TISSUE REPAIR

applied to many interventions - drug therapy, manual therapy, exer- cise therapy. All involve the use of an intervention in order to achieve a physiological shift or change. The treatment is just a tool to stimulate the physiological change. It is a tool that when applied at the right time at the right dose and for the right reason has the capacity to be beneficial. Applied inappropriately, it is not at all surprising that is has the capacity to achieve nothing or in fact to make things worse.

Therapeutic windows Windows of opportunity are topical in many areas of medical prac- tice and are not a new phenomenon. It has long been recognised that the ‘amount’ of a treatment is a critical parameter. This is no less true for electrotherapy than for other interventions.

Given the research evidence, there appear to be several aspects to this issue. Using a very straightforward model, there is substantial evidence for example that there is an ‘amplitude’ or ‘strength’ win- dow. An energy delivered at a particular amplitude has a beneficial effect whilst the same energy at a lower amplitude may have no demonstrable effect. The laser example above is a simple extension of this case - one level will produce a distinct cellular response whilst a higher dose can be considered to be destructive. Karu (1) demonstrated and reported these principles related to laser energy and the research produced since has served to reinforce the concept.

Along similar lines, ‘frequency windows’ are also apparent. A modal- ity applied at a specific frequency (pulsing regimen) might have a measurable benefit, whilst the same modality applied using a dif- ferent pulsing profile may not appear to achieve equivalent results. There is evidence for the same frequency windows in TENS.

Assuming that there are likely to be more than two variables to the real world model, some complex further work needs to be invoked. There is almost certainly an energy or time-based window (2) and then another factor based on treatment frequency (number of ses- sions a week or treatment intervals).

One research style which has proved to be helpful in this context is to test a treatment on non-injured subjects in the laboratory using a variety of doses, and then to take the same protocol out into the clinical environment and repeat the testing procedure with real patients with particular clinical problems. Preliminary results indi- cate that there are distinct differences between the responses on ‘normal’ and ‘injured’ tissues at equivalent doses and further work is essential to maximise our understanding of these behaviours (3) (in press).

MODALITY SPECIFIC INFORMATION General issues - overlap effects and differences in absorption Whilst there are some (relatively minor) differences in the research findings, it appears that the majority of the therapeutic effects of ultrasound, pulsed shortwave and laser overlap for the majority. The logical query at this point is why might it be necessary to ever employ more than one of them? The essential difference between

the modalities is that although they all have essentially similar effects, these outcomes are not primarily achieved in the same tis- sues - different forms of energy are preferentially absorbed by dif- ferent types of tissue.

The dominant effects of the modality are achieved in the tissue in which the energy is best absorbed, hence knowing the relative absorption of the different energies in the various tissues will enable the practitioner to discriminate between modality use in a clinical decision making process. It is appreciated that not all modalities will be available to all therapists in all circumstances, but in the ‘ideal world’ the availability of all three modalities would offer maximal flexibility and thus effectiveness.

Ultrasound Therapeutic ultrasound is one of the more established and most widely used of the electrophysical agents. The energy output of the machine is a sound wave which, whether audible or not, is a mechanical wave form, and in the case of therapeutic ultrasound, it is most often applied with frequencies between 1 and 3 MHz.

Not all tissues will absorb US equally, and thus the effectiveness of the modality will be influenced by the type of tissue being treated.

Dense collagenous tissues absorb US energy most efficiently, these include: ■ ligaments ■ tendons ■ fascia ■ capsules ■ scar tissue.

Clearly ultrasound can have an effect in other types of tissue such as muscle but it would be less effective if used to treat an acute muscle tear than it would be if used to treat an acute ligament tear.

KEY POINT

The nature of the tissue is a critical element in the clinical decision mak- ing process (4).

Recent (animal) stud- ies have clearly demonstrated this phenomena with no significant effect being demonstrated immediately follow-

ing muscle contusion injury (5,6) whilst benefits are achieved fol- lowing ligament injury (7,8).

Ultrasound modes Ultrasound can be used in THERMAL or NON THERMAL modes. In thermal mode, it will be most effective in heating the dense col- lagenous tissues and will require a higher intensity, preferably in continuous mode to achieve this effect. In the non thermal appli- cation, lower energy levels, preferably in pulsed mode are applied in order to achieve cell ‘up regulation’ without heating. The prima- ry non thermal effects involve enhancement of the tissue repair process by optimising the normal inflammatory, proliferative and remodelling events (4).

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