Biomedical Engineering Reference
In-Depth Information
16.3 Basic Biotribology Studies
of PEEK Articulations
The early research of CFR-PEEK hip and knee
bearings by Howmedica, culminating in the clinical
trial of the ABG, described in Section
16.2
, has fueled
interest in the basic biotribology of PEEK. Bio-
tribology refers to the study of wear under biologically
relevant conditions. The simplest and most widely
accepted model for basic biotribological simulation of
candidate biomaterials is the multidirectional pin-on-
disc test, sometimes also referred to as the “pin-on-
plate” test. In this experiment, a pin is rubbed against
a plate in an elliptical or square waveform to create the
multidirectional “crossing shear” sliding conditions
typical for a total hip replacement. Standard guide-
lines for conducting a pin-on-disc experiment are
available (ASTM F732), and a picture of a pin-on-
plate apparatus is shown in
Fig. 16.7
.
Because wear is a system and not a material
property, the conditions of testing must be carefully
chosen to replicate the clinical situation. The pin may
be subjected to a constant or variable load, and the
Figure 16.6
CFR-PEEK ABG II acetabular liner.
Image provided courtesy of Stryker Orthopedics
(Mahwah, NJ).
was observed in two femurs, at the greater trochanter.
Retrieval analysis of one liner, retrieved due to
infection from a 55-year-old highly active male
patient, revealed head penetration of 0.13 mm after
28 months
[47]
. Histology demonstrated a “low”
amount of particles in the periprosthetic tissue from
this patient. The ABG CFR-PEEK trial was later
expanded to include 121 patients by 2003. According
to the manufacturer, five revisions have occurred to
date, due to reasons unrelated to the bearing (infec-
tion, loosening, and periprosthetic fracture). This
clinical trial is still ongoing, and the detailed results
have not yet appeared in a journal publication.
Overall, the available preliminary clinical data
support the short-term effectiveness of CFR-PEEK as
a bearing material for total hip replacement.
However, in a traditional total hip replacement
design, current data do not yet demonstrate a long-
term clinical advantage of CFR-PEEK over other
well-established bearing alternatives, such as highly
cross-linked UHMWPE, MOM, or COC. Although
initial hip simulator data illustrate the superiority of
CFR-PEEK as compared to historical gamma
e
air
sterilized UHMWPE, highly cross-linked formula-
tions of UHMWPE have also demonstrated order-
of-magnitude improvement in wear as compared to
historical controls. Nevertheless, the successful,
albeit short-term, ABG experience with CFR-PEEK
provided strong motivation for developing a more
detailed understanding of the biotribology of PEEK
articulations, and these recent studies have been
summarized in the following section.
Figure 16.7
Schematic representation of multidirec-
tional pin-on-plate test machine employed by Scholes
and Unsworth
[15,16,49]
.
