Does in vitro low-intensity pulsed ultrasound stimulate endochondral ossification?

The objective of this study was to examine the effects of low-intensity pulsed ultrasound treatment of murine fetal metatarsal (MT) bone anlagen in vitro. Metatarsal preparations of 17 mice fetuses stage 17.5 dpc were dissected en bloc and cultured for 7 days with and without low-intensity ultrasound stimulation. The total length of the metatarsal rudiments and the length of the calcified diaphysis were measured at days 1, 3, 5, and 7. After 7 days in culture, histological and histomorphometric analyses were performed. The increase in total length of the metatarsal bones and in length of the calcified diaphysis during in vitro culture was not affected by ultrasound treatment. Histological analysis of the MT preparations after 7 days of in vitro culture showed a healthy appearance of all specimens and revealed no differences in the general histological outcome between the stimulated and control groups. All histomorphometric parameters were unaffected by ultrasound stimulation, except for the length of the proximal hypertrophic zone which was significantly shorter in the stimulated bones compared to controls (p=0.043). Our results illustrate no stimulating effect of ultrasound treatment on endochondral ossification which may be based on different experimental conditions in comparison to other studies demonstrating a positive effect of sonication. Thus, ultrasonically induced stimulatory effects on endochondral ossification seem to be highly dependent on experimental conditions.