Biomedical Engineering Reference
In-Depth Information
Table 2.5 Wear behavior of CoCr alloys used in total hip replacement
(Dumbleton and Manley, 2005; Windler and Klabunde, 2001)
Femoral head
Cup
Linear wear
Debris size
(m/y)
(m)
CoCr
UHMWPE
100±300
0.5
Ceramic
UHMWPE
50±150
0.2
CoCr
CoCr
2±5
0.05
Ceramic
Ceramic
2±5
0.2
integration. This is because elements such as cobalt, chromium, and nickel
included in cobalt±chromium alloys have controversial effects on immune
responses and cytotoxicity (Spriano et al., 2005).
The cobalt±chromium alloys used in the second generation of total hip
replacements proved to be successful after short- to medium-term follow-up
clinical studies. For example, Doerig et al. (1999) observed a 96% survival rate
out from a total of 218 hip stems after 2±6 years. Korovessis et al. (2002) found
a 96.8% survival rate for such stem after 4.3 years and 99.4% for cups after 7.6
years. However, large patient numbers and long-term clinical follow-up will be
needed to further confirm the efficacy of cobalt±chromium alloys.
Biological issues related to cobalt±chromium alloys used in load-bearing
applications continue to be a concern today. Specifically, metal ions released
may have carcinogenic effects and wear debris from cobalt±chromium alloys
may be toxic to cells (Spriano et al., 2005). Thus, a harder and more protective
cobalt±chromium surface is desirable to address these problems.
2.4 Advances in titanium and cobalt±chromium
alloys used for joint implant
So far the advantages and disadvantages of titanium and cobalt±chromium
alloys used as in joint replacements have been reviewed. As stated earlier,
continued innovations have been made in these fields and some of them are
discussed here.
2.4.1
Selection of new composition alloys
As mentioned above, Ti-6Al-4V ELI is the most widely used titanium alloy in
hip prostheses (stems and cups). Other first generation titanium alloys include
Ti-6Al-7Nb (Semlitsch et al., 1992) and Ti-5Al-2.5Fe (Borowy and Kramer,
1995). Nb and Fe are used to substitute V in response to concerns about potential
cytotoxicity of V and adverse tissue reactions.
To enhance biocompatibility and lower the modulus of hip prostheses, second
generation titanium alloys have been recently developed. Some earlier examples
