Diathermy and therapeutic ultrasound are physical therapy treatments that use energy to facilitate healing. While both treat muscle and joint conditions, they operate on different principles. Diathermy generates deep heat using high-frequency electrical currents, while therapeutic ultrasound uses sound waves to produce its effects. Understanding their distinctions helps clarify their roles in a clinical setting.
The Underlying Physics of Each Modality
Diathermy uses high-frequency electromagnetic energy to create heat deep within tissues. The common shortwave form utilizes a frequency of 27.12 megahertz. As this energy passes through soft tissues, it causes molecules to oscillate rapidly. This molecular friction generates heat from the inside out, a process called conversion. This method allows for uniform heating of tissues high in water content, like large muscles, and the energy is delivered through applicators placed near the skin.
Therapeutic ultrasound uses high-frequency acoustic vibrations. A transducer head, applied to the skin with a coupling gel, contains a crystal that vibrates from an electric charge. This produces sound waves, in the range of 1 to 3 megahertz, that travel into the body. As these waves propagate, they cause molecules to vibrate, which generates heat. Ultrasound also produces non-thermal effects, including “acoustic streaming” and “cavitation,” which influence cellular activity.
Therapeutic Effects and Applications
The deep heat from diathermy leads to vasodilation, an expansion of blood vessels that increases blood flow to the targeted area. Enhanced circulation brings more oxygen and nutrients to tissues while helping remove metabolic waste. This process can reduce pain, alleviate muscle spasms, and increase the flexibility of collagen tissues. Because it heats large areas uniformly, diathermy is used for conditions affecting broad muscle groups like the lower back, quadriceps, and hamstrings, as well as bursitis and some forms of arthritis.
Therapeutic ultrasound provides both thermal and non-thermal benefits. Its thermal effects involve localized heating that increases circulation and reduces pain, which is effective in tissues with high collagen content like tendons and ligaments. The non-thermal effects, acoustic streaming and cavitation, can stimulate cellular repair and help reduce inflammation. Consequently, ultrasound is often used for tendonitis, breaking down scar tissue, and treating neuromas.
Key Distinctions in Treatment Administration
A primary difference between diathermy and ultrasound is the depth and size of the treatment area. Diathermy is designed to penetrate deeply and heat a large volume of tissue simultaneously. This makes it a good choice for treating generalized pain across a large body part, such as the lower back.
Ultrasound, in contrast, provides more focused treatment. The transducer head is small and delivers a concentrated beam of acoustic energy. This allows a therapist to target specific, localized injuries, such as an inflamed tendon or a trigger point within a muscle.
The modalities also differ in their selectivity for tissue types. Ultrasound is efficient at heating tissues with high collagen content, like tendons, ligaments, and fascia, making it a targeted choice for injuries affecting them.
Diathermy is more effective for heating tissues that have high water and ion content. Muscle tissue responds well to this energy, making it a superior option for treating general muscle soreness, spasms, and conditions affecting the bulk of a muscle.
Contraindications are another point of distinction. Diathermy’s electromagnetic energy is contraindicated for patients with any metal implant, including pacemakers or surgical screws. The metal can concentrate the energy, leading to a dangerous temperature increase and internal burns.
Ultrasound is a safer option for patients with metal implants, though it should not be applied directly over the implant. The sound waves can reflect off the metal, potentially causing a concentration of energy at the bone-implant interface, but the risk is much lower than with diathermy.
How a Professional Chooses the Right Modality
The decision to use diathermy or ultrasound is not based on which modality is superior, but which is most appropriate for a patient’s diagnosis. A physical therapist conducts a thorough evaluation to determine the best course of action. This assessment involves identifying the specific tissue that is injured, the depth of the structure, and the size of the area that requires treatment.
The choice is guided by tissue selectivity and treatment area. For a patient with generalized pain across a large area, like the lumbar region, a therapist would likely choose diathermy for deep, uniform heating. If another patient has a precise injury, such as Achilles tendonitis, ultrasound would be the logical choice to deliver focused energy to the tendon.
A patient’s medical history, particularly the presence of any contraindications, is a deciding factor. If a patient with low back pain has internal surgical hardware from a past spine surgery, diathermy would be ruled out. In such a case, the therapist might use ultrasound on specific soft tissue structures around the hardware or opt for a different heating modality.