Microstructural features in fractured high nitrogen stainless steel hip prostheses: a retrieval study of polished, tapered femoral stems.

Six fractured high nitrogen stainless steel (HNSS), polished, tapered hip stems have been reviewed for analysis. Clinical data suggests that poor proximal support (loosening), varus positioning, and canal morphology are implicated in the failure of these stems. Metallurgical assessment reveals a number of microstructural deficiencies contributing to failure. Of significance is poor grain homogeneity and larger grain size near the surface of the fractured stems. It appears some polished, tapered HNSS stems are at risk when combinations of these clinical and metallurgical features occur. As the control of grain size, microstructural uniformity, and inclusion content are critical for optimum mechanical performance, it is important the manufacturers review processing methods to further minimize the risk of component failure.