Assessing the Differences in Measurement of Degree of Spondylolisthesis Between Supine MRI and Erect X-Ray: An Institutional Analysis of 255 Cases

Degenerative spondylolisthesis is the displacement of one vertebral body over the adjacent one. While standing and flexion-extension X-rays are preferred for determining listhesis, magnetic resonance imaging (MRI) is often utilized to assess the compression of nerve root or spinal cord.To investigate the difference in radiographic measurements of spondylolisthesis between X-rays and MRI.We retrospectively reviewed the records and radiographic images of patients with a confirmed diagnosis of spondylolisthesis undergoing operation in 2016. Primary variable of interest was the degree of slippage as per the Meyerding method. Agreement between the 2 reviewers was assessed using the 2-way intraclass correlation coefficient (ICC) for slippage percentage and Cohen's Kappa for grade. Agreement of Meyerding grade between the 2 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 1-way ICC.A total of 255 cases were analyzed. ICC between the 2 reviewers was found to be 0.75 (95% confidence interval [CI] = 0.64-0.83, P .001) for X-ray and 0.76 (95% CI = 0.66-0.83, P .001) for MRI. Agreement between X-ray and MRI for grading of spondylolisthesis was found to be poor (kappa = 0.32, P .001). BA plot between X-ray and MRI measurements revealed an MD of 4.4% (95% limits of agreement: -10.3% to 19.3%) with 5.16% observations outside the limits of agreement and 1-way ICC of 0.35 showing poor agreement.Our results demonstrate the discrepancy of spondylolisthesis grade measurements between weight-bearing X-ray and nonweight-bearing MRI. Careful evaluation of both imaging technique is warranted to determine the final severity of pathology and tailoring of management plan.