Journal of Ultrasound in Medicine, Vol 20, Issue 3 197-205, Copyright © 2001 by American Institute of Ultrasound in Medicine
Low-intensity pulsed ultrasound initiates bone healing in rat nonunion fracture model
S. Takikawa, N. Matsui, T. Kokubu, M. Tsunoda, H. Fujioka, K. Mizuno and Y. Azuma
Department of Orthopedic Surgery, Kobe University School of Medicine, Japan.
Low-intensity pulsed ultrasound exposure has been shown clinically to
shorten the fracture repair process and to induce healing of nonunions in
humans, but its mechanism of action remains unclear. In this study we
investigated the effect and mechanism of low-intensity pulsed ultrasound on
nonunion fracture healing in rat tibias. A consistently reproducible
nonunion was produced in rat tibias by muscle interposition without
osteotomy. This model was produced by creating a closed tibial fracture
with only the distal end of the tibialis anterior muscle interposed into
the fracture site. One limb was noninvasively exposed to low-intensity
pulsed ultrasound (a 200-millisecond burst of sine waves of 1.5 MHz,
repeating at 1.0 kHz) for 20 minutes daily. The incident intensity was
approximately 30 mW/cm2. Rats were killed at intervals between 2 and 6
weeks. The events were assessed by radiographs, microfocus X-ray computed
tomograms, and histologic examination. After 6 weeks of exposure, 7 of 14
nonunion fractures showed healing on radiologic assessment. The results of
three-dimensional microfocus X-ray computed tomographic reconstruction and
histologic examination also supported this finding. On the other hand, all
control tibias remained in a state of nonunion during the same period.
These results indicate that low-intensity pulsed ultrasound promotes
healing in the rat nonunion fracture model.