Bone neogenesis in domes made of expanded polytetrafluoroethylene: efficacy of rhBMP-2 to enhance the amount of achievable bone in rats

For bone reconstructive purposes, it would be a great advantage to be able to gain bone without grafting. In experimental studies, barrier membranes have been used to accomplish this, however, with limited efficacy. In this study, the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the early onset of bone formation, as well as on the final amount of achievable bone, was investigated in an experimental osteo-neogenesis model. In 60 adult rats, dome-shaped barrier membranes made of expanded polytetrafluoroethylene (Gore-Tex membrane), with an inside volume of approximately 60 mm3, were placed on the left parietal bone. The domes were pretreated according to four different alternatives: (1) filled with autogenous blood only (n = 15); (2) filled with 5 microg of rhBMP-2 in an absorbable collagen sponge carrier (n = 15); (3) filled with 15 microg of rhBMP-2 in absorbable collagen sponge carrier (n = 15); or (4) filled with the absorbable collagen sponge carrier only (n = 15). The animals treated according to each alternative were then divided into three equal groups with five rats in each, and subsequently killed after 3, 6, or 12 weeks. The amount of bone formed within the domes was evaluated by light microscopy and computer-assisted image analysis. It was found that the amount of newly formed bone could be enhanced by approximately 100 percent by simultaneous implantation of rhBMP-2, irrespective of dose. The early onset of bone formation was, however, not affected by the rhBMP-2 supplementation. This finding was interpreted as being due to the delivery system used, because as long as the carrier was still present, no significant difference between the treatment groups was observed. The bone formed in domes with carrier implantation, with or without rhBMP-2, displayed more marrow spaces in comparison to controls. The combined treatment with barrier membranes and local delivery of rhBMP-2 may be a useful tool in reconstructive surgery, for instance replacing onlay grafting, especially when a more delicate anatomy is necessary, because membranes can be shaped in multiple ways.