Muscle and Tendon Heating Rates with Therapeutic Ultrasound in Horses

OBJECTIVE: To (1) determine the temperature change in equine tendon and muscle during therapeutic ultrasound and (2) develop guidelines for treating horses for muscular or tendinous injury using therapeutic ultrasound. STUDY DESIGN: Experimental, in vivo study. ANIMALS: Adult horses (n = 10). METHODS: Thermistors were inserted in the superficial and deep digital flexor tendons (SDFT and DDFT) of the thoracic limbs of 10 adult horses. On the left, 3.3 MHz therapeutic continuous ultrasound was done for 10 minutes at an intensity of 1.0 W/cm² and for the right thoracic limb at 1.5 W/cm². Thermistors were placed at 1 cm, 4 cm, and 8 cm depths in the epaxial muscles of the same 10 horses, for a 20‐minute treatment at a frequency of 3.3 MHz and intensity of 1.5 W/cm². Temperature was recorded before, during, and after treatment. Data were statistically analyzed. RESULTS: Mean temperature rise was 3.5°C in the SDFT and 2.5°C in the DDFT at the end of the 1.0 W/cm² treatment (P = .94) and 5.2°C in the SDFT and 3.0°C in the DDFT at the end of the 1.5‐W/cm² treatment (P = .48). Mean temperature rise in epaxial musculature was 1.3°C at a depth of 1.0 cm, 0.7°C at 4.0 cm, and 0.7°C at 8 cm. CONCLUSIONS: The SDFT and DDFT are heated to a therapeutic temperature using a frequency of 3.3 MHz and intensity of 1.0 W/cm². The epaxial muscles are not heated to a therapeutic temperature using a frequency of 3.3 MHz and an intensity of 1.5 W/cm².