On the fracture of a zirconia ball head.

Y-TZP ball heads were introduced into the market in 1985. Since then these components have had wide diffusion in hip replacements, due to their good mechanical performance and reliability. Namely, only a few papers were published up to year 2000 reporting failures of Y-TZP ball heads. The worldwide recall in August 2001 of some Y-TZP batches changed this situation. This paper analyse the material of a ceramic ball head that fractured in vivo 34 months after surgery. The retrieved fragments were submitted for visual inspection, fractographic analysis by optical microscopy, X-ray diffractometry, and FEG-SEM ceramography analysis. The results obtained show that the hydrothermal stability of the material had only a secondary role in the fracture. The literature reporting on failures of THR making use of Y-TZP ball heads is discussed.