Using low-intensity pulsed ultrasound to improve muscle healing after laceration injury: an in vitro and in vivo study.

The purpose of this study was to determine whether low-intensity pulsed ultrasound (LIPUS) could enhance the regeneration of myofibers and shorten the healing time in injured muscle. NIH C2C12 cells, a well-known myoblastic cell line, are subclones derived from the mouse myoblast cell line established from normal adult C3H mouse leg muscle. The cells differentiate rapidly and produce extensive contracting myotubes expressing characteristic muscle proteins. We exposed C2C12 cells to LIPUS therapy using the EXOGEN 2000+ system ultrasound apparatus (Exogen Inc., Piscataway, NJ, USA) with a total treatment of 20 min every 24 h. At intervals of 2, 4, 6 and 8 days, cell growth was measured by the increase in cell number and western blot analysis of myogenin and actin. Forty mice (C57BL10J+/+) were divided into five groups of eight animals each and used in the published laceration injury model. The gastrocnemius muscle of the left leg was lacerated in all the animals. The control group (sham ultrasound) did not undergo LIPUS therapy. The ultrasound 7-, 14-, 21- and 28-day groups (only changing the number of days during which the ultrasound was applied to the injured muscle) were treated with LIPUS (20 min/day) for 7, 14, 21 and 28 consecutive days, respectively. All animals were sacrificed at 4 weeks after the injury. Evaluation methods included muscle regeneration and muscle contractile properties. LIPUS therapy produced a significantly higher proliferative rate and cell number at days 6 and 8 (p < 0.05). Densitometric evaluation revealed an increase in myogenin and actin proteins in cells treated with LIPUS in the 4-, 6- and 8-day groups. The regeneration of myofibers, fast-twitch and tetanus of LIPUS-treated muscles (21 and 28 days) was significantly greater relative to control muscles. There was no major strength difference between the normal non-injured muscle and the group treated with LIPUS for 28 days. In conclusion, this was the first experimental study to show that LIPUS therapy is able to enhance the regeneration of myofibers with better physiologic performance in injured mice muscles after laceration, especially prior to postoperative week 4. Findings of this study demonstrate a scientific basis for future clinical trials and establish an indication for LIPUS in enhancing muscle healing after laceration injury.