Radiographic and histologic evaluation of intramedullary implants intended for biological fixation.

Three mechanisms of direct biological attachment of implants to bone were examined using femoral intramedullary implants. The implant systems studied were; low temperature isotropic (LTI) pyrolytic carbon, carbon coated porous Co-Cr-Mo alloy and 45S5 bioglass coated Co-Cr-Mo alloy. A detailed radiographic examination revealed that all three implant systems caused significant remodeling of the femurs resulting in an hour-glass appearance. The implants were also associated with a densification of cancellous bone proximal and distal to the ends of the implant. Histologically, all three implant systems exhibited a direct bone-implant bond at the majority of the interfaces. The LTI pyrolytic carbon implants were associated with a higher incidence of fibrous tissue encasement in the proximal cancellous bone region. Active bone remodeling was observed within the pores of the porous Co-Cr-Mo alloy implants even after 8 months in situ.