• Kanji Mori, Toshiyuki Kasahara, Tomohiro Mimura, Kazuya Nishizawa, Yoshitaka Murakami, Yoshitaka Matsusue, and Shinji Imai.
• From the Departments of *Orthopaedic Surgery and †Medical Statistics, Shiga University of Medical Science, Tsukinowa-cho, Seta, Otsu, Shiga, Japan.
• Spine. 2013 Sep 1; 38 (19): E1216E1222E1216-22.

Study DesignA cross-sectional study.ObjectiveTo gain an insight for the prevalence, morphology, and distribution of thoracic ossification of the yellow ligament (OYL) by computed tomography (CT) and review of the literature.Summary Of Background DataThe epidemiology and etiology of OYL remains obscure. To date, to the best of our knowledge, there is no study that comprehensively evaluated thoracic spine by CT to assess the prevalence, distribution, and morphology of OYL in a large enough sample size with wide age distribution.MethodsThe participants of this study were the patients who have undergone chest CT for the examination of pulmonary diseases in our institute. The patients with previous thoracic spine surgery and younger than 15 years were excluded. Prevalence, distribution, and morphology of thoracic OYL were reviewed.ResultsA total of 3013 patients (1261 females and 1752 males) with the mean age of 65 years were recruited. The CT-based evidence of OYL was noted in 1094 (428 females and 666 males) individuals (36%). Single-level involvement was noted in 532 cases, whereas 562 individuals presented multilevel involvement.Statistical analyses revealed that OYL was noted at a significantly higher rate among the males (P = 0.022). Of a total of 2051 OYLs, 779 central type OYLs, a mushroom-shaped ossification localized at the center of laminae, and 1272 noncentral type OYLs were noted. Distribution of the thoracic OYL formed 2 peaks with the highest and second highest peak found at T10-T11 and T4-T5, respectively. Interestingly, OYL is noted at consistent rates after the age of 30; however, its size increased in age-dependent manners.ConclusionThe prevalence of thoracic OYL in Japanese was 36%. A further study disclosing the association between clinical manifestations and size and/or morphology of OYL is warranted.

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