Fig 1.
The cervical aliment was classified as lordotic (a) and kyphotic (b).
Fig 2.
Morphological types of OPLL were classified into the continuous type (a), segmental type (b), circumscribed type (c) and mixed type (d) according to Hirabayashi's classification.
Fig 3.
The shape of ossification was defined as the wide-base type and narrow-base type on CT axial imaging.
Fig 4.
The occupying ratio of the spinal canal was defined as the ratio of the maximal ossification thickness (a) to the anterioposterior spinal canal diameter (b) on CT axial imaging.
Fig 5.
The K-line is a straight line that connects the midpoints of the spinal canal at C2 and C7 on the lateral cervical radiographs.
Patients without OPLL exceeding the line were considered as K-line (+) ones (a) and those does exceed it were considered as K-line (-) ones (b).
Fig 6.
The cross-sectional area of the spinal cord was measured on MR axial imaging at the most compressed segment.
The compression ratio of the spinal cord was measured as the ratio of anteroposterior diameter to transverse diameter of the spinal cord on MR axial imaging at the most compressed segment.
Fig 7.
Intramedullary changes in signal intensity on both T1-weighted imaging (T1WI) and T2-weighted imaging (T2WI) of MRI were assessed.
Fig 7a shows a T2 hyper-intensity intramedullary change (arrow) and Fig 7b shows a T1 hypo-intensity intramedullary change (arrow) on saggital MRI scan.
Fig 8.
Dural ossification was assessed by the presence of the double-layer sign (arrow).
Table 1.
Descriptive characteristics of the patient population.
Table 2.
Comparison of characteristics of patients with different recovery ratios of JOA score.
Table 3.
Comparison of characteristics of patients with and without minor trauma.
Table 4.
Stepwise logistic regression for lower recovery ratio of JOA score.