OTA 1997 Posters - Scientific Basis for Fracture Care

*Healing Time Course of Tibial Segmental Defects in Dogs using the OP-1 Device

Paul P. Hospodar, MD, Eric H. Ledet, MS, Barton L. Sachs, MD, Richard L. Uhl, MD

Albany Medical College, Albany, New York, USA

Introduction: Long bone defects and non-unions due to trauma or disease occur commonly in humans. Critical size defects will not normally heal without intervention. Currently there is no reliable and rapid way to promote successful healing of these pathologic conditions (Einhorn, 1995).

Purpose: The purpose of this study is to determine whether the OP-1 Device, consisting of 2.5 mg of rhOP-1 and 1g of bovine type I collagen, administered as a surgical implant, can enhance and accelerate healing of segmental defects in long bones.

Materials and Methods: A cortical segmental defect two times the mid-shaft major axis dimension was created in the mid-tibia of 25 skeletally mature beagles with an oscillating saw. This was a critical-sized defect (i.e. the defect would not heal spontaneously) (Heiple et al, 1987). A Kirschner Type I external fixator was used to stabilize the tibia. The OP-1 Device was placed into the tibial defect of each animal at the time of surgery. Animals were assessed for osseous formation during the healing period by standard radiographs and DEXA scans. Bone fluorochromes were administered at 1, 2, 4, and 6 weeks postoperatively. Animals were sacrificed at 2, 4, 6, 8, and 12 weeks post-operatively. Non-destructive fourpoint bending tests were performed on the excised tibiae followed by histomorphometric analysis.

Results: Radiographs and DEXA scans indicate that mineralized bone was present in some animals as early as 2 weeks post-operatively. Bone mineral density and bone stiffness increased significantly over the healing time course. Mineralized dense bone filled the defect as early as 4 weeks post operatively. In animals tested at 8 weeks, the mechanical stiffness of the experimental limb was 75% of the matched control contralateral limb.

Discussion: Results of this study appear to indicate future promise of the OP-1 Device to segmental long bone defects in clinical applications.

Conclusion: The OP-1 Device was successful in repairing segmental defects in the tibia of dogs.