Journal of materials science: materials in medicine vol:6 pages:685-689
A cementless stem for a total hip replacement (THR) was designed aiming at some mechanical advantages of a cemented stem. It is called elastomer coated prosthesis (ECP) and has a metal core, coated with an elastomer layer as a mechanical buffer between the core and the femoral cortex. For the ECP coating a thermoplastic polyolefin elastomer (TPO) was chosen. Required implant sizes were determined from a measurement campaign on the intramedullar canal of German Shepherds' femora. Stress distribution in photo-elastic models of the ensemble ECP core and TPO coating was studied and compared to a model of a cementless system. The core was tested for fatigue resistance in a simulator.
Extensive in vitro testing of all ECP components (both core and elastomer coating) has shown that the prosthesis is mechanically suitable for its application. Animal testing was limited to a strict minimum for ethical reasons. Only after obtaining sufficient evidence for biocompatibility in vitro, the elastomer was studied in vivo. Implantation of non-loaded TPO samples in dogs has shown acceptable behaviour in contact with bone and marrow. ECP prototypes are currently being implanted in German Shepherds and post mortem histology will have to deliver final proof of this concept's validity.