Osteointegration of femoral stem prostheses with a bilayered calcium phosphate coating

Our purpose was to evaluate the osteointegration of bilayered calcium phosphate (CaP)-coated femoral hip stems in a canine model. A first layer of hydroxyapatite (HA) 20 microm thick and a superficial layer of Biphasic Calcium Phosphate (BCP) 30 microm thick were plasma-sprayed on to the proximal region of sandblasted Ti6Al4V prostheses. Bilayered CaP-coated and non-coated canine femoral stems were implanted bilaterally under general anesthesia in 6 adult female Beagle dogs. After 6 and 12 months, a significant degradation of the bilayered coating occurred with a remainder of 33.1+/-12.4 and 23.6+/-9.2 microm in thickness, respectively. Lamellar bone apposition was observed on bilayered coated implants while fibrous tissue encapsulation was observed on non-coated femoral stems. The bone-implant contacts (BIC) were 91+/-3% and 81+/-8% for coated and 7+/-8% and 8+/-12% for non-coated implants, at 6 and 12 months, respectively. Our study supports the concept of a direct relationship between the biodegradation of CaP coating and the enhanced osteointegration of titanium prostheses. A bilayered CaP coating might therefore enhance bone apposition in the early stages because of the superior bioactivity of the BCP layer while the more stable HA layer might sustain bone bonding over long periods.