Hip Implant Recall Due to Manufacturing Error

400,000 hip implants were recalled in 2001 because of a single manufacturing mistake.

Zirconia femoral heads were supposed to be the future of hip replacements, stronger and better

than alumina. But here's what went wrong. The material exists in two crystal phases:

tetragonal, which is strong, and monoclinic, which is weak. Manufacturers used

different cooling methods after heating the implants. Some used a slow batch furnace,

others used a fast conveyor belt system. The faster cooling created more of the weak monoclinic

phase. When these implants were steam sterilized, they degraded rapidly in the body.

Heads that should have lasted decades failed in just four years. The difference between