Titanium-alloy is a metal with excellent biocompatibility, but its osteoconduction is not as efficient as hydroxyapatite materials. Calcium-ion (Ca-ion) implantation is a surface modification technique that can improve osteoconduction of titanium without an additional layer of coating. We studied the effects of Ca-ion-implantation on osseointegration of a titanium-alloy stem in a bilateral canine THA model. The stem surface was grit-blasted and Ca-ion-implanted by the ion mixing technique. Fifteen mongrel dogs had bilateral single-stage THAs, with a Ca-ion-implanted stem used in one side and a non-Ca-ion-implanted stem in the contralateral side. They were sacrificed at 1, 6, and 12 months postoperatively, and microradiographs were taken. Undecalcified cross-sections were evaluated histologically. For quantitative evaluation, the length of new bone apposition to the implant surface was obtained using computer image analysis. Most implants were well integrated, and there was no apparent qualitative difference between the two types of stems radiographically and histologically. However, Ca-ion-implanted stems had significantly greater new bone apposition than non-Ca-ion-implanted stems at 1 month, although the overall effect of Ca-ion-implantation was not significant.

The results showed enhanced osteoconduction with Ca-ion-implantation only in the early postoperative period. This could be related to the previous data of immersion tests that the dissolution rate of Ca-ion from Ca-ion-implanted titanium decreases with time. Clinically, early osteoconduction is desirable and could accelerate rehabilitation and outcome. Although further improvement of the Ca-ion-implantation technique for a sustained osteoconductive effect is necessary, Ca-ion-implantation will be beneficial for early fixation of titanium-alloy implants.