Gersten’s 1955 article on the effect of ultrasound on tendon extensibility began six decades of continuous published research, which has demonstrated the tried and true benefits of ultrasound. 1 These benefits include pain reduction, a high degree of patient comfort and acceptability, increased cellular microcirculation, relaxation of trigger points and improved collagen extensibility. All of these physiological benefits are dependent on proper dosage and application technique. Ultrasound can provide both mechanical and thermal effects. An effective, skilled ultrasound treatment requires the use of high-quality ultrasound equipment, evidence-based patient-specific parameters, the appropriate treatment area, proper transducer movement speed, and optimal incorporation of the treatment with other therapy procedures.
Subthermal Ultrasound
• The typical subthermal ultrasound dose is 0.5 w/cm2 for 5mins over 2x the effective radiating area (ERA) or slightly less than 2x the size of the transducer ‘sound head’.
• The ultrasound frequency should be selected based on evidence-based-practice guidelines specific to each clinical indication and not determined solely by the depth of the target tissue.
• At a subthermal intensity, research demonstrates the creation of acoustic streaming, stable cavitation and micromassage, thereby increasing local circulation.
• When applied over acupuncture and trigger points, subthermal ultrasound studies demonstrate that ultrasound compares favorably with needle acupuncture in degree of pain reduction.
Thermal Ultrasound
• Thermal ultrasound is typically delivered from 1.0 W/cm2 to 1.5 W/cm2 for varying durations. Intensity settings and treatment durations are determined by the degree of tissue heating desired. Longer treatment times generally result in greater tissue temperature rise.
• To adhere to the evidence, the correct dosage must be applied with the tissue treatment area limited to 2x the effective radiating area of 2x the transducer.
• Thermal ultrasound is often used to relax tissue and to improve extensibility before stretching, exercise, or cross friction massage used to break up adhesions. Wessling et al found that static stretching following ultrasound increased muscle extensibility by 20% over stretching alone.2
• For more superficial tissue, 3MHz frequency is used. Ultrasound applied at a 3MHz frequency is absorbed superficially and is ideal for treating target tissue that lie within 1 to 2 cm tissue depth.
• For deeper tissue, 1MHZ treatment should be used, as this frequency stimulates target tissue up to 5 cm below the skin.
• To maximize range of motion, apply stretches during and immediately after thermal ultrasound application.3,4
Clinical Bottom Line: Due to the multitude of benefits of ultrasound which include pain reduction, decreasing trigger point hypersensitivity, increasing microcirculation, and decreasing stiffness, adding ultrasound to your patient’s plan of treatment can improve their function. An example of this is demonstrated in a 2012 study by Ebadi et al, which showed that adding continuous ultrasound to a supervised exercise program significantly improved function, lumbar ROM, and endurance for patients experiencing non-specific chronic low back pain.5
References:
1. Gersten JW. Effect of Ultrasound on tendon extensibility. Am J Phys Med 34:362-369, 1955
2. Wessling KC, DeVane DA, Hylton CR. Effects of static stretch versus static stretch and ultrasound combined on triceps surae muscle extensibility in healthy women. Phys Ther 67:674-679, 1987
3. Draper DO, Ricard MD: Rate of temperature decay in human muscle following 3 MHz ultrasound: The stretching window revealed J Athl train 30:304-307, 1995
4. Rose S, Draper DO, Schulthies SS, Durrant E: The Stretching Window Part Two: Rate of Thermal Decay in Deep Muscle Following 1-MHz Ultrasound. J Athl Train 31(2):139-43, 1996
5. Ebadi S, Ansari NN, Naghdi S, Jalaei S, Sadat M, Bagheri H, Vantulder MW, Henschke N, Fallah E: The effect of continuous ultrasound on chronic non-specific low back pain: a single blind placebo-controlled randomized trial. BMC Musculoskelet Disord 13:192, 2012