Abstract
Objective: To (1) characterize the warming pattern of canine calcaneal tendons during and after four different therapeutic ultrasound (US) treatment protocols, and (2) to quantify changes in tarsal flexion immediately after therapeutic US treatment, and following return to baseline temperature.Design: A prospective, crossover, experimental study.Animals: Ten adult hound-type breed dogs.Procedure: Therapeutic ultrasound (3.3 MHz) was applied to one calcaneal tendon of anesthetized dogs using four different settings applied in random fashion (1.5 and 1.0 W/cm2 continuous, and 1.5 and 1.0 W/cm2 pulsed US) while the temperature of the tendon was recorded by a thermistor needle. The contralateral tendon was used to compare extensibility of the treated soft tissues by measuring changes in tarsal joint flexion before, immediately after, and 5-min after continuous US treatment at 1.5 W/cm2 for 10 min.Results: The greatest increase in tendon temperature occurred with continuous US at 1.5 W/cm2. Pulsed US resulted in minimal tendon heating. Most of the increase in tissue temperature occurred within the first 3 min of US application. Tarsal flexion increased significantly following US treatment; however, it returned to near baseline within 5 min after US was discontinued.Conclusion and Clinical Relevance: Continuous US of the calcaneal tendon at 1.5 W/cm2 resulted in the greatest increase in tissue temperature while maintaining a safe range of tissue temperature increase. Tendon heating and heat dissipation were slightly different from what has been reported for muscle. Our results suggest that 3.3 MHz US applied to tendon for >3 min may not provide additional tissue temperature increase. Therapeutic US resulted in increased tarsal flexion, however the change was only transitory. Therefore, stretching exercises should be performed during and immediately after US.
Highlights
Therapeutic ultrasound (US) is a commonly used modality for the rehabilitation of soft tissues of the musculoskeletal system
Experimental procedures were approved by the University of Tennessee Animal Care and Use Committee
The second phase assessed the effect of one protocol on the extensibility of the calcaneal tendon and related soft tissues
Summary
Therapeutic ultrasound (US) is a commonly used modality for the rehabilitation of soft tissues of the musculoskeletal system. The physical effects resulting from compression and rarefaction of energy are referred to as acoustic streaming and acoustic cavitation. These non-thermal phenomena have been shown to accelerate the inflammatory phase of wound healing [1], promote ion transport, increase cellular permeability [2], increase fibroblast protein synthesis [3, 4], and promote shifts in extracellular ion concentration gradients [5]. As the US beam penetrates into the tissues, molecules absorb energy from the waves, which increases the rate of molecular oscillation, and results in tissue warming. Previous research has demonstrated a correlation between the magnitude of temperature increase and the thermal effects produced. An increase of 4◦C is required to increase collagen tissue extensibility, improving the flexibility of the tissues, requiring less force to stretch tissues [6, 8,9,10,11]
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