The inhibitory effect of pulsed ultrasound on skeletal muscle fibrosis after injury in elderly rats

Objective To explore the inhibitory effect of pulsed ultrasound on skeletal muscle fibrosis after injury. Methods Thirty elderly male rats with gastrocnemius muscle injury were divided into an ultrasound group (UG) and a control group (CG) using a random number table. The injured muscles in the UG were treated using pulsed ultrasound (frequency 1 MHz, average strength 40 mW/cm2, duty cycle 20%) for 10 min daily from day 3 after the injury. The CG was given no treatment. On days 3, 7, 14, 21 and 28 after the injury, histological and immunohistochemical analyses of the gastrocnemius muscles of both groups were performed. Results The collagen fiber mean optical density of the muscles increased gradually after the injury and reached its peak on day 21. It was significantly lower in the UG than in the CG on each test day. The expression of α-SMA increased gradually after the injury, but it too remained significantly lower in UG than that in CG. Conclusion Pulsed ultrasound may reduce collagen formation and α-SMA expression in injured skeletal muscle, and then inhibit muscle fibrosis. Key words: Pulsed ultrasound; Skeletal muscles; Fibrosis