Information for Patients

Information for patients photo

4. How does cementless fixation work?


The process of your bone interacting with the implant is different on the cup side to the stem side.

The pinnacle cup is a hemispherical cup that is placed into the pelvis. The initial fixation is a press-fit. This is achieved by creating a bed for the implant which is slightly smaller than the size of the cup that is place in it. This normally achieves a good press-fit fixation but if there is any concern about stability there are three screw holes in the cup that can be used to allow screws to be passed through the cup into the bone and improve stability.

The long-term fixation occurs when bone interlinks with the surface of the implant, the implant is covered by a layer of porocoat (Depuy). This is three layers of beads burnt onto the metal shell, leaving spaces into which the bone will grow.  This technique has been used for over 30 years with considerable success and will normally achieve good long term fixation.  

On the femoral side the titanium stem is covered. Hydroxyapatite. This is a substance with the same mineral content as bone. The host bone believes it is coming into contact with more bone and will join onto it as if it is healing a fracture. Therefore there is good bonding of the bone onto the Hydroxyapatite to give good fixation. This implant was designed in France and has been used since 1986. I have used it since 2001.