Today’s hip replacements comprise a number of different modular hip joint systems.
The acetabular cup (metal shell), which is implanted in the pelvic bone, is fitted with a cup insert. The cup insert provides the articulating surface for the implant. The ball head, which is attached to the femur by means of the prosthetic stem, provides the other articulating surface. The ball head and the cup insert form what is called a wear couple and they continually rub against each other when the patient moves.
Cup inserts and ball heads are available in different materials. For the cup insert you can choose between conventional polyethylene, highly cross-linked polyethylene, metal or ceramic. For the ball head you can choose between metal or ceramic. Different material combinations are possible for wear couples.
Hip prostheses incorporating ceramic parts provide an excellent treatment option, which helps provide patients with a high quality of life for a long period of time. Ceramics have been proven effective in long term clinical use due to the many advantages they offer. Ceramic ball heads and cup inserts offer the best possible solution, particularly for younger and more active patients and for patients who are allergic to metal.
BIOLOX® ball heads and cup inserts made from advanced ceramics are available in most modular hip systems (see illustration).
Ceramic Ball Heads: Less Polyethylene Wear Debris than with Metal Ball Heads
If a metal ball head is used in combination with a polyethylene (plastic) cup insert, the wear rate is especially high and as a consequence, so is the risk of early loosening of the prosthesis. Clinical studies demonstrate that the polyethylene cup insert can wear by more than 0.2 mm per year. Frequently the surface of the metal head exhibits fine scratches, which can increase the wear rate even further. Laboratory studies using scratched metal ball heads indicated an increase in the amount of polyethylene wear debris of roughly 30 times.
Ceramic ball heads reduce the wear of the polyethylene cup inserts to less than 0.1 mm per year. Moreover, in contrast to a metal surface, the ceramic surface cannot be scratched. Ceramic/polyethylene wear couples (BIOLOX®delta or forte polyethylene wear couples) can reduce the rate of implant loosening, implant revision and associated complications by 2 to 5 times when compared to metal/polyethylene wear couples.
These conclusions are based on scientific articles and medical publications.
