Healing Course of Primate Ulna Segmental Defects Treated With Osteogenic Protein-1

Twelve African green monkeys were implanted with recombinant human osteogenic protein-1 (rhOP-1) placed on a bovine bone-derived Type I collagen carrier to characterize healing in an ulna segmental bone defect model at 1, 3, 12, and 20 weeks postoperative. Defect healing was evaluated by plain film radiography, computed tomography (CT), magnetic resonance imaging (MRI), bone mineral density (BMD), and histologic analysis. Radiographically, new bone formation was observed as early as 3 weeks postoperative. By 6 weeks, new bone was visible in five of six defects. Increased quantity and mineralization of the new bone were apparent by 12 weeks. Reformation of the medullary cavity with appearance of marrow elements was demonstrated by CT and MRI at 20 weeks. BMD studies revealed a significant increase in the presence of bone with time. Histology at 1 week demonstrated that the implant material was well contained in the defect, and a proliferation of cells occurred at the defect borders. At 3 weeks cell proliferation continued and cell phenotype differentiation was recognized. By 12 weeks substantially less residual carrier was found in the defects, and calcifying tissues with plump chondrocytes, osteoblasts, and immature woven bone were observed. Areas of lamellar and woven bone were identified at 12 weeks, with advanced remodeling and revascularization observed at 20 weeks. The use of osteoinductive implants may provide an alternative to autologous and allogeneic bone tissue in the therapeutic approach to bone defects and promotion of fusion by eliminating the donor site morbidity associated with autogenous bone and the decreased efficacy and potential for disease transmission associated with allogeneic bone.