Morphological Changes in the Ligamentum Flavum in Degenerative Lumbar Canal Stenosis: A Prospective, Comparative Study

STUDY DESIGN: Prospective, comparative. PURPOSE: To compare the histopathological and electron microscopic changes in the ligamentum flavum (LF) between degenerative lumbar canal stenosis (LCS) and lumbar disk herniation (LDH). OVERVIEW OF LITERATURE: The LF has been implicated as a key structure in the pathogenesis of LCS. With aging, the LF undergoes morphological changes–a decrease in the elastic component and an increase in the collagen component, in addition to other focal changes. By comparing the histopathological and electron microscopic picture of the LF in elderly patients with LCS with that in young patients with LDH, the role of this ligament in the pathogenesis of LCS may be clarified. METHODS: Forty patients were prospectively recruited and divided into two groups: group 1 included 20 patients with degenerative LCS aged >55 years and group 2 included patients with LDH aged <35 years. The ligament flava were collected during the patients’ surgery. The features noted on histopathological examination included the fibrosis score, the loss of elastic fibers, calcification, chondroid metaplasia, mucinous degeneration, vascularization, long septa, clefts, granulation tissue, and ganglion-like cysts. The features noted on electron microscopic examination included the elastic fiber thickness, the quality of elastic fibers, the elastic:collagen ratio, calcification, melanin fibers, remnants of necrotic cells, and electron-dense material in the LF. All parameters were compared between group 1 and group 2. RESULTS: On histopathological examination, the two groups exhibited significant differences regarding three parameters: chondroid metaplasia, long septa, and ganglion-like cysts. On electron microscopy examination, significant differences were observed between the two groups regarding two parameters: the quality of elastic fibers and the elastic:collagen ratio. CONCLUSIONS: Characteristic morphological changes may be noted on histopathological and electron microscopic examination that mark the degenerative changes in the LF that contribute to the occurrence and pathogenesis of degenerative LCS.