Ultrasound Therapy With High-Pressure Pulses Is Effective to Reduce the Effects of Collagenase-Induced Tendinopathy in Rat's Achilles Tendon

Abstract

ObjectiveWe propose an ultrasonic treatment for collagenase-induced tendinopathy in rat's Achilles tendon using pulses with a low number of cycles, high acoustic pressure and very low duty cycle. MethodsTwenty rats were used to perform the experiment. Four experimental groups of calcaneal tendons were studied: control (n = 6), sham (n = 4), collagenase-induced tendinopathy (n = 8) and ultrasound-treated collagenase-induced tendinopathy (n = 8). Surgical intervention was performed to expose the tendons prior to collagenase injection. A 1 MHz ultrasonic tansducer with a focusing lens was used. Ultrasonic treatments were used with an average total treatment time of 2.5 min, 20-cycle pulses, pressure amplitude p = 7 MPa, and 0.02% duty cycle. Histopathology of the samples was performed to evaluate nuclear density, acute inflammation, and signs of neovascularization. Collagen (types I and III), elastic fibers, and glycosaminoglycans were also analyzed. ResultsNo tendon involvement was found by the surgical process. Ultrasonic treatment is safe, as it does not affect healthy tendons. When collagenase infiltrated animals were treated with US, a clear predominance of type I collagen fibers and a similar collagen ratio profile to that observed in the control and sham groups was observed, with a higher density of elastic fibers compared to the control and sham groups and a significant increase in the density of glycosaminoglycans. ConclusionThe ultrasound treatment proposed reduces the effects of the artificial collagenase lesion to reach the basal level after 45 d.