Table 2.

Brantigan and Steffee spine fusion classification.

Grade	Characteristics
A	Obvious structural collapse due to pseudoarthrosis, loss of intervertebral height, vertebral slippage, broken screws, cage displacement, and bone graft absorption
B	Significant bone resorption, possibly due to pseudoarthrosis, with large radiolucencies or visible fissures in the fusion area (2 mm from all implant edges)
C	In an indeterminate nonunion, the density of the graft in the fusion area is comparable to that immediately after surgery. Small radiolucencies or cracks are visible in at least half of the fusion area
D	The entire bone graft area can be seen with bone bridges that may be fused and have a density equivalent to that immediately after surgery. There is no translucent zone between vertebral bodies. The bone density in the fusion area is greater than that immediately after surgery
E	Even if a sclerotic line between the implant and the vertebral body indicates fusion, ideally there should be no clear demarcation between the implant and the vertebral body. Other signs of fusion include bone bridging within the fusion zone, resorption of anterior bone spurs, and fusion of facet joints