Biomechanical Evaluation of Screw-In Femoral Implant in Cementless Total Hip System


  • James Y. Kim DVM,

  • Kei Hayashi DVM, PhD, Diplomate ACVS,

    Corresponding author
    1. JD Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine, University of California-Davis, CA
    • Corresponding Author

      Kei Hayashi, DVM, PhD, Diplomate ACVS, Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, 1 Shields Avenue, Davis, CA 95616–8745


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  • Tanya C. Garcia MS,

  • Sun-Young Kim DVM, MS,

  • Rachel Entwistle MS,

  • Amy S. Kapatkin DVM, MS, Diplomate ACVS,

  • Susan M. Stover DVM, PhD, Diplomate ACVS

  • Presented in part at the American College of Veterinary Surgeons Symposium, Washington D.C., October 2009



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.

Study Design

In vitro study.

Sample Population

Cadaveric canine femora (n = 5 pair).


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.


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.


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.