Evaluation of ground cortical autograft as a bone graft material in a new canine bilateral segmental long bone defect model.

The recent orthopaedic literature reflects a growing number of bone graft substitutes and osteogenic growth factors under investigation in a number of animal models. We attempted to establish a well-controlled, large animal model of a segmental defect in a weight-bearing long bone by developing a bilateral diaphyseal radial defect model in the canine. We also evaluated the effectiveness of ground cortical autograft as a graft material. Twenty-three adult mongrel dogs underwent bilateral radial osteotomies with creation of a 2.0-2.5-cm diaphyseal defect on each side. All dogs received cancellous autograft (CAN) on one side, nine received no graft material (DEF) on the opposite side, and 14 received morselized cortical autograft (CORT) on the opposite side. Radii were stabilized by external fixation. Animals were followed radiographically at 6-week intervals to evaluate the healing process. Thirteen dogs were sacrificed at short-term follow-up (8-12 weeks postsurgery) and 10 at long-term (16-24 weeks). Biomechanical torsion testing to failure and histological evaluation were performed on each defect. All CAN radii achieved union (100%) while only one of nine DEF radii (11%) and none of 14 (0%) of CORT radii achieved union. Statistically significant differences in biomechanical parameters between both test groups and their corresponding autograft control radii were found. Histology revealed fibrous nonunions in the DEF and CORT radii. These results demonstrate that the bilateral canine radial defect model represents a consistent and reproducible model for bone healing of segmental defects in weight-bearing long bones and that ground cortical autograft is an ineffective graft material.