Author Name: Maria John; BSc (Hons) Veterinary Nursing Science
Low Level Laser Therapy (LLLT) is proven to promote wound healing by increasing fibroblast proliferation, decreasing inflammatory cells, formulating granulation tissue and increasing collagen synthesis, however there is no firm evidence to support its use as an alternative therapy on open wound healing in veterinary practice. The current literature shows that LLLT is an effective therapeutic modality to promote healing and reduce inflammation but the biological effects are highly dependent on dose, wavelength and application time, thus causing negative results due to the incorrect use of LLLT. With regards to these dose parameters the results are conflicting and do not lead to clear treatment protocols. Therefore there is a lack of scientific based evidence that LLLT would be beneficial in veterinary practice for open wound healing as there are no guidelines for practitioners to follow. Comparative studies have been conducted using modalities such as ultrasound and electrical stimulation. LLLT was found to be more beneficial than ultrasound but electrical stimulation decreased the inflammation stage significantly more than LLLT, resulting in faster healing times. In order to gain veterinary professional approval on the efficacy of LLLT scientific research needs to be conducted using well-controlled investigations with treatment parameters that can be used in a veterinary practice on open wounds successfully.
Low level laser therapy (LLLT) is used to aid fast wound healing by stimulating fibroblast development and producing collagen (Millis and Saunders, 2014). LLLT is a drug free, non-invasive technique and uses photobiostimulation to accelerate wound healing (Millis and Saunders, 2014; Chow et al., 2009; Hopkins et al., 2004). It promotes tissue repair, reduces inflammation and relieves pain (Mao, Yao and Fang, 2012) by stimulating local sensory nerve pathways to produce endorphins. LLLT also increases blood circulation and immune system responses which also contributes to fast wound healing (Millis and Saunders, 2014; Venter 2013). LLLT is believed to affect all three phases of wound healing (Andrade, Clark and Ferreira, 2014; Venter, 2013) the inflammatory phase, proliferative phase and the remodelling phase (Chung et al., 2012). Therefore this alternative therapy could be highly useful in veterinary practice as it effectively treats wounds and has the advantage of being non-invasive, such that since patients feel no sensation compliance is greater (Venter 2013).
The first LLLT studies on wound healing were conducted in the 1980’s/1990’s on experimentally induced skin lesions (Petersen et al., 1999; Fretz and Li, 1992; Rupp et al., 1991; Kanepset al., 1984). However, the use of LLLT in veterinary practice has only become popular in the last 5 years (Pryor and Millis, 2015), thus raising the debate as to why it has not been developed sooner and why it is not more widely used in veterinary practice as an alternative therapy or alongside other treatment protocols.
According to Buckner and Schildboek (2006) and Chung et al. (2012) the inconsistency in clinical outcomes of current studies has resulted in an unclear understanding of the efficacy of LLLT in open wound healing. Many of the studies on LLLT contain negative results; Avci et al. (2013) stated that this could have been due to the lack of skin preparation before application, failure to account for skin pigmentation and inappropriate choice of light source and dosage. These findings were confirmed by Chaves et al. (2014) who also stated that the importance of an appropriate treatment protocol is key to promoting healing of open wounds (Silva et al., 2010) . Currently there is firm evidence supporting the success of LLLT as a treatment for chronic joint disorder or as an analgesia (Chung et al., 2012). Anecdotally LLLT is often used as an adjunct therapy in treatment regimes for open wounds and is suggested to reduce healing time; however no research has confirmed this application. Further reviews should be conducted (Pryor and Millis, 2015; Saltmarche, 2008) using experimental wounds in rats and mice and controlled research in humans and animals (Peplow, Chung and Baxter, 2010) to determine if LLLT should be used as a recognised viable modality for open wound healing in veterinary practice.
2.0 Efficacy of Low Level Laser Therapy in open wound healing
Research is inconclusive as to whether LLLT is effective in reducing healing time for open wounds (Chung et al., 2012; Emshoff et al 2008).
Both Hodjati et al. (2014) and Hussein et al. (2011) used rabbits as subjects to evaluate the efficacy of wound healing using LLLT. Results showed that wound diameter and inflammation had significantly decreased in the LLLT groups compared to the control, thus supporting the use of LLLT in open wound healing. Both studies used 26-28 rabbits but the lasers used and treatment times were not the same. These discrepancies may cause a lack of validity as LLLT relies on set dosimetric parameters to target tissues at particular biological states (Fernandes et at., 2015). This lack of consistency causes veterinary clinicians to lack confidence in the method as there is no clear standard dose for use of LLLT as a therapeutic treatment in practice (Andrade, Clark and Ferreira 2014). Hussein et al. (2011) used a Gallium Aluminium-arsenide diode. This is different to Hodjati et al. (2014) study but both concluded that LLLT is an effective modality in open wound healing, as it enhances contraction of superficial wounds and aids in collagen synthesis therefore speeding up healing (Chaves et al 2014; Hussein et al 2011).
The treatment stages were also different in the above studies. Hussein et al (2011) used the LLLT consecutively for 7 days whereas Hodjati et al (2014) used the treatment on days 0, 3 and 6. This could have had an impact on discrepancies in wound healing due to gaps in treatment (Fernandes et at., 2015) and therefore discourage the use of LLLT as a therapeutic modality in veterinary practice due to lack of scientific research on appropriate treatment protocols (Posten et al., 2005; Petersen et al., 1999).
A study conducted on ten dogs by Kurach et al. (2015) is an example of this and disputes the efficacy of LLLT in open wound healing. They treated the subjects 3 times a week for 32 days. There was no significant difference between contraction of wound or levels of inflammatory cell types between the control group and LLLT group. This conflicts with the studies by Hussein et al (2011) and Hodjati et al (2014) that found an increase in inflammatory cells due to LLLT treatment.
An argument against Kurach et al. (2015) is that a very low power laser was used therefore the tissues were not delivered sufficient energy to cause the cell membranes to be disrupted enough to speed up healing by faster collagen production (Fernandes et al., 2015). This could be why LLLT treatment was ineffective in the dog subjects. Further study is needed to develop specific energy density and dose frequencies for each species (Kurach et al 2015; Andrade, Clark and Ferreira 2014; Silva et al 2010).
These differences further show the lack of studies done that have considered standardisation of lasers and similar research methodologies (Chaves et al 2014), however there is progression in this field as the parameters of LLLT are becoming more understood due to further scientific studies (Chung et al 2012).
A human study by Saltmarche (2008) found that LLLT was effective for healing acute and chronic open wounds. This is confirmed by Hopkins et al. (2004) who stated that the use of LLLT enhanced healing and concluded that it is an effective modality for wound contraction. Although both studies were conducted over 20 days the methods varied. Hopkins et al. (2004) used 22 young (mean age 21 years) healthy participants and the abrasions were induced for the study purposes whereas Saltmarche (2008) had 16 participants from a nursing home (mean age 85.1 years) with 12 chronic wounds and 9 acute wounds being treated. For the analysis of wound healing it is beneficial if wounds are as similar as possible to determine the difference in healing due to LLLT and other factors (Chung et al., 2012; Hopkins et al., 2004). Although the results of Saltmarche (2008) are not derived from a randomised controlled trial, the study found LLLT to be effective in both chronic and acute wound healing. These finding are supported by older studies conducted (e.g. Allendorf et al 1997; Enwemeka, 1988).
There are a range of studies that state that LLLT is effective at promoting wound healing (Chaves et al.,2014), however the lack of standardisation has caused the results that are currently available to be conflicting and therefore no clear conclusion can be drawn (Chung et al., 2012; Chaves et al.,2014). Further study needs to be conducted in vivo with controlled and blinded procedures to clarify the differences between laser-treated wounds and non laser-treated wounds (Posten et at.,2005; Hopkins et al., 2004). This will encourage veterinary practitioners to become aware of LLLT as a scientifically based therapy (Chung et al.,2012).
2.1 The use of comparative studies to establish the effectiveness of Low Level Laser Therapy in wound healing
Comparative studies have been conducted to determine the efficacy of alternative therapies on healing time in wounds (Beigon et al., 2015). When looking at the comparison of ultrasound and LLLT, Murgod, Sreekumaran and Danesh (2012) found that LLLT was more beneficial at wound healing. This was confirmed by Araujo et al. (2007) who stated that LLLT showed an increased number of fibroblasts. In contrast Demir et al. (2004) found no significant difference between modalities but confirmed that there was a benefit of both in comparison to the control group.
All three studies were carried out on healthy rats, with sample sizes ranging from 28 to 84 subjects. The above studies all used a Gallium Arsenide (GaAs) (904 nm) laser to conduct the experiments but the dosages were different, Araujo et al. (2007) used 4 J/cm2 for 90 seconds, Demir et al. (2004), 1 J/cm2 for 60 seconds and Murgold, Sreekumaran and Denesh (2012) at 0.5 to 4.0 J/cm2 for 2 minutes. This difference alone has an impact on how LLLT is perceived as Demir et al.’s (2004) study that showed no significant difference used a lower dose for the shortest amount of time. This shows that LLLT needs to be applied at an energy level sufficient to be absorbed by the targeted tissue and if this is not achieved then LLLT will not be effective at speeding up healing (Fernandes et al., 2015).
The ultrasound frequencies used and times of treatment were also different, with Murgold, Sreekumaran and Denesh (2012) and Demir et al. (2004) giving 5 minutes of treatment at 3mHz and 1mHz respectively and Araujo et al. (2007) using 1mHz for 60 seconds. This highlights the inconsistency in these methods with different activating frequencies making it difficult to compare results and choose the parameters of treatment that are effective at speeding up healing processes (Silva et al., 2010). This further causes conflict amongst veterinary clinicians as to which protocol is sufficient (Bayat, Azari and Golmohammadi, 2010). The timescales of the therapies were also different thus making it difficult to compare the results of both modalities between each other and as individual therapies, as the methodology is inconsistent (Andrade, Clark and Ferreira, 2014; Posten et al., 2005). In order to obtain valid results of the efficacy of LLLT, studies with the same treatment timescales and protocols should be conducted using wounds that are as similar as possible to provide results that are comparable with each other (Gonclaves et al., 2013).
Araujo et al. (2007) also compared the effect of electrical stimulation with LLLT and ultrasound thus determining the wider scope of modalities existing in wound healing. The study stated that although LLLT was more effective than ultrasound, electrical stimulation showed a higher increase in fibroblasts and was therefore more beneficial in collagen synthesis than LLLT. Demir, Balay and Kirnap’s (2004) study confirms this and states that electrical stimulation decreases the inflammatory phase significantly more than LLLT. It does not conclude that LLLT was ineffective but states that electrical stimulation allows the wound to reach proliferation phase earlier. This is the rebuilding phase of wound healing (Venter, 2013). The results of these studies could be questioned as although the same Low level laser was used (GaAs) the method of treatment was not the same; Araujo et al. (2007), 4 J/cm2 for 90 seconds, 5 sessions a week for 5 weeks and Demir, Balay and Kirnap’s (2004), 1 J/cm2 for 10mins for 10 consecutive days. Electrical stimulation treatment was also not conducted in the same manner for both studies. This further demonstrates the lack of studies done in conjunction with each other (Avci et al., 2013) and highlights the need for more research to be conducted on specific wounds with specific LLLT parameters including dose, time of exposure and wound (Andrade, Clark and Ferreira, 2014) as all of these factors influence the efficacy of LLLT by affecting the rate of energy delivered to the tissues.
In order to obtain a convincing verdict on LLLT and its impact on wound healing more comparative studies should be conducted (Chung et al., 2012). These studies should be performed on other species, not just rats, to determine the parameters of effective LLLT in veterinary practice (Avici et al.,2013). Future study could be focused on different tissue types in accordance with Watson (2008) who states that the difference in findings of LLLT and ultrasound efficacy lies in the type of tissue being treated. Ultrasound is absorbed mainly in collagen dense tissue therefore the studies conducted with LLLT and ultrasound could reflect on where each modality is best utilised in veterinary practice.
As seen in the study conducted by Araujo et al. (2007), clinicians use a variety of strategies simultaneously, this causes difficulties when trying to measure the effects of a single intervention (Hopkins et al., 2004). This highlights that studies should be carried out with the same methodological structure to help form a firm base on the efficacy of LLLT so that it can be used in veterinary practice.
Studies on low level laser therapy have thus far failed to establish clear positive results on the efficacy of it as an alternative therapy to be used in veterinary practice. To gain clinicians’ approval proper guidance on how to use LLLT on open wounds at a range of skin depths should be given. As stated in the current literature this is still an underdeveloped area of LLLT treatment in regards to open wound healing. A range of studies have been conducted to compare modalities and overall LLLT does have a clinical edge over ultrasound, however with the lack of comparable methodologies the findings are varied in terms of what dosages, wavelengths and frequencies should be used in a clinical veterinary setting. There are also a lack of studies being conducted on a range of species, contributing to the lack of use in veterinary practice patients. This being said, once the protocol guidelines have been put in place LLLT could have a high success rate as an alternative modality in a veterinary setting for a range of ailments.
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