Ultrasound has been a part of the equine vet’s armoury for a number of years and the term covers a wide range of applications that use different wavelengths and intensities.
The purpose of this article is to describe how low-intensity pulsed ultrasound (LIPUS) works, how it differs from other ultrasound therapies in common use in small animal and equine veterinary practice and to describe some of the clinical evidence which supports its use in treating tendon, ligament and fracture injuries.
Ultrasound in all its forms is mechanical energy transmitted into the body as high-frequency pressure waves. Ultrasound signals with intensities between 0.2 and 100 W/cm2 are used in surgical and therapeutic applications. In general, this type of signal results in energy conversion to heat within the tissues, which in turn can increase blood flow to the surrounding tissues.
In contrast, LIPUS uses a much lower intensity pulsed signal (0.03-0.1 W/cm2) and this has been shown to create micromechanical effects which result in biochemical events at the cellular level. LIPUS therapy has been proven to be effective in treating damaged tendon, ligaments and fractures.
The LIPUS acoustic waves travel through skin into soft tissue and bone to the site of the injury and stimulate a biological response at the cellular level. Studies have shown that osteoblasts respond to ultrasound stimulation and initiate an intracellular response that accelerates repair at all stages of the healing process.
The LIPUS waves cause integrins (cell membrane receptors found on all cells) to change shape and cluster on the cell membrane. These receptors are critical in the process of soft tissue and fracture repair as they transmit mechanical forces across the cell membrane and initiate intracellular signalling.
This signalling cascade results in the up-regulation of protein expression, and the release of factors that are essential to fracture healing and soft tissue repair, including PGE-2, COX-2, VEGF, BMP-4, BMP-7 and IGF-1, osteocalcin, osteonectin I, and osteopontin, alkaline phosphatase, MMP-13, and IGF-1.
The evidence base
LIPUS has been in common use in human medicine worldwide for around 20 years and was first introduced to the UK in 2001. A number of medical devices using LIPUS for the treatment of fractures are in use in the NHS and NICE (the National Institute for Health and Care Excellence) recently issued guidance supporting the use of LIPUS in the treatment of long bone fractures after examining some 13 clinical studies involving 1,300 patients.
Amongst many of the striking conclusions from the studies that NICE reviewed was that the use of LIPUS accelerated the healing of fractures on average by 38%. This accelerated healing of fractures using LIPUS has also been observed in animal studies with healing rates observed to be faster at every stage of recovery.
There have also been animal studies showing accelerated healing of soft tissue injuries (for example of medial collateral ligament injuries and Achilles tendon) and a reduction in the rate of re-injury.
How LIPUS differs
LIPUS shares a number of benefits with other ultrasound treatments: it is non-invasive and requires no sedation; however, it differs from therapeutic non-pulsed ultrasound in a number of ways.
Unlike therapeutic ultrasound which uses a continuous waveform, the pulsing of the ultrasound signal (on for two milliseconds, off for eight) produces a biological effect on the cells involved in fracture and soft tissue repair.
The low-intensity pulsed signal generates no discernible heat. This has a dual benefit in that the animal feels no sensation during use and the low-energy output means the application can be done with a small, portable, battery-powered device which is comfortable and practical for animal applications.
Traditional therapeutic ultrasound treatments that generate heat often require the probe to be moved constantly whereas a LIPUS device is stationary and can be placed with great accuracy over the injury. This is particularly advantageous in lower limb bone and soft tissue equine injuries. The LIPUS therapy is easy to use and is administered once a day for 20 minutes.
Common questions
Can LIPUS be used with metal fixation? Because LIPUS does not generate heat it can be used with metal fixation and implants present. How close does the probe need to be to the injury? LIPUS signals have been shown to penetrate between seven and 10cm; ideally, the transducer is placed as close as possible to the injury.
- References for all the clinical trials and research mentioned in this article can be found at www.curar.co.uk.
- Curar is exhibiting Sonivet at the London Vet Show, stand G60.
