Hip stem fatigue test prediction

The accuracy of fatigue test prediction methods for the standard fatigue testing of hip stems was evaluated against the experimental results of static and fatigue tests. Axial unnotched strain-controlled material fatigue tests provided the required cyclic material properties. Finite element analysis of the hip stems predicted a maximum tensile stress to within 3–7% of strain gauge measurements. The four methods investigated accurately predicted hip stem fatigue strength at 5 million cycles (−1% to −9% errors). The strain–life methods successfully predicted fatigue life (factors 1/7.0–9.2 of the test) at high and low stress amplitudes of 352 and 315 MPa, respectively. The classical stress–life method was only accurate (factor 1/1.9) for the low stress level. The current study has demonstrated that fatigue test prediction methods can be applied with confidence to support standard fatigue testing of hip stems. Further studies can expand the understanding of these methods and their clinical relevance by investigating effects due to variable amplitude loading and environment.