Ceramic Femoral Heads Age Over TimeMaterials used in hip replacement implants have varied over time. Ceramic femoral heads were popular in the late 1980s. Zirconia ceramic was favored at one time because of its resistance to crack formation. If a crack did occur, the zirconia could expand to stop the crack from getting worse. The crack would be sealed in place.
In this study, researchers tested zirconia heads removed due to failure. All implants included were the same size and type to make comparisons equal.
The zirconia heads were scanned with a special microscope. Tests were done to measure surface roughness. Fracture toughness was calculated. The content of the material was also analyzed.
The authors report a direct link between length of time the implant was in the body and breakdown of the surface. Over time, fracture toughness decreased and surface roughness increased. Wear and tear was worse in implants with an irregular surface. There was no link between patient age, weight, or level of activity as a cause of implant failure.
Aging-induced wear seems to affect only the outer layer of the zirconia heads. The surface changes seen in this study did not affect the entire femoral head. Surgeons should be aware that zirconia ceramic may not hold up over time. The risk of implant fracture and uneven wear increases over time.
Mariano Fernandez-Fairen, PhD, MD, et al. Aging of Retrieved Zirconia Femoral Heads. In Clinical Orthopaedics and Related Research. September 2007. Vol. 462. Pp. 122-129.
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