title: Effect of arthroplasty design on cervical spine kinematics: analysis of the Bryan Disc, ProDisc-C, and Synergy disc.
abstract: OBJECTIVE
  Cervical total disc replacement has emerged as a surgical option to preserve motion and potentially avoid adjacent-segment disease after anterior cervical discectomy and fusion. Recently, much attention has been directed at the ability of a given device to maintain and/or restore normal segmental alignment. Nonphysiological disc and segmental angulation could result in increased stresses transmitted to the facet joints and posterior elements, conflicting with the essence of arthroplasty and potentially leading to adjacent-segment disease. The goal of this study was to contrast device alignment and segmental kinematics provided by 3 different cervical disc prostheses.
  
  
  METHODS
  Sixty patients were retrospectively analyzed and divided into 3 groups receiving the Bryan, ProDisc-C, or Synergy disc. Only single-level arthroplasty cases were included in the study. Lateral dynamic radiographs of the cervical spine were analyzed using quantitative motion analysis software (Medical Metrics, Inc.) to analyze the kinematics at the index level both preoperatively and postoperatively. Several parameters were noted, including range of motion, disc angles, shell angles, anterior and posterior disc heights, translation, and center of rotation. Preoperative and postoperative data were compared using the Student t-test with a significance level of p < 0.05.
  
  
  RESULTS
  Postoperatively, all 3 disc groups maintained adequate range of motion at the implanted level. With respect to the shell angles, the Synergy disc demonstrated the least variability, maintaining 6 degrees lordotic configuration between the device endplates. In the Bryan disc group, significant shell kyphosis developed postoperatively (p < 0.0001). Both ProDisc-C and Synergy discs significantly increased anterior and posterior disc heights (p < 0.0001). The Bryan and Synergy discs maintained the natural center of rotation, whereas significant anterior shift occurred with ProDisc-C.
  
  
  CONCLUSIONS
  The goal for motion preservation at the implanted level was achieved using all 3 devices. The Synergy disc was unique in its ability to alter device angulation by 6 degrees. The Bryan disc demonstrated device endplate kyphosis. Both the Synergy disc and ProDisc-C increased disc space height.
authors.affiliation: Department of Clinical Neurological Sciences, Division of Neurosurgery, The University of Western Ontario, London, Ontario, Canada.
authors.forename: Bruno C R
authors.initials: BC
authors.lastname: Lazaro
authors.forename: Kemal
authors.initials: K
authors.lastname: Yucesoy
authors.forename: Kasim Z
authors.initials: KZ
authors.lastname: Yuksel
authors.forename: Izabela
authors.initials: I
authors.lastname: Kowalczyk
authors.forename: Doron
authors.initials: D
authors.lastname: Rabin
authors.forename: Marie
authors.initials: M
authors.lastname: Fink
authors.forename: Neil
authors.initials: N
authors.lastname: Duggal
mesh_terms: D000328:Adult; D000368:Aged; D001178:Arthroplasty / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D001696:Biomechanical Phenomena / Q000502:physiology; D002574:Cervical Vertebrae / Q000503:physiopathology / Q000601:surgery*; D017586:Diskectomy / Q000295:instrumentation / Q000379:methods; D019544:Equipment Failure Analysis / Q000379:methods; D019416:Head Movements / Q000502:physiology; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000503:physiopathology / Q000601:surgery*; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods; D019736:Prostheses and Implants / Q000592:standards; D011474:Prosthesis Design / Q000379:methods; D019919:Prosthesis Implantation / Q000379:methods; D016059:Range of Motion, Articular / Q000502:physiology*; D012189:Retrospective Studies; D055009:Spondylosis / Q000503:physiopathology / Q000601:surgery*