Which property led to the abandonment of zirconia (yttria-stabilised tetragonal zirconia polycrystal) ceramic femoral heads in total hip arthroplasty during the late 1990s?

• A Rapid dissociation of yttria stabiliser leading to systemic yttrium toxicity
• B Excessive brittleness resulting in catastrophic intraoperative head fracture during impaction
• C Release of radioactive trace elements causing malignancy at the bearing surface
• D Low-temperature degradation causing phase transformation from tetragonal to monoclinic zirconia with surface roughening and increased wear ✓

Explanation

Zirconia heads were withdrawn after it became clear that exposure to body-temperature moisture causes spontaneous tetragonal to monoclinic phase transformation (low-temperature degradation). The transformation increases grain volume, roughens the articulating surface and dramatically accelerates polyethylene wear. Fracture was rare rather than the dominant failure mode, so B is the attractive distractor. Alumina ceramic lacks this metastable phase behaviour and remains in wide use.

Reference: Miller's Review of Orthopaedics, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.