title: Malaligned dynamic anterior cervical plate: a biomechanical analysis of effectiveness.
abstract: METHODS
  Biomechanical evaluation.
  
  
  OBJECTIVE
  To evaluate the kinematic and load-sharing differences of dynamic anterior cervical plates when placed in-line at 0° and off-axis at 20°.
  
  
  BACKGROUND
  The use of dynamic anterior cervical plating systems has recently gained popularity due to the theoretical benefit of improved load sharing with graft subsidence. Occasionally, due to anatomical restraints, the anterior cervical plate may be placed off-axis in the coronal plane. This may potentially decrease the dynamization capability of the plate, leading to less load sharing and potentially decreased fusion rates. The purpose of this study was to comprehensively evaluate the kinematic and load-sharing differences of a dynamic plate placed in-line versus off-axis in the coronal plane.
  
  
  METHODS
  Thirteen fresh-frozen human cadaveric cervical spines (C2-T1) were used. Nondestructive range-of-motion testing was performed with a pneumatically controlled spine simulator in flexion/extension, lateral bending, and axial rotation using the OptoTrak motion measurement system. A C5 corpectomy was performed, and a custom interbody spacer with an integrated load cell collected load-sharing data under axial compression at varying loads. A dynamic anterior cervical plate was placed in-line at 0° and then off-axis at 20°. Testing conditions ensued using a full-length spacer, followed by simulated subsidence by removing 10% of the height of the original spacer.
  
  
  RESULTS
  There were no kinematic differences noted in the in-line model versus the off-axis model. After simulated subsidence, the small decreases in stiffness and increases in motion were similar whether the plate was placed in-line or off-axis in all 3 planes of motion. There were also no significant differences in the load-sharing characteristics of the in-line plate versus the off-axis plate in either the full-length model or the subsided interbody model.
  
  
  CONCLUSIONS
  This study suggests that off-axis dynamic plate positioning does not significantly impact construct kinematics or graft load sharing. As such, we do not recommend removal or repositioning of an off-axis placed dynamic plate because the kinematic and load-sharing biomechanical properties are similar.
  
  
  METHODS
  N/A.
authors.affiliation: *Department of Orthopaedics, University of Utah, Salt Lake City; and †Department of Orthopaedics, Northwestern University, Chicago IL.
authors.forename: Brandon D
authors.initials: BD
authors.lastname: Lawrence
authors.forename: Alpesh A
authors.initials: AA
authors.lastname: Patel
authors.forename: Andrew
authors.initials: A
authors.lastname: Guss
authors.forename: W
authors.initials: W
authors.lastname: Ryan Spiker
authors.forename: Darrel S
authors.initials: DS
authors.lastname: Brodke
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001860:Bone Plates; D002574:Cervical Vertebrae / Q000502:physiology* / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation*; D016474:Weight-Bearing