Segmental replacement of the femur in baboons

Abstract

A titanium-fiber metal implant was used to replace large segments of both femurs in four baboons. Immediate mechanical stabilization was produced by short intramedullary rods at each end of the implant and a plate bridging the bony gap. On the left side the rods were coated by fiber-metal permitting fixation through bone Ingrowth. On the right side the rods were solid and fixation achieved with methylmethacrylate. Autologous bone grafts were added on both sides. Two animals were sacrificed at three months, and two after six. The results were evaluated histologically and pullout tests were done to determine the strength of the fixation. Complete bone bridging of the replacement segment occurred in all limbs. In the fiber-metal coated rods bone Ingrowth was always found, more so after six than after three months. The strength of the bone increased from three to six months in both groups of animals. It is concluded that in the specimens with fiber-metal coated intramedullary rods this increase in bond strength was due to an increase in bone Ingrowth mainly into the coating of the rod, and that in the cemented specimens, it was due to Ingrowth of bone into the fiber-metal of the prosthetic segment where it faced the cut ends of the residual femoral cortex.