Evaluation of posterolateral spinal fusion using mesenchymal stem cells

Study Design. An animal study to achieve posterolateral intertransverse process spine fusion using mesenchymal stem cell (MSC). Objective. We investigated the effectiveness of graft material for spinal fusion using a rabbit model by examining the MSC with or without osteogenic differentiation. Summary of Background Data. Posterolateral spinal fusion is commonly performed. Autogenous bone graft is the gold standard, although various problems are reported. Recently, MSCs from bone marrow have been studied in various fields. Thus, we supposed that MSCs have the ability to spinal fusion. Methods. Twenty-four mature male Japanese white rabbits (weight, 3.0-4.0 kg) were divided into 4 groups: 1) autologous bone (AG), 2) hydroxyapatite (HA), 3) MSC, and 4) osteogenic MSC (OMSC). Each group underwent fusion of the intertransverse processes. The lumbar spine was harvested en bloc, and the fusion mass was evaluated radiographically, by manual palpation test, and by histologic analysis at 6 weeks after surgery. Results. Fusion success or failure was assumed based on the results from manual palpation of the harvested spine. Four of 5 rabbits in the OMSC group, 4 of 6 rabbits in the AB group, 2 of 6 rabbits in the MSC group, and none of 6 rabbits in the HA group achieved fusion. In the OMSC group and AG group, new bone formation was observed histologically. In the HA group, fibrous tissue and cartilage were observed and there was no new bone. In the MSC group, less mature bone formation was present in the grafted fragments. Conclusion. The present study suggested that MSCs that have been cultured with osteogenic differentiation medium may induce the formation of new bone in experimental spinal fusion. Further studies are needed to determine the suitable level of osteogenic differentiate of MSC as well as the most appropriate carrier for MSC.