LAUSR

BACKGROUND Heterotopic ossification (HO) and anterior bone loss (ABL) are two complications in cervical disc replacement (CDR), which have impacts on the clinical outcomes. Physiologically, bone formation (HO) and bone loss are two sides of bone remodeling. However, clinically, some patients occurred anterior HO (AHO) after CDR, while other patients occurred 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 the above questions. METHODS Seventy patients with one-level Prestige-LP CDR were retrospectively reviewed and were divided into AHO group or ABL group. Radiological outcomes, including cervical lordosis, sagittal vertical axis (SVA), functional spine unit (FSU) angle, disc angle, range of motion (ROM), implant migration, subsidence, adjacent segment degeneration (ASD) were evaluated. Patient-reported clinical outcomes were also evaluated. RESULTS AHO group showed significantly lower disc angle after surgery (0.9±4.2˚), compared to ABL group (6.7±4.7˚) (p<0.001). The preoperative segmental ROM was significantly higher in AHO group (10.2±3.3˚) than that in ABL group (8.2±3.7˚) (p=0.042). No correlation was observed between clinical outcomes and the presence of anterior bone remodeling. Both groups maintained cervical alignment and FSU angle during long-term follow-up. No significant difference was found in the endplate preparation, implant subsidence, migration, or ASD rate between the two 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.