Calvarial regeneration in primates with autolyzed antigen-extracted allogeneic bone

The limited regenerative capacity of calvarial membranous bone provides an ideal system for investigation in the comparative physiology of bone regeneration. Cranial defects, 25 mm in diameter, were created in 24 adult male baboons (Papio ursinus). In each animal, defects were implanted with chemosterilized antigen-extracted, autolyzed allogeneic (AAA) bone, grafted with iliac corticocancellous grafts, or left ungrafted to monitor the spontaneous regeneration potential of the adult baboon calvaria. Antigen-extracted, autolyzed allogeneic bone implants were prepared from donor sub-adult baboon calvariae and processed so as to retain bone morphogenetic protein (BMP) in the bone matrix. Histomorphometric analysis of undecalcified sections (7-microns thick) prepared from specimens harvested at three, six, and nine months after surgery showed superior osteogenesis in AAA bone matrix implants, compared with autografts and untreated defects. The morphogenetic response was characterized by vascular invasion and mesenchymal cell aggregation after partial resorption and dissolution of the implanted matrix, followed by bone deposition at the calvarial interfaces, the pericranial and endocranial surfaces of the implants, and within the open diploic spaces of the implanted original AAA bone matrix. The superior osteogenesis in AAA bone implants appeared consistent with extensive osteoconductive invasion from the open diploic and endosteal spaces of the recipient calvariae. In addition, the finding of a delicate, trabecularlike bone, appositional to the central areas of the implanted matrix, suggests that AAA bone implants might also have acted as inductive substratum for bone differentiation.