Bone In-Growth and Porous Implant Stability with Bioactive Substances

Abstract

The objective of this research was to investigate materials and methods promoting bone in-growth into porous implants. The work involves a nonweight bearing canine model in short and long term studies, up to 6 months. Porous coated rods were implanted into both femurs and one femur supplemented with bone growth stimulating materials. We have investigated the effect of ground bone graft, demineralized bone matrix, tricalcium phosphate and electrical direct current stimulated bone in-growth into porous coated cobalt chromium rods with porosity from 50 to 400 micrometers.

The analytical techniques involved measurement of pullout strength and elongation, microradiography, histology of the bone-metal interface and scanning electromicrographs of the bone in the porous surface. The results have been encouraging and shown that the porous implants are rigidly fixed in the femoral canal of dogs with clearly defined sharp break at the ultimate load. Autogenous ground bone graft filler showed high and low interface strength, indicating that in-growth effects may be masked by some aspect of the bone graft. Inorganic tricalcium phosphate filler could enhance the immediate strength of implants without deleterious effects in the long term. Decalcified bone matrix appears to significantly promote long term bony fixation of porous implants in the dog femoral canal.

The collective evidence from histology, x-rays and microradiographs suggests the importance of cortical nearness to the implant for strong bone in-growth into the porous surface.