Biomedical Engineering Reference
In-Depth Information
prosthetic implant. Repeat (revision) joint surgery due to premature failure of
the prosthetic joints by aseptic loosening is morbid, risky, and costly. It accounts
for approximately 25% of the total hip and knee replacement surgeries
performed annually (Crowninshield et al., 2006; Emery et al., 1997).
Ceramics have been used as an alternative to the metal±polyethylene bearing
couple in THA and TKA for several decades (Rahaman et al., 2007). Alumina
(Al
2
O
3
), introduced as an orthopedic bearing material in the early 1970s
(Boutin, 1971), is by far the most widely used ceramic in THA. The micro-
structure of the basic Al
2
O
3
material has been manipulated in recent years to
produce composites in an attempt to improve its resistance to catastrophic brittle
fracture. Stabilized zirconia (ZrO
2
) was introduced in the mid-1980s in response
to concerns about Al
2
O
3
femoral head fractures in THA (Christel, 1989; Piconi
and Maccauro, 1999). Silicon nitride (Si
3
N
4
) bearings are currently undergoing
clinical trials for application in THA and TKA (Bal et al., 2008, 2009a). A list of
ceramics currently used or under development for bearings in total
joint
replacement is given in Table 7.1.
Ceramic bearings significantly reduce wear in THA and TKA articulations
(Skinner, 1999), thereby contributing to the longevity of THA and TKA, and
reducing the likelihood of repeat hip and knee joint surgery (Harris, 1995; Kurtz
et al., 2005; Lavernia et al., 1995). Al
2
O
3
femoral heads articulating against
UHMWPE leads to lower wear than CoCr±UHMWPE articulations (Skinner,
1999). Al
2
O
3
heads can also be used with sockets of the same material, with the
resulting Al
2
O
3
±Al
2
O
3
articulations having the lowest wear of any THA bearing
combination (Bizot et al., 2004; D'Antonio et al., 2002; Hamadouche et al.,
2002; Oonishi et al., 2002; Sedel et al., 1998; Urban et al., 2001, Wroblewski et
al., 1996). At intermediate follow-up, THA with Al
2
O
3
±Al
2
O
3
articulations is
associated with less femoral bone loss than THA with metal-on-polyethylene
bearings (D'Antonio et al., 2005).
The limitation of ceramic bearings in total joint replacement is related to their
characteristic property of brittleness, which can lead to catastrophic failure in
vivo. Improvements in material quality, manufacturing methods, and implant
design over several years (1980s and 1990s) have resulted in a drastic reduction
of the incidence of such failures (Heros and Willmann, 1998; Willman, 2000).
The incidence of catastrophic failure of modern Al
2
O
3
femoral heads in vivo is
rare, approximately 1 in 5000±10 000, but this risk has persisted during the last
decade or so despite many improvements in Al
2
O
3
starting materials, manu-
facturing, and quality control (Garino et al., 2006). A less serious issue with
Al
2
O
3
±Al
2
O
3
THA articulations in vivo is `squeaking' (audible noise), which
has been recognized within the last 5 years or so (Capello et al., 2008; Walter et
al., 2008). The overall occurrence of this `squeaking' phenomenon is in the
range 0.5±10% (Walter et al., 2008).
While modern Al
2
O
3
ceramic bearings are safe and reliable if used with THA
and TKA components with proven design and durability (Bierbaum et al., 2002;
