Biomechanical and histological aspects of fracture healing, stimulated with osteogenic protein-1

Fracture healing could be stimulated with osteoinductive bone morphogenetic proteins (bmp's), such as osteogenic protein-1 (OP-1), but little is known about its effectiveness in stimulation of fracture healing. In this study, biomechanical and histological aspects of fracture healing after an injection of OP-1 in the fracture gap were investigated. In 40 goats, a closed fracture was created in the left tibia. The fractures were stabilized with an external fixator and the animals were assigned to four different groups: no injection, injection of 1 mg OP-1, injection of 1 mg OP-1 with collagenous carrier material, and injection of carrier material alone. Twenty-one animals were sacrificed after 2 weeks and 19 after 4 weeks. Biomechanical testing was perfomed on both explanted tibiae. Four longitudinal samples of the fracture were sawn, processed for histology, and examined by two observers. Biomechanical evaluation showed a higher stiffness and strength at 2 weeks after injection of OP-1. Histological evaluation showed normal fracture healing patterns in all animals without adverse effects of the given injections. These data show that fracture healing can be accelerated with a single injection of OP-1, eventually resulting in normally healed bone.