The influence of ultrasound on the mechanical properties of healing tendons in rabbits

Abstract

Background Therapeutic ultrasound is commonly used for treatment of injuries to tendons, ligaments and joint capsules. Opinions still differ, however, as to the beneficial effects of ultrasound treatment of the above-men-tioned conditions. Methods We studied the effect of various ultrasound intensities on the healing of tenotomized, sutured and immobilized Achilles tendons of adult rabbits. Different intensities of pulsating ultrasound (0, 50, 100, 200, 500, 750, 1 000 and 2 000 mW/cm2, frequency 3 MHz) were given over the healing tendons for 5 min daily, using a gel as the coupling agent between the ultrasound probe and the skin. Eleven days after the tenotomy, the healing tendons were analyzed in a materials testing machine. Results The extensibility of the healing tendons was greater after sonication at an intensity of 2 000 mW/cm2than after 50 mW/cm2. We found no significant effect on the load at rupture and normalized load at rupture of the ultrasound-treated healing tendons compared with mock-sonicated healing tendons. A gradual decline was observed, however, in the stiffness and collagen content of the healing tendons with increasing intensity of the ultrasound treatment. Interpretation The pulsating ultrasound treatment applied did not improve the mechanical properties of healing Achilles tendons at day 11 after the operation. On the other hand, a slight decline in stiffness was observed with increasing intensity of ultrasound treatment.