HEALING BONE USING RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN-2 ANDCOPOLYMER

Middiaphyseal 2.5-cm segmental defects in the right femurs of 12 sheep were stabilized with stainless steel plates and implanted with (1) 2 mg recombinant human bone morphogenetic protein 2 and poly[D,L-(lactid e-co-glycolide)] bioerodible polymer with autologous blood (n = 7), (2 ) 4 mg recombinant human bone morphogenetic protein 2 and poly[D,L-(la ctide-co-glycolide)] and blood (n = 3), or (3) poly[D,L-(lactide-co-gl ycolide)] and blood only (n = 2), Bone healing was evaluated for 1 yea r using clinical, radiographic, gross pathologic, and histologic techn iques, Union occurred in three sheep in Group 1, two in Group 2, and n one in Group 3, In the animals that healed, new bone first was visible radiographically between Weeks 2 and 6 after implantation; new bone m ineral content equaled that of the intact femur not surgically treated by Week 16; recanalization of the medullary cavity approached complet ion at Week 52; and at necropsy the surgical treated femurs were rigid ly healed, the poly[D,L-(lactide-co-glycolide)] was resorbed completel y, and woven and lamellar bone bridged the defect site, In two Group 1 sheep euthanized at Weeks 2 and 6, polymer particles were permeated b y occasional multinucleated giant cells, Some plasma cells, lymphocyte s, and neutrophils were present locally The poly[D,L-(lactide-co-glyco lide)] tended to fragment during surgical implantation, Despite these observations, the recombinant human bone morphogenetic protein 2/poly[ D,L-(lactide-co-glycolide)] implant was able to heal large segmental b one defects in this demanding model.