Is Anterior Bone Loss the Opposite of Anterior Heterotopic Ossification in Prestige-LP Cervical Disc Replacement?

BACKGROUND: Heterotopic ossification (HO) and anterior bone loss (ABL) are 2 complications in cervical disc replacement (CDR), which have impacts on the clinical outcomes. Physiologically, bone formation (HO) and bone loss are 2 sides of bone remodeling. However, clinically, some patients experienced anterior HO (AHO) after CDR, whereas other patients experienced ABL. Is there any factor in determining the fate of the vertebral bone in the anterior region? Is ABL the opposite of AHO? This study aims to answer these questions. METHODS: Seventy patients with 1-level Prestige-LP CDR were retrospectively reviewed and were divided into an AHO group or ABL group. Radiologic outcomes, including cervical lordosis, sagittal vertical axis, functional spine unit angle, disc angle, range of motion, implant migration, subsidence, and adjacent segment degeneration were evaluated. Patient-reported clinical outcomes were also evaluated. RESULTS: AHO group showed significantly lower disc angle after surgery (0.9 degrees +/- 4.2 degrees), compared with ABL group (6.7 degrees +/- 4.7 degrees) (P < 0.001). The preoperative segmental range of motion was significantly higher in the AHO group (10.2 degrees +/- 3.3 degrees) than in the ABL group (8.2 degrees +/- 3.7 degrees) (P = 0.042). No correlation was observed between clinical outcomes and the presence of anterior bone remodeling. Both groups maintained cervical alignment and functional spine unit angle during long-term follow-up. No significant difference was found in the end plate preparation, implant subsidence, migration, or adjacent segment degeneration rate between the 2 groups. CONCLUSIONS: The differences in the disc angle showed the role of mechanical load in the anterior bone remodeling. Combined the results with the basic concepts of bone remodeling, ABL may be the opposite of AHO.