The Use of Ultrasound in Physiotherapy
Therapeutic ultrasound is utilized in combination with a number of other modalities to treat various soft tissue injuries. It is estimated that about 20% of the treatments in NHS physiotherapy departments make use of ultrasound technology. It is estimated that approximately 100,000 of the initial appointments in the South and West Region made use of ultrasound (Bryant, 1998).
The benefits of ultrasound technology in physiotherapy include a reduction of pain and inflammation, increased mobility and functionality, as well as a reduced recovery time for the patient.
The use of therapeutic ultrasound was first seen the early 1950s, and has been used extensively by physiotherapists for a number of different conditions. Proper use of ultrasound technology has been indicated in the reduction of oedema, relieve pain, and in the acceleration of tissue repair. The widespread use of ultrasound in physiotherapy indicates that it has been relatively accepted. However, the biological effects of ultrasound in not fully understood. It is proposed, based on empirical evidence, that ultrasound enhances recover as a result of its mechanical and chemical effects on tissue (Bryant, 1998). According to consultations conducted by Bryant, et al. in 1998, it was revealed that ultrasound technologies were utilized mostly on soft tissue injuries, such as ligament strains of the ankle and knee. It was often used during the early stages of therapy to accelerate the inflammatory process. It is also used at the end of the treatment session, and after other techniques such as manual manipulation to aid in circulation.
Each ultrasound session usually lasts between three and seven minutes depending on the size of the area being treated, the nature of the ailment.
The use of therapeutic ultrasound has been used for nearly half a century in physiotherapy, its use in a clinical environment has changed significantly over the years. In the past, it was used mostly for its thermal effect, today for its “non thermal” effects especially in relation to tissue repair and wound healing (Watson).
It is these non-thermal effects of ultrasound energy that is believed to be more effective, and many of the clinical applications focus on these. In fact, Gallo, et al. demonstrated that both continuous and pulsed ultrasound interventions generated measurable thermal changes in the tissues, but because of the low temperature changes achieved, it was believed that there would be little therapeutic value. However, Garrent, et al. went further and compared the heating effect of a pulsed shortwave treatment with an ultrasound treatment, and showed that the shortwave treatment was more effective at achieving the temperature needed for therapeutic benefit.
Ultrasound consists of high frequency sound waves that are not audible. Standard therapeutic ultrasound frequencies usually fall in between the range of 0.5 to 3 MHz in the United Kingdom. In use, the ultrasound waves penetrate homogenous tissues and are absorbed by those with high protein content. Because of this characteristic, ultrasound is often used to treat deep structures, such as joints, muscle, and in some cases even bone. In fact, more and more treatments for relief of pain and joint immobility in musculoskeletal disorders have used ultrasound as a significant portion of the therapy.
Specifically ultrasound affects both normal and damaged tissue, and it is believed that damaged tissue is more responsive to the ultrasound waves (Bryant, 1998).
There is also growing clinical evidence that fracture sites, previously thought to be untreatable through ultrasonic technology might be more susceptible to ultrasound rehabilitation. Previous thinking restricting the use of ultrasound on fracture sites were mainly due to early animal studies that indicated that ultrasound treatment delayed, or even damaged healing bone. However, recent work has indicated that the effect of therapeutic ultrasonagraphy on healing bone is dictated by the intensity utilized during the treatment process. A relatively high intensity, such as 1.0W/cm2 continuous wave ultrasound signal as applied to earlier animals studies do appear to be harmful, or at least counterproductive. However, lower intensities, such as 30mW, appears to promote accelerated healing. These findings are also further supported by animal testing on smaller fractures in animals, which also had statistically positive findings, including shorter overall healing times. It should be noted, however, that these animal results do not completely coincide with human therapeutic results, which is still mixed. Because of this, many reviewers of fracture management do not recommend use of therapeutic ultrasound until further information is obtained (Busse, 2002).
In addition to the rehabilitation uses for ultrasound, it also has been shown to be effective in diagnostic purposes as well. In this modality, ultrasound uses extremely low intensity sound waves to generate images. This method of diagnostic medicine is becoming more popular than X-Ray, Computed Tomography or nuclear medicine, since those three require ionization radiation, and ultrasound does not. In addition, ultrasound technology does not require a contrasting media, which can potentially cause adverse effects in a significant amount of patients.
Another difference in the use of an ultrasound instrument is in how it actually operates. Unlike other diagnostic methods, which use a constant influx of information and output f energy, ultrasound only has an output of energy approximately 10% of the time. The remaining portion of the diagnostic test is conducted passively, with the instrument simply “listening” to the ultrasonic echoes produced. This allows for a relatively overall cost of operation.
In addition to the diagnostic and rehabilitation benefits of ultrasonic technology, there is also the extensive safety record. In over half a century of widespread clinical use, there have been no recorded adverse effects from exposure to diagnostic ultrasound. According to the American Institute of Ultrasound in Medicine, a prestigious multi-specialty professional society, “There are n confirmed biological effects on patients or instrument operators caused by exposure from the present ultrasound instruments.”
In addition to having a fairly stable safety record, more ultrasound systems incorporate a range of safety mechanisms to further improve the modality of ultrasound technology. For example, nearly all ultrasound instruments have a way to limit the power output of the system, including transducers that force a system to shut down if they detect an excessive operating temperature. Many modern ultrasound systems also have software operating systems, enabling them to be easily shut down if they operate outside their specifications.
In general terms, the waves of an ultrasound instrument are generated by a piezoelectric effect caused by the vibration of crystals within the head f the wand or probe. The sound waves that pass through the skin cause a vibration of local tissues. These vibrations can potentially cause a rise in the temperature of the muscle tissue, although there may not be a significant sense of heat in the skin of the patient (Family Physiotherapy Center, 2009).
Improving Modality
There are of course, a number of reasons why improvement in the modality of ultrasound in the medical community is important. The first is safety and ergonomic concerns. These issues have always been on the forefront for technology development in diagnostic imaging modalities. High levels of work related injuries to ultrasound operators, for example have led to improved design aspects, including the development of more ergonomically friendly wands, and devices. In addition to influencing the overall system designs in the United Kingdom, the ergonomic concerns have also begun to influence production of these systems in Europe as well. For example, a number of companies have addressed the situation by making use of Bluetooth ® wireless technology into their ultrasound devices, which contribute to a less stress, and less injury prone environment.
Another reason why the improvement of ultrasound system modality is necessary in the medical community is that the training specified to utilize these instruments is not uniform. Europe, for example does not have a uniform training requirement for medical ultrasound as a vocational career path. In addition, regulations vary considerably among countries in Europe, and therefore ultrasound technicians which are qualified to operate in one geographical area of the European Union, might find their expertise unusable in another portion.
A recent study evaluated the efficacy of a locally applied thermal modality with ultrasound with regards to their effect on soft tissue extensibility. Both modalities were found to be effective; however the ultrasound did not show any significant benefit over the heat treatment. In fact, the thermal intervention was shown to produce a greater overall benefit.
As indicated above, there are ultrasound generated thermal changes in the tissues, but it is important to differentiate between those produced in the skin, and those generated at depth. In one case study, ultrasound was applied for five minutes at 1.5 W centimeter squared in continuous mode using a 3 MHz application. The area covered was twice the area of the treatment head. The change in peak temperature changed from 34.3°C to 37.3°C by the end of the session. This was easily felt by the patient as a warming sensation, but it should be noted that this temperature change does not necessarily correspond with therapeutic healing at depth (Watson).
On the surface, the therapeutic effects of ultrasound are remarkably similar t those of laser therapy and some pulsed electromagnetic fields. The fundamental differences relate back to the three energies are preferentially absorbed in different tissues. In addition, there does appear to be some differences between the physiological effects of these interventions, but in some areas they do overlap.
Clinical studies have indicated that ultrasound technology and treatment is most effective at achieving statistically significant results with tissues that absorb mechanical energy, or those tissues with a dense collagenous nature such as muscle and nerves, or where there is significant oedema (Watson).
Available Systems on the Market
While there are a number of choices available on the market today for ultrasound technology, two of the most often used machines include the single frequency unit (1.0 MHz) and the three frequency unit (0.75, 1.5 and 3.0 MHz). The mode of delivery may be either continuous or pulsed output, with both modes being used by NHS departments.
In most cases, physiotherapists utilize lower intensities, usually below 1.0W per centimeter. The actual settings used are dependent on the condition being treated; chronic conditions may require stronger intensities (Bryant, 1998).
References:
Busee, J., Bhandari, M. Kulkami, A., Tunks, E. (2002) “The effect of low-intensity pulsed ultrasound therapy on time to fracture healing: a meta-analysis” Canadian Medical Association Journal (CMAJ) Vol 166 No. 4
Bryant, J, Miline R (1998) “Therapeutic ultrasound in physiotherapy” Bristol: NHS Executive South and West Development and Evaluation Committee Report No. 90
Family Physiotherapy Centre of London (2009) “Therapeutic Ultrasound” Family Physiotherapy Centre Publications
Parhar, Gordon (2006) “Advances in Ultrasound Move Modality into New Fields” Radiology Management
Research and Markets (2002) “Advances in Diagnostic Ultrasound Imaging In Europe (Technical Insights) www.researchmarkets.com/reports/365670/
Watson, T. (2000) “Ultrasound in Contemporary Physiotherapy Practice” Ultrasonics Special Issue www.electrotherapy.org Accessed July 20, 2009