Laser engravings as reason for mechanical failure of titanium-alloyed total hip stems.

INTRODUCTION: Two revisions of broken ß-titanium total hip stems had to be performed in our hospital after 2 and 4 years in situ. Since both fractures were located at the level of a laser engraving, a failure analysis was conducted. MATERIALS AND METHODS: Both retrieved hip stems were disinfected and collected in our retrieval database after patient's signed agreement. Each fragment was macroscopically photographed. Fracture surfaces were analyzed using scanning electron microscopy (SEM). Quantification of element content was conducted using energy dispersive X-ray (EDX) analysis. RESULTS: Both stems show fatigue fracture, as displayed by the lines of rest on the fracture surface. The origin of fracture was identified directly at the laser engraving of the company logo at both stems by means of SEM. The EDX analysis showed an oxygen level beneath the laser engraving about twice as high as in the substrate, causing material embrittlement. CONCLUSIONS: Laser engravings need to be reduced to a minimum of necessary information, and should be placed at locations with minimum mechanical load. Biomechanical analyses are recommended to identify less loaded areas in implant components to avoid such implant failures.