Significance of ligamentum flavum hypertrophy in developmental spinal stenosis

Abstract

Introduction: Developmental spinal stenosis (DSS) manifests as a narrowed spinal canal. These subjects are potentially at-risk of developing symptoms with smaller degrees of canal pathologies including ligamentum flavum (LF). However, its relationship is currently unknown. This study aims to address the association of DSS with LF hypertrophy in an attempt to better understand its clinical relevance and natural course. Methods: This prospective study consists of 31 patients who had surgical decompression (28 stenosis patients, 3 controls). Preoperative MRIs were used for anteroposterior spinal canal diameter measurement, which classifies patients having either developmental or degenerative spinal stenosis. Ligamentum flavum was collected during surgery for analysis. The degree of fibrosis is evaluated microscopically by Masson Trichrome staining. Results: There were 17 females and 14 males with mean age of 63.9 years. L5/S1 was most frequently degenerative. Spinal canal diameters can vary between the intervertebral levels within the same patient. Degrees of fibrosis vary between levels and between sides. For degenerative spinal stenosis, the degree of fibrosis significantly correlates with LF thickness. In DSS, the most narrowed spinal canal did not associate with thickening of the LF. Conclusions: For DSS, spinal canal can be relatively much narrowed, yet LF may not be greatly thickened with large degrees of fibrosis. This suggests that in DSS, symptoms can occur with a smaller degree of intracanal pathology. Fibrosis within hypertrophic LF is location and site-specific. Further analysis with immunohistochemistry can better delineate the associations between LF and DSS.