Biomedical Engineering Reference
In-Depth Information
this in materials in total hip and knee implants. A recent study analyzing total disc
implants with up to 16 years' in vivo service has found significantly increased
penetration rates with increasing implantation time (Kurtz et al., 2008).
3.7
Future trends
Despite some problems, total joint arthoplasty is one of the most successful
medical operations with low mortality and high functional outcomes. It is also
the only feasible option for patients with end-stage arthritis. Today, joint
replacement operations are increasing at a fast pace and the average of the
patients is decreasing (Kurtz et al., 2007). There is more demand than ever on
the performance of the materials.
It appears that crosslinked UHMWPEs are gaining more acceptance clinically
as they finish their first decade of service because of the clearly superior wear
resistance provided by crosslinking. If the additional concerns involving the
mechanical properties and oxidation resistance of these materials are addressed
satisfactorily, then UHMWPE offers benefits over alternative hard-on-hard
bearing couples, which suffer from their own associated problems such as metal
hypersensitivity (Willert et al., 2005; Daniel et al., 2006; Jacobs and Hallab,
2006), aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL)
(Counsell et al., 2008), pseudotumors (Pandit et al., 2008) for metal-on-metal
implants and squeaking (Jarrett et al., 2009) and fracture (Park et al., 2006;
Rahaman et al., 2007) for ceramic-on-ceramic implants.
Aside from the surgeons', researchers' and manufacturers' views of
successful materials for total joint replacement, economics also plays an
important role, especially when complicated payment plans are involved as in
the US. Implant `average selling price' has increased 135% from 1996 to 2007
(Orthopaedic Network News, 2009). In 2009, total hip implants pairing uncoated
femurs with polyethylene liners were listed at $9989, coated femurs and
polyethylene liners were listed at $12 433 compared with $13 843 for metal-on-
metal implants and $13 112 for ceramic-on-ceramic implants. Implant list prices
have increased substantially, which may be partly due to increased costs of
implant manufacture, but the cost of making UHMWPE implants remains less
than the alternative hard-on-hard bearings.
3.8 References
Affatato, S., Bersaglia, G., Foltran, I., Taddei, P., Fini, G. & Toni, A. (2002) The
performance of gamma- and EtO-sterilised UHWMPE acetabular cups tested under
severe simulator conditions. Part 1:
role of
the third-body wear process.
Biomaterials, 23, 4839±4846.
Amstutz, H., Campbell, P., Kossovsky, N. & Clarke, I. (1992) Mechanism and clinical
significance of wear debris-induced osteolysis. Clin Orthop, 276, 7±18.
