Failure analysis of uncemented total hip stem due to microstructure and neck stress riser

Total hip arthroplasty has been one of the most successful techniques in orthopedics providing good results in long term. Despite the early relative high incidence of catastrophic stem fracture, in the last years some improvements such as the use of higher resistant materials, better manufacture techniques and the control through standard tests have greatly reduced the number of failures. However, some short-term catastrophic stem failures have been noticed, usually arising from design and material misuses. Efforts should be employed to reduce these events, since the revision surgery is a more expensive procedure which further reduces the bone support, inducing a lower performance to the revision. In this paper, an uncemented hip stem failure which experienced premature catastrophic fracture at the stem neck was analyzed. The fracture originated at a hole machined to assist the stem extraction by an impact in the eventual revision. Failure analysis and numerical simulation using the loads recommended by the ISO 7206-6 fatigue test method highlighted the causes of failure. The stem experienced corrosion fatigue due to unfavorable microstructure as well as the effect of the stress raiser induced by the hole machined in the neck.