title: Factors that may affect outcome in cervical artificial disc replacement: a systematic review.
abstract: OBJECTIVE
  To identify the factors that may affect outcome in C-ADR and provide the pooled results of postoperative success rate of implanted segment range of motion (ROM), incidence of heterotopic ossification (HO), incidence of radiographic adjacent segment degeneration (r-ASD)/adjacent segment disease (ASD), and surgery rate for ASD.
  
  
  METHODS
  We systematically searched in PubMed, Embase, Cochrane library and Web of knowledge from 2001 to May 2015. Two independent reviewers screened the primary records. Eleven questions regarding the effect of patient selection issues and radiographic parameters issues on outcome were posed previously. Studies addressing the framed questions were included for analysis.
  
  
  RESULTS
  Twenty-two studies were included for the final analysis. Results showed that number of surgical level (single versus double-level) had no effect on primary clinical outcome and radiographic outcome, surgical level had no effect on clinical and radiographic outcome, and smoking habits had negative effect on clinical outcome. No evidence for the effect of patient's age and pathology category (radiculopathy or myelopathy) on outcome was found. The overall success rate of ROM was 79.4%. ROM of the implanted segment and cervical sagittal alignment had no effects on clinical outcome. The pooled incidences of grade 1-4 HO and grade 3-4 HO were 27.7 and 7.8%, respectively. The pooled incidence of r-ASD and surgery rate for ASD were 42.4 and 3.8%, respectively.
  
  
  CONCLUSIONS
  The available evidence showed that most of the pre-selected factors had no effect on outcome after C-ADR, and the ROM success rate, incidence of HO and r-ASD/ASD, and surgery rate for ASD are acceptable. There is a lack of evidence from RCTs for some factors.
authors.affiliation: Department of Spine Surgery, Changzheng Hospital, Second Military Medical University, 415 Fengyang Road, Shanghai, 200003, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Kang
authors.forename: Changgui
authors.initials: C
authors.lastname: Shi
authors.forename: Yifei
authors.initials: Y
authors.lastname: Gu
authors.forename: Chengwei
authors.initials: C
authors.lastname: Yang
authors.forename: Rui
authors.initials: R
authors.lastname: Gao
mesh_terms: D000367:Age Factors; D002574:Cervical Vertebrae / Q000601:surgery*; D006801:Humans; D015994:Incidence; D055959:Intervertebral Disc Degeneration / Q000150:complications / Q000601:surgery*; D007595:Joint Prosthesis; D009999:Ossification, Heterotopic / Q000453:epidemiology; D010147:Pain Measurement; D011183:Postoperative Complications / Q000453:epidemiology; D011843:Radiculopathy / Q000209:etiology / Q000601:surgery*; D016059:Range of Motion, Articular; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology; D013118:Spinal Cord Diseases / Q000209:etiology / Q000601:surgery*; D059145:Total Disc Replacement / Q000379:methods*; D016896:Treatment Outcome