TRICALCIUM-PHOSPHATE BLOCK (BETA-TCP) IMPREGNATED WITH TRANSFORMING GROWTH FACTOR BETA3: EXPERIMENTAL STUDY IN THE PRIMATE

Abstract

Purpose: A preliminary biomechanical test conducted on cadaver specimens validated a new technique for vertebral bone harvesting for anterior intervertebral grafting of the lumbar spine. A cylinder of autologous bone harvested from a neighboring vertebra was used for the intervertebralimplant. The harvesting site was filled with a bone substitute. The biomechanical tests confirmed good restoration of the vertebral body structure. An in vivo study was conducted in the baboon. A block of tricalcium-phosphate (beta-TCP) impregnated with transforming growth factor beta3 (TGF-beta3) was used to fill the bone gap. The purpose of the present study was: 1) to assess the efficacy of this in vivo technique on a primate model, 2) to validate the surgical technique.

Material and methods: The retroperitoneal approach was used to operate nine baboons. Eighteen bone cylinders were harvested. The harvesting hole was left empty or filled with a 15 mm diameter beta-TCP cylinder, or with a beta-TCP cylinder impregnated with TGR-beta3. Control scans were obtained at three and six months postoperatively. The baboons were sacrificed at 6 months and the vertebral bodies were removed for histology study.

Results: There was no evidence of fracture or loss of vertebral body height. The harvesting holes left empty did not fill, while osteointegration and substantial resorption of the bone substitute was observed in the two other groups. In the group with beta-TCP impregnated with TGF-beta3 the resorption of the cylinder was more complete and signs of prevertebral neoformation of subperiosteal bone, not observed in the beta-TCP group, was observed. There was no neoformation of bone in the spinal canal or in the foramens. The scans showed progressive resorption starting three months postoperatively in the beta-TCP group impregnated with TGF-beta3.

Conclusion: The beta-TCP block used is a very good bone substitute for the primate spine. TGF-beta3 accelerates bone resorption and induces neoformation of subperiosteal bone. The new surgical technique for local harvesting of vertebral bone was validated.