Abstract

Data from animals have revealed that osteogenic protein-1 induces solid intertransverse process fusion more reliably than autograft, and has motivated the question: What is the difference in the fusion bed environment engendered by the addition of osteogenic protein-1? To address this question, an established New Zealand White rabbit model of spinal arthrodesis was used to evaluate the effect of iliac crest autograft, and alternatively osteogenic protein-1, on cytokine gene expression in the developing spinal fusion mass. The autograft group and the osteogenic protein-1 group had a similar pattern of gene expression for most of the cytokines investigated, highlighting the finding that the application of one bone morphogenetic protein to the fusion bed results in nearly the same gene expression as that resulting from application of autologous bone. Some differences in cytokine expression were observed at the fusion bed with the addition of osteogenic protein-1. The increased level of expression of particular osteogenic, chondrogenic, and angiogenic growth factors at the later stages of fusion may be responsible for the improved rate of solid fusion with osteogenic protein-1 as compared with autograft alone. Sequences for bone morphogenetic protein-5 and bone morphogenetic protein-7 were determined, and their respective expression in the developing spinal fusion mass was observed for the first time.