Correlation Between Obliquity of Exiting Nerve Root on Lateral Sagittal MRI Images and Degenerative Spondylolisthesis.

BACKGROUND: MRI has become the investigation of choice for patients of low back pain with radiculopathy. However, MRI does not consistently detect spondylolisthesis. In far lateral sagittalT2 MRI images, exiting nerve roots are seen descending vertically. We observed that the obliquity of these descending nerve roots may be related to spondylolisthesis.

OBJECTIVE: Aim of this study is to evaluate the correlation between obliquity of exiting nerve root on MRI and lumbar instability on dynamic radiographs.

METHODS AND MATERIAL: We retrospectively studied 248 patients who underwent discectomy or laminectomy and stabilization for degenerative lumbar disease at our institute from January 2017 to February 2020. For objectively measuring the obliquity of the exiting nerve root, we described an angle between the vertebra and exiting nerve root on far lateral T2 MRI images. We measured the exiting root angle and studied its correlation with degenerative spondylolisthesis on dynamic X-rays.

RESULTS: Out of 108 patients having spondylolisthesis, 106 (98.15%) had an angle of obliquity of the exiting nerve root as >105° and only two (1.85%) had an angleof <105°. Among 140 patients without spondylolisthesis, 137 (97. 86%) had an angle of obliquity of <105°and only three (2.14%) had an angle of >105°. Statistical parameters for our test of "angle of obliquity for the exiting nerve root in spondylolisthesis"are as follows: sensitivity of the test- 98.14%, specificity of the test- 97.85%.

CONCLUSION: Obliquity of the exiting nerve root is a very easy to detect. It has avery high sensitivity and very high specificity for detecting spondylolisthesis on supine MRI.