Orthopaedic implant fixation is strongly dependant upon the effective mechanical properties of newly formed tissue. In this study, we evaluated the potential of modal analysis to derive viscoelastic properties of periprosthetic tissue. We hypothesized that Young's modulus and loss factor could be obtained by a combined theoretical, computational and experimental modal analysis approach. This procedure was applied to ex vivo specimens from a cylindrical experimental implant placed in cancellous bone in an unloaded press-fit configuration, obtained after a four week observation period. Four sections each from seven textured titanium implants were investigated. The first resonant frequency and loss factor were measured. Average experimentally determined loss factor was 2% (SD 0.4%) and average first resonant frequency was 2.1 KHz (SD: 50). A 2D axisymmetric finite element (FE) model identified effective Young's modulus of tissue using experimental resonant frequencies as input. Average value was 42 MPa (SD: 2.4) and no significant difference between specimens was observed. In this pilot study, the non-destructive method allowed accurate measure of dynamic loss factor and resonant frequency and derivation of effective Young's modulus. Prior to implementing this dynamic protocol for broader mechanical evaluation of experimental implant fixation, further work is needed to determine if this affects results from subsequent destructive shear push-out tests.
Bibliographical noteFunding Information:
The French Ministry of Education and Research is acknowledged for its assistance. Related experimental studies were conducted with the support of NIH AR4205, Institute of Pathology at Aarhus University Hospital, Danish Research Foundation for Health, Master of a guild, butcher Peter Ryholts Foundation and the Danish Rheumatism Association, and Anna and Jakob Jakobsens Foundation. Biomet donated the titanium implants.
Copyright 2010 Elsevier B.V., All rights reserved.
- Bone viscoelasticity
- Finite Element Method
- Implant fixation
- Modal analysis