Evaluation of the measuring methods of the spinal canal occupation rate in thoracic ossification of ligamentum flavum.

OBJECTIVE: The degree of hypertrophy of thoracic ossification of ligamentum flavum (TOLF) is related to the severity of the myelopathy. There is no uniform measuring method to calculate the spinal canal occupation ratio (COR) of TOLF simply and effectively. The study was to determine an appropriate measuring method to calculate the COR of TOLF. METHODS: A total of 37 computed tomography cross-sectional imaging scans (bone window) from 22 patients were analyzed retrospectively in this study. The ventral side of the lamina or superior facet was selected as bottom in Method 1, and a line perpendicular to the anteroposterior diameter and on the dorsal side of the spinal canal was selected as bottom in Method 2. The maximum thickness of the bilateral ossified mass to the bottom is d1 and d2. The maximum distance from the anterior wall of the spinal canal to the bottom is d. COR of Method 1 or 2 was (d1 + d2)/2d x 100%. Standard COR values calculated by software served as controls. RESULTS: The standard COR values were <50% in 10 images, 51%-60% in 9 images, 61%-70% in 10 images, and >71% in 8 images. There was no significant difference between COR1 and COR in every range. There were significant differences between COR2 and COR in the <= 50%, 51%-60%, and 61%-70% groups but they were not statistically significant in the >70% group. CONCLUSIONS: Method 1 is a convenient and practical method to measure the COR of ossification in patients with TOLF.