Chapter 8: Therapeutic Ultrasound in the Management of Diabetic Foot Ulcers
Therapeutic ultrasound is one of the oldest and most widely used electrophysical modalities in rehabilitation medicine. Initially introduced for the treatment of musculoskeletal disorders, ultrasound has gradually gained attention in wound management because of its ability to influence cellular activity, improve tissue repair, and promote healing. In patients with diabetic foot ulcers, where normal wound healing is impaired by peripheral neuropathy, vascular insufficiency, chronic inflammation, and metabolic abnormalities, therapeutic ultrasound offers a promising adjunctive treatment designed to enhance the body’s natural repair mechanisms.
The systematic review that forms the basis of this ebook included one randomized controlled trial investigating therapeutic ultrasound for diabetic foot ulcers. Although only a single study was available, it reported more favorable healing outcomes in the ultrasound-treated group than in the control group. However, the limited amount of clinical evidence prevented definitive conclusions regarding its overall effectiveness, emphasizing the need for further high-quality randomized trials.
Ultrasound refers to sound waves with frequencies higher than the upper limit of human hearing, generally above 20,000 Hertz (20 kHz). Therapeutic ultrasound devices commonly operate at frequencies between 1 and 3 megahertz (MHz). Unlike audible sound, these high-frequency waves penetrate biological tissues, transferring mechanical energy that produces a variety of physiological responses beneficial to healing.
Ultrasound energy is generated by a transducer containing piezoelectric crystals. When an electrical current passes through these crystals, they rapidly expand and contract, producing high-frequency sound waves. These waves travel through a coupling medium, usually a water-based ultrasound gel, before entering the patient’s tissues. The coupling gel eliminates air between the transducer and the skin, ensuring efficient transmission of ultrasound energy.
The biological effects of therapeutic ultrasound are traditionally divided into thermal and non-thermal effects. Both contribute to tissue repair, although non-thermal effects are generally considered more important in the treatment of chronic wounds such as diabetic foot ulcers.
Thermal effects occur when ultrasound energy is absorbed by tissues and converted into heat. Controlled tissue heating increases local blood flow, enhances oxygen delivery, improves tissue elasticity, reduces muscle spasm, and may temporarily decrease pain. While these effects are valuable in musculoskeletal rehabilitation, excessive heating is generally avoided during wound management because damaged tissues are more vulnerable to thermal injury.
The primary therapeutic value of ultrasound in diabetic foot ulcer management lies in its non-thermal effects. As ultrasound waves pass through tissues, they create microscopic mechanical vibrations known as acoustic streaming and stable cavitation. These physical phenomena stimulate cellular activity without significantly increasing tissue temperature.
Acoustic streaming refers to the movement of fluids around cells in response to ultrasound energy. This microscopic fluid movement alters cell membrane permeability, allowing nutrients, oxygen, and signaling molecules to enter cells more efficiently while facilitating the removal of metabolic waste products. Improved cellular transport enhances tissue metabolism and supports wound repair.
Stable cavitation involves the rhythmic expansion and contraction of microscopic gas bubbles naturally present within body fluids. These oscillating bubbles generate gentle mechanical forces that stimulate cellular activity without causing tissue damage. Controlled cavitation has been associated with increased protein synthesis, enhanced cell signaling, and improved tissue regeneration.
Fibroblasts respond particularly well to therapeutic ultrasound. These connective tissue cells are responsible for producing collagen and extracellular matrix proteins that provide structural support for healing tissues. Ultrasound stimulates fibroblast proliferation and increases collagen synthesis, contributing to stronger granulation tissue and improved wound closure.
The systematic review notes that electrophysical therapies have demonstrated the ability to enhance fibroblast activity and promote tissue repair. These biological effects help explain why ultrasound has attracted interest as a potential adjunctive treatment for diabetic foot ulcers.
Angiogenesis is another important target of ultrasound therapy. Formation of new blood vessels is essential for delivering oxygen and nutrients to healing tissues. Chronic diabetic wounds often exhibit poor vascularization because diabetes damages both large and small blood vessels. Experimental studies suggest that therapeutic ultrasound stimulates endothelial cell activity and promotes the release of angiogenic growth factors, encouraging the development of new capillaries within the wound bed.
Improved microcirculation also enhances immune function. Adequate blood flow enables white blood cells to reach the wound more effectively, strengthening the body’s defense against bacterial infection. Better circulation also improves the delivery of antibiotics and nutrients required for tissue repair.
Ultrasound influences the inflammatory process as well. Chronic diabetic wounds frequently remain in a prolonged inflammatory phase characterized by excessive inflammatory mediators, tissue destruction, and delayed healing. Therapeutic ultrasound appears to regulate inflammatory responses by reducing excessive inflammation while preserving the normal immune activity required for wound repair.
Another beneficial effect is stimulation of macrophage activity. Macrophages play a central role in wound healing by removing bacteria and dead tissue while releasing growth factors that stimulate fibroblast proliferation, collagen synthesis, and angiogenesis. Enhanced macrophage function facilitates progression from inflammation to tissue regeneration.
Ultrasound also promotes keratinocyte migration. Keratinocytes are responsible for re-epithelialization, the process by which new skin covers the wound surface. Faster epithelialization reduces the duration of wound exposure and decreases the risk of infection.
Modern therapeutic ultrasound may be delivered in continuous or pulsed modes. Continuous ultrasound produces both thermal and non-thermal effects because energy is delivered without interruption. Pulsed ultrasound delivers energy intermittently, minimizing tissue heating while preserving mechanical stimulation. For chronic wound management, pulsed ultrasound is generally preferred because it emphasizes the beneficial non-thermal effects while reducing the risk of excessive heat generation.
Several treatment parameters influence clinical outcomes. These include ultrasound frequency, intensity, duty cycle, treatment duration, treatment frequency, and transducer movement. Lower frequencies penetrate deeper tissues, whereas higher frequencies are absorbed more superficially. Clinicians select treatment parameters according to wound depth, tissue characteristics, and therapeutic objectives.
During treatment, the ultrasound transducer is moved slowly across the treatment area using circular or overlapping linear movements to ensure uniform energy distribution. Adequate coupling gel is applied throughout the procedure to maintain efficient transmission of ultrasound waves.
Treatment sessions are generally painless. Most patients experience either no sensation or only mild warmth during therapy. Because ultrasound is non-invasive and well tolerated, it can be incorporated easily into comprehensive wound management programs without causing significant patient discomfort.
Patient selection remains important. Therapeutic ultrasound is typically considered for chronic diabetic foot ulcers that have failed to respond adequately to standard wound care. Before initiating treatment, clinicians should ensure that infection is appropriately controlled, necrotic tissue has been removed, vascular supply is sufficient, and effective pressure offloading has been implemented. Ultrasound should always complement rather than replace conventional wound care.
Certain precautions should be observed when using therapeutic ultrasound. It should generally be avoided over areas of active malignancy, untreated osteomyelitis, severe hemorrhage, or directly over electronic implants unless safety has been confirmed. Care should also be exercised when treating patients with impaired sensation, as they may not perceive excessive heat or discomfort.
The systematic review identified only one randomized controlled trial evaluating therapeutic ultrasound in diabetic foot ulcers. Despite the limited evidence, the study reported superior healing outcomes in the experimental group compared with controls. Because of the small number of available studies and differences in treatment methodologies, the authors concluded that further research involving larger patient populations is required before firm clinical recommendations can be established.
One challenge in interpreting the available literature is the lack of standardized treatment protocols. Published studies have used different ultrasound frequencies, intensities, treatment durations, and outcome measures, making direct comparison difficult. Future clinical trials should adopt standardized methodologies to determine the most effective treatment parameters for diabetic foot ulcers.
Recent advances in ultrasound technology continue to improve treatment precision and ease of use. Portable ultrasound devices, computerized treatment systems, and integrated wound care platforms are becoming increasingly available in clinical practice. Future developments may include smart ultrasound systems capable of adjusting treatment parameters automatically based on wound characteristics or combining ultrasound with advanced wound dressings and regenerative therapies.
Therapeutic ultrasound represents a promising adjunctive treatment capable of stimulating multiple biological processes involved in wound healing. By enhancing fibroblast activity, promoting angiogenesis, regulating inflammation, improving microcirculation, and accelerating tissue regeneration, ultrasound may contribute to improved healing outcomes when integrated with comprehensive diabetic foot care. However, current clinical evidence remains limited, and larger randomized controlled trials are necessary to establish its definitive role in routine wound management.
