Failure analysis of three uncemented titanium-alloy modular total hip stems

The reasons leading to the in vivo failure of three Acumatch M-series titanium-alloy modular implants in cementless total hip arthroplasty were investigated. The implants were in service for a period ranging from 18 to 36 months. Two were fractured in vivo and the other was retrieved secondary to aseptic loosening after 18 months in service. Macroscopic examination showed close topographical similarities between the two fractured implants. Dark elliptical region on the fractured surface indicated the occurrence of fatigue process accompanied with corrosion (corrosion fatigue). The presence of numerous latent microcracks demonstrates additional embrittlement of implant structure assisted by environment (hydrogen). Light microscopy and scanning electron microscopy confirmed the presence of fretting, pitting, plastic deformation, and stress-induced corrosion cracking. Two implants (Cases I and II) fractured in identical way, while the third modular implant subjected to lower loads did not exhibit fracture, but it exhibited significant Al release. Taper performance is influenced by metallurgy, the load carried and the effect of the local microenvironment. Methods to reduce the impact of these factors may reduce the incidence of taper related failure.