An experimental study of pulsed ultrasound for treating skeletal muscle contusions

Objective To evaluate the effects of pulsed ultrasound at different intensities on the healing of standardized contusions in an animal model. Methods Forty-eight 3-month-old, male Sprague-Dawley rats were given experimental contusions of the right gastrocnemius muscle before being divided into four groups randomly ( n =12 in each group): (1) a muscle injury control group (muscle injury without treatment); (2) a muscle injury and pulsed ultrasound (0.25 W/cm2 ) group; (3) a muscle injury and pulsed ultrasound ( 0.5W/cm2 ) group; and (4)a muscle injury and pulsed ultrasound ( 0.75 W/cm2 ) group. Pulsed ultrasound treatment ( frequency 3 mega Hz)was started 24 hours post injury and delivered 5 min daily for 14 days on the injured right hindlimb. At days 4, 7 and 14 after injury, muscle samples were analyzed through hematoxylin-eosin staining and immunohistochemistry for the detection of muscle satellite cells and desmin. Results The average optical density (IOD) of desmin-positive mononucleated cells had increased significantly at days 4, 7 and 14 post injury in the treatment groups compared to the control group, but with no statistically significant difference among the 3 ultrasound treatment groups. Conclusions The pulsed ultrasound treatment played a beneficial role in skeletal muscle regeneration after contusion. There was no significant dose-dependent effect over the intensity range of 0.25-0.75 W/cm2. Key words: Ultrasound; Skeletal muscle contusions; Muscle satellite cells; Proliferation