Case study and analysis of a fatigue failure in a THA stem

This paper presents a case of a collared, polished and cemented hip stem which presented premature fracture due to “cantilever beam” effect. The study consisted of radiographic analysis, fracture analysis, material characterization and S–N fatigue tests. Numerical simulation of the stem was also carried out in two ways: under the ISO 7206-4 standard test and under a well stabilized arthroplasty hypothesis. The failure was predicted through both numerical simulations. The mechanical aspect of the premature failure is associated to the use of the cast stainless steel. This article aims at reinforcing the idea that the use of the “as cast” austenitic stainless steel ASTM F 745 is harmful for implants that have potential for fatigue failure. The article also discusses the application of collars in polished and cemented stems whose stability is based on the distal migration.