title: Sagittal alignment and kinematics at instrumented and adjacent levels after total disc replacement in the cervical spine.
abstract: BACKGROUND
  The purpose of the study was to report radiological outcomes after total disc replacement (TDR) in the cervical spine through a 24 months follow-up (FU) prospective study with a special focus on sagittal alignment and kinematics at instrumented and adjacent levels.
  
  
  METHODS
  Thirty-two patients, who sustained one-level TDR with a ball-and-socket arthroplasty (Discocerv(™) implant, Scient'x/Alphatec Spine, USA) were consecutively included in the study. Clinical (visual analogical scale and neck disability index) and radiological parameters were measured preoperatively and postoperatively at 3/6 months, 1-year and 2-year FU. Sagittal alignment, ranges of motion (ROM) and center of rotations (CORs) were analyzed using specific motion analysis software (Spineview(™), Paris, France). Patients CORs were compared with those of a control group of 39 normal and asymptomatic subjects.
  
  
  RESULTS
  Both local and C3-C7 lordosis significantly increased postoperatively (+8° and +13° at 2 years, respectively). At instrumented level ROM in flexion-extension (FE) was measured to 10.2° preoperatively versus 7.5° at 1 year and 6.1° at 2 years. There were no differences in ROM at adjacent levels between pre and postoperative assessments. When compared with control group and preoperative measurements, we noted postoperative cranial shift of the COR at instrumented level for patients group. In contrast, there was no difference in CORs location at adjacent levels.
  
  
  CONCLUSIONS
  Through this prospective study, we observed that cervical lordosis consistently increased after TDR. In addition, although ball-and-socket arthroplasty did not fully restore native segmental kinematics with significant reduction of motion in FE and consistent cranial shift of the COR, no significant changes in terms of ROM and CORs were observed at adjacent levels.
authors.affiliation: Department of Spine Surgery, Hôpital Neurologique P. Wertheimer, Hospices Civils de Lyon, Lyon, France. c.barrey@wanadoo.fr
authors.forename: Cédric
authors.initials: C
authors.lastname: Barrey
authors.forename: Sabina
authors.initials: S
authors.lastname: Champain
authors.forename: Sophie
authors.initials: S
authors.lastname: Campana
authors.forename: Aymen
authors.initials: A
authors.lastname: Ramadan
authors.forename: Gilles
authors.initials: G
authors.lastname: Perrin
authors.forename: Wafa
authors.initials: W
authors.lastname: Skalli
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000502:physiology / Q000601:surgery*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D017060:Patient Satisfaction; D011446:Prospective Studies; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D059145:Total Disc Replacement; D016896:Treatment Outcome