Incisional wound healing: a controlled study of low and high dose ultrasound.

Ultrasound is commonly used by physical therapists, but there is no consensus regarding the most effective therapeutic dose for accelerating healing of open or closed wounds. A controlled, single-blind, posttest experimental study was carried out to compare differences in wound breaking strength and collagen deposition [hydroxyproline (HoPro)]. Forty-eight incisions were surgically induced in three mini Yucatan pigs. Each incision was randomly assigned to a control or an ultrasound treatment group with the sonated incisions further randomly assigned to 5 or 10 days of ultrasound treatment with either high dose ultrasound (HUS) (1.5 W/cm2, continuous mode, 1 MHz, 5 minutes) or low dose ultrasound (LUS) (0.5 W/cm2, pulsed mode, 20% duty cycle, 1 MHz, 5 minutes). Using the nonparametric two-sample Wilcoxon test, the breaking strength was found to be significantly higher in the sonated incisions compared with the control incisions (p < or = 0.02), but there were no significant differences in HoPro. For all groups, the level of HoPro measured the second week was significantly higher (an average of 60%) than measured the first week (p < or = 0.001). A significant interaction was found between the number of days of treatment and the dose of ultrasound. Hydroxyproline was significantly higher in the LUS group compared with the HUS group after 5 days of ultrasound. Both the wound breaking strength and the HoPro levels were significantly higher in the LUS group compared with the HUS group after 10 days of treatment (p < or = 0.02 and 0.01, respectively). The findings from this study suggest that physical therapists can use either LUS or HUS for approximately 1 week to enhance wound breaking strength in an acute incisional wound. However, if the goal is to continue to facilitate collagen deposition and wound strength, then a low dose of ultrasound should be used when treatment is continued for 2 weeks or more.