title: The Effects of Interlocking a Universal Hip Cementless Stem on Implant Subsidence and Mechanical Properties of Cadaveric Canine Femora.
abstract: OBJECTIVE
  To determine if an interlocking bolt would limit subsidence of the biological fixation universal hip (BFX(®)) femoral stem under cyclic loading and enhance construct stiffness, yield, and failure properties.
  
  
  METHODS
  Ex vivo biomechanical study.
  
  
  METHODS
  Cadaveric canine femora (10 pairs).
  
  
  METHODS
  Paired femora implanted with a traditional stem or an interlocking stem (constructs) were cyclically loaded at walk, trot, and gallop loads while implant and bone motions were captured using kinematic markers and high-speed video. Constructs were then loaded to failure to evaluate failure mechanical properties.
  
  
  RESULTS
  Implant subsidence was greater (P = .037) for the traditional implant (4.19 mm) than the interlocking implant (0.78 mm) only after gallop cyclic loading, and cumulatively after walk, trot, and gallop cyclic loads (5.20 mm vs. 1.28 mm, P = .038). Yield and failure loads were greater (P = .029 and .002, respectively) for the interlocking stem construct (1155 N and 2337 N) than the traditional stem construct (816 N and 1405 N). Version angle change after cyclic loading was greater (P = .020) for the traditional implant (3.89 degrees) than for the interlocking implant (0.16 degrees), whereas stem varus displacement at failure was greater (P = .008) for the interlocking implant (1.5 degrees) than the traditional implant (0.17 degrees).
  
  
  CONCLUSIONS
  Addition of a stabilizing bolt enhanced construct stability and limited subsidence of a BFX(®) femoral stem. Use of the interlocking implant may decrease postoperative subsidence. However, in vivo effects of the interlocking bolt on osseointegration, bone remodeling, and stress shielding are unknown.
authors.affiliation: Animal Specialty Group, Los Angeles, California.
authors.forename: Yonathan
authors.initials: Y
authors.lastname: Buks
authors.affiliation: Animal Specialty Group, Los Angeles, California.
authors.forename: Kirk L
authors.initials: KL
authors.lastname: Wendelburg
authors.affiliation: JD Wheat Veterinary Orthopedic Research Laboratory, University of California, Davis, California.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Stover
authors.affiliation: JD Wheat Veterinary Orthopedic Research Laboratory, University of California, Davis, California.
authors.forename: Tanya C
authors.initials: TC
authors.lastname: Garcia-Nolen
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails / Q000662:veterinary; D002102:Cadaver; D004285:Dogs / Q000601:surgery*; D005269:Femur / Q000502:physiology* / Q000601:surgery*; D006622:Hip Prosthesis / Q000662:veterinary*; D011474:Prosthesis Design