title: Kinematics of the cervical adjacent segments after disc arthroplasty compared with anterior discectomy and fusion: a systematic review and meta-analysis.
abstract: METHODS
  Systematic review and meta-analysis.
  
  
  OBJECTIVE
  To determine the kinematics of the adjacent segments and global cervical spine after cervical arthroplasty compared with anterior cervical discectomy and fusion (ACDF).
  
  
  BACKGROUND
  Adjacent segment pathology after ACDF is a significant concern. Arthroplasty may decrease the risk of adjacent segment degeneration by maintaining normal spinal kinematics compared with fusion. However, the differences in the in vivo kinematics of the adjacent segments after cervical fusion versus arthroplasty have not been clearly established.
  
  
  METHODS
  A systematic literature review of studies comparing adjacent segment kinematic changes between fusion and arthroplasty was performed. We included randomized controlled trials and cohort studies that compared cervical arthroplasty with ACDF in adults with degenerative disease and reported on at least 1 outcome of interest. Meta-analysis was performed using a random-effects model where appropriate. The standardized mean difference of changes from baseline to follow-up between treatment groups was determined. Recommendations were made using Grades of Recommendation Assessment, Development, and Evaluation criteria.
  
  
  RESULTS
  We identified 12 studies, including 7 randomized controlled trials, 4 cohort studies, and 1 case-control study that evaluated kinematic measurements at the adjacent segments or the global cervical spine (C2-C7) after cervical arthroplasty compared with ACDF. We found no statistically significant differences between treatment groups in the change in range of motion (ROM) at the cranial or caudal adjacent segments from baseline to 2 years of follow-up. However, there was low evidence that the global cervical spine (C2-C7) had significantly greater change in ROM after arthroplasty compared with ACDF: patients had a greater angular ROM as measured up to 2 years after arthroplasty. We found no statistically significant differences between treatment groups in the change in the horizontal or vertical centers of rotation at the adjacent segments as measured up to 2 years after surgery. Regarding sagittal alignment, the cranial and caudal adjacent segments both became significantly more lordotic after arthroplasty compared with fusion at 1 to 2 years after surgery. However, there was no statistically significant difference between treatment groups in the change in global cervical sagittal alignment from baseline to 2 years. CONCLUSION.: There is no statistically or clinically significant difference in the adjacent segment ROM or centers of rotation after cervical arthroplasty compared with ACDF. However, the change in sagittal alignment at the cranial and caudal adjacent segments was significantly more lordotic after arthroplasty compared with fusion. In addition, although we found that there was no statistically significant difference between treatment groups in the change in global cervical (C2-C7) sagittal alignment, there was a significantly greater change in the angular ROM of the cervical spine at up to 2 years after arthroplasty than occurred after fusion.
  
  
  METHODS
  Patients can be advised that single-level arthroplasty and ACDF result in clinically similar kinematic changes at short-term follow-up. Strength of Statement: Strong.
authors.affiliation: Department of Orthopedics and Rehabilitation, University of Wisconsin, Madison, WI, USA. anderson@ortho.wisc.edu
authors.forename: Paul A
authors.initials: PA
authors.lastname: Anderson
authors.forename: Rick C
authors.initials: RC
authors.lastname: Sasso
authors.forename: John
authors.initials: J
authors.lastname: Hipp
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Norvell
authors.forename: Annie
authors.initials: A
authors.lastname: Raich
authors.forename: Robin
authors.initials: R
authors.lastname: Hashimoto
mesh_terms: D001178:Arthroplasty / Q000009:adverse effects / Q000379:methods; D001696:Biomechanical Phenomena / Q000502:physiology; D002574:Cervical Vertebrae / Q000473:pathology* / Q000601:surgery; D017586:Diskectomy / Q000009:adverse effects / Q000379:methods; D006801:Humans; D007403:Intervertebral Disc / Q000473:pathology*; D013123:Spinal Fusion / Q000009:adverse effects / Q000379:methods; D016896:Treatment Outcome