Table 2.

Classification criteria to assess bony fusion on computed tomography scans.

Grade	Classification	Description
1	Definite fusion	Presence of 2 or more bridging bony trabeculae passing from one vertebral endplate to the other in both the sagittal and coronal planes
2	Probable fusion	At least 1 bridging bony trabecula passing from one vertebral endplate to the other in the sagittal or coronal plane, but not grade 1
3	Probable pseudarthrosis	Absence of clear bridging bony trabeculae passing from one vertebral endplate to the other, but close bone approximation (less than 2 mm apart)
4	Definite pseudarthrosis	Clear separation of bone from both segments (more than 2 mm apart)