The induction of bone in osteogenic composites of bone matrix and porous hydroxyapatite replicas: an experimental study on the baboon (Papio ursinus).

This study evaluated the morphogenetic properties of osteogenic composites of bone matrix and porous coralline hydroxyapatite (HA) replicas after intramuscular implantation in adult baboons (Papio ursinus). Composite implants were prepared by inserting rods of nonresorbable HA replicas, 20 mm in length, and 5 or 7 mm in diameter, into the medullary canals of 90 diaphyseal baboon bone cylinders, 20 mm in height, sequentially extracted and chemosterilized to obtain autolysed antigen-extracted allogeneic (AAA) bone matrix, preserving the bone morphogenetic protein (BMP) activity. Composites were implanted in the rectus abdominis and in the dorsal musculature of 24 adult male baboons. Before implantation, 45 composites were coated with an allogeneic fibrin-fibronectin protein concentrate (AFFP) prepared from fresh-frozen baboon plasma. Histologic analysis of undecalcified and decalcified specimens procured at 3, 6, and 9 months showed bone differentiation by induction along the endosteal surfaces of the chemosterilized matrix and within the porous spaces of the HA substratum. Bone formation was often extensive, culminating in complete penetration of the porous spaces. Histomorphometry showed that bone in the HA substratum increased at each time period. The biochemical treatment of the composite implants with AFFP did increase significantly the amount of induced bone, although only in the HA substratum. Bone differentiation was confirmed by fluorescence microscopy of the mineralization fronts after intravital double tetracycline labeling. The differentiation of bone in composites of bone matrix and porous HA replicas in extraskeletal sites of adult baboons may help to design appropriate delivery systems for the controlled therapeutic initiation of bone formation for craniofacial and orthopedic applications in man.