Recombinant human BMPs are soluble factors and tend to diffuse a wa y from the fusion site w hen used alone. Therefore, in larger animal models and human clinical trials, these factors are combined with a carrier matrix that serves to contain the BMPs and release them gradu­ally. These carriers may also act as osteoconductive scaf­folds (130). The ideal carrier system will retain and release the BMP in a controlled fashion, be biocompati­ble, not interfere with normal bony healing, be porous to promote osteoconductivity, be biomechanically suited for the site of implantation, be easy to apply, and be easy to manufacture. Once these BMPs are released, appropri­ately responding osteogenic cells must be present in the area for any significant bone formation to occur. In ani­mal models, such as rabbit, dog, sheep, goat, and nonhu­man primate, researchers have performed posterolateral intertransverse spinal arthrodesis or interbody arthrodesis with cages containing rhBMP-loaded carriers (collagen sponges, autogenous bone graft, DBM, ceramics, degrad­able polymers) (131–138). Uniformly, these studies have reported a dose-dependent increase in bone formation, consolidation, and remodeling with the rhBMP-loaded scaffolds compared to unloaded controls. Multiple ani­mal studies have shown that rhBMP-mediated fusions rates were equivalent or superior to those obtained with autogenous bone graft and may generate fusion masses that are biomechanically stronger and stiffer (43,131, 138–141). The use of BMPs has been shown to obviate the need for decortication of the posterior elements that is usually required to provide endogenous osteoinductive growth factors that are necessary for obtaining postero­lateral fusion (142). The osteoinductive activity of BMPs may even compensate for the inhibitory effects of nico­tine and nonsteroidal antiinflammatory medications on spinal fusions (143–145).