Biomedical Engineering Reference
In-Depth Information
Chapter 16
Arthroplasty Bearing Surfaces
Steven M. Kurtz Ph.D. and Jim Nevelos Ph.D.
16.1 Introduction
studies that are relevant to high-conformity,
low-contact stress bearings, such as hip resurfacing,
mobile bearing unicondylar knees, and certain types
of artificial discs. Scientific developments during the
past 5 years have prompted the commercial release of
a carbon-fiber-reinforced (CFR)-PEEK formulation
intended specifically for orthopedic bearings with
a metallic or ceramic counterface.
Due to its excellent thermomechanical properties,
polyaryletheretherketone (PEEK) and its composites
have been subjected to intensive scrutiny as bearing
materials since the 1980s for industrial and aerospace
applications
[1
e
9]
. Tribological investigations for
PEEK were typically conducted under dry, unidirec-
tional sliding conditions, using a pin-on-disc or
wheel-on-flat configuration (explained further below
in Section 16.3). These basic studies established that
the friction and wear behavior of PEEK depended not
only upon the type and amount of fiber reinforcement
but also on the surface roughness of the PEEK surface
and the counterface, as well as temperature, sliding
speed, and contact pressure. Although an extensive
body of tribological literature exists for PEEK and its
composites, when we restrict ourselves to conditions
relevant to total joint replacement applications, only
a limited number of investigations have been reported
in the peer-reviewed literature
[10
e
18]
.
This chapter reviews the published biotribology
literature for PEEK both for artificial joints and from
a basic science perspective. Early research on hip and
knee applications of PEEK is discussed, leading to
the development of novel hip resurfacing designs.
This chapter also covers niche tribological applica-
tions for PEEK for upper and lower extremities, such
as finger joints and mobile bearing, unicondylar knee
replacements
[17]
. For readers interested in more
details regarding the applications of PEEK for arti-
ficial discs, please refer to Chapter 13.
In recent years, the encouraging preliminary results
of orthopedic and spine applications have spurred
interest in the basic biotribology of medical grade
PEEK. Consequently, this chapter also summarizes
the latest findings from multidirectional pin-on-disc
16.2 Total Hip and Knee
Replacement
Starting in the 1990s, CFR-PEEK composites
were evaluated as candidate bearing materials for
hip and knee replacement
[10,11]
and were
compared with ultrahigh-molecular-weight poly-
ethylene (UHMWPE), which has been used for
these applications since 1962
[19]
.Duringthe
1990s, gamma-sterilized UHMWPE was the poly-
meric material of choice for total joint replacements.
However, the orthopedic community was searching
for alternate bearing surfaces due to concerns about
the major clinical problem of wear debris-induced
osteolysis
[20]
. Around that time, manufacturers were
also transitioning from gamma sterilization in air to
alternative sterilization methods, such as gamma
irradiation in a low oxygen environment, gas plasma,
or ethylene oxide, to reduce oxidation during pro-
longed shelf storage
[21]
. These distinctions are
important when interpreting the literature, because the
control material originally chosen as a benchmark
for PEEK wear tests
d
gamma
e
air sterilized
UHMWPE
d
is currently considered a historical
reference and has since been superseded by conven-
tionally sterilized UHMWPE, as well as highly
cross-linked UHMWPE, which exhibits substantially
