Roles of Physical Therapists in Wound Management, Part III: Select Biophysical Technologies and Management of Patients With Diabetic Foot Ulceration

Abstract

Physical therapists (PTs) have several decades of history of using high-frequency (1-and 3-MHz) ultrasound (US) to facilitate healing of musculoskeletal tissues (eg muscle, fascia, tendon, ligament, joint capsule) that become wounded or inflamed following many accidents or sports injuries, but not exposed, because the trauma leaves the skin intact. These US frequencies (often referred to as therapeutic US) transmit acoustic energy, which delivers the nonthermal physical properties of stable cavitation and microstreaming to the closed wound tissues via direct contact gel or water coupling to the skin. With megahertz US, the acoustic pressure waves created by stable cavitation and microstreaming are less forceful than the pressure waves created by unstable cavitation that is associated with low-frequency (kilohertz) US. This is because acoustic pressure is inversely proportional to frequency, and since higher frequencies have shorter wavelengths, at the power (wattage) levels used for megahertz US, less acoustic energy is transmitted to tissues per unit of time. The more prominent unstable cavitation produced by low-frequency US (eg 22.5, 25, and 35 kHz) is a major contributing source of energy by which contact US debrides nonviable, adherent fibrin and slough via fragmentation, emulsification, or a combination. The combination of stable cavitation and microstreaming that are characteristic of megahertz US do not generate the destructive energy levels that are associated with kilohertz US frequencies. Owing to the lower level nonthermal effects that 1-and 3-MHz acoustic energy has on tissues and cells, these frequencies are also used to treat open wounds by applying the US to the periwound skin with either aqueous gel or water as the coupling medium. Bear in mind that megahertz US is also capable of generating thermal energy in soft tissues. Although mild heating of closed and open wounds may be desirable when the objective is to enhance blood flow, generally the nonthermal effects of US on wound healing are considered more desirable and are supported by more research evidence. Essentially, the combined effects of stable cavitation and acoustic streaming excite or upregulate the cell membrane, thereby increasing the activity levels of the entire cell. The US energy acts as a trigger for this process, but it is the increased cellular activity that is in effect responsible for the therapeutic benefits of the modality.