An indirect comparison of third-body wear in retrieved hydroxyapatite-coated, porous, and cemented femoral components.

The osteoconductive properties of hydroxyapatite (HA)-coated titanium implants are well documented, but eventual coating degradation may result in HA particles adjacent to the substrate, and if the particles were to migrate into the joint space then accelerated polyethylene wear might be expected. As an indirect indication of third-body wear, the authors used laser interference microscopy to measure and compare surface roughness on modular heads from 15 clinically retrieved HA-coated femoral components, with heads from 15 retrieved uncemented (porous) and 15 cemented implants. The results showed increased median surface roughness over initial manufacturer specifications in all groups, but the cobalt-chrome heads from the HA-coated group showed significantly less surface roughness and less deep scratches than the heads from either the porous or uncemented group. Three-body wear appears to be a common problem, but evidence available suggests that it is no more of a problem with HA-coated devices than porous or cemented.