The effect of therapeutic ultrasound intensity on the ultrastructural morphology of tendon repair.

This study evaluated the effects of ultrasound intensity on the ultrastructural morphology of Achilles tendon healing. Twenty Sprague-Dawley rats with surgically hemi-transected Achilles tendons were randomly assigned into four groups of 0, 0.5, 1.2 and 2 W/cm(2) for ultrasound treatment, with five rats in each group. The treatments were administered with 1 MHz continuous ultrasound daily starting from day 5 after injury. On day 30, ultrathin slides of the Achilles tendons were prepared and examined with transmission electron microscopy. Results showed that the mean collagen fibril size of all treatment groups was higher than the control (p < 0.05). There was no significant difference in the collagen fibril size among the treatment groups. These findings suggest that therapeutic ultrasound can enhance the maturation of collagen fibrils of repairing tendons, and this was not dependent on the intensity of ultrasound applied.