Hydroxyapatite-coated implants have demonstrated extensive bone apposition
in animal models. The osseous interface develops even in the presence of gaps
of 1 mm and relative motion of up to 500 µm.
Development of implant-bone interfacial strength is due to the biological
effects of released calcium and phosphate ions, although surface roughness
leads to increased interface strength in the absence of interface gaps.
The clinical results at fifteen years after total hip replacements have
demonstrated that hydroxyapatite-coated femoral stems perform as well as, and
possibly better than, other types of cementless devices, with the added
benefit of providing a seal against wear debris.
Hydroxyapatite-coated acetabular components must have a mechanical
interlock with bone in order to take advantage of the coating effects.
Clinical analyses of these types of designs at seven years have indicated good
The performance of a hydroxyapatite-coated implant depends on coating
properties (thickness, porosity, hydroxyapatite content, and crystallinity),
implant roughness, and overall design. The most reliable predictor of the
performance of a device is success in long-term clinical studies.