Growth factor modulation of distraction osteogenesis in a segmental defectmodel

A model was established in 39 dogs to investigate the growth factor modulat ion of regenerate bone in distraction osteogenesis. A segment of the diaphy sis of the radius was resected unilaterally, An osteotomy was made proximal to the segmental defect to create a transport segment. A monolateral exter nal fixator was applied. After a latency period, the segment was transporte d across the defect. One week after the transport assembly contacted the di stal pin clamp, an ipsilateral osteotomy of the proximal ulna was performed . In 20 dogs, transforming growth factor-beta was injected into the regener ate bone halfway through the transport period. Four dogs were sacrificed be fore docking, when the regenerate bone was still immature. In specimens har vested halfway through the transport period, evidence was found of intramem branous ossification during distraction. In specimens harvested after the t ransport assembly contacted the distal pin clamp, evidence was found that t he mature regenerate formed by endochondral ossification. Therefore, a comb ined mechanism of ossification is proposed for this segmental defect model that includes mechanical stimulus for bone differentiation. The onetime adm inistration of transforming growth factor-beta retarded the formation of a stable, united regenerate. It is concluded that transforming growth factor- beta caused an effect opposite to that which was desired.