P43. Magnetic resonance imaging is inadequate to assess cervical sagittal alignment parameters

Abstract

<h3>BACKGROUND CONTEXT</h3> Cervical sagittal alignment (CSA) parameters are helpful in determining the surgical technique used to treat cervical spondylotic myelopathy. Upright lateral radiographs are routinely used to measure CSA parameters, but obtaining adequate imaging is difficult. Utilizing magnetic resonance imaging (MRI) to evaluate sagittal parameters has been explored; however, the impact of positional changes on these parameters has not been elucidated. <h3>PURPOSE</h3> To evaluate CSA parameter measurement reliability and correlation between XR and MRI modalities in patients undergoing posterior decompressive procedures for cervical spondylotic myelopathy. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study. <h3>PATIENT SAMPLE</h3> We evaluated adult patients who had undergone laminoplasty or laminectomy and fusion for cervical spondylotic myelopathy between 2017 and 2019 and who had cervical spine XR and MRI within a 6-month timespan of one another. <h3>OUTCOME MEASURES</h3> Outcomes of interest included intra- and interobserver reliability assessment of C2-C7 sagittal angle, C2-C7 sagittal vertical axis (SVA), and T1 tilt measurements as well as correlations in these parameters between imaging modalities. <h3>METHODS</h3> Two clinicians completed two independent rounds of C2-C7 sagittal angle, C2-C7 sagittal vertical axis (SVA), and T1 tilt measurements; intra- and interobserver reliability were assessed by intraclass correlation coefficient (ICC). Correlations between imaging modalities were analyzed using parametric and nonparametric statistical tests. <h3>RESULTS</h3> Intra- and interobserver reliabilities were highly correlated with correlations greater than 0.85 across all permutations; ICCs were highest with MRI measurements. The C2-C7 sagittal angle was highly correlated between XR and MRI at 0.76 with no significant difference (p = 0.46). Weaker correlations existed for C2-C7 SVA (0.48) and T1 tilt (0.62) measurements with significant differences observed in the mean values between the two imaging modalities (p < 0.01). <h3>CONCLUSIONS</h3> The C2-C7 sagittal angle is highly correlated and not significantly different between upright XR and supine MR images. However, cervical SVA and T1 tilt change with patient position. As MRI does not accurately reflect the CSA in the upright position, upright lateral radiographs should be obtained to assess global sagittal alignment when planning posterior based cervical fusions. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.