Image-Based Markers Predict Dynamic Instability in Lumbar Degenerative Spondylolisthesis

OBJECTIVE: To identify possible radiographic predictors markers of dynamic instability including disc height (DH), disc degeneration, and spondylosis in the setting of degenerative spondylolisthesis (DS). METHODS: A retrospective review with prospectively collected data was performed on 125 patients with L4–5 DS who underwent decompression and fusion. Patients were divided into groups with dynamic instability and those without. Radiographs of the lumbar spine in neutral, flexion, and extension were used to determine degree of slip, DH, translational motion, angular motion, spondylotic changes, and lumbar lordosis. Magnetic resonance imaging (MRI) scans were reviewed to assess disc degeneration. RESULTS: Thirty-one percent of the patients met criteria for dynamic instability. Significant correlations (p < 0.05) were found between preserved DH and dynamic instability; increased spondylotic changes and decreased translational motion; as well as advanced MRI-based disc degeneration scores with decreased angular motion, respectively. Six radiographic parameters were utilized to create a predictive model for dynamic instability, and a receiver operating characteristic curve was able to validate the predictive model (area = 0.891, standard error = 0.034, p < 0.001). CONCLUSION: In DS patients, preserved DH was significantly related to dynamic instability. This finding may represent a greater potential for slip progression over time in these patients. In contrast, disc degeneration on MRI, and spondylotic changes were inversely related to dynamic instability and may represent restabilization mechanisms that decrease the chance of future slip progression in DS.