Imaging
locations of tissue damage as determined by knowledgeable and experienced practitioners and instructors, after careful history taking and examination of the injured sites.
Meta-analysis of Randomized Controlled Trials LLL therapy might not be a panacea for all pain syndromes; the conditions where the modality is most beneficial remain to be defined. Published data from multicenter, randomized double-blind placebo-controlled studies in comparable large groups of patients are lacking. Meta-analysis data on LLL combining several smaller published randomized controlled trials to achieve a larger sample size have thus far yielded more convincing results for certain pain syndromes. However, limitations in the varying methodologies, laser parameters and outcome measures among the different studies should be kept in mind when considering these data. Here are a few that have been published. Chow and Barnsley showed the favorable use of infrared LLL in acute and chronic neck pain in four out of five randomized controlled trials.45
The same authors also later published
a double-blind, randomized, placebo-controlled study demonstrating the efficacy and relief of chronic neck pain over a three-month period.24
Bjordal and others performed a Medline and library literature search on randomized controlled trials applying LLL to treat plantar fascia, Achilles, patellar, lateral epicondyle and rotator cuff tendinopathy.46
The authors
looked at 78 trials, 20 of which involved tendinopathy, and they predetermined their inclusion criteria, which consisted of treatments using various ranges of power or energy densities. When optimal treatments for specific tendinopathies were applied, there was a high correlation with successful treatment. The authors concluded that there was a significant effect using LLL if a valid treatment procedure and location-specific dose was used. Enwemeka and colleagues searched the literature to determine the effects of LLL on pain control and tissue repair. Of the hundreds of randomized controlled trials, they found 34 tissue repair studies and nine pain control papers that met their inclusion criteria. Their results showed that LLL was effective in promoting tissue repair and pain relief. They further statistically determined a ‘fail-safe number’ or the number of neutral or negative studies needed to nullify the positive LLL effects, which was 370 and 41 for tissue repair and pain control, respectively.47
Evaluating Pain has its Limitations
The task of evaluating LLL in the management of pain is challenging because the subject of pain is still not yet completely understood. The greatest limitation is that there are no laboratory values and simple imaging studies with which to measure pain. Pain is what patients say it is, and reporting pain can be subjective. What one person says is terribly painful; another might relate to as a minor ache. According to the International Association for the Study of Pain (IASP), pain is defined as ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.’ Stating it another way, pain is an individual’s perception and expression of existing tissue damage. Perceived pain by the patient is subjectively measured by a visual analog scale based on a numerical scale from 0 (no pain) to 10 (very severe pain). When evaluating pain, assumptions are made that the patient can accurately and consistently provide a score that measures the actual or potential tissue damage.
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Understanding Pain as it Relates to Tissue Damage
When human soft tissue is traumatized, the injured tissues release chemical mediators and breakdown products from phospholipids. A variety of chemical mediators, including prostaglandins, kinins, serotonins, histamine, substance P, and other inflammatory chemicals, are liberated, causing a cascade of events that includes vasomotor changes, edema, increased muscle tension, and spasm, and release of substances from platelets and mast cells. Pain receptors (nociceptors) or free nerve endings in the skin, scalp, periosteum, fascia, muscles, cranial sinuses, and arterial wall can be activated by either one or a combination of mechanical, thermal, and chemical stimuli. Damage to any of the aforementioned tissue can incite pain. The pain impulse is propagated along one or two types of nerve fiber—the A delta and C fibers—to the central nervous system via the dorsal horn of the spinal cord. The A delta fibers are myelinated, fast-acting fibers producing sharp and stabbing pains, whereas the C fibers are unmyelinated, thin, slow-acting fibers causing dull, aching, burning pain. Stimulating the A delta fibers enables one to localize precisely the site of injury, whereas activating C fibers produces the perception of diffuse widespread injury.48
Once the pain impulse crosses the dorsal horn of the spinal cord, it continues up the ascending pathway of the spinothalamic tract to the reticular system and the thalamus in the midbrain, and then to the cerebral cortex, where the pain is interpreted. When the ascending pathway is activated, the descending inhibitory pathway is stimulated by releasing morphine-like substances, such as endorphins and enkephalins, to modulate the oncoming train of pain impulses. Some of the incoming impulses from the dorsal horn can innervate the anterior horn, which causes increase tension and contraction of extrafusal muscles. Muscle spasm and ischemia result, giving rise to additional sites of pain. In some severe situations, some of the incoming impulses can innervate the lateral horn of the cord to activate the autonomic nervous system and, in particular, stimulate sympathetic nerves that not only carry the sensation of pain and paresthesia, but also induce other activities, such as vasoconstriction, sweating, and smooth-muscle contraction.49
We believe that LLL improves lymphatic drainage of inflammatory pain chemicals and edema from areas of tissue damage. Noxious chemicals that sensitize nociceptors are reduced, thus diminishing or interrupting pain pathways that give rise to neurogenic and neuromuscular pain.26 Once the pain chemicals are cleared, homeostasis in that area is re-established. Consistent with this hypothesis is the enhancement of the lymphatic system by LLL in animal studies,14,15
and the
demonstration of significantly less prostaglandin E2 in patients with activated Achilles tendonitis following LLL.29
The Challenges and Pitfalls of Pain Studies Given that there are many conflicting reports in the literature in terms of the LLL modality in treating pain, it is important to elucidate the challenges and pitfalls of pain studies. Pain might not always be perceived at the site of actual tissue damage, and even when pain is felt at the site of damage, all injuries are not the same. It is imperative to perform meticulously a detailed history and physical examination of patients to determine the site of the injury, define the type of injury, and specify the amount and extent of tissue damage. Furthermore, pain can
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