Authors: Mohamad Bydon, MD, FAANS ; Mohammed Alvi, MBBS; Mohammed Sebai, MBBS; Yagiz Yolcu, MD; Waseem Wahood, MS; Timothy Kaufmann, MD (Rochester, MN)

Introduction: Degenerative Spondylolisthesis(DS) is the displacement of one vertebral body over the adjacent one secondary to degenerative changes in the vertebral column. While standing and flexion extension X-Rays are preferred for determining listhesis and instability, MRI is often utilized to assess the compression of nerve root or spinal cord. In the present study, we sought to investigate the difference in radiographic measurements of spondylolisthesis between lateral standing X-rays and supine MRI. Methods: We retrospectively reviewed the records and radiographic images of all cases with a confirmed diagnosis of spondylolisthesis undergoing an operation in 2016. Only those cases with available preoperative X-ray and MRI were selected for review. Primary variable of interest was the degree of slippage as per the Meyerding method, measured independently by 2 reviewers on lateral X-ray and sagittal MRI sections. Agreement between the two reviewers was assessed using the two-way intraclass correlation coefficient (ICC) for slippage percentage and Cohen’s Kappa for grade. Agreement of Meyerding grade between the two imaging techniques was assessed using Cohen’s Kappa while the slip percentage measured for each technique was compared using a Bland-Altman(BA) plot, mean difference(MD) and one-way ICC. Results: A total of 255 cases were considered eligible for analysis. ICC between the two reviewers was found to be 0.75(95%CI=0.64-0.83,p<0.001) for X-ray and 0.76(95%CI=0.66-0.83,p<0.001) for MRI showing good agreement. Agreement between X-ray and MRI for grading of spondylolisthesis was found to be poor(Kappa=0.32,p<0.001). BA plot between X-ray and MRI measurements revealed a MD of 4.4%(95% limits of agreement:-10.3%,19.3%) with 5.16% observations outside the limits of agreement and one-way ICC of 0.35 showing poor agreement. Conclusion: Our results demonstrate the discrepancy of spondylolisthesis grade measurements between weight-bearing X-ray and non-weight-bearing MRI. Careful evaluation of both imaging technique is warranted to determine the final severity of pathology and tailoring of management plan.