Arthroplasty Bearing Surfaces - PEEK Biomaterials - page 257

materials for total hip replacements, especially in
combination with ceramic as opposed to CoCr
heads. On the other hand, this study also suggested
that PEEK composites were unsuitable for knee
applications, regardless of the fiber content of the
composite or the type of counterface. The authors
recommended that “the composite materials should
not be used as a tibial component for a total knee
replacement.”
Although CFR-PEEK has superior wear perfor-
mance than neat PEEK, the type of fibers has also
been shown to play a role in the tribological
behavior of the composite [8,10] . In unlubricated
pin-on-disc studies against steel, the tribological
performance of pitch vs. PAN fibers depends upon
the contact pressure and sliding speed [8] . In the hip
simulator studies by Wang et al. [10] , composites
produced by blending pitch fiber yielded lower wear
rates than with PAN fibers, which were stiffer and,
hence, more abrasive. Recent pin-on-disc studies of
CFR-PEEK pins on metal and ceramic plates have
demonstrated comparably low wear rates using
both PAN and pitch-fiber reinforcement. These
basic biotribology studies are summarized in
Section 16.3 .
Additional hip simulator testing was reported by
Jones et al. [41] in a conference abstract. The
researchers sought to determine the effect of surface
finish and clearance on the wear rate in a hip simu-
lator. A series of inserts with a 28 mm inner diameter
and outer diameters ranging between 50 and 58 mm
were evaluated. The inserts were produced by
injection molding 151 G resin blended with 30 w/w%
milled carbon fibers. The final diameter was achieved
by direct injection molding or machining. Both
zirconia and alumina heads were examined. They
found that when they controlled the diametral clear-
ance to less than 600 m m and the surface finish was
less than 2.5 m m, they did not observe darkening of
the test fluid, indicative of low wear. Furthermore, the
authors concluded that “machining of the internal
form had no significant effect on wear rate”. The
average wear for all the composite cups was 0.43

longer considered a candidate bearing surface, even
though it was initially found to be an “optimal”
choice in combination with PEEK in early hip
simulator experiments. Following the withdrawal of
zirconia, alumina became the femoral head material
of choice for THA applications with CFR-PEEK.
CoCr heads, when used in conjunction with CFR-
PEEK liners, exhibited substantially higher wear,
with observations of scratching of the metallic

surface by the carbon fibers [10] .
Careful consideration has been given to the
bioactivity of wear particles that may be produced
from articulation. Jones et al. [41] reported that wear
debris from pitch CFR-PEEK acetabular cups, when
subjected to cytotoxicity testing, Ames test and
the evaluation of chromosomic aberration in human
lymphocytes, demonstrated no cytotoxic or muta-
genic potential. As part of a larger study on
composite candidate biomaterials, Howling et al.
[12] investigated the bioactivity of wear debris
generated by 30% PAN CFR-PEEK composite
pins articulating against alumina plates in a bidirec-
tional pin-on-disc tester. The wear particles were
extracted from the test fluid and exposed to L929
and U937 cells in an in vitro culture model to eval-
uate their effect on cellular viability. The PEEK
composite wear debris had no cytotoxic effects on
either types of cells in vitro. Blunn and co-workers
[43] evaluated CFR-PEEK as potential prosthetic
knee joint material and found that fibroblast
attachment to CFR-PEEK wear debris particles was
greater than UHMWPE and comparable to CoCrMo
and titanium alloy. Maharaj et al. [44] examined the
wear debris from zirconia femoral heads when
attached to CFR/PEEK trunnions and found that
every carbon fiber wear particle was surrounded
by PEEK.
To validate the in vivo wear behavior and
compatibility of CFR-PEEK wear debris, a clinical
study was initiated in Italy, along with other sites in
Europe, starting in April 2001 using the ABG II total
hip system (Stryker SA, Montreux, Switzerland). The
ABG liners were fabricated from injection-molded
PEEK blended with 30% pitch fibers ( Fig. 16.6 ), and
the bearing surfaces were machined to achieve the
desired final tolerance. The status of the ABG CFR-
PEEK trial has been reported in conference abstracts
[45] . Thirty patients (40% F) with a mean age of
65 years were initially enrolled in the study. After
a mean follow-up of 3 years, none of the liners had
been revised due to aseptic loosening [46] . Osteolysis

0.17 mm 3 /million cycles.
In 2001, St. Gobain Demarquest suspended its
international sales of zirconia ceramics from implant
applications and withdrew from the market [42] . Due
to an unforeseen manufacturing change, certain
batches of zirconia femoral heads experienced
unacceptably high fracture rates [42] . Consequently,
in more recent PEEK tribology studies, zirconia is no