Table 1.

Brantigan–Steffee criteria for interbody fusion

Nonunion	Collapse of construct, loss of disc height, vertebral slip, broken screws, displacement of cage, resorption of graft, or visible lucency around the periphery of the graft or cage
Locked pseudoarthrosis	Lucency visible in the middle of the cages with solid bone growing into the cage from each vertebral endplate
Fusion	At least half of the fusion area with at least the density originally achieved at surgery. Radiographical fusion through one cage (half of the fusion area) is considered to be mechanically solid fusion even if there is lucency on the opposite side