Muscle and tendon heating rates with therapeutic ultrasound in horses.
Authors: Montgomery Leslie, Elliott Sarah B, Adair H Steve
Journal: Veterinary surgery : VS
Summary
# Editorial Summary: Therapeutic Ultrasound Heating Efficacy in Equine Tissues Montgomery and colleagues conducted an in vivo investigation into how effectively therapeutic ultrasound raises tissue temperature in horses, addressing a fundamental gap in understanding safe and effective treatment parameters for common musculoskeletal injuries. Using implanted thermistors, the researchers measured temperature changes in the superficial and deep digital flexor tendons (SDFT and DDFT) of ten horses treated with continuous 3.3 MHz ultrasound at two intensities (1.0 and 1.5 W/cm²), and in epaxial musculature at varying depths during 20-minute sessions at 1.5 W/cm². The digital flexor tendons reached therapeutically meaningful temperatures—rising 3.5°C (SDFT) and 2.5°C (DDFT) at 1.0 W/cm² intensity, and 5.2°C and 3.0°C respectively at 1.5 W/cm²—suggesting these parameters are suitable for treating tendinous injuries; conversely, epaxial musculature showed minimal heating (1.3°C at superficial depths, declining to 0.7°C at 4 and 8 cm depth), indicating that 3.3 MHz ultrasound at 1.5 W/cm² is inadequate for treating deep muscular pathology. These findings provide evidence-based guidance for practitioners: therapeutic ultrasound can reliably heat flexor tendons to therapeutic thresholds using moderate intensities, but clinicians should recognise that this modality offers limited penetration for treating deep muscular conditions and may require longer treatment durations or alternative protocols for such injuries.
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Practical Takeaways
- •Therapeutic ultrasound at 3.3 MHz and 1.0-1.5 W/cm² is effective for treating superficial and deep digital flexor tendon injuries, achieving clinically relevant temperature increases
- •Do not rely on this ultrasound protocol for treating deep epaxial muscle injuries—deeper muscle tissues do not reach therapeutic temperatures with these parameters
- •Treatment duration of 10 minutes at 1.0 W/cm² appears sufficient for flexor tendon heating; higher intensity (1.5 W/cm²) provides greater temperature rise if tolerated
Key Findings
- •At 1.0 W/cm² intensity, SDFT reached mean temperature rise of 3.5°C and DDFT 2.5°C after 10 minutes of 3.3 MHz ultrasound
- •At 1.5 W/cm² intensity, SDFT reached mean temperature rise of 5.2°C and DDFT 3.0°C after 10 minutes of 3.3 MHz ultrasound
- •Epaxial muscle temperature increases were subtherapeutic: 1.3°C at 1 cm depth, 0.7°C at 4 cm and 8 cm depths with 1.5 W/cm² for 20 minutes
- •3.3 MHz ultrasound at 1.0-1.5 W/cm² effectively heats flexor tendons to therapeutic range but does not achieve therapeutic heating in deep epaxial musculature