Ceramic Bearing Surfaces

Types of Ceramics!

Aluminum Oxide (Alumina)

Modern Alumina is made up of very small crystal of aluminum oxide resulting in a 99.5% pure substance. This pure material structure results in a more fracture resistant material with high strength. The close packing of the molecules is produced by Hot Isostatic Pressure.   

Zirconia is characterized by fine grained microstructures which results in  one of the strongest types of ceramics available for medical use.  In addition to its high strength, the surface of Zirconia can be made a lot smoother than alumina. This is one of the reasons it is popularly used in femoral ball heads. One of the drawbacks of this material is its instability. The crystals in Zirconia sometimes transform into other formations rather than tetragonal resulting in different properties. However the stability is marinated by adding an metal oxide, yttrium.

Calcium Phosphate Ceramics
Utilizing the bodies own fixation process of bone growth could results in a better implant. Creating porous structures with oseoconductive materials such as Tricalcium phosphate (Ca3(PO4)2) and HAP (Ca10(PO4)6(OH)2)  promote fixation with the natural bone . However calcium phosphates ceramics have poor mechanical properties, such as low strength and low fracture resistance.  Synthetic HAP provide a stronger bond by eliciting a chemical response at the interface to form a tighter bond.

Bioactive Ceramics
Strong bonds are produced by using ceramics with compositions of glass containing SiO2, NA2O, CaO, and P2O5. These materials bond to soft tissues as well as bone. But currently,  these materials have only been limited to  use as bioglass coatings on the femoral and acetabular components.

© 2007 Dhondup Pemba