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Lumbar Spondylolisthesis: Radiographic Criteria of Instability

Introduction The goal of this study was to compare the radiographic criterias of “static” and “dynamic” lumbar degenerative spondylolisthesis. The sensitivity of standing lateral flexion/extension (SLFE) radiographs and magnetic resonance imaging (MRI) was used to categorize the spondylolisthesis to provide the patient with the ideal treatment. Material and Methods Prospective study where patients were screened using standing lumbar spine SLFE radiographs and MRI. They had their plain films assessed for the degree of spondylolisthesis and were designated “dynamic” or “static” based on the current literature criteria. Axial and sagittal T2 MRIs were evaluated for associated facet fluid (FF) and interspinous fluid (ISF). We compared then the radiographic results with our per-op findings and studied the sensitivity of SLFE radiographs and MRIs. Results 22 patients were included and evaluated for the presence of spondylolisthesis. Patients with greater than 3mm of instability on SLFE films were more likely to have FF (p = 0.026) and ISF (p = 0.027). If ISF was present on MRI, there was a positive predictive value (PPV) of 83.3% that there would be greater than 3mm instability on plain films. Absence of FF on MRI has a PPV of 75% for instability less than 3 mm on plain films. If ISF is present on MRI, the likelihood ratio of finding greater than 3mm instability on plain films was 3.45. The presence of FF on MRI had a likelihood ratio of 2.53 for instability. The presence of both parameters FF and ISF increased the likelihood ration to 5.08. Conclusion The presence of FF and/or ISF on MRI is associated with instability greater than 3mm on SLFE films. The presence of 1 or more of the following criteria: slip distance greater than 3mm, FF greater than 3mm and positive ISF permit us to consider the spondylolisthesis as dynamic and allow us to perform a posterior spinal fusion.