Title: Initial fixation of a femoral knee component: an in vitro and finite element study

Authors: Travis A. Burgers, Jim Mason, Heidi-Lynn Ploeg

Addresses: Department of Mechanical Engineering, University of Wisconsin-Madison, 1513 University Avenue, Madison, WI 53706-1572, USA. ' Zimmer, Inc., PO Box 708, MS 1901, Warsaw, IN 46581-0708, USA. ' Department of Mechanical Engineering and Biomedical Engineering, University of Wisconsin-Madison, 1513 University Avenue, Madison, WI 53706-1572, USA

Abstract: Loosening is the primary cause of total knee arthroplasty implant failure; therefore, to investigate this failure mode, femoral knee components were implanted in vitro on three cadaveric femurs. Bone-implant finite element (FE) models were created to predict the initial fixation of the interface of each femur. Initial fixation of the femoral knee component was successfully measured with the strain-gauged implants. Specimen-specific FE models were calibrated using the in vitro strain measurements and used to assess initial fixation. Initial fixation was shown to increase with bone density. The geometry of the implant causes the distal femur to deform plastically. It also causes higher stresses in the lateral side and higher pressures on the lateral surfaces. The implementation of plasticity in the bone material model in the FE model decreased these strains and pressures considerably from a purely elastic model, which demonstrated the importance of including plasticity.

Keywords: distal femur; femoral knee components; initial fixation; implant loosening; in vitro testing; finite element analysis; FEA; press-fit; cementless; experimental biomechanics; computational biomechanics; knee arthroplasty; knee implants; bone implant modelling; strain measurements; plasticity.

DOI: 10.1504/IJECB.2009.022857

International Journal of Experimental and Computational Biomechanics, 2009 Vol.1 No.1, pp.23 - 44

Available online: 30 Jan 2009 *

Full-text access for editors Access for subscribers Purchase this article Comment on this article