The current gold standard of therapy for treatment of tibial fracture nonunion is iliac crest bone graft. However, this intervention is associated with significant morbidity to the donor site. Research into alternative interventions highlights the role of mesenchymal stem cells (MSCs). MSCs are capable of differentiating into mature, organized osseous tissue as well as recruiting local vascular cells. However, there are few prospective studies demonstrating the therapeutic potential of MSCs in fracture nonunion. The proposed study is a multicenter single-blinded controlled study of MSC application compared to iliac crest bone graft in the setting of fracture nonunion of the tibia. The study subjects will be evaluated at each return to care with mRUST radiographic scoring as well as Short-Form 12 evaluation of general health. These results will be correlated with MSC concentrations as assessed by FACS analysis. The data from this study will help to characterize MSCs as a possible therapeutic intervention in fracture nonunion.