Ultrasonic Debridement For Wounds: Where Are We Now?

Whether it is the eradication of biofilm or treating wounds in locations not conducive to sharp debridement, ultrasonic debridement can be a key tool for promoting improved wound healing. These authors discuss their experience with this modality and the evolution of the technology.

Chronic wounds have plagued the quality of life for millions of patients and increased their medical expenditures. Venous insufficiency wounds alone are responsible for about 70 percent of non-healing wounds in the lower limbs.¹ In 2011, 366 million people were diagnosed with diabetes and the prevalence of those individuals developing ulceration is about 1 to 4.1 percent annually.²

While the fundamental principle of wound care is regular and frequent wound debridement, wounds are often too painful for clinic debridement, are in precarious places on the foot/ankle or they are within a deep cavity.³ There are several treatment modalities for chronic wound debridement including surgical, enzymatic, maggot, mechanical or autolytic debridement.⁴ The purpose of this article, however, is to discuss low frequency ultrasound debridement and how it has progressed since its original design to better address the treatment of wounds in the foot and ankle.

The surgical debridement of nonviable tissue is essential in the wound care process. While sharp debridement with or without pulse lavage is the most common method, the use of ultrasonic debridement is a more recent option that one should consider. Physicians originally developed ultrasonic debridement for dentistry in the 1950s and later adapted it for debulking soft tissue and dissecting bone.⁵

For the foot and ankle surgeon, ultrasound debridement is a valuable modality for several reasons. It aids in biofilm destruction and removal; allows for surgical preparation of a wound bed prior to initiation of advanced wound care therapies; and facilitates easy excision of all non-viable soft tissue and bone. However, the foot and ankle surgeon must remember that ultrasonic debridement cannot replace a thorough workup. This includes assessment of the wound etiology, the vascularity to the area in question, the presence or absence of infection, the management of foot deformities, and the use of proper offloading strategies. Once one determines the need for more aggressive wound debridement after the patient has failed conservative management, ultrasonic debridement can be a great addition to the surgeon’s treatment armamentarium.

The indications for ultrasonic debridement therapy include chronic, slow or non-healing ulcers that would benefit from OR debridement. These include a wide variety of etiologies including diabetic ulcerations, venous stasis wounds, pressure ulcers, traumatic wounds and burns. Ultrasonic debridement often serves as a stepping stone prior to the beginning of new adjunctive therapies to facilitate healing. Contraindications are relatively limited and are similar to contraindications of sharp debridement, namely lack of perfusion to the foot as demonstrated through non-invasive studies or intraoperative evaluation.⁶

When using ultrasonic debridement devices, be sure to wear the appropriate personal protective equipment. There is a potential for a fine mist of saline to mix with blood products of the patient that may spray into the air around the surgical field. However, standard sterile gowning alleviates this concern.

What You Should Know About Acoustic Streaming And Cavitation
Low frequency ultrasonic therapy occurs when an electrical current converts into sound waves at frequencies that range from 20 to 40 kHz. The primary mechanisms for the function of ultrasonic debridement devices are “acoustic streaming” and “cavitation.” Acoustic streaming is the steady mechanical force that goes directly to the tissues from the fluid medium emitted from the probe (i.e. sterile saline).⁷ It is important, therefore, for the operator to ensure the tip of the device is in direct contact with the area of interest for maximum effectiveness.

Cavitation is the other mechanism of action through which ultrasonic debridement theoretically works. Cavitation is a phenomenon in which the fluid medium creates vapor bubbles that form and collapse near the tissue surface, effectively disrupting and debriding the exposed tissue. In theory, these mechanisms create a bacteriostatic effect and stimulate healing to the wound by promoting cell division, angiogenesis, release of growth factors and ultimately stimulation of collagen synthesis.⁷ Other theories relate to dynamic reciprocity whereby ultrasonic debridement alters a chronic wound and converts it back into an acute wound because of inflammatory cells.

An additional advantage of ultrasonic debridement is a reduced threat of thermal necrosis to nearby healthy cells. Since there is less thermal danger at 20 to 40 kHz, this can allow for better healing of acute and chronic wounds.⁴

A Viable Adjunct For Wound Healing
Researchers have classically described chronic wounds as wounds that fail to decrease in volume by approximately 50 percent within one month’s time or decrease at 10 to 15 percent per week in order to achieve closure within 12 weeks of the initiation of treatment.⁸ Furthering this idea was the work of Lavery and colleagues in 2008.⁹ In a study of 162 patients with diabetic foot ulcers following amputation, the authors demonstrated that the healing area after one week of treatment was indicative of healing at 16 weeks. Panuncialman and Falanga found debridement to be critical in transforming a chronic wound into an acute wound.¹⁰

Several studies compare the effectiveness of ultrasonic debridement to sharp debridement, which physicians have considered the standard method of wound debridement. In one study by Ennis and colleagues, 40.7 percent of 55 patients with diabetic foot ulcers treated with 40 kHz of ultrasound debridement healed by 12 weeks in comparison to only 14.3 percent of patients who received standard of care treatment via offloading, sharp debridement and wound evaluation.¹¹ Voigt and coworkers found that patients who had low-frequency ultrasonic debridement demonstrated early healing at less than five months for venous stasis and diabetic foot ulcers, but there was no significant difference between the sharp debridement group and the ultrasonic debridement group at six months.⁴

Ultrasonic debridement is also beneficial for treating wounds that are in locations that are difficult to access with sharp debridement and those wounds with deep cavities. Deep cavities may harbor bacteria and if one does not eradicate the bacteria with debridement, these wounds will almost always have difficulty healing. Finally, ultrasonic debridement is also beneficial in the debridement of necrotic tissue on avulsed skin flaps following traumatic degloving injuries.¹² With the current literature, ultrasonic debridement is clearly a viable adjunct for wound healing in a variety of clinical settings.

How Ultrasound Debridement Can Address Biofilm And Facilitate The Use Of STSGs
Biofilms are a particularly difficult obstacle in the treatment of chronic wounds. A biofilm is an aggregation of microbial cells that are enclosed in a matrix of primarily polysaccharide material. This biofilm matrix may also contain noncellular materials such as mineral crystals, corrosion particles, clay or silt particles, or blood components, depending on the environment in which the biofilm has developed. Research shows that as much as 65 percent of human infections are associated with biofilms.¹³

In order to form a biofilm, bacteria must participate in “quorum sensing,” which is a chemical signaling process that acts on the overall phenotype through a series of receptor signaling pathways. Once in the biofilm structure, bacteria become fairly resistant to antimicrobials and antibiotics, and are therefore increasingly difficult to treat. This may in part be due to an antiphagocytic property within the biofilm, which causes the host leukocytes to become ineffective.¹⁴ However, ultrasonic debridement in theory disrupts quorum sensing in biofilms and therefore leads to decreased coordinated virulence, although more research needs to occur.¹⁴

Once one has removed biofilm, wounds and ulcerations can still be difficult to close primarily and it may not be in the patient’s benefit to have a wound close by secondary intention. When one uses ultrasonic debridement in combination with a definitive wound closure plan, it is a good adjunct for wound bed preparation prior to placement of split thickness skin grafts (STSGs), which are excellent for covering open wounds. In order for a STSG to be successful, the wound base should be granular without visible tendon or bone, no sloughing or exudates in the wound, no necrotic tissue, peripheral arterial disease or signs of local or systemic infection.¹⁵ In a 2010 retrospective review of 142 patients, Blume and colleagues found that the primary contributor to graft failure was infection, which emphasizes the importance of biofilm removal prior to STSG application.¹⁶

At our institution, we utilize the SonicOne (Misonix) ultrasonic debridement system in a variety of settings. This system is compact and has easy OR setup, allowing for the most efficient use of our time.

Our settings include superficial debridement of both grossly infected and non-infected wounds that are considered chronic or slow healing. We perform the ultrasonic debridement initially prior to placement of a synthetic skin graft. By doing this, it serves to be an excellent form of wound bed preparation, even allowing for us to flatten the often uneven surface in ulcerations on the foot and ankle.

Following ultrasonic debridement, we place a bilayered silicone bioengineered alternative skin graft in order to allow wound granulation prior to the final step in the process, which is the harvesting and application of a STSG.

Other Potential Uses For Ultrasonic Debridement
Another setting in which one can use this technology is with superficial debridement of necrotic bone. While this is not a tool to formally resect all non-viable bone, it surely can obliterate bone to a level of bleeding, which will again aid in healing of a wound. Ultrasound debridement can also be useful to remove any excessive scar tissue that may be in the area as well. While our evidence is anecdotal at this point, we have found increasingly favorable results in using ultrasonic debridement to prepare the wound bed for more advanced closure techniques.

Final Thoughts
The uses of ultrasonic debridement in chronic wounds are expansive and have changed since the technology’s inception. Of course, ultrasonic debridement cannot replace the astute physician’s workup. Physical examination and determination of the wound etiology direct care. One should use surgical debridement as a tool when it is necessary and not as a first-line treatment choice.

There are currently several available ultrasonic devices for wound debridement. These modalities include Versajet (Smith & Nephew), the Sonoca line (Söring), the SonicOne O.R. system (Misonix) and the Qoustic Wound Therapy System (Arobella Medical). The OR setup of many of the aforementioned devices are similar in that they include a portable reusable ultrasonic generator with foot pedal activation, a handpiece and a tubing assembly in conjunction with sterile saline.¹¹ Systems differ, however, in the shape of the handpieces, the amount of saline required for use and the frequency at which they are set.
Regardless of the device, ultrasonic debridement has proven to be a viable option for the debridement of chronic wounds, the eradication of biofilms and the preparation of wound beds for STSGs.

Dr. Bruno is a first-year resident with the Podiatric Medicine and Surgery Residency Program at the Yale School of Medicine.

Dr. Schmidt is affiliated with the Section of Podiatric Surgery in the Department of Orthopedics and Rehabilitation at Yale New Haven Hospital in New Haven, CT.

Dr. Blume is an Assistant Clinical Professor of Surgery in the Department of Surgery and an Assistant Clinical Professor of Orthopaedics and Rehabilitation in the Department of Orthopaedics, Section of Podiatric Surgery at the Yale University School of Medicine in New Haven, Ct. Dr. Blume is a Fellow of the American College of Foot and Ankle Surgeons.

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