General Session: Diagnostic Imaging
Presented by: R. Guyer
R. Guyer(1), D. Ohnmeiss(2)
(1) Texas Back Institute, Plano, TX, United States
(2) Texas Back Institute Research Foundation, Plano, TX, United States
Introduction: The severity of the slip in patients with spondylolisthesis is often evaluated with imaging studies, including MRI. One potential problem is the imaging being performed with the patient lying supine in the scanner, usually with a support under the legs. This creates imaging the spine in a somewhat unnatural and unloaded position. Use of upright MRI provides imaging in a weight bearing, normal position. The purpose of this study was to determine if there were differences in the severity of spondylolisthesis seen on MRIs made in the supine vs. weight bearing positions.
Methods: MRIs in the supine and upright weight bearing positions were made on 28 patients with spondylolisthesis. All scans were performed using the Esaote G-scan. This is an open scanner in which the table rotates with the patient on it, so the supine and upright weight bearing images (table rotated 84o vertically) were obtained during the same scanning session. The imaging parameters used for the study was the T2 fast spin echo sequence. MRIs from both positions were measured using semiautomated OrthoCAD software in which each vertebral body from L1 to S1 is registered allowing various measurements be to made automatically. Measurements made for the current study included as the primary measure, the listhesis at level of the spondylolisthesis (difference in the inferior posterior margin of the superior vertebrae). Also analyzed were the vertebral body translation (difference in the location of the midpoint of the vertebral body), segmental angle (angle of the disc space at the level of the slip), and the overall lumbar lordosis (L1-L5).
Results: In the weight bearing position, the mean listhesis value was 4.2 mm, which was significantly greater than the value of 3.1 mm recorded for the supine position (paired t-test p< 0.01). The figure below shows the supine and upright MRIs with the vertebral segmentation and the listhesis measurement that changed 4.4 mm at L4-5 when comparing the images made with the patient in the two positions. Among the secondary outcome measures assessed, the vertebral body translation increased significantly at the level of the slip in the upright position (4.3 mm vs. 5.3 mm; p< 0.01). Lumbar lordosis was significantly greater in the weight bearing position (57.6o vs. 55.3o; p< 0.05) while there was a trend for the angle at the level of the spondylolisthesis to be less in the weight bearing position (7.8o vs. 9.1o; 0.05< p< 0.075) compared with supine.
Discussion: There were statistically significant differences in the severity of listhesis, vertebral body translation, and lordosis when comparing MRI scans made in the supine and weight bearing positions. These results support that body position during MRI can effect the images. This may have implications on evaluating severity of spondylolisthesis.
Figure 1. Imaging in the two positions.]