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Mehren classification of heterotopic ossification (HO).
|
Grade |
Characteristics of HO Grades |
| 0 | No HO present |
| I | HO in front of vertebral body but not in the interdiscal space |
| II | HO is growing into the disc space. Possible effect on function of prosthesis |
| III | Bridging ossification which allows for movement of prosthesis |
| IV | Complete fusion without movement in flexion/extension |
