Improved bone anchorage of hydroxyapatite coated implants compared with tricalcium-phosphate coated implants in trabecular bone in dogs

Tricalcium phosphate (TCP) and hydroxyapatite (HA) ceramic coatings are bio active coatings that have been shown to stimulate bone apposition onto cera mic-coated implants. TCP and HA ceramics have well-documented differences i n physical properties, but both types of ceramics are used for stimulation of bone ongrowth to cementless endo-prosthetic components clinically. Howev er, little is known about the difference in osteoconductive properties betw een these coatings when inserted into trabecular bone in a controlled exper imental situation. Unloaded cylindrical gritblasted titanium (Ti-6Al-4V) im plants (6 x 10 mm) coated with either hydroxyapatite (HA) or tricalcium pho sphate (TCP) ceramic were inserted into the proximal humerus of 20 skeletal ly mature dogs. The implants were initially surrounded by a 2 mm gap. Each animal received one HA-coated implant and one TCP-coated implant, All dogs were sacrificed 6 weeks after surgery, Results were evaluated by histomorph ometry and mechanical push-out test. Push-out tests demonstrated that HA-co ated implants were 10-fold stronger fixated in comparison to TCP-coated imp lant. Bone ongrowth was significantly higher for HA-coated implants compare d to TCP-coated implants. Bone volume in the gap showed a tendency to less bone volume around HA-coated implants compared to TCP-coated implants but t his difference was insignificant. As expected almost all of the TCP coating were resorbed after 6 weeks and almost none of the HA coating. HA-coated i mplants with a grit-blasted surface provide a favorable early mechanical im plant anchorage most likely due to superior ceramic stability compared to T CP-coated implants. (C) 1999 Elsevier Science Ltd. All rights reserved.