Fatigue Strength of Cobalt-Base Alloys with High Corrosion Resistance for Artificial Hip Joints

Abstract

Loosening of the anchorage in the bone is a problem in hip-joint arthroplasty which up to now has not been entirely solved. In the loosened condition, anchorage stems of artificial joints are subject to alternating overload which causes rupture if the fatigue strength is exceeded by the stress amplitude. At Sulzer a hip-joint anchorage stem made from wrought CoNiCrMo alloy Protasul-10 has been developed which has substantially higher fatigue strength than stems made from stainless steel of grade AISI-316L or CoCrMo cast alloy. It is therefore essentially safe from fatigue cracking and this offers the possibility of significantly easier removal in case of re-operation after loosening. This paper deals with some rules to be observed in choice or development of materials for long-term implants subject to fatigue. The results of laboratory investigations on the fatigue behaviour of cobalt-base alloys for surgical implants are discussed.