Selective retention of bone marrow-derived cells to enhance spinal fusion.

Connective tissue progenitors can be concentrated rapidly from fresh bone marrow aspirates using some porous matrices as a surface for cell attachment and selective retention, and for creating a cellular graft that is enriched with respect to the number of progenitor cells. We evaluated the potential value of this method using demineralized cortical bone powder as the matrix. Matrix alone, matrix plus marrow, and matrix enriched with marrow cells were compared in an established canine spinal fusion model. Fusions were compared based on union score, fusion mass, fusion volume, and by mechanical testing. Enriched matrix grafts delivered a mean of 2.3 times more cells and approximately 5.6 times more progenitors than matrix mixed with bone marrow. The union score with enriched matrix was superior to matrix alone and matrix plus marrow. Fusion volume and fusion area also were greater with the enriched matrix. These data suggest that the strategy of selective retention provides a rapid, simple, and effective method for concentration and delivery of marrow-derived cells and connective tissue progenitors that may improve the outcome of bone grafting procedures in various clinical settings.