[Experimental study on the stability of cementless porous coated endoprosthesis]

This study investigated cementless fixation of titanium porous coated endoprosthesis using canine weight-bearing model. Though immature and thin, ingrown trabeculae reached the deepest region of porous coating four weeks after implantation, and gradually matured and thickened thereafter. Pull-out tests of the porous stem at eight weeks showed excellent fixation with average ultimate pull-out force of 142 kgf and average ultimate shear strength of 2.6 GPa. Bone ingrowth rate gradually increased at the proximal and distal region of the stem and, conversely, it gradually decreased at the middle level, suggesting the dependence of bone ingrowth upon the distribution of the amount of stress transferred from implant to the femur. Severe bone remodeling was found on some specimens in which stress transfer was not physiological. Porous coated femoral stems achieve excellent fixation by bone ingrowth, but require physiological stress transfer in order to avoid significant bone remodeling after implantation.