• Toshitaka Yoshii, Takashi Hirai, Akio Iwanami, Narihito Nagoshi, Kazuhiro Takeuchi, Kanji Mori, Tsuyoshi Yamada, Shoji Seki, Takashi Tsuji, Kanehiro Fujiyoshi, Mitsuru Furukawa, Soraya Nishimura, Kanichiro Wada, Masao Koda, Takeo Furuya, Yukihiro Matsuyama, Tomohiko Hasegawa, Katsushi Takeshita, Atsushi Kimura, Masahiko Abematsu, Hirotaka Haro, Tetsuro Ohba, Masahiko Watanabe, Hiroyuki Katoh, Kei Watanabe, Hiroshi Ozawa, Haruo Kanno, Shiro Imagama, Kei Ando, Shunsuke Fujibayashi, Morio Matsumoto, Masaya Nakamura, Masashi Yamazaki, Atsushi Okawa, and Yoshiharu Kawaguchi.
• Department of Orthopedic Surgery, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo Ward, Tokyo 113-8519, Japan; Japanese Multicenter Research Organization for Ossification of the Spinal Ligament, Japan. Electronic address: yoshii.orth@tmd.ac.jp.
• J Orthop Sci. 2019 Jan 1; 24 (1): 35-41.

BackgroundPrevious studies have shown that patients with cervical ossification of the posterior longitudinal ligament (OPLL) often have co-existing ossification of the nuchal ligament (ONL). However, no studies have focused on ONL and its relevance to the severity of OPLL or ossification of other spinal ligaments, such as anterior longitudinal ligament (OALL), ligamentum flavum (OLF), and supraspinous/interspinous ligament (OSIL).MethodsIn this multicenter study, we investigated ossification of the spinal ligaments in the whole spine computed tomography (CT) images of 233 cervical OPLL patients. The severity of ossification was evaluated using ossification index for each spinal ligament, calculated as the sum of the level of ossification. We compared the severity of ossification in each spinal ligament between patients with ONL and those without ONL. Furthermore, we investigated how the number of segments, where ONL exists, affects the severity of ossification in each spinal ligament.ResultsOne hundred thirty patients (55.8%) had co-existing ONL in the cervical OPLL patients included in this study. The ONL (+) group included more male and aged patients. The cervical ossification indexes of OPLL and OALL were higher in ONL (+) patients than in ONL (-) patients. The thoracolumbar ossification indexes of OALL and OSIL were also higher in ONL (+) patients. Logistic regression analysis revealed that age, gender and cervical OA-index were independent factors correlating to the existence of ONL. In the cervical spine, both the ossification indexes of OALL and OPLL increased as the levels of ONL increased. Similarly, in the thoracolumbar spine, both the ossification indexes of OALL and OSIL were increased as the levels of cervical ONL increased. In the multiple regression analysis, cervical OA-index and thoracolumbar OSI-index showed significant correlation with the number of ONL levels.ConclusionsCo-existence of ONL in cervical OPLL patients was associated with the severity of spinal hyperostosis especially in cervical OPLL, OALL, thoracolumbar OALL and OSIL.Copyright © 2018 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.

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