A review of ceramic coatings for implant fixation

The present series of eight studies was performed in order to investigate t he effect of various clinically relevant factors on bone ingrowth in relati on to hydroxyapatite (HA) and titanium-alloy (Ti) coating when subjected to pathological and mechanical conditions mimicking the clinical situation. H A- and Ti-coated implants were inserted into the femoral condyles of mature dogs and one study was performed on humans. The observation period ranged from 4 to 52 weeks, and the results were evaluated by mechanical push-out t esting, histomorphometric analysis, polarized light microscopy, UV fluoresc ence microscopy and collagen analysis. There were no complications related to the operative procedures, and all dogs were killed according to the orig inal time schedule. Two studies focused on in vivo mechanisms and factors i nfluencing resorption of HA coating. The overall conclusions from these stu dies are that HA coatings do resorb in vivo, that micromotion accelerates r esorption, and that resorbed HA is partly replaced by newly formed bone, su ggesting that implants fixation is durable. The other studies focused on th e significance of mechanical stabilization and loading conditions of the im plant immediately after surgery. From these studies, it can be concluded th at HA-coating has a positive effect on bone-implant fixation in various sit uations, i.e., under stable loaded conditions and under unstable mechanical conditions. The most striking effect of HA coating was that it enhanced bo ne growth across a gap around the implant both during stable and unstable m echanical conditions; it even converted a motion-induced fibrous membrane t o bony anchorage.