title: Biomechanical assessment of the stabilization capacity of monolithic spinal rods with different flexural stiffness and anchoring arrangement.
abstract: BACKGROUND
  Spinal disorders can be treated by several means including fusion surgery. Rigid posterior instrumentations are used to obtain the stability needed for fusion. However, the abrupt stiffness variation between the stabilized and intact segments leads to proximal junctional kyphosis. The concept of spinal rods with variable flexural stiffness is proposed to create a more gradual transition at the end of the instrumentation.
  
  
  METHODS
  Biomechanical tests were conducted on porcine spine segments (L1-L6) to assess the stabilization capacity of spinal rods with different flexural stiffness. Dual-rod fusion constructs containing three kinds of rods (Ti, Ti-Ni superelastic, and Ti-Ni half stiff-half superelastic) were implanted using two anchor arrangements: pedicle screws at all levels or pedicle screws at all levels except for upper instrumented vertebra in which case pedicle screws were replaced with transverse process hooks. Specimens were loaded in forward flexion, extension, and lateral bending before and after implantation of the fusion constructs. The effects of different rods on specimen stiffness, vertebra mobility, intradiscal pressures, and anchor forces were evaluated.
  
  
  RESULTS
  The differences in rod properties had a moderate impact on the biomechanics of the instrumented spine when only pedicle screws were used. However, this effect was amplified when transverse process hooks were used as proximal anchors.
  
  
  CONCLUSIONS
  Combining transverse hooks and softer (Ti-Ni superelastic and Ti-Ni half stiff-half superelastic) rods provided more motion at the upper instrumented level and applied less force on the anchors, potentially improving the load sharing capacity of the instrumentation.
authors.affiliation: École de technologie supérieure, 1100 Notre-Dame Street West, Montreal, QC H3C 1K3, Canada; Research Center, Hôpital du Sacré-Cœur de Montréal, 5400, Gouin Boul. West, Montreal, QC H4J 1C5, Canada.
authors.forename: Yann
authors.initials: Y
authors.lastname: Facchinello
authors.affiliation: École de technologie supérieure, 1100 Notre-Dame Street West, Montreal, QC H3C 1K3, Canada; Research Center, Hôpital du Sacré-Cœur de Montréal, 5400, Gouin Boul. West, Montreal, QC H4J 1C5, Canada. Electronic address: vladimir.brailovski@etsmtl.ca.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Brailovski
authors.affiliation: École de technologie supérieure, 1100 Notre-Dame Street West, Montreal, QC H3C 1K3, Canada; Research Center, Hôpital du Sacré-Cœur de Montréal, 5400, Gouin Boul. West, Montreal, QC H4J 1C5, Canada.
authors.forename: Yvan
authors.initials: Y
authors.lastname: Petit
authors.affiliation: École de technologie supérieure, 1100 Notre-Dame Street West, Montreal, QC H3C 1K3, Canada; Research Center, Hôpital du Sacré-Cœur de Montréal, 5400, Gouin Boul. West, Montreal, QC H4J 1C5, Canada.
authors.forename: Martin
authors.initials: M
authors.lastname: Brummund
authors.affiliation: Research Center, Hôpital du Sacré-Cœur de Montréal, 5400, Gouin Boul. West, Montreal, QC H4J 1C5, Canada.
authors.forename: Jaëlle
authors.initials: J
authors.lastname: Tremblay
authors.affiliation: Research Center, Hôpital du Sacré-Cœur de Montréal, 5400, Gouin Boul. West, Montreal, QC H4J 1C5, Canada; Department of Surgery, Faculty of Medicine, University of Montreal, Pavillon Roger-Gaudry, S-749, C.P. 6128, succ. Centre-ville, Montreal, QC H3C 3J7, Canada.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Mac-Thiong
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D004195:Disease Models, Animal; D055119:Elastic Modulus; D008159:Lumbar Vertebrae / Q000503:physiopathology / Q000601:surgery; D019736:Prostheses and Implants; D016059:Range of Motion, Articular; D013122:Spinal Diseases / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013552:Swine
keywords: Biomechanical assessment; Rod with variable flexural stiffness; Spinal fusion; Spinal rod; Transverse process hook