Pre-yield and post-yield shear behavior of the cement-bone interface

Area of Science:

• Biomaterials Science
• Orthopedic Biomechanics
• Mechanical Engineering

Background:

• Aseptic loosening is a primary failure mode for cemented total hip replacements.
• The mechanical behavior of the cement-bone interface, especially post-yield, is not fully understood.

Purpose of the Study:

• To characterize the constitutive behavior of the cement-bone interface under shear loading.
• To investigate the post-yield mechanical response and failure mechanisms.

Main Methods:

• Utilized a combination of experimental testing on 55 human cadaveric cement-bone specimens and finite element analysis.
• Employed a custom shear test jig for displacement-controlled loading to failure.
• Developed nonlinear finite element models incorporating a two-parameter interface model.

Main Results:

• Observed a complex load-displacement response with initial linearity, followed by softening and exponential load decrease.
• Determined ultimate shear strength of the interface to be 2.25+/-1.49 MPa.
• Identified interface strength (2.71+/-1.90 MPa) and softening exponent (4.96+/-3.47 1/mm) parameters that accurately modeled experimental data.

Conclusions:

• The cement-bone interface demonstrates significant post-yield strain-softening, absorbing substantial energy before complete debonding.
• Failure initiation was observed at the base of the specimen in finite element models prior to peak load.
• Findings provide critical insights into the mechanical integrity of cemented hip implants and potential failure mechanisms.