Transforming growth factor beta and bone morphogenetic protein 2 for bone ingrowth: A comparison using bone chambers in rats

We compared the ability of transforming growth factor beta 1 (TGFβ1) and bone morphogenetic protein 2 (BMP-2) to increase the penetration distances for fibrous tissue and bone into porous coralline hydroxyapatite. Forty-four rats received pairs of titanium bone chambers implanted bilaterally in their proximal tibiae. These chambers allow tissue ingrowth from one end of a long cylinder, so that ingrowth distances along the cylinder axis can be measured. Since bone never grows as far as fibrous or undifferentiated mesenchymal tissue, we measured both total tissue ingrowth and bone ingrowth distances. All chambers were implanted with cylinders of porous hydroxyapatite (Interpore 200). The hydroxyapatite cylinders were treated with either 1, 33, or 1000 ng of TGFβ1 or BMP-2 prior to implantation, and compared with untreated contralateral control implants at 6 weeks. The bone ingrowth distance into the porous hydroxyapatite showed a trend toward inhibition with TGFβ1 as compared to untreated controls (p< 0.08), and there was a negative correlation between TGFβ1 dose and ingrowth distances for both bone (p< 0.01) and total tissue (p< 0.01). BMP-2 greatly increased bone (p< 0.001) and total tissue (p< 0.001) ingrowth distances.