Effects of therapeutic ultrasound on fetal limb development in an organ culture system

Abstract

The use of therapeutic ultrasound by physical therapists on pregnant women is currently contraindicated due to unknown effects it may have on the developing fetus. This study examines the effects of therapeutic ultrasound (US) on the development of fetal mouse limbs in an in vitro organ culture system by placing mouse limbs (N 241) in a culture and exposing them to daily US treatments lasting 5 minutes for 4 days at a frequency of 3 MHz and one of the following intensities (SATP) : 1.0 W/cm2 and 100% duty cycle (CONT), 1.0 W/cm2 (1.0 PULSED) or 0.1 W/cm2 (0.1 PULSED) at 20% duty cycle, and sham controls (SHAM). Limbs were examined histologically and serial cross sections were rated by blinded observers using a predetermined criteria for relative limb development. The percentage of nonviable limbs was elevated in limbs treated with 1.0 PULSED ultrasound and was two times higher after treatments with CONT ultrasound. Quantitative analysis of collagen distribution was performed using computerized image analysis of Sirius Red/Fast Green stain. Collagen distribution within the dermis and bone of fetal limbs was significantly increased by the lowest dose of pulsed US (0.1 PULSED) and tended to be attenuated by treatment using higher intensities of US (p < 0:05). A signifi cant elevation in histological scores of limb development was produced in both the bone and dermis by 1.0 PULSED US and in the bone region following CONT US administration. Both pulsed and continuous US treatment can cause signifi cant changes in the histological appearance and collagen distribution of day 14 and day 18 fetal mouse limbs when treated in vitro.