS Institutional Review Board approval was achieved. Patient demographics and surgical characteristics were collected through a Structured Query Language search and manual chart review of the electronic medical records. All measurements were made on preoperative MRIs for all levels of diagnosed spondylolisthesis and adjacent undiagnosed levels. The axial MRI most clearly demonstrating the facets was used to determine the average facet fluid index, which was calculated by dividing the combined diameter of both facet fluid measurements by the combined diameter of the facet widths on axial MRI. Bivariate analysis was conducted to compare facet characteristics based on radiographic spondylolisthesis and spondylolisthesis stability. Significance was set at a P value of <0.05. RESULTS A total of 149 vertebral levels had spondylolisthesis, while 206 levels did not. The average facet fluid index was significantly higher in patients with a spondylolisthesis (0.27 + 0.08 vs 0.25 + 0.08, p<0.031). In addition, both fluid width (4.61 + 2.58 vs 6.19 + 2.55 mm, p<0.001) and facet width (17.9 + 7.12 vs 23.0 + 6.66 mm, p<0.001) were significantly larger in levels with spondylolisthesis. However, the presence of facet fluid was not associated with spondylolisthesis (p=0.611). Analysis of levels with spondylolisthesis revealed that 106 had an unstable spondylolisthesis while 43 had a stable spondylolisthesis. Facet width (20.3 + 0.09 vs 24.0 + 6.16 mm, p=0.019) and fluid width (5.20 ± 2.25 vs 6.55 ± 2.47, p=0.019) were greater in patients with unstable spondylolisthesis, but no association was seen with facet fluid index. There was also no difference in the percentage of levels that had facet fluid between the two groups. CONCLUSIONS Our study is the first to demonstrate that facet fluid index, facet width, and fluid width is significantly associated with spondylolisthesis. We also found larger facet and fluid widths to be associated with unstable spondylolisthesis. High-quality studies are needed to further investigate the relationship between facet characteristics and spondylolistheses in the cervical spine. FDA Device/Drug Status This abstract does not discuss or include any applicable devices or drugs. Given the well-reported relationship between facet fluid and lumbar spondylolisthesis, intuitively, a similar relationship may exist in the cervical spine. However, there is a lack of literature investigating facet fluid in degenerative cervical spondylolisthesis. Therefore, an investigation of facet fluid association with spondylolisthesis is needed in the cervical spine. To identify cervical facet characteristics associated with (1) radiographic spondylolisthesis and (2) spondylolisthesis instability. Single institution retrospective cohort. One hundred and fifty-four patients >18 years old with preoperative MRIs available who underwent ACDF for primary degenerative spondylolisthesis below C3 during 2015-2021. Spondylolisthesis was defined as >3.0 millimeters (mm) of anterior translation of a vertebral body and vertebral instability was defined as translational difference of >3.5 mm between flexion and extension radiographs. Institutional Review Board approval was achieved. Patient demographics and surgical characteristics were collected through a Structured Query Language search and manual chart review of the electronic medical records. All measurements were made on preoperative MRIs for all levels of diagnosed spondylolisthesis and adjacent undiagnosed levels. The axial MRI most clearly demonstrating the facets was used to determine the average facet fluid index, which was calculated by dividing the combined diameter of both facet fluid measurements by the combined diameter of the facet widths on axial MRI. Bivariate analysis was conducted to compare facet characteristics based on radiographic spondylolisthesis and spondylolisthesis stability. Significance was set at a P value of <0.05. A total of 149 vertebral levels had spondylolisthesis, while 206 levels did not. The average facet fluid index was significantly higher in patients with a spondylolisthesis (0.27 + 0.08 vs 0.25 + 0.08, p<0.031). In addition, both fluid width (4.61 + 2.58 vs 6.19 + 2.55 mm, p<0.001) and facet width (17.9 + 7.12 vs 23.0 + 6.66 mm, p<0.001) were significantly larger in levels with spondylolisthesis. However, the presence of facet fluid was not associated with spondylolisthesis (p=0.611). Analysis of levels with spondylolisthesis revealed that 106 had an unstable spondylolisthesis while 43 had a stable spondylolisthesis. Facet width (20.3 + 0.09 vs 24.0 + 6.16 mm, p=0.019) and fluid width (5.20 ± 2.25 vs 6.55 ± 2.47, p=0.019) were greater in patients with unstable spondylolisthesis, but no association was seen with facet fluid index. There was also no difference in the percentage of levels that had facet fluid between the two groups. Our study is the first to demonstrate that facet fluid index, facet width, and fluid width is significantly associated with spondylolisthesis. We also found larger facet and fluid widths to be associated with unstable spondylolisthesis. High-quality studies are needed to further investigate the relationship between facet characteristics and spondylolistheses in the cervical spine.