Ceramic Wear Data
Wear Characteristics of the LINEAGE® Ceramic Articulation System
There are many studies that report wear rates for articulating couplings. There is no single study that tests all available orthopaedic couplings in the same manner and reports volumetric wear. From all the articles that do exist, however, it is possible to approximate annual linear wear rates for several orthopaedic couplings. This information is shown in Table 1.19, 20, 21, 22, 23, 24 Alumina ceramic on alumina ceramic clearly has the lowest wear rate of these orthopaedic couplings.
TABLE 1 | Approximate Annual Linear Wear Rates for Various Orthopaedic Couplings.
As stated in the introduction, Sedel, et al followed 86 THAs with alumina on alumina articulation for nine years and reported a prosthesis life expectancy of 97.8% even with the inclusion of revision cases. The authors suggest that "an important contributory factor may well be the small amount and good tolerance of wear debris".
Huo, et al reported on another group of alumina on alumina THAs for eight years and stated that there was no occurrence of osteolysis in the young and active patient group.25
Reports such as these in the scientific literature suggest that an alumina/alumina articulating couple can produce successful clinical outcomes in terms of survivorship and potential reduction in the generation of wear debris.
Published clinical data with ceramic-on-ceramic hip implants suggest that surface finish, diametrical clearance, material and sphericity/roundness were key factors affecting historical wear behavior. Wright Medical Technology has conducted extensive studies in order to optimize these critical design features.
Surface Finish
LINEAGE® ceramic inserts and alumina ceramic femoral heads are produced by state-of-the-art equipment to ensure optimal surface finish parameters.
Diametrical Clearance
LINEAGE® ceramic/ceramic interface articulation has been designed with the optimal diametrical clearance. Critical to the function of the ceramic articulation is the clearance between the head and cup. If the clearance is too large, the contact area is polarized and can lead to high surface stress resulting in increased wear. If the clearance is too small, the head and liner can potentially jam putting stresses on the implant that can lead to early loosening.26 | Figures 13 & 14
Material
Wright Medical Technology uses aluminum oxide ceramic for the LINEAGE® liners and femoral heads. From a material standpoint, alumina ceramics provide high strength with low wear debris generation.
Sphericity/Roundness
Wright Medical Technology's manufacturing processes utilize state of the art equipment to maintain very tight tolerances to produce the LINEAGE® ceramic liners and heads with optimal sphericity.
