Critically sized osteo-periosteal femoral defects: A dog model

A 21-mm defect was created in 1 femoral diaphysis each of 15 dogs. Perioste um as well as a cylinder of bone was removed, and the defect was stabilized with a bone plate. Twelve of the defects were filled with an equal volume of autogenous cancellous bone harvested from the ipsilateral ilium. Three d efects were left untreated. Cranial to caudal radiographs were taken postop eratively and every 4 weeks for 16 weeks. The radiographs were evaluated fo r healing using two ordinal scales. At 16 weeks, the dogs were euthanized a nd the femurs harvested for biomechanical testing and histologic evaluation . Both operated and contralateral not operated femurs were mechanically tes ted to failure in torsion, and load at failure and stiffness were calculate d. All dogs tolerated the procedure well, and were using the operated limb within 1 or 2 days postoperatively. There were no complications noted durin g the 16 weeks of the study. Unfilled defects did not heal and became atrop hic nonunions. The defects filled with autogenous cancellous bone healed in a consistent pattern of consolidation, incorporation, and remodeling, with uniform increases of both ordinal scales used. The femoral cortex opposite the bone plate demonstrated most mature remodeling, evident both radiograp hically as well as histologically. Unoperated femurs failed at 13.61 +/- 3. 88 N-m acid grafted femurs failed at 2.96 +/- 1.3 N-m, which was 23 % of th e measurement of the unoperated femur. Relative stiffness of the unoperated femurs was 5974 +/- 4316 N-m(2)/radian, and grafted femurs had a relative stiffness of 642 +/- 561 N-m(2)/radian, which was 10.4% of the measurement of unoperated femur. This model proved to be a critically sized defect, whi ch when left unfilled resulted in an atrophic nonunion, and when filled wit h cancellous bone resulted in a consistent healing pattern.