Biomedical Engineering Reference
In-Depth Information
A mid-term evaluation is reported of OxZr femoral components of cemented
TKA: 50 patients, 51 years of mean age and mean follow-up of 79 months. Radio-
graphic review revealed one nonprogressive tibial radiolucency. There were no
femoral radiolucencies or osteolysis and no other negative findings attributable to
the oxidized zirconium. Longer clinical use is needed before deciding that the new
material results in a longer in vivo performance [205].
An interesting evaluation is reported of experiments on six Oxinium femoral
heads retrieved from revision surgery. The heads showed various degrees of abrasive
damage but confined to one quadrant of the surface. Subsequently, they were cou-
pled with XLPE (cross-linked polyethylene) liners and compared to new Oxinium
and CoCr heads, respectively, coupled to XLPE liners and conventional PE liners.
The hip simulator testing was performed using a standard walking gait program
(peak load 3,000 N, 1 Hz). The in vivo damaged heads showed enhanced wear
of the PE liner, although substantially less than the new heads used for compari-
son. The authors concluded that the observed wear would not lead to catastrophic
damage [206].
Metal hypersensitivity has been identified as possible cause of arthroplasty fail-
ure. In these cases, the use of ceramic implants is recommended at revision. Nasser
and colleagues report the outcome of a prospective study of patients with recognized
hypersensitivity. Neither of the patients developed, after revision knee arthroplasty
with either alumina or Oxinium implants, adverse clinical symptoms or changes in
antibody profile. The results suggest that Oxinium offers the same hypoallergenic
properties as ceramics but a lower cost [207].
To conclude, time as often said, is an important parameter. Long-term assess-
ment, however, is not yet possible. So, mild optimism is probably the best attitude
for the time being.
5.3
Tantalum and Niobium
Tantalus, a rich and famous king in Greek mythology, was a son of Zeus. Mortal but
honored by the gods, he was allowed to the dinner with the Gods. Dazzled by so
much honor he revealed the secrets of the Gods to men. Zeus punished him, forced
to stand in the Hades, where the water was receding when he tried to drink, and
other kinds of everlasting torments. His daughter Niobe was not less an ambitious
person. Niobe had vaunted one day her superiority to the goddess Leto but Apollo
and Artemis, Leto's children, punished Niobe by killing her seven sons and seven
daughters!
A new metal was discovered by the English chemist Hatchett in 1801 and by the
Swedish chemist Ekeberg in 1802 in two different minerals. Ekeberg found it such
a
tantalizing
task to trace the element down, that he called it
tantalum
. In 1844,
however, it became clear that in fact the discovery concerned two closely related
elements:
tantalum
and
niobium
. When in 1844 Heinrich Rose had to name the
