Stimulation of bone repair by ultrasound.

The repair of fibular fractures has been accelerated and modified by treatment with ultrasound. Complete bilateral transverse fibular fractures were made in adult female Wistar rats. Twelve were maintained as untreated controls. In seventy rats, one fracture was treated with ultrasound and the other mock-irradiated. Ultrasound was delivered at an intensity of 0.5 W cm-2 (spatial average, temporal peak), pulsed 2 ms on, 8 ms off for 5 minutes on 4 consecutive days during each week of treatment. The effects of treatment for different combinations of weeks, and at frequencies of 1.5 MHz and 3.0 MHz, were compared microradiographically and histologically. Ultrasonic therapy was most effective when given during the first two weeks after injury, that is, during the inflammatory and early proliferative phases of healing (before hard callus formation). Bone repair tended to be of the juvenile type, involving rapid ossification with little cartilage production when treatment was limited to this period.