Light and confocal laser scanning microscopic evaluation of hydroxyapatite resorption patterns in medullary and cortical bone.

An animal study was conducted with unloaded blocks and hydroxyapatite (HA)-coated titanium implants. Four HA blocks were positioned in rabbit tibiae and four HA-coated titanium implants were positioned in pig tibiae. Implants were positioned so that half was placed in cortical bone and half in medullary space. Biopsy specimens were taken 4 months after implant placement for histologic evaluation. Light microscopy and confocal laser scanning microscopy demonstrated that the HA resorption rate was higher in the medullary spaces, whereas resorption was almost absent in the areas embedded in cortical bone.