Pulsed low intensity ultrasound enhances mineralisation in preosteoblast cells

Pulsed low intensity ultrasound has been shown to be highly efficacious in the treatment of nonunion fractures and in the acceleration of fresh fracture healing. MC3T3-E1 subclone 14 cells were cultured for up to 25 days either with or without a daily treatment with low intensity pulsed ultrasound. It was determined that, on day 10 there was a dramatic increase in alkaline phosphatase and MMP-13 mRNA levels detected in ultrasound-treated cultures compared with untreated controls. The activity of alkaline phosphatase was significantly increased at days 6, 8 and 10. On day 10, the amount of mineralisation within cultures, assessed using alizarin red staining, was significantly increased in ultrasound-treated cultures compared with untreated controls. These results suggest that one of the mechanisms that low intensity pulsed ultrasound has on fracture repair is to enhance the process of endochondral ossification where the soft callus is converted to mineralised hard callus.