Case study: Failure of a high nitrogen stainless steel femoral stem

This paper presents a case study summarising the failure analysis of a high nitrogen stainless steel femoral stem. The failure of the stem occurred after only 4.5 years in service by fatigue failure across the proximal region. The experimental work consisted of a visual inspection, macroscopic inspection, fractography and microscopic examination, surface profilometry and chemical analysis of the material. All metallurgical tests revealed the material to be satisfactory in terms of microstructure, hardness and composition. Inspection of the introducer slots revealed mechanical damage created during surgery to install the stem. The fatigue crack was shown to have initiated from a point of mechanical damage present in one of the introducer slots. This study highlights the detrimental effect of surface damage to initiate fatigue cracks under cyclic loading conditions and the need for greater awareness regarding the possibilities of creating stress raisers such as scratching, scoring and impacts which can lead to premature failure of prostheses.