261 / 460
R.J. de Jong, H.P.W. van Jonbergen, A. van Kampen
260
encountered in the first designs, such as
catching and malalignment/-tracking remain a
challenge today, and that each specific design
often comes with its own specific problems.
When searching available literature on the
different designs of PFA the following
observations are made: first of all, many recent
designs do not have long-, middle- or even
short-term results. Making evidence based
decisions to choose between PFA implants
based on available literature therefore
impossible. There is only one type (Richards
I-III (Smith & Nephew, Memphis, TN, USA))
of which long-term results are available (Table
1) [1, 2, 3, 36]. Obviously further research is
warranted. Secondly, in most cases of failure
and/or additional surgery the problems are
caused by mechanisms that can be contributed
to either specific design problems, surgical
errors or inadequate patient selection.
Especially not recognized pre-existent
femorotibial OAand pre-existing PF instability
are factors that worsen PFAmid-term outcome.
In most of these cases conversion to TKA was
inevitable. We summarized the encountered
problems with PFA as we found them in the
available literature in Table 2, which provides
on overview and an insight in the complex
task of creating a well-functioning prosthesis.
Despite of these problems, promising results
have been published with the early PF prosthe
sis with 10-year survival rates of approximately
80%. As to make a choice between available
PF prosthesis based on current knowledge,
literature slightly favors the Avon and Kine
Matic prosthesis, based on the low prosthesis
related revision rate and high survival rates.
The differences in outcome measures between
studies do not allow objective comparison and
no definitive conclusions can be made.
An interesting question is if there is something
like one PFA solution. As briefly mentioned
earlier one theory is that the three different
etiologies of PFOA require different approaches
in regard to PFA. When you look at PFOA with
underlying PF instability, it is tempting to make
an analogy to TKA; in unstable knees more
constrained (PS, hinged) types of TKAare used.
Hence, a more constrained type of PFA (e.g.
Richards) might be more suitable for PFOA
with underlying instability. Using the same
analogy, posttraumatic, stable, PFOAis probably
better addressed with a less constrained type of
PFA, which allows the PF joint to retain its own
alignment characteristics. Although a tempting
thought, current data does not suggests different
outcomes in PFA when different etiologies are
compared. Prospective research is needed.
Another interesting fact is that up till now no
one has tried replacing just the trochlear
surface; without a patellar component. This is a
tested and proved concept in TKA and might
be an option in PFA.
Conclusively PFA is here to stay; since its
introduction many patients have been helped
with good results. There is room for
improvement however. The low patient
numbers and the diversity of underlying causes
make it a challenge for the future to come up
with either one perfect fit for all types of PFOA
or the perfect customization possibilities to
meet the knees’ needs.
Study
Number of
knees/
patients
FU
Age
Satisfaction
(good/excellent)
Survival
Conversion
to TKA (%)
Jonbergen
[1]
181/161 13.3 (2-30.6)
52
N/A
84% at 10 years
69% at 20 years
13 (23/181)
Hoogervorst
[36]
33/24
9.2 (2-20)
48 (33-82)
95%
88% at 10 years
80% at 20 years
18 (6/33)
Table 1: Long-term PFA results, recent own publications on Richards II prosthesis