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▸ 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 survivorship.▸ 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.