Clinical use of Therapeutic Ultrasound
Evidence-based therapeutic ultrasound (US) can be administered at any stage throughout the healing process (inflammation, proliferation and remodelling phases), including most chronic inflammatory conditions. The main objective of therapeutic ultrasound is to enhance the natural healing process of tissue repair. For optimum clinical benefits, therapeutic ultrasound should be used with other suitable treatment modalities to complement and enhance each stage of healing throughout the repair and rehabilitation process.
Principles of ultrasound
Ultrasound machines convert electrical energy into mechanical energy which generates sound waves. These waves consist of mechanical compressions and rarefactions, which can be continuous or pulsed (Figure 1). Therapeutic US machines commonly delivery frequencies of 1 and/or 3 MHz (Figure 2). As the waves travel through the tissues, decreasing exponentially, the ultrasound energy is absorbed bringing about biophysical effects. It is widely accepted and clinically significant that ultrasound energy is preferentially absorbed by high-protein, dense collagenous tissues (1,2,3,4). According to Watson (4), the therapeutic effectiveness of any treatment (i.e. manual therapy or electrotherapy) is both ‘modality’ and ‘dose’ sensitive - and therefore represent key issues.
Figure 1 - Adapted from: Cameron
Figure 2 - Adapted from: Cameron
Furthermore, treatment settings (e.g. dose, intensity, pulse ratio, treatment duration) are based on the clinical findings presented by the patient (e.g. acute, sub-acute and chronic). Similar to all other forms of treatment modalities and rehabilitation strategies - they should be based on sound scientific principles underlying tissue healing (5,6).
Physiological and psychological benefits
While ultrasound is recognised for physiological effects, it can also have significant psychological placebo effects (7,8). Subsequently, it is purported that correct evidence-based settings can provide a combined optimum effect, to include both physiological and psychological benefits.
What does the research say?
Much of the published research literature relating to the use of ultrasound in the treatment of musculoskeletal conditions, including systematic reviews have failed to support the efficacy of its continued use (9,10,11,12,13). However, Watson (14) reports that many studies lack accurate data on clinical settings, while, Robertson et al. (3) reports many studies lack evidence of equipment calibration. Furthermore, many authors of the systematic reviews report that the quality of studies is often poor, and further efforts are necessary to provide stronger evidence.
Ultrasound is not without its hazards to both patient and therapist. Recent equipment surveys have highlighted an infection risk (15), major calibration problems (16), and electrical safety issues (17). These findings substantiate the need for regular training and machine testing.
Although research findings are equivocal, the use of ultrasound remains extensive. Absence of evidence does not always mean that there is evidence of absence. If one looks critically at the full range of physiotherapy treatments, there is simply insufficient evidence to support or reject many of them in all known circumstances (18). Meanwhile, the literature clearly demonstrates the need for therapists to critically engage in current ultrasound literature and undertake regular training to keep abreast of evidence-based practice (EBP). Below is a proposed strategy for EBP guidelines based on a simple integrated management system - designed to assist in the safe and effective delivery of US.
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Nussbaum, E. (1997). Ultrasound: to heat or not to heat-that is the question. Physical Therapy Review, 2, 59-72.
Sparrow, K.J., Finucane, S.D., Owen, J.R., Wayne, J.S. (2004). The effects of low-intensity ultrasound on medial collateral ligament healing in the rabbit model. The American Journal of Sports Medicine. 33 (7), 1048-1055.
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Watson, T. (2006). Electrotherapy and tissue repair. Journal of Sportex Medicine, 29, 7-13.
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Kannus, P., Parkkari, T.L., Jarvinen, T., et al. (2003). Basic science and clinical studies coincide: active treatment approach is needed after a sports injury. Scandinavian Journal of Medicine and Science in Sports. 13, 150-154.
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Kitchen, S.S., Partridge, C.J. (1990). A review of therapeutic ultrasound. Physiotherapy, 76(10), 593-600.
Gam, A., Johannsen, F. (1995). Ultrasound therapy in musculoskeletal disorders: a meta-analysis. Pain, 63, 85-91.
Ogilvie-Harris, D.J., Gilbart, M. (1995). Treatment modalities for soft tissue injuries of the ankle: a critical review. Clinical Journal of Sport Medicine, 5(3), 175-186.
Van der Heijden, G., Van der Windt, D.A.W., De Winter, A.F. (1997). Physiotherapy for patients with soft tissue shoulder disorders: A systematic review of randomised clinical trials. British Medical Journal, 315, 25-30.
Van der Windt, D.A., Van der Heijden, G.J., Van der Berg, S.G., Ter Riet, G., de Winter, A.F., Bouter, L.M. (1999). Ultrasound therapy for musculoskeletal disorders: a systematic review. Pain, 81(3), 257-271.
Van der Windt, D.A.W.N., Van der Heijden, G.J.M.G., Van den Berg, S.G.M., Ter Riet, G., De Winter, A.F., Bouter, L.M. (2002). Therapeutic ultrasound for acute ankle sprains. Cochrane Database of Systematic Reviews.
Watson, T. (2000). The role of electrotherapy in contemporary physiotherapy practice. Manual Therapy, 5, 132-141.
Schabrun, S., Chipchase, L., & Richard, H. (2006). Are therapeutic ultrasound units a potential vector for nosocomial infection? Physiotherapy Res. Int. 11(2), 61-71.
Athro, P., Thyne, J., Warring, B., Willis, Brismee, J., & Latman, N. (2002). A calibration study of therapeutic ultrasound units. Physical Therapy, 82, 257-263.
Daniel, D.M., & Rupert, R.L. (2003). Calibration and electrical safety status of therapeutic ultrasound used by chiropractic physicians. Journal of Manipulative Physiological Therapy, 26, 171-175.
Watson, T. (2005). Current concepts in electrotherapy. Theoretical & practical ultrasound workshop literature. University of Hertfordshire, Oct. 2005.