DEVELOPMENT OF AN ELASTOMER COATED HIP-PROSTHESIS

A cementless stem for a total hip replacement (THR) was designed aimin g at some mechanical advantages of a cemented stem. It is called elast omer coated prosthesis (ECP) and has a metal core, coated with an elas tomer layer as a mechanical buffer between the core a nd the feme ra I cortex. For the ECP coating a thermoplastic polyolefin elastomer (TPO ) was chosen. Required implant sizes were determined from a measuremen t campaign on the intramedullar canal of German Shepherds' femora. Str ess 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 coati ng) has shown that the prosthesis is mechanically suitable for its app lication. Animal testing was limited to a strict minimum for ethical r easons. Only after obtaining sufficient evidence for biocompatibility in vitro, the elastomer was studied in vivo. Implantation of non-loade d TPO samples in dogs has shown acceptable behaviour in contact with b one 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.