Arthroplasty Bearing Surfaces - PEEK Biomaterials - page 263

confirms that most of the implants are doing well at
3 years ( Fig. 16.11 ). One implant developed
a problem and was revised after approximately
18 months. These implants will be closely followed
for several years before further patients are enrolled.

previously evaluated on the Durham simulator.
Based on friction tests, Scholes and Unsworth [17]
classified the CoCr/CFR-PEEK unicondylar bear-
ings as operating within a boundary-mixed lubrica-
tion regime.
Because there are many designs of total knee
replacement (TKR) that operate under much higher
bearing stresses than the Oxford unicondylar knee,
and the performance of CFR-PEEK knee bearings
under third body wear remains as-yet unproven, one
must be cautious about overgeneralizing the results
of this study to the entire field of knee arthroplasty at
the present time. Indeed, joint simulator testing of
fixed-bearing, nonconforming unicondylar knee
replacements by Grupp et al. [61] has confirmed that
PAN CFR-PEEK is unsuitable for such applications
and, further, suggested that it was “doubtful” whether
Pitch CFR-PEEK lowered wear relative to
UHMWPE in a nonconforming knee design. Never-
theless, the encouraging findings from Scholes and
Unsworth's pilot study of mobile bearings warrant
further exploration to determine which tribological
conditions and where in the knee design space con-
forming CFR-PEEK knee bearings may be suitable.

16.5 Mobile-Bearing, Unicondylar
Knee Joint Replacements

CFR-PEEK has been considered unsuitable for
knee joint applications following the early experi-
ments performed in the late 1990s by Wang et al.
[10] . Recently, there has been interest in revisiting
CFR-PEEK as a bearing material in conforming
mobile-bearing knees. Mobile-bearing designs are
intended to operate under low-contact stress-bearing
conditions [60] , that appear suitable for CFR-PEEK
bearings based on the biotribology testing summa-
rized earlier ( Table 16.2 ). Furthermore, the conclu-
sions reached by Wang et al. [10] for industrial PEEK
grades and knee arthroplasty were based on testing
performed in a cylinder-on-flat bidirectional recip-
rocating wear tester and not in a modern multidi-
rectional knee simulator.
Scholes and Unsworth [17] tested the hypothesis
that CFR-PEEK would result in low wear rates when
evaluated in a unicondylar mobile-bearing design
(Oxford) on the Durham 6-station multidirectional
total knee wear simulator. The unicondylar implants
were incorporated into the total knee simulator by
simultaneously testing both a lateral and a medial
condyle in each station. The dynamic axial force
loading history conformed to the Paul loading curves
with a range of 300 e 3000 N for the entire knee joint,
but the loading was distributed more heavily on the
medial condyle (1733 N) than on the lateral
condyle (1267 N). The Durham simulator allowed
free internal e external rotation of up to 10 degrees
but a forced anterior e posterior motion (

16.6 Other Total Joint
Replacement Applications

PEEK has been considered for other niche total
joint replacement products, including finger joint
replacements and total disc replacement. Details
about the applications of PEEK in total disc
replacement are covered in Chapter 13. In this
section, we focus on novel bearing applications of
PEEK in the upper and lower extremities.
Mathys AG (Bettlach, Switzerland) currently
offers an all-PEEK, two-part metacarpophalangeal
finger joint ( Fig. 16.12 ). This involves an image
contrast grade of PEEK-OPTIMAwith a thin titanium
coating. Although no data relating to PEEK-on-PEEK
wear has been published in the open literature, PEEK
was selected due to its lower wear against cartilage
when compared to a previous, polyacetal prosthesis.
Joyce et al. [62] have also studied the meta-
carpophalangeal wear behavior of neat, unfilled
PEEK and UHMWPE caps against titanium in
a finger joint simulator. No details about the PEEK or
UHMWPE resins or sterilization conditions were
reported. The UHMWPE components exhibited
undetectable wear, while PEEK components had

2.5mm)
and flexion e extension rotation (60 e 0 ). The poly-
meric components were fabricated from Pitch-based
CFR-PEEK OPTIMA. After 5 million cycles, the
total extent of wear for the unicondylar knee
components corresponded to an average wear rate
of 1.02 e 1.70mm 3 /million cycles per condyle (on
average, 2.9 mm 3 /million cycles for the entire knee
joint). The CFR-PEEK wear rates were judged by
the authors to be lower than metal-on-UHMWPE
wear rates, which ranged from 3.2 to 4.1 mm 3 /
million cycles for the entire knee joint when