Biomechanical investigations of bone‐porous carbon and porous metal interfaces

The mechanical strengths of four types of ingrown porous carbon and two types of porous metal bone implants were correlated with the type of osseous ingrowth into the porous interfaces. Intracortical cylinders were implanted into canine long bones and examined at 3, 6, and 12 weeks. Histological techniques were used to study bone ingrowth. Tetracycline labelling and electron microprobe analysis were used to characterize the degree of mineralization of the ingrowth. Shear strengths of bone‐porous material interfaces were measured on cylinders forced out in compression. Histology revealed readily identifiable bone in most porous specimens. Mineralization was found to various depths in all porous specimens. After ingrowth, the porous metals, possessing appreciable inherent strength, displayed interfacial shear strengths from one‐third to two‐thirds that of cortical bone. The very porous carbon lattices, possessing little inherent strength, developed interfacial strength after ingrowth approaching that of the ingrowing cortical bone. The less open, more rigid porous carbon implants developed smaller interfacial strengths, averaging between one‐eighth and one‐half that of the ingrowing cortical bone.