Compare Different Cervical Anterior Discectomy Procedures by After Procedure Sagittal Alignment on Radiograph

Patients with single-level cervical degenerative disc disease commonly undertook anterior discectomy. To compare the effect of anterior cervical discectomy without fusion (ACD), anterior cervical discectomy with fusion by stand-alone cage (ACDF) or anterior cervical discectomy with arthroplasty (ACDA)， a multiple center randomised controlled trial will be performed in patients with single-level cervical disease. The primary outcome will be cervical alignment by upright cervical spine radiographs estimated by Harrison posterior tangent method.