Fig 1.
Cervical ossification of the posterior longitudinal ligament index (OP-index) and ossification of the anterior longitudinal ligament index (OA-index) are shown.
Cervical OP-index classification was defined 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).
Table 1.
Demographics of patients with cervical OPLL only and patients with OPLL in multiple spinal regions.
Table 2.
Demographics of male and female patients.
Fig 2.
A: Incidence of ossification of the posterior longitudinal ligament (OPLL) at each vertebral and intervertebral level (black bars, vertebral levels; gray bars, intervertebral levels). B: Histograms of the OP-index of the whole spine for male and female patients.
Fig 3.
A: The OP-index correlates significantly with the cervical OP-index in both men (p < 0.001, R2 = 0.536) and women (p < 0.001, R2 = 0.464). B: The OP-index of the whole spine was significantly associated with the cervical OA-index in men (p < 0.001, R2 = 0.0735), but not in women.
Fig 4.
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. The number of ossified lesions in the thoracolumbar spine was significantly different among the three grades (**p < 0.01 and ***p < 0.001).
Table 3.
Categorization of the cervical OP-index and relationship between the classification and incidence of ossified lesions in the lumbar and thoracic spine.
Table 4.
Increased risk of OPLL in multiple regions based on the cervical OP-index grade.
Table 5.
Factors influencing the OP-index of the whole spine.