Table 3

Definitions of radiographic parameters for outcome measurement.

Radiographic ParametersDefinition
Fusion statusThe Bridwell interbody fusion grading system:
Grade 1: fused with remodeling and trabeculae present
Grade 2: graft intact, not fully remodeled and incorporated, but no lucency present
Grade 3: graft intact, potential lucency present at top and bottom of the graft
Grade 4: fusion absent with collapse/resorption of graft
SubsidenceLoss of disc height by >2 mm compared with 6-wk postoperative disc height, as measured from the vertebral endplate to the caudal or cranial margin of the cage
Subsidence typeType 1: cage subsidence into the contralateral caudal endplate without anterior cage tilt
Type 2: bilateral cage subsidence into the anterior aspect of the caudal endplate, producing an anterior tilt of the cage
Type 3: cage subsidence into both the caudal and cranial endplates bilaterally without cage tilt
Index-level segmental lordosisThe angle between the inferior endplate of the caudal vertebral body to the superior endplate of the cephalad vertebral body of the fusion segment
Anterior disc heightThe distance at the most anterior point of the vertebral body from endplate to endplate
Posterior disc heightThe distance at the most posterior point of the vertebral body from endplate to endplate, as a surrogate marker for foraminal height