Age, sex, presence of diabetes, and body mass index (BMI) were collected as basic clinical data (S1 Table ). CT images of the whole spine, including the cervical, thoracic, and lumbosacral spine from the occipital bone to the sacrum, were obtained in each patient. The incidence of OPLL in the cervical spine from the clivus to C7 and in other spinal regions from T1 to S1 was evaluated on mid-sagittal CT images. Image analysis was independently performed by five senior spine surgeons (T.H., K.T., K.M., A.I., and T.Y.). To quantify hyperostosis of the posterior longitudinal ligament, the distribution of OPLL at each vertebral body and intervertebral disc level was recorded, and the number of levels at which OPLL was present was defined as the ossification index (OP-index), as described previously [9 (link)]. The number of ossified lesions in the cervical spine was defined as the cervical OP-index. Patients were categorized into three groups according to the cervical OP-index: Grade 1, cervical OP-index ≤ 5; Grade 2, cervical OP-index 6–9; and Grade 3, cervical OP-index ≥ 10 (cervical OP-index classification). In addition to the OP-index, the sum of the intervertebral segments showing ossification of the anterior longitudinal ligament (OALL; cervical OA-index) was noted (S1 Table ). The cervical OP-index classification and two indexes are shown in Fig 1 .
Prior to image review, all testers read images from the same 20 patients to check inter-observer agreement. The average Kappa coefficient of inter-observer agreement was 0.76 (95% confidence interval [CI] = 0.71–0.81). Kappa values 0.00–0.20 were considered to indicate slight agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, substantial agreement; and 0.811.00, almost perfect agreement [17 (link)]. Therefore, this finding indicates substantial agreement and consistency with the results of the previous study [9 (link)]. We also evaluated the degree of OPLL occupying the cervical spinal canal, with classification of the canal narrowing ratio (CNR) [18 (link)] at the most compressed segment defined as follows: Grade 1, 0% < CNR ≤ 25%; Grade 2, 25% < CNR ≤ 50%; Grade 3, 50% < CNR ≤ 75%; and Grade 4, CNR > 75%. First, we compared male and female populations in terms of the physical and radiologic data. We next evaluated the usefulness of the cervical OP-index classification for predicting the presence of OPLL in the thoracolumbar spine. Finally, we used a multiple regression model to investigate the factors associated with the OP-index in all patients.
Prior to image review, all testers read images from the same 20 patients to check inter-observer agreement. The average Kappa coefficient of inter-observer agreement was 0.76 (95% confidence interval [CI] = 0.71–0.81). Kappa values 0.00–0.20 were considered to indicate slight agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, substantial agreement; and 0.811.00, almost perfect agreement [17 (link)]. Therefore, this finding indicates substantial agreement and consistency with the results of the previous study [9 (link)]. We also evaluated the degree of OPLL occupying the cervical spinal canal, with classification of the canal narrowing ratio (CNR) [18 (link)] at the most compressed segment defined as follows: Grade 1, 0% < CNR ≤ 25%; Grade 2, 25% < CNR ≤ 50%; Grade 3, 50% < CNR ≤ 75%; and Grade 4, CNR > 75%. First, we compared male and female populations in terms of the physical and radiologic data. We next evaluated the usefulness of the cervical OP-index classification for predicting the presence of OPLL in the thoracolumbar spine. Finally, we used a multiple regression model to investigate the factors associated with the OP-index in all patients.
Free full text: Click here
