TISSUE REPAIR KEY POINTS

■ Different forms of energy are preferentially absorbed by dif- ferent types of tissue

■ US in thermal mode will be most effective in heating the dense collagenous tissues and will require a higher intensi- ty, preferably in continuous mode

■ US in the non-thermal application will be most effective at lower energy levels, preferably in pulsed mode and applied in order to achieve cell ‘up regulation’ without heating

■ During the inflammatory phase, US has a stimulating effect on the mast cells, platelets, white cells with phagocytic roles and the macrophages

■ During the proliferative phase (scar production) US has a stimulative effect (cellular up regulation)

■ During the remodelling phase - ultrasound applied to tissues enhances the functional capacity of the scar tissues and may also have the capacity to influence collagen fibre orientation

■ Pulsed shortwave energy is preferentially absorbed in the ionic, low impedance tissues (eg. nerve, muscle, oedematous tissue, haematoma)

■ Laser (light) energy is best absorbed in tissue that is (a) superficial and (b) vascular (14)

■ Therapeutic laser at appropriate doses appears to enhance the inflammatory and proliferative cascades in much the same way as US. There is less evidence with regards the effects in the remodelling stage.

regards to why then are three different modalities needed if they all ‘do the same job’? The evidence would support this contention but furthermore, it also identifies the critical difference between the three modalities - that of absorption - ie. where the effect is achieved. The three different forms of energy are preferentially absorbed in different types of tissue, and thus, the primary benefit is differentially achieved.

Ultrasound is best absorbed (as above) in the dense collagenous tissues. Pulsed shortwave energy (when delivered with the monode or drum applicator) is preferentially absorbed in the ionic, low impedance tissues (eg. nerve, muscle, oedematous tissue, haematoma) and the laser (light) energy is best absorbed in tissue that is (a) superficial and (b) vascular (14).

Clearly, it would be wrong to claim an absolute difference between the energy forms, but there is a difference in preferential absorp- tion, and hence, a differential clinical effect. Ultrasound might have some beneficial effect on recently injured muscle, but given a choice, pulsed shortwave or laser (if the muscle is superficial) would be likely to achieve better outcomes.

Laser The light energy delivered from a therapeutic laser essentially acts as a trigger for physiological reactions in the same way that ultra- sound does. Much of the really impressive clinical work with laser has involved patients who have long term, chronic open wounds

though clearly, this is of less importance with regards to the con- text of this paper.

Laser light has a relatively short penetration depth into living tis- sue, though there is substantial disagreement as to what kind of ‘average’ distance should be cited. The light energy itself is rapidly absorbed, and a reasonable figure would be that some 95% of the surface energy is absorbed by 10-15mm into the tissues (depend- ing on the light source - infrared laser light will penetrate further than visible red light). It is proposed however, that although the actual absorption is relatively superficial, the cellular and tissue reactions that take place in the superficial tissue initiate chemical- ly-mediated cascades, and these are able to influence deeper tis- sues and those at some distance (see reference 14 for some useful review material).

Recent papers by several authors have illustrated very similar findings to those identified above with ultrasound. For example, Vinick et al (15) reported on a nicely conducted (lab) study, in which laser irradiation was shown to stimulate fibroblast prolifera- tion. Interestingly, green light was found to have a stronger effect than red light. The problem with this in the clinical environment is that green light has a very minimal tissue penetration (a millime- tre or two) and hence the red light is more clinically appropriate. Brondon et al (16) demonstrated with a controlled study that laser light increases the metabolic activity and proliferation of a variety of cells in culture - again, in the same way that ultrasound does. One of the more recent publications by Karu (17) showed that nitric oxide (a very trendy inflammatory/healing chemical mediator being investigated by many research groups round the world) is influenced by laser therapy. Nitrous oxide (NO) is believed to be a signalling agent controlling cell respiration.

Of the most recent papers that might be considered to be more directly relevant to this paper concern the problems of Achilles tendinitis. Bjordal et al (18) report the results from a well-struc- tured randomised, placebo-controlled trial of laser therapy for this problem, working on the basis that laser is thought to act as an inflammatory modulator. A relatively small (n=7) groups of patients with bilateral Achilles tendonitis were treated with an infrared ther- apy laser. The concentration of prostaglandin E2 (an inflammatory mediator) was significantly reduced following the treatment com- pared with both the control and placebo conditions, and the pain threshold had increased following intervention.

Fillipin et al (19) also investigated Achilles tendinitis (in a rat model) using low level laser therapy (LLLT) in relation to the levels of oxidative stress and fibrosis. It was found that the use of LLLT for 14 or 21 days provided significant improvement over the control condition, reducing histological abnormalities and collagen con- centration. The observed reduction in oxidative stress could, it is proposed, result in less fibrosis during the repair phase.

The production of reactive oxygen species (from excessive nitric oxide production and phagocytic overactivity) is thought to increase cell damage, and the LLLT effect in this study was to ame-

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