Chronic wounds are a common problem in health care settings. Given the rising incidence of complex, non-healing wounds, there is a need for new adjunct therapies that can aid wound healing. Ultrasound is one such non-invasive treatment modality that is now being considered for its potential therapeutic benefits in wound care.

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What Is Ultrasound Therapy?

Even though the use of ultrasound devices has been well established as a diagnostic tool, wound care specialists and podiatrists are increasingly considering ultrasound therapy for wound healing. Ultrasound refers to the frequency of sound waves that are not audible to human ears, with frequencies over 20,000 hertz. The pressure waves generated by the ultrasound cause the molecules in the medium to vibrate. It is believed that these movements of tissue molecules induced by ultrasound waves could be the reason for their therapeutic effects.

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MIST therapy is one of the most common forms of non-contact, low-frequency ultrasound treatment method used in wound care. The ultrasound waves are transmitted to the tissues by a mist generated by placing saline in front of the transducer of the ultrasound machine. The mist is delivered at a distance of about 5 to 15 mm from the wound. Low-frequency ultrasound therapy stimulates wound healing by improving local blood flow, wound cleansing, and decreasing bacterial burden. 

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Mechanism Of Action

The proposed mechanism through which ultrasound therapy improves wound healing is “cavitation”. Cavitation results in the breakdown and erosion of devitalized tissue present in the wound bed. Therefore ultrasound therapy improves wound healing through debridement. Unlike other forms of debridement, ultrasound debridement is painless and might be better tolerated by patients. 

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It is also suggested that ultrasound therapy can reduce the bacterial bioburden of the wound. The energy from ultrasound waves penetrates deep into the tissues and kills the bacteria that are present. As the presence of bacterial biofilms can impede wound healing, the antiseptic effect of ultrasound therapy might have a beneficial effect on wound healing. Other suggested mechanisms for the therapeutic effects of ultrasound therapy on wound healing include stimulation of cell division, angiogenesis, and collagen synthesis. Studies suggest that ultrasound therapy reduces the amount of tumour necrosis factor, interleukins, and vascular endothelial growth factors. Ultrasound therapy should be used at least three times per week for a maximal benefit.

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Therapeutic Effects Of Ultrasound Therapy 

Ultrasound therapy has shown promising results in wound care. Some of the main therapeutic effects of ultrasound therapy that wound care specialists and podiatrists need to be aware of include:

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• Decreased Wound Slough: The use of ultrasound therapy has been linked with a significant reduction in wound exudate and slough. It might also help to reduce skin edema, odor, and signs of infection at the wound site.
• Wound Closure: Research suggests that ultrasound therapy has a positive effect on the rate of wound closure. One study reported a reduction in wound size of about 85.2% over 7 weeks with the use of ultrasound therapy. Ultrasound therapy might also help to reduce the healing time for wounds.
• Pain Relief: Unlike other popular methods of wound debridement, ultrasound therapy is a painless procedure. In addition, MIST therapy has been linked with pain relief in patients with ischemic ulcers. Another study reported a 79% reduction in subjective pain scores with ultrasound therapy.
• Decreased Wound Bioburden: ultrasound therapy reduces the bioburden of chronic wound beds. As the presence of biofilm is a known impediment to wound healing, the reduction of wound bioburden improves the healing time.

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Contraindications

Ultrasound therapy should be avoided in the following situations:

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• Malignancy
• Acute infection 
• Ischemia
• Thrombo-embolic disease
• Electrical implants or pacemakers

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In addition to the above-mentioned conditions, ultrasound therapy should also be avoided over sensitive areas such as the eyes, genitals, and abdomen. If a patient is experiencing increased pain with ultrasound therapy, it should be discontinued.

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Limitations

Clinical studies suggest that ultrasound therapy has the potential to improve healing time. In addition, ultrasound therapy has also been found to be promising for deep wounds. However one of the main limitations of ultrasound therapy is the determination of the exact dose that would produce a therapeutic effect. Moreover, there is no consensus regarding the efficacy of ultrasound therapy in the treatment of chronic wounds. As a result, ultrasound therapy is currently not included in standard wound care practice.

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