Early failure of a zirconia femoral head prosthesis: fracture or fatigue?

BACKGROUND

Zirconium ceramics are one of the most controversial prosthetic biomaterials with good mechanical properties on the one hand, but early failure incidents on the other hand. A case of an early failure of zirconia femoral head in a 73-year-old clergy man, who underwent a total hip arthroplasty 28 months before, is reported.

METHOD: The retrieved femoral head fragments, during revision surgery, were studied using scanning electron microscopy.

FINDINGS: Although a randomly occurred fracture without biomechanical significance can be a possible explanation, the collected data give evidence that initial non-critical microcracks or crazes due to contact stresses or strain mismatches or both between the ceramic head and the metallic tapered neck of the prosthesis led to the fatigue of the material. The final outcome was a catastrophic fracture of the head.

INTERPRETATION: Fixation of the neck into the zirconia head, with no mismatching or stress differences, would solve the fatigue-induced head destruction.