title: The effect of deviated center of rotation on flexion-extension range of motion after single-level cervical arthroplasty: an in vivo study.
abstract: METHODS
  A retrospective study.
  
  
  OBJECTIVE
  To report the clinical outcomes and sagittal kinematics after cervical total disc replacement (TDR). To evaluate the in vivo effect of deviated center of rotation (COR) on flexion-extension range of motion (ROM) at the instrumented level.
  
  
  BACKGROUND
  A few studies showed that the location of COR after cervical TDR deviated from its preoperative location or inherent location in healthy subjects. However, little is known about the effect of deviated COR on ROM at the instrumented level.
  
  
  METHODS
  A total of 24 patients who underwent C5-C6 single-level TDR with Prestige LP (Medtronic Sofamor Danek) were retrospectively included. Japanese Orthopedic Association score and visual analogue scale were used to assess the clinical outcomes. ROM and COR were measured for radiographical analysis. Patients were categorized into 2 groups according to the change of ROM for further evaluation. Group 1, characterized by decreased postoperative ROM, consisted of 16 patients; group 2, characterized by increased postoperative ROM, consisted of 8 patients.
  
  
  RESULTS
  Ten males and 14 females comprised the study cohort. The mean age was 45.05 years, and the mean follow-up time was 15.5 months. The Japanese Orthopedic Association score increased significantly and the neck and arm visual analogue scale decreased significantly after cervical TDR. On average, ROM was preserved after cervical TDR. The postoperative COR had a significant cranial shift from its preoperative location. The COR shift in anterior-posterior direction was larger in group 2 than that in group 1. No difference was observed in the COR shift in cranial-caudal direction between the 2 groups.
  
  
  CONCLUSIONS
  Single-level cervical TDR with Prestige LP obtained satisfactory clinical outcomes and partially restored the natural cervical kinematics. At instrumented level, the deviated COR had a negative correlation with the flexion-extension ROM.
authors.affiliation: *Department of Orthopaedic Surgery and †Operating Room, West China Hospital, Sichuan University, Chengdu, Sichuan Province, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Rong
authors.forename: Quan
authors.initials: Q
authors.lastname: Gong
authors.forename: Hao
authors.initials: H
authors.lastname: Liu
authors.forename: Ying
authors.initials: Y
authors.lastname: Hong
authors.forename: Jigang
authors.initials: J
authors.lastname: Lou
authors.forename: Wenjie
authors.initials: W
authors.lastname: Wu
authors.forename: Yang
authors.initials: Y
authors.lastname: Meng
authors.forename: Hua
authors.initials: H
authors.lastname: Chen
authors.forename: Yueming
authors.initials: Y
authors.lastname: Song
mesh_terms: D000328:Adult; D001178:Arthroplasty / Q000379:methods; D002574:Cervical Vertebrae / Q000601:surgery*; D017586:Diskectomy / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*; D012189:Retrospective Studies; D012399:Rotation; D059145:Total Disc Replacement / Q000379:methods; D016896:Treatment Outcome