Chapter 94Electrophysical Agents in Physiotherapy
Electrotherapy has been a component of physiotherapy practice since the early days, but its delivery has changed remarkably and continues to do so. All electrotherapy modalities involve the introduction of some physical energy, which brings about one or more physiological changes that are used for therapeutic benefit. To appropriately select the most suitable modality, it is necessary to:
The effectiveness of electrotherapeutic treatment is influenced by a number of factors, including the time after the injury at which treatment is applied, the “dose” administered, the amplitude or strength applied, and the frequency. An energy delivered at a particular amplitude has a beneficial effect, whereas the same energy at lower amplitude may have no demonstrable effect. Laser therapy provides a good example—one level will produce a distinct cellular response, whereas a higher dose may be destructive. A modality applied at a specific frequency (pulsing regimen) may have a measurable benefit, whereas the same modality applied using a different pulsing profile may not achieve equivalent results.
Ultrasound (US) is a form of mechanical energy, not electrical energy, and therefore, strictly speaking, is not electrotherapy but falls into the group of electrophysical agents.1 Mechanical vibration at increasing frequencies is known as sound energy. In children and young adults, the normal audible sound range is 16 Hz to 15,000 to 20,000 Hz. Higher frequencies are known as US. The frequencies used in therapy are typically between 1.0 and 3.0 MHz (1 MHz = 1 million cycles/sec).
Sound waves are longitudinal waves consisting of areas of compression and rarefaction. When exposed to a sound wave, particles of a material oscillate about a fixed point rather than move with the wave itself. Any increase in the molecular vibration in a tissue can result in heat generation; thus US can be used to produce thermal changes in the tissues, although current therapeutic usage does not focus on this phenomenon.1,2 The vibration of the tissues may also have nonthermal effects. As the US wave passes through the tissue, the energy levels within the wave decrease as energy is transferred to the tissues.1
US waves are characterized by frequency, wavelength, and velocity. Frequency is the number of times a particle experiences a complete compression/rarefaction cycle in 1 second. The wavelength is the distance between two equivalent points on the waveform in the particular medium. In an “average tissue,” the wavelength at 1 MHz is 1.5 mm and at 3 MHz is 0.5 mm. The velocity is the speed at which the wave (disturbance) travels through the medium. In a saline solution, the velocity of US is approximately 1500 m/sec compared with approximately 350 m/sec in air (sound waves can travel more rapidly in a denser medium). The velocity of US in most tissues is thought to be similar to that in saline.
These three factors are related but are not consistent for all types of tissue. Typical average therapeutic US frequencies are 1 and 3 MHz, although some machines produce additional frequencies (e.g., 0.75 and 1.5 MHz), and the “long wave” US devices typically operate at 40 to 50 kHz, a much lower frequency than “traditional US” but still beyond human hearing range.
The US beam is not uniform and changes in its nature with distance from the transducer. The US beam nearest the treatment head is called the near field. The behavior of the US waves in the near field is not regular, and areas of interference and energy can be many times greater than the output set on the machine (up to 12 to 15 times greater).
Tissues present impedance to the passage of sound waves. The specific impedance of a tissue is determined by its density and elasticity. For the maximal transmission of energy from one tissue to another, the impedance of the two tissues needs to be as similar as possible. An air gap between the generator and the skin will result in the majority of the US energy being reflected rather than transmitted to the underlying tissues.
Coupling media, water, various oils, creams, and gels, are used to bridge the air gap. Ideally, the coupling medium should be fluid so as to fill all available spaces, be relatively viscous so that it stays in place, have an impedance appropriate to the media it connects, and allow transmission of US with minimal absorption, attenuation, or disturbance. At present, the gel-based media appear to be preferable to the oils and creams. Water is a good medium and can be used as an alternative. The addition of active agents (e.g., antiinflammatory drugs) to the gel is widely practiced but remains incompletely researched.
Studies3,4 have considered the effect of animal hair on the transmission of US to the underlying tissue and report that best penetration is achieved by clipping the hair. In addition to the reflection that occurs at a boundary because of differences in impedance, there will also be some refraction if the wave does not strike the boundary surface at 90 degrees. Essentially, the direction of the US beam through the second medium will not be the same as its path through the original medium; its pathway is angled. The treatment head is ideally placed perpendicular to the skin surface (i.e., at 90 degrees). If the treatment head is at an angle of 15 degrees or more from the perpendicular to the plane of the skin surface, the majority of the US beam will travel through the dermal tissues (i.e., parallel to the plane of the skin surface) rather than penetrate the tissues as would be expected.
Records should be maintained of the machine used, the machine settings (frequency, intensity, time, and pulse parameters), the area to be treated (size and location), and any immediate or untoward effects.
The absorption of US energy follows an exponential pattern: more energy is absorbed in the superficial tissues than in the deep tissues.7,8 Thus as the US beam penetrates further into the tissues, a greater proportion of the energy has been absorbed; therefore there is less energy available to achieve therapeutic effects. The half value depth represents the depth in the tissues at which half the surface energy is available and is different for each tissue and US frequency. Tissues with high protein content are greatest absorbers of US energy. Those with higher water and low protein content absorb little. This is very important when electing US as a suitable modality.1 It is impossible to know the thickness of each tissue layer in an individual horse; therefore average half value depths are used for each frequency: 3 MHz = 2.0 cm; 1 MHz = 4.0 cm. Tissues with absorption are tendon, ligament, fascia, joint capsule, and scar tissue. In cartilage and bone, a majority of US energy striking the surface is likely to be reflected.7-9
The therapeutic effects of US are influenced by the treatment parameters chosen and are commonly divided into thermal and nonthermal.
Therapeutic US may produce heat,10 especially in periosteum, collagenous tissues (ligament, tendon, and fascia), and fibrotic muscle. If the temperature of the damaged tissues is raised to 40 to 45° C, there is hyperemia, which may be therapeutic and help resolve chronic inflammation.11 However, nonthermal effects are probably more important.
The nonthermal effects of US are from cavitation and acoustic streaming.7,12 Cavitation, the formation of gas-filled voids within tissues and body fluids, occurs in two types—stable and unstable—which have different effects. Stable cavitation occurs at therapeutic doses of US and is the formation and growth of dissolved gas bubble accumulation. The “cavity” acts to enhance the acoustic streaming phenomena. Unstable (transient) cavitation is the formation of bubbles at the low pressure part of the US cycle. These bubbles then collapse very quickly, releasing a large amount of energy that is detrimental to tissue viability. However, this does not occur at therapeutic levels if good technique is used.
Acoustic streaming is a small-scale eddying of fluids near a vibrating structure such as cell membranes and the surface of a stable cavitation gas bubble and affects diffusion rates and membrane permeability.11 Sodium ion permeability is altered, resulting in changes in the cell membrane potential. Calcium ion transport is modified, which in turn leads to an alteration in the enzyme and cellular secretions.
The result of the combined effects of stable cavitation and acoustic streaming is that the cell membrane becomes “excited” (up-regulates), thus increasing the activity levels of the whole cell. The US energy acts as a trigger for this process, but it is the increased cellular activity that is in effect responsible for the therapeutic benefits of the modality.1,2,13
Some US machines offer variable time: typical pulse ratios are 1 : 1 and 1 : 4. In 1 : 1 mode, the machine offers an output for 2 ms followed by 2 ms of rest. In 1 : 4 mode, the 2-ms output is followed by 8-ms rest period.
The process of tissue repair is a complex series of cascaded, chemically mediated events that lead to the production of scar tissue.
US induces the degranulation of mast cells, causing the release of arachidonic acid and its subsequent cascade.9,13 Thus therapeutic US is proinflammatory rather than antiinflammatory. The benefit of US may not be to “increase” inflammation, although if applied too intensely at this stage, it is a possible outcome; rather, US should act as an “inflammatory optimizer.”1 The inflammatory response is essential for effective tissue repair, and the more efficient the process, the more effectively it can advance to the next phase (proliferation). Studies have failed to demonstrate an antiinflammatory effect of US, and results suggest US is ineffective.14 US may be effective at normalizing inflammatory events and may have therapeutic value in promoting overall repair.1,7
During the proliferative phase (scar production), US is proproliferative and stimulates (cellular up-regulation) fibroblasts, endothelial cells, and myofibroblasts.1,9 US may maximize efficiency, producing the required scar tissue in an optimal fashion. Low-dose pulsed US increased protein synthesis and enhanced fibroplasia and collagen synthesis.15-17 Recent work has identified the critical role of numerous growth factors in relation to tissue repair, and there is some evidence for an effect of US on growth factors and heat shock proteins.13,17
During the remodeling phase of repair, the somewhat generic scar is refined such that it adopts functional characteristics of the tissues that it is repairing. Remodeling involves reorientation of the collagen fibers18 and a change from predominantly type III to more mature type I collagen. Therapeutic US increases tensile strength and scar mobility by enhancing collagen fiber orientation and the collagen profile change from type III to type I.19 US enhances functional capacity scar tissue.19
The application of very low-dose US over a fracture (whether healing normally, delayed, or nonunion) can be of benefit, but the effective “dose” is lower than most therapy machines can deliver. Higher-intensity US over a fracture can initiate a strong pain response, a property that may be helpful to locate stress fractures.1
Wires carrying an electric current produce a surrounding magnetic field. The magnetic field around a long straight wire is in the form of concentric circles around the central wire. When a current flows in a circular coil, an electromagnetic field is induced. A pulsed electromagnetic field (PEMF), which is emitted from an applicator, is transmitted through the tissues and is absorbed in those of low impedance (muscle and nerve), which are highly vascular, and tissues in which there is edema, effusion, or recent hematoma.21 PEMF therapy may have beneficial effects on damaged tissue cells, particularly at the cellular level.
Normal healthy cells have a selectively permeable membrane.22 When membrane integrity is lost through disease, chemicals that would otherwise not enter the cell can now enter, drastically lowering the voltage potential across the cell. The application of a PEMF to affected cells may restore cell membrane potential, transport, and ionic balance by either a direct ionic transport mechanism or an activation of various pumps (sodium/potassium).23,24 PEMF therapy is important in the inflammatory phase and reduced healing time after oral surgery in people.25 PEMF therapy may reduce pain.
Bone is a calcified collagenous structure and can develop a piezoelectric potential on its external and internal surfaces. Most studies have failed to show PEMF therapy significantly improves bone remodeling.26 A small but statistically significant effect of PEMF stimulation on cancellous bone graft incorporation was found in a small study (eight ponies), but missing data prohibit drawing any strong conclusions.27
The clinical effects of PEMF therapy, US, and laser are all similar; the key difference in clinical use relates to where the energy is absorbed rather than the effects achieved.21 They have little or no effect on normal cells because “abnormal” cells respond to lower energy levels than normal cells.21 US is better absorbed by dense collagen-based tissues and laser by superficial vascular tissues, whereas PEMF therapy is absorbed primarily in wet, ionic, low-resistance tissues such as muscle, nerve, areas of edema, hematomas, and effusion.
Low-level laser therapy (LLLT) is popular in people and animals. Laser is an acronym for light amplification by the stimulated emission of radiation. Laser light differs from ordinary light in that it is highly amplified and nondivergent. It forms part of the electromagnetic spectrum.29 High-power lasers (>10 W) are commonly used surgically but are not discussed here.30 Low-power lasers (<500 mW, <35 J/cm2) are used in the management of pain, wound healing, and soft tissue injury.31
Light wavelengths between 600 and 1300 nm are typically used with laser therapy.32 This includes both visible light and the near part of the infrared spectrum. Laser differs from other radiation in its unique properties of monochromacity (single wavelength), coherence (waves in phase), and collimation (waves in parallel).29 However, there exists some debate as to the necessity of such expensive properties, especially coherence.33 Superluminous diodes, lacking the property of coherence, are also used therapeutically.31 Superluminous diodes (660 and 870 nm) are equally effective in stimulating fibroblast proliferation as coherent, laser light (820 nm).
The lasing medium determines the wavelength emitted, and media such as helium neon (HeNe, 632.8 nm), gallium arsenide (GaAs, 904 nm), and gallium–aluminum–arsenide (GaAlAs, 820 nm) are used clinically.33 When used, the laser beam is scattered, reflected, transmitted, or absorbed.32 The magnitude of each depends on the application technique, the nature of the tissue being treated, and the wavelength of the incident light.30 Given the low irradiation level used, the effects are likely to be photochemical because there is no appreciable temperature increase.32
When applying LLLT, energy density (J/cm2) is an important recorded value, and ranges of 0.1 to 4 J/cm2 and 1 to 10 J/cm2 are used.29,32 However, some advocate values as high as 30 J/cm2.31
Because penetration is wavelength dependent, an infrared beam (wavelength, 800 to 900 nm) penetrates further than a visible red beam (wavelength, 600 to 650 nm).31 As a result, visible red laser light is used to treat wounds and skin conditions, whereas infrared laser light is used for deeper conditions.29,31
Energy density (J/cm2) is measured at the skin surface, but energy density applied to deep target tissues is unknown because of the exponential tissue absorption of the energy and uncertainty about penetration depth.29 Longer wavelengths penetrate further than shorter wavelengths.33,34 However, actual penetration and energy density at a target site can only be speculated. Hair and skin pigmentation may adversely influence penetration.
Laser therapy is used widely in animals,35 and 50% of UK veterinary surgeons surveyed in 1993 were aware of it.36 Of animal physiotherapists surveyed, 64% used laser therapy, which equaled the number using US therapy.37 Although LLLT has gained popularity during the past 20 years,31 acceptance is hampered by a paucity of supportive studies using standard research protocols,38-40 and there are both advocates30 and detractors.41 In a randomized controlled clinical trial, LLLT had a significant pain-relieving effect, reduced joint swelling, and caused an objective improvement in hand function in people with rheumatoid arthritis.42
LLLT may be used in the treatment of nerve compression, bruising, wounds, tendon and ligament injuries, edema, and for pain relief.35,43-46
In cell cultures, LLLT wavelengths of 660 and 870 nm (noncoherent) and 820 nm (coherent) encouraged macrophages to release factors that stimulate fibroblast proliferation and thus promote healing.33 LLLT reduced experimentally induced inflammation by 20% to 30%.47,48 In vitro experiments showed an effect of laser on cells; however, the results of in vivo study results are inconsistent.49-51
There is general agreement on dose guidelines for LLLT,39 but an infinite number of combinations and permutations of parameters are possible.52 Rationale behind protocols remains unclear, although laboratory findings indicate effects are dose dependent.53
Tissue healing and pain control are the main areas for which laser therapy is used in people.29 Wound healing, soft tissue injuries, and pain apparently respond well.
LLLT may be used for management of pain.29 Laser significantly reduced pain and improved movement in people with rheumatoid arthritis42 and osteoarthritis.53
LLLT can directly induce analgesia when locally applied and indirectly when used at acupuncture and trigger points.32 People with cervical pain were managed with LLLT, and axonal beading by delayed nerve transmission was thought to occur.52
Studies in horses are lacking, but 14 horses diagnosed with chronic back pain were treated with laser (904 nm) acupuncture in an uncontrolled clinical trial.54 Back pain was eliminated in 10 horses, nine of which continued to perform at an acceptable standard 1 year later.
Twelve musculoskeletal conditions (excluding osteoarthritis) were included in a meta-analysis, in which there was an equal number of positive and negative outcomes.55 There was no evidence to support the use of LLLT for posttraumatic joint disorder, myofascial pain, and rheumatoid arthritis. A Cochrane review of the use of a 904-nm laser concluded that LLLT was effective for fast pain relief and quicker functional recovery, most specifically in the treatment of rheumatoid arthritis.56 Using ultrasonographic assessment, there was a decrease in tendon diameter in people with de Quervain’s tenosynovitis after 2 to 4 J/cm2 LLLT (wavelength not specified).57
Of U.K. chartered physiotherapists surveyed in 1994, 64% used laser in the treatment of horses and dogs.58 Laser therapy in animals is used for pain relief, wound healing, and to promote hoof growth.43
There are mixed results in research studies of LLLT in animals.31 In an uncontrolled clinical trial in Standardbreds, there was a successful outcome after treatment of soft tissue injuries using a 904-nm laser.59
In experimental studies using LLLT, results are often inconclusive or mixed, with both positive59 and negative outcomes.60 Closure of chronic canine wounds was thought to be enhanced in a noncontrolled case report,61 but this article is typical of much of the LLLT literature—anecdotal evidence lacking the necessary scientific format for appropriate analysis. Sutured teat wounds in dairy cattle were irradiated by LLLT, and histopathological examination and laser Doppler flowmetry demonstrated improved healing.62 The effect of laser on equine wound healing was reported.63 Surgically transected rat medial collateral ligaments exposed to laser (GaAlAs) gained a larger fibril diameter compared with controls.64 Laser research is generally poor quality, with inadequate study design, lack of controls, and inconsistent recording of treatment parameters.32 However, enough evidence exists to justify continued investigation.65
Transcutaneous electrical nerve stimulation (TENS) is widely used to modify pain, whereas neuromuscular electrical stimulators (NMES) are used for muscle reeducation, prevention of muscle atrophy, and enhanced joint movement. Almost all electric stimulators are TENS units; they work transcutaneously through surface electrodes to excite nerves. TENS can stimulate muscle fiber activation in both normal and denervated muscle. NMES is used to treat a wide variety of physiological disorders and injuries in people and animals. It is the administration of an electrical current generated by a stimulator that travels through leads to electrodes placed on the skin to depolarize the motor nerve and produce a skeletal muscle contraction.
Three types of current are commonly used:
The phase duration is the time in which the current flows from the baseline in one direction and back to the baseline. The current may be monophasic, in which the pulse duration and the phase duration are the same, or biphasic, when the two phases make up one pulse. Pulsed current consisting of a bidirectional flow of charge is called biphasic pulsed current. When the duration of flow in each direction is the same, but the amplitude-dependent features differ, then the biphasic current is termed asymmetrical. Zero net DC current occurs when the total charge in one phase equals the total charge of the other phase. Both pulsed AC and DC current forms are commonly used in portable and clinical model NMES units.
Increasing the current intensity (milliamps) induces a stronger force of muscle contraction by recruitment of motor nerves at greater distances from the electrode. Lowering the skin’s resistance decreases the driving voltage necessary for skin penetration, making stimulation more comfortable. Fortunately, horses have low skin resistance, and less current intensity is required to produce a sensory and motor effect.
Increased current amplitude is required to produce a given amount of muscular force if the pulse or phase durations are short. Symmetrical or asymmetrical biphasic pulsed currents use intermediate current amplitude levels.
Pulse duration of 200 to 400 µs produces powerful contractions while minimizing the likelihood of recruiting many pain fibers. As the pulse duration increases, smaller-diameter pain fibers are recruited.
Pulse rate (frequency and pulse per second) is the number of pulses delivered per second and is measured in hertz (Hz). Tetanic muscle contractions may be produced with frequencies as low as 20 Hz. A maximum force contraction generally occurs between 60 and 100 Hz, and fatigue will occur as frequency increases.
Duty cycle is the ratio of on time to total cycle time, expressed as a percentage. On time is the period in which a series of pulses is delivered. Off time is the time between on times. As the on time increases, muscle fatigue increases. A horse with severe atrophy may require a longer off time to recover between contractions; therefore monitoring of fatigue is required.
NMES recruits type II (fast-twitch) fibers before type I (slow-twitch) fibers, the reverse of the muscle recruitment pattern seen in a volitional contraction.66 Increasing the pulse duration increases the recruitment of smaller diameter motor units at the same depth. Increasing the amplitude or pulse duration affects the strength of contractions because additional muscle fibers are recruited. Increasing the frequency results in the existing motor units firing at a faster rate and increases the strength of contractions, but it will also result in more fatigue.
NMES is commonly used for the treatment and rehabilitation of people who have had neurological or orthopedic injury. Examples include spinal cord injury, paralysis, or paresis from neurological disease and more commonly in joint disease or joint pain. NMES is used to mobilize and strengthen after edema, contractures, or surgical procedures resulting in nerve injury, to minimize atrophy, improve strength, halt the loss of volitional control, improve sensory awareness, decrease pain, and correct gait.
NMES was shown to halt muscle atrophy and improve recovery after reinnervation in rats with surgically severed peroneal nerves,67,68 although there may be detrimental effects, including altered muscle structure69 and muscle-generating capacity.70 NMES of the triceps brachialis muscle in monkeys enhanced oxidative capacity and increased fiber size.71 Capillary proliferation was seen in response to increased muscle blood flow, resulting in proliferation of endothelial cells. Microvascular perfusion is enhanced when applied at intensities that produce muscle contractions.72
Increased muscle strength, muscle mass, and oxidative capacity plus the ability to overcome the effects of reflex inhibition on muscles are possible effects.73,74 Care must be taken to avoid muscle fatigue, probably caused by the preferential recruitment of type II muscle fibers. If current intensity is too high, painful contractions may develop.
TENS provides a degree of pain relief (symptomatic) by specifically exciting sensory nerves and thereby stimulating either the pain gate mechanism or the opioid system. These different physiological mechanisms dictate how TENS is applied.
TENS is noninvasive and has few side effects compared with drug therapy. The most common side effect is an allergic-type skin reaction seen in 2% to 3% of people and usually caused by the material of the electrodes, the conductive gel, or the tape used to hold electrodes in place. Most TENS applications are now made using self-adhesive, pregelled electrodes, which have several advantages, including reduced cross-infection risk, ease of application, lower allergy incidence rates, and lower overall costs.
The current intensity (strength) is in the range of 0 to 80 mA (up to 100 mA). Although small, this current is sufficient because the primary targets are the sensory nerves, and provided these nerves are depolarized, TENS can be effective. The machine delivers “pulses” of electrical energy, and pulse rate varies from about 1 or 2 pulses/sec (pps) up to 200 or 250 pps. In addition to the stimulation rate, the duration (or width) of each pulse may be varied from 40 to 250 µs.
Most modern machines have a burst mode in which the pulses are allowed out in bursts or “trains,” usually at a rate of 2 to 3 bursts/sec. Modulation mode, which uses a method of making the pulse output less regular and therefore minimizing the accommodation effects, is sometimes available. Short-duration pulses can be effective because the sensory nerves have relatively low thresholds and depolarize following stimulation for less than a millisecond. The pulses delivered by the TENS stimulators vary between manufacturers but tend to be asymmetrical biphasic modified square wave pulses. Biphasic pulses have no net DC component, so skin reactions from a buildup of electrolytes under the electrodes are uncommon.
Pain relief from TENS occurs by activating the pain gate mechanism and/or the endogenous opioid system. Pain relief from the pain gate mechanism involves excitation of the Aβ sensory fibers, and by doing so, reduces transmission of noxious stimuli from the “c” fibers through the spinal cord and hence onto the higher centers. Ideal pulse rate for Aβ fibers is high (90 to 140 Hz or pps), but it is unlikely a single frequency works well for every horse.
Alternatively, Aδ fibers respond preferentially to much lower stimulation rates (2 to 5 Hz), and when stimulated activate an opioid mechanism that causes the release of endogenous opiates (enkephalins) in the spinal cord.
Both nerve types can be stimulated simultaneously by using burst mode stimulation. High-frequency stimulation (about 100 Hz) is interrupted (or burst) at the rate of about 2 to 3 bursts/sec.75 Pulses at 100 Hz activate Aβ fibers and the pain gate mechanism, but burst excitation of Aδ fibers activates the opioid mechanism with release of enkephalins.75 For some horses, this is by far the most effective approach to pain relief.
Traditional TENS uses stimulation at a relatively high frequency (90 to 130 Hz) and uses a relatively narrow pulse width (start at about 100 µs). Thirty minutes is the minimal effective time, but it can be delivered for as long as needed. The main pain relief is achieved during the stimulation, with a limited “carryover” effect, that is, pain relief after the machine has been switched off.
Acupuncture TENS uses low-frequency stimulation (2 to 5 Hz) with wider (longer) pulses (200 to 250 µs). The intensity used is usually greater than with traditional TENS, resulting in a definite strong sensation. Thirty minutes are needed to deliver a minimally effective dose. Opioid levels are slow to build up, and the onset of pain relief may be slower than with the traditional mode. Once sufficient opioid has been released, it keeps working after cessation of the stimulation. Many human patients find that the stimulation at this low frequency at intervals throughout the day is an effective strategy. The “carryover” effect may last for several hours.75
Brief intense TENS achieves rapid pain relief, but the strength of the stimulation may be too intense and intolerable. The pulse frequency (90- to 130-Hz band) and the pulse width (200-µs plus) are high. The current is delivered at, or close to, the tolerance level, and the energy delivered is high compared with the other approaches. Fifteen to 30 minutes is all that can be tolerated.
In human medicine, the most effective intensity management appears to be related to what the patient feels during stimulation, and this may vary from session to session. In veterinary medicine, it is not possible to determine the sensory response in the same way. Horses show a visible endorphin response demonstrated by body posture and eye dilation. Resentment is clearly displayed by a high head carriage, tail swishing, and an obvious dislike to what is being done.
For maximal benefit, target the stimulus at the appropriate spinal cord level (appropriate to the pain) by placing the electrodes on either side of the lesion (painful area). Some alternatives that are effective, most of which are based on the appropriate nerve root level: stimulation of appropriate nerve root(s), the peripheral nerve, motor point(s), trigger point(s), or acupuncture point(s),76 or appropriate dermatome, myotome, or sclerotome.77
A two-channel application can be effective for treatment of vague, diffuse, or particularly extensive pain or the management of a local and a referred pain combination (one channel used for each component).
TENS is a noninvasive method of giving pain relief; however, despite extensive studies in people,66,67,72,76-80 there are few studies analyzing the therapeutic effect in veterinary medicine.