title: Biomechanical evaluation of screw-in femoral implant in cementless total hip system.
abstract: OBJECTIVE
  To compare (1) proximal femoral axial strains, (2) femoral head deflection, and (3) failure mechanical properties, between Helica head and neck prosthesis implanted femora and normal femora.
  
  
  METHODS
  In vitro study.
  
  
  METHODS
  Cadaveric canine femora (n = 5 pair).
  
  
  METHODS
  Femoral bone strains and head displacement during in vitro simulation of midstance of the gallop were evaluated using cadaveric femurs cyclically loaded in vitro. Strains and displacements were compared within femurs, before and after, prosthesis implantation; and throughout cycling to seek evidence of movement with cyclic loading. Subsequently, implanted femurs and contralateral, intact femurs were loaded to failure to compare failure mechanical properties and modes of failure.
  
  
  RESULTS
  Proximal femoral axial strains were significantly different between intact and implanted femora on all 4 cortical surfaces (P < .05). Compressive strains were lower in the implanted femur on all cortical surfaces, except on the caudal surface which was higher. No difference was noted for femoral head angle under an axial load corresponding to gallop (P > .05). Vertical head displacement was ∼0.1 mm greater for implanted femora than intact femora (P < .05). Yield and failure loads and yield energy of implanted femora were 39-54% lower than those for intact femora (P < .05). Mode of failure for both the intact and implanted femora did not appear to be different.
  
  
  CONCLUSIONS
  Helica femoral prosthesis alters strain distribution in the proximal aspect of the femur and exhibits initial micromotion. Failure load in axial compression of the Helica-implanted femur is less than that of the normal femur, but greater than that expected in vivo.
authors.affiliation: JD Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine, University of California-Davis, CA 95616-8745, USA.
authors.forename: James Y
authors.initials: JY
authors.lastname: Kim
authors.forename: Kei
authors.initials: K
authors.lastname: Hayashi
authors.forename: Tanya C
authors.initials: TC
authors.lastname: Garcia
authors.forename: Sun-Young
authors.initials: SY
authors.lastname: Kim
authors.forename: Rachel
authors.initials: R
authors.lastname: Entwistle
authors.forename: Amy S
authors.initials: AS
authors.lastname: Kapatkin
authors.forename: Susan M
authors.initials: SM
authors.lastname: Stover
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002102:Cadaver; D004285:Dogs; D019544:Equipment Failure Analysis; D006622:Hip Prosthesis / Q000662:veterinary*; D011474:Prosthesis Design; D013314:Stress, Mechanical