title: Biomechanical Analysis of Cervical Disc Replacement and Fusion Using Single Level, Two Level, and Hybrid Constructs.
abstract: METHODS
  A biomechanical study comparing arthroplasty with fusion using human cadaveric C2-T1 spines.
  
  
  OBJECTIVE
  To compare the kinematics of the cervical spine after arthroplasty and fusion using single level, 2 level and hybrid constructs.
  
  
  BACKGROUND
  Previous studies have shown that spinal levels adjacent to a fusion experience increased motion and higher stress which may lead to adjacent segment disc degeneration. Cervical arthroplasty achieves similar decompression but preserves the motion at the operated level, potentially decreasing the occurrence of adjacent segment disc degeneration.
  
  
  METHODS
  11 specimens (C2-T1) were divided into 2 groups (BRYAN and PRESTIGE LP). The specimens were tested in the following order; intact, single level total disc replacement (TDR) at C5-C6, 2-level TDR at C5-C6-C7, fusion at C5-C6 and TDR at C6-C7 (Hybrid construct), and lastly a 2-level fusion. The intact specimens were tested up to a moment of 2.0 Nm. After each surgical intervention, the specimens were loaded until the primary motion (C2-T1) matched the motion of the respective intact state (hybrid control).
  
  
  RESULTS
  An arthroplasty preserved motion at the implanted level and maintained normal motion at the nonoperative levels. Arthrodesis resulted in a significant decrease in motion at the fused level and an increase in motion at the unfused levels. In the hybrid construct, the TDR adjacent to fusion preserved motion at the arthroplasty level, thereby reducing the demand on the other levels.
  
  
  CONCLUSIONS
  Cervical disc arthroplasty with both the BRYAN and PRESTIGE LP discs not only preserved the motion at the operated level, but also maintained the normal motion at the adjacent levels. Under simulated physiologic loading, the motion patterns of the spine with the BRYAN or PRESTIGE LP disc were very similar and were closer than fusion to the intact motion pattern. An adjacent segment disc replacement is biomechanically favorable to a fusion in the presence of a pre-existing fusion.
authors.affiliation: *Department of Biomedical Engineering, The University of Iowa, Iowa City, IA†Center for Computer Aided Design, The University of Iowa, Iowa City, IA; and‡Department of Orthopaedics and Rehabilitation, University of Iowa Hospitals and Clinics, The University of Iowa, Iowa City, IA.
authors.forename: Anup A
authors.initials: AA
authors.lastname: Gandhi
authors.forename: Swathi
authors.initials: S
authors.lastname: Kode
authors.forename: Nicole A
authors.initials: NA
authors.lastname: DeVries
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Grosland
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Smucker
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Fredericks
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D002574:Cervical Vertebrae / Q000601:surgery*; D017586:Diskectomy / Q000379:methods; D006801:Humans; D016059:Range of Motion, Articular / Q000502:physiology*; D013123:Spinal Fusion / Q000379:methods*; D059145:Total Disc Replacement / Q000379:methods*