In the 1960’s the British
surgeon John Charnley succeeded to promote his prosthesis system called "Low friction
arthroplasty of the hip". The low friction theory postulated that the majority of
total joint failures are caused by high friction between the bearing surfaces
of the
total
hip.
At the end of 1960’s the low friction theory was more
and more questioned. Many surgeons began to suspect that the wear particles produced from
the surface of the polyethylene cups are
causing loosening, not the friction between
the total joint surfaces.
The attention turned
in the
late
1960's to ceramic materials because they are
hard and have been known to produce low quantity of wear particles.
Besides
laboratory
tests
found
that
ceramic
joint
surfaces
have
very
low
friction.
Some
scientists,
however,
claimed
that
the
friction
resistance
of
ceramic
surfaces
depends
on the
liquid
used
for
lubrication;
according
to
them
the
friction
resistance
was
low
when
the
surfaces
were
lubricated
by
distilled
water.
and
very
high
when
bovine
joint
fluid
was
used.
These
results
were
neglected,
to be
rediscovered
in the
early
21th
century
French surgeon Boutin implanted the first
ceramic-on-ceramic cemented total hip joint in France in 1970. There were many problems
with this first total hip system, mainly with the fixation of the ball to the stem
component. Initially, doctor Boutin pasted the fragile ceramic ball to the metallic stem
with epoxy resin; many failures of this amateurish fixation followed.
The laboratory experiments, however, demonstrated that
alumina ceramic is a safe material, well tolerated by the tissues, and producing very low
quantities of wear particles. The innovative surgeons thus began constructing new total
hip systems with ceramic ball and cup components. Successively, this endeavor produced
better taper fixation of the ball and better quality of ceramic materials.
(For
details
see
the
chapter
The
Morse
taper)
As it happens so often in the development of total joints,
some of the ceramic total hip systems achieved good results, but there were also examples
of total hip systems that produced catastrophic rates of failures. For example, 80% of
ceramic surface replacement hip systems failed within two years after the surgery. But
also many ceramic total hip systems failed too often; many reports from that time
demonstrate that less than 70% of all ceramic total hips survived five years; eventually
the surgeons were forced to admit that some of these ceramic total hip systems were worse
than the conventional polyethylene-on-metal systems.
One cause of these disquieting results was
that
there
were many
manufacturers of ceramic components that produced ceramic material of bad quality. There
were no specifications and no requirements for testing of the ceramic components – so
that the fractures of the ceramic components in some of the very early total hip systems
achieved 15%.
Fracture of the ceramic component,
especially
fracture
of the
ceramic
ball, is a dramatic event that
attracts more attention than the slowly progressing loosening. However, the main cause of
failure of the old ceramic total hips systems was loosening of the components, the
fracture of the components coming as the good second.
Most notable in this respect is the experience with the
Autophor (Smith & Nephew Richards, Memphis, TN), which was the only ceramic-ceramic
prosthesis marketed in the United States in the 1985. This implant, originating in
Germany, had multiple design flaws not involving the ceramic bearings. These included a
monoblock screw-in acetabular component without metallic back up, and a cementless femoral
stem without any biological coating. Hence, the results with this total hip system were
disastrous, not because fracture of the ceramic components but because of loosening. The
authors of one such report stated "the combined failure rate of 35% of the acetabular
and femoral components is unacceptable…most of the failures were attributable to
lysis of bone and the ceramic articulations performed well". After such disastrous
experience, almost two decades ensued before the next generation of ceramic devices was
reintroduced to the United States. The ceramic total hip system was FDA approved for
general use in the USA in 2003 and is offered by several companies.
The feared fractures of ceramic components, most
notable the ball components, successively disappeared. One French report followed 5500
ceramic total hips operated on from 1977 through to 2001. During this period of 25 years
there were recorded 13 fractures of
the alumina components for a frequency of 0.002%
(Hannouche D et al.: Clin Orthop. 2003; 417: 19-26).
The German manufacturer of the alumina ceramic,
which
is used in
almost all ceramic total hip systems, CeramTech AG, published another report concerning
fractures observed among 2. 5 million alumina femoral balls (Willmann G.: Clin Orthop.
2000 379:22-8.) According to this report the fracture rate of ceramic Biolox femoral heads
has been 0.026 % for first generation alumina, 0.014% for second-generation alumina,
0.004% for femoral heads manufactured after 1994.
Comparison of these two data demonstrates a rather good
agreement and supports the statement that indeed the fracture of a modern third generation
alumina ceramic is extremely rare.
Two technological advancements in the manufacture of the
ceramic components produced this change in the quality of the third generation of medical
grade alumina ceramic in the 1994.
One was introduction of individual testing of every ceramic
component before is it shipped and sold to the surgeon.
Second was introduction of hot isostatic pressing (HIP)
technology in the production of ceramic balls. As a result of HIPing process, today’s
alumina ceramics are produced with a dense fine grain alumina with a grain size less than
two microns and very limited grain boundaries and inclusions. The grain size of these
materials has been reduced from a high of 4.2 micrometers in 1984 to 1.8 micrometers in
1995. Corresponding to that reduction in grain size, burst strength has increased from 46
kN (kilonewtons) in 1984 to 65 kN in 1995. ( In lay terms, the modern ceramic balls will
sustain 86 times the weight of an average patient(weight=77 kg), whereas the old
components sustained "only" 60 times the weight of an average patient.)
The zirconia ceramic is probably an exception to
this statement. It is an enigma why it was introduced in the total hip surgery at all,
when it cannot be used in a ceramic-on-ceramic couple. Moreover, there are almost no
positive reports on the total hip systems using this ceramic and yet more than 400 000
zirconia femoral heads were sold by one manufacturer (and there are other
manufacturers). When so many zirconia ceramic balls failed as so many reports suggest,
what happened with the failed and removed zirconia balls? There are namely no records
describing the findings made on the removed and failed zirconia balls.
There is a more recent spectacular catastrophic failure of
zirconia balls that occurred in between 1998 – 2000. (Prozyr, Smith-Nephew). This
failure was caused by change of manufacturing process by the French manufacturer of the zirconia femoral balls (Clarke 2003). Also this catastrophe was "sustained" by
the manufacturers and no data are available about the extent of the catastrophe.
The past results
of
medical
ceramic
All recently published long-term results are
statistics based on patients operated on with ceramic hips before 1995, before the third
generation medical grade ceramic came into use. The majority of these results are coming
from France on patients operated on before 1991. As such, these results are mainly of
historical interest, not fully applicable for the patients operated on with the total hips
fabricated from the modern (third generation) ceramic.
The annual failure rate of ceramic total hips in these
statistics varied from 1,3% to 1.6%, and totally there were 0.5% ceramic ball fractures.
(Hamadouche 1999, Hamadouche 2002).
For comparison, the annual failure rate of the conventional
polyethylene-on-metal total hip operations done in about the same period is 1% (Berry
2002).
Obviously, the failure rate of the "old"
ceramic total hip was about 60% higher than the failure rate of the conventional total
hips used then.
In one report, the surgeons (Hamadouche 2002) also
acknowledge that "the survival rate in the current series was notably lower than the
survival rates that have been reported for the Charnely hip system (the conventional
polyethylene-on-metal total hip)". This is one of the many examples in the history of
total joints that the innovation was worse than the original. In the retrospect one must
ask why these ceramic total hips were used at all?
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Heisel Ch et al.: J Bone Joint Surg-Am,
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Wright Medical Technology - www.wmt.com
Stryker Howmedica Osteonics –
www.stryker.com