Effect of ultrasound therapy on the repair of gastrocnemius muscle injury in rats

The aim of this study was to evaluate the effect of the pulsed ultrasound therapy (PUT) in stimulating myoregeneration and collagen deposition in an experimental model of lacerative gastrocnemius muscle lesion in 30 Wistar rats. Fifteen rats were treated (TG) daily with 1 MHz pulsed ultrasound (50%) at 0.57 W/cm² for 5 min, and 15 were control animals (CG). Muscle samples were analyzed on postoperative days 4, 7 and 14 through H&E, Picrosirius-polarization and immunohistochemistry for desmin. The lesions presented similar inflammatory responses in both treated and control groups. The areal fraction of fibrillar collagen was larger in the TG at 4 days post-operatively (17.53 ± 6.2% vs 6.79 ± 1.3%, p = 0.0491), 7 days (31.07 ± 7.45% vs 12.57 ± 3.6%, p = 0.0021) and 14 days (30.39 ± 7.3% vs 19.13 ± 3.51%, p = 0.0118); the areal fraction of myoblasts and myotubes was larger in the TG at 14 days after surgery (41.66 ± 2.97% vs 34.83 ± 3.08%, p = 0.025). Our data suggest that the PUT increases the differentiation of muscular lineage cells, what would favor tissue regeneration. On the other hand, it is also suggested that there is a larger deposition of collagenous fibers, what could mean worse functional performance. However, the percentage of fibers seems to have stabilized at day 7 in TG and kept increasing in CG. Furthermore, the collagen supramolecular organization achieved by the TG is also significant according to the Sirius red staining results.