Effect of Low‐Intensity Pulsed Ultrasound on Bone Morphogenetic Protein 7–Induced Osteogenic Differentiation of Human Nonunion Tissue‐Derived Cells In Vitro

OBJECTIVES: Low-intensity pulsed ultrasound (US) has been shown to have positive effects on the healing of nonunions, and bone morphogenetic protein 7 (BMP-7) is known to be a strong stimulator of osteogenic differentiation. Recently, we showed that nonunion tissue contains multilineage mesenchymal progenitor cells, suggesting that nonunion tissue-derived cells may play an important role during the healing process of nonunions. In this study, we investigated whether low-intensity pulsed US promoted BMP-7-induced osteogenic differentiation of nonunion tissue-derived cells in vitro. METHODS: Nonunion tissue-derived cells were isolated from 7 patients. The cells were divided into two groups: (1) BMP-7 alone, consisting of nonunion tissue-derived cells cultured in osteogenic medium containing BMP-7 without low-intensity pulsed US treatment; and (2) BMP-7 + low-intensity pulsed US, consisting of nonunion tissue-derived cells cultured in osteogenic medium containing BMP-7 with low-intensity pulsed US treatment. The osteogenic differentiation potential and proliferation of nonunion tissue-derived cells were compared between the two groups. RESULTS: The alkaline phosphatase activity, gene expression levels of alkaline phosphatase and runt-related transcription factor 2, and mineralization were higher in the BMP-7 + low-intensity pulsed US group than in the BMP-7-alone group. There was no significant difference in cell proliferation between the two groups. CONCLUSIONS: These findings show a significant effect of low-intensity pulsed US on the osteogenic differentiation of nonunion tissue-derived cells induced by BMP-7. This study may provide substantial evidence for the clinical combined application of BMP-7 and low-intensity pulsed US for nonunion treatment.