Ossification of the posterior longitudinal ligament (OPLL) is a disease characterized by an ectopic development of hyperostotic changes in the posterior longitudinal ligament,1 and appears predominantly at the cervical spine.2, 3, 4 While majority of OPLLs at the cervical spine remain asymptomatic, progression of the disease can lead to disabling neurologic alterations including myelopathy or radiculopathy and certainly require clinicians’ attention. While OPLL was regarded as a disease of interest in the far-east Asia in the past, recent reports have reported a relatively high incidence even in North American population,5 and the disease is getting more attention worldwide. Despite the clinical significance of the disease, we still know little regarding the pathogenesis of OPLL. Both genetic and environmental factors as well as physical stress are known as multifactorial components contributing to the development and progression of OPLL, but it largely remains unclear so far. 2, 6, 7, 8, 9

The lack of knowledge regarding development and progression of OPLL results in difficulty predicting the possibility of myelopathy in these patients. Some OPLLs present with myelopathy while the others do not, and this difference are not always predictable by current classifications. Static compression factors, morphologic classifications as well as some dynamic factors representing the motion at the cervical spine with OPLL have been suggested as possible factors related with myelopathy.10, 11 Although these studies have provided valuable information, they have limitations in describing the behavior of the disease or predicting progression of OPLL or development of comorbid myelopathy. Furthermore, radiologic measures differ in each studies and thorough consideration on the possible effect of comorbid spondylosis or disc degeneration have not been reported to date. Thus, we aimed to evaluate the difference of various radiologic measures in OPLL patients with or without myelopathy and present possible radiologic risk factors that are associated with myelopathy in cervical OPLL patients.