Biomedical Engineering Reference
In-Depth Information
5
Biomechanical Testing of Orthopedic Implants; Aspects of
Tribology and Simulation
Yoshitaka Nakanishi
5.1
Introduction
Orthopedic implants have been the subject of considerable research in recent years.
They are generally made of biocompatible materials. They are considered to be
artificial and external components that compensate for a movement disturbance
under load. The most representative implants are total knee- or hip-joint prosthesis,
where two weightbearing surfaces suffer from a variety of tribological problems,
namely, friction, wear, and lubrication. In addition to wear damage on the bearing
material, the wear debris are also of concern because they can induce tissue
reaction. The prosthesis loosening produced from such a reaction is of major
consideration in the long-term survival of contemporary joint prosthesis,
in vivo
.
Although joint simulators investigate the performance and wear rate of joint
prostheses under
in vivo
kinematic conditions prior to clinical trials, such simulators
are complex and expensive to construct [1-6]. Furthermore, the multifactorial
nature of each joint involves many complex factors that influence the development
of wear,
in vivo
. Simple configurationwear testing, such as the pin-on-platewear test,
has been used extensively for screening novel materials for use in joint prostheses
prior to more complex joint simulation tests. Such a simple configuration of the
test allows for better control of individual tribological variables, leading to a better
fundamental understanding of how these factors independently influence wear.
However, these simple configuration wear devices underestimate the kinematic
and physiological conditions found in the joint.
In this chapter, the physiological and kinematic conditions of joint implants
in
vitro
are evaluated in an attempt to simulate
in vivo
wear conditions.
5.2
Tribological Testing of Orthopedic Implants
Relative movement between two bearing surfaces may be classified into two main
groups, sliding and rolling. However, when there is a difference in severity of
