Biomedical Engineering Reference
In-Depth Information
Intracutaneous Reactivity: USP XXII Class VI Rabbit Injection Test
Systemic Toxicity: USP XXII Class VI Mouse Injection Test
Hemolysis: Autian Method Rabbit Blood Contact Test
Pyrogenicity: USP XXII Class VI Rabbit Injection Test
Intramuscular Implantation: USP XXII Class VI and 90-Day rabbit Tests
Genotoxicity: Ames Mutagenicity and Mouse Bone Marrow Micronucleus
The tests described by USP are used worldwide for biocompatibility testing.
Updated versions can be downloaded from Internet.
The daily uptake of zirconium is estimated as high as 125 mg/day which is
not unexpected as being an omnipresent element. A relation between Crohn's dis-
ease and zirconium was suggested in the 1990s, reminiscent of the relationship of
Alzheimer and aluminum. As far as we are aware, the hypothesis is not supported.
For the time being, toxicity of zirconium seems not to be an item of concern.
Performance
The goal of all the trouble invested in the production of reliable OxZr components
was to marry the advantages of both metals and ceramics. Is it a lucky marriage?
We a r .
A back and forth sliding of a spherical tipped bone cement pin on test
specimens is a technical control test shown in Fig.
5.4
a and described by Hunter
et al. [198]. Wear of a specimen of OxZr is different: hardly visible for OxZr, visi-
ble for the naked eye for CoCr worn under identical conditions. This remarkable
difference is easily demonstrated by our simple qualitative test set-up, which is
schematically shown in Fig.
5.4
b: a laser beam is pointed on the wear path and
the beam is partly reflected or partly diffused, depending on the roughness of
the surface. The results shown in (c) do not need further comment. The test can
occasionally be made semiquantitative.
In-patient use of a metal/polyethylene (PE) articulation requires more realistic
testing. Wear of PE is often cited as responsible for hip and knee replacements
by periprosthetic osteolysis and thus an important issue. Mainly two wear mecha-
nisms are operating: adhesive and abrasive wear, the first being caused by frictional
shear of PE against a hard counterface, the second by sliding against either hard
counterface asperities or by abrasive particles in the PE-metal or ceramic inter-
space, the latter usually quoted as a separate class of wear:
third body wear
.The
wear behavior as shown in Fig.
5.4
is performed under more realistic conditions
by wear tests in a four-axis displacement controlled, physiological knee simulator
(Fig.
5.5
). The applied conditions were: 6 million cycles of 90% walking-gait and
10% stair-climbing activity. In Fig.
5.5
(left), the newest guided motion knee prosthe-
sis of Smith & Nephew: Journey BCS prosthesis (bicruciate stabilized). The insert
was made of UHMWPE (ultra-high-molecular-weight-PE).
Collectively, the hip and knee simulator tests indicate that OxZr components can
reduce wear of the polyethylene counterface by 40-90% (in volume or weight)
depending on test conditions. These tests also indicate that the number of wear
