Definitions of radiographic parameters for outcome measurement.
| Radiographic Parameters | Definition |
| Fusion status | The 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 |
| Subsidence | Loss 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 type | Type 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 lordosis | The 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 height | The distance at the most anterior point of the vertebral body from endplate to endplate |
| Posterior disc height | The distance at the most posterior point of the vertebral body from endplate to endplate, as a surrogate marker for foraminal height |