Differences in osseointegration rate due to implant surface geometry can be explained by local tissue strains

Experimental evidence indicates that the surface geometry of bone-interfaci ng implants influences the nature and rate of tissues formed around implant s. In a previously reported animal model study, we showed that non-function al, press-fitted porous-surfaced implants placed in rabbit femoral condyle sites osseointegrated more rapidly than plasma-sprayed implants. We hypothe sized that the accelerated osseointegration observed with the porous-surfac ed design was the result of this design providing a local mechanical enviro nment that was mon favourable for bone formation. In the present study, we tested this hypothesis using finite element analysis and homogenization met hods to predict the local strains in the pre-mineralized tissues formed aro und porous surfaced and plasma-sprayed implants. We found that, for loading perpendicular to the implant interface, the porous surface structure provi ded a large region that experienced low distortional and volumetric strains , whereas the plasma-sprayed implant provided little local strain protectio n to the healing tissue. The strain protected region, which was within the pores of the sintered porous surface layer, corresponded to the region wher e the difference in the amount of mineralization between the two implant de signs was the greatest. Low distortional and volumetric strains are believe d to favour osteogenesis, and therefore the model results provide initial s upport far the hypothesis that the porous-surfaced geometry provides a loca l mechanical environment that favours more rapid bone formation in certain situations. (C) 2001 Orthopaedic Research Society. Published by Elsevier Sc ience Ltd. All rights reserved.