Effect of therapeutic ultrasound on endochondral ossification.

The effect of therapeutic doses of ultrasound was tested on endochondral ossification of in vitro developing metatarsal long bone rudiments of 16- and 17-day-old fetal mice. Bone growth, calcification and resorption following exposure to several doses of pulse-wave (PW) or continuous-wave (CW) ultrasound were examined. PW was applied at intensities between 0.1 W cm-2 and 0.77 W cm-2 (Isatp) and CW intensities were 0.1 W cm-2 or 0.5 W cm-2 (Isata). After 1 week of culture, the metatarsal long bone rudiments were fixed and paraffin sections were prepared for histological evaluation and for measurement of the relative contribution of the various cartilage zones to the total bone length. In contrast to treatment with CW ultrasound, treatment of 16-day-old metatarsal long bone rudiments with PW ultrasound resulted after 4 days of culture in significantly increased longitudinal growth. Histology revealed a significant increased length of the proliferative zone, whereas the length of the hypertrophic cartilage zone was unaltered. This might indicate that proliferation of the cartilage cells is stimulated without influence on cell differentiation.