CONCLUSION: Our study showed that an appropriate size of Zero-profile implant system is crucial to achieving favorable clinical and radiological outcomes after performing ACDF. Implants with a larger height but not oversize could maintain the cervical sagittal balance and FSU height and achieve early bone fusion. Therefore, a larger height might be a better choice for achieving a satisfactory long-term prognosis if Zero-profile implants of adjacent size both fit the disc space …