• Yoshihito Sakai, Sadayuki Ito, Tetsuro Hida, Kenyu Ito, Atsushi Harada, and Ken Watanabe.
• National Center for Geriatric and Gerontology, Department of Orthopaedic Surgery, Japan. Electronic address: jsakai@ncgg.go.jp.
• J Orthop Sci. 2017 Jan 1; 22 (1): 27-33.

BackgroundThe ligamentum flavum hypertrophy is considered to be one of the important causes of development of lumbar spinal stenosis (LSS). Several histologic and biologic mechanisms in hypertrophied flavum have proposed. However, no study that investigated the relationship between clinical outcome and ligamentum flavum hypertrophy has been published. The purpose of this study was to identify a new classification of LSS, in ligamentous and nonligamentous stenosis, according to the cutoff value of the area proportion of the ligamentum flavum in the spinal canal, and to assess the value of surgical and conservative treatments for LSS based on the classification of the ligamentous stenosis.MethodsA total of 230 surgical patients with LSS were evaluated based on the cross-sectional area and intraoperative findings of the ligamentum flavum. LSS was classified as ligamentous or nonligamentous stenosis, according to the cutoff value of the proportion of the ligamentum flavum in the spinal canal. Based on the classification, the results of 234 surgical patients (103 patients with spinal fusion surgery and 131 patients with spinal decompression) and 191 patients under conservative treatment with prostaglandin E1 were evaluated, 1 year after treatments.ResultsROC analysis revealed that the area under the curve for the cutoff value of the proportion of the ligamentum flavum in the spinal canal was 0.4275 (sensitivity = 0.861, specificity = 0.854). Based on these criteria, ligamentous and nonligamentous stenoses were 115 and 119 in surgical patients, 97 and 94 in conservative patients, respectively. In the surgical treatment group, no significant difference was found in any of the evaluations conducted for the group with ligamentous and nonligamentous stenosis. However, in the conservative treatment group, the patients with ligamentous stenosis showed significant improvement compared with patients with nonligamentous stenosis.ConclusionsLigamentous stenosis in LSS patients had favorable outcome on conservative treatment with prostaglandin E1 derivative.Copyright © 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.

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