Ossification of the posterior longitudinal ligament (OPLL) can cause severe and irreversible paralysis in not only the cervical spine but also the thoracolumbar spine. To date, however, the prevalence and distribution of OPLL in the whole spine has not been precisely evaluated in patients with cervical OPLL. Therefore, we conducted a multi-center study to comprehensively evaluate the prevalence and distribution of OPLL using multi-detector computed tomography (CT) images in the whole spine and to analyze what factors predict the presence of ossified lesions in the thoracolumbar spine in patients who were diagnosed with cervical OPLL by plain X-ray. Three hundred and twenty-Two patients with a diagnosis of cervical OPLL underwent CT imaging of the whole spine. The sum of the levels in which OPLL was present in the whole spine was defined as the OP-index and used to evaluate the extent of ossification. The distribution of OPLL in the whole spine was compared between male and female subjects. In addition, a multiple regression model was used to ascertain related factors that affected the OP-index. Among patients with cervical OPLL, women tended to have more ossified lesions in the thoracolumbar spine than did men. A multiple regression model revealed that the OP-index was significantly correlated with the cervical OP-index, sex (female), and body mass index. Furthermore, the prevalence of thoracolumbar OPLL in patients with a cervical OP-index ≥ 10 was 7.8 times greater than that in patients with a cervical OP-index ≤ 5. The results of this study reveal that the extent of OPLL in the whole spine is significantly associated with the extent of cervical OPLL, female sex, and obesity.
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