Physical Therapy Modalities for Older Persons
10.8 Electrotherapy
10.8.3 Transcutaneous Electrical Nerve Stimulation (TENS)
TENS is a non-pharmacological method, which is widely used for the management of acute and chronic pain in a variety of conditions. TENS is a noninvasive, inexpensive, and safe intervention, defined by the American PRM Association as the application of
10 Physical Therapy Modalities for Older Persons
86
an electrical stimulation to the skin for pain management. The Food and Drug Administration (FDA) has approved TENS as a method of pain alleviation and classi- fied it as class II device in 1972 [41]. The most popular theory to explain the mecha- nism of action of TENS is “gate control theory” of pain proposed by Melzack and Wall in 1965. They suggested that TENS stimulates large-diameter A-β fibers induc- ing an inhibition of substantia gelatinosa interneurons, localized in the spinal cord.
The result is a repression of smaller A-δ and C pain fibers, with consequent presynap- tic inhibition of the T-cells, closing of the “gate,” and control of pain perception [42].
In 1977, Mayer et al. investigated the “opioid theory” as a second explanation for the mechanism of action of TENS. They hypothesized that naloxone, an opioid receptor antagonist, blocks the analgesia produced by low- frequency electroacupuncture (<10 Hz), suggesting that it works through the release of endorphins [43].
TENS devices are small portable contraptions powered by rechargeable or replaceable batteries, based on a one- or two-channel mode (Fig. 10.6). The unit is usually connected to the skin using two or more electrodes. A typical battery- operated TENS unit is able to modulate pulse width, frequency, and intensity.
Generally TENS is applied at high frequency (>50 Hz) with an intensity below motor contraction (sensory intensity) or low frequency (<10 Hz) with an intensity that produces motor contraction.
Fig. 10.6 TENS device
A. Musumeci et al.
87
Electrodes of 4–30 cm2 size can deliver current as biphasic, spike (Fig. 10.7a) or rectangular, symmetric (Fig. 10.7b), or asymmetric (Fig. 10.7c) waveform. The presence of the negative wave prevents accommodation of nervous fibers so that current cannot induce membrane damages.
The correct placement of the electrodes represents one of the reasons of the successful treatment. The correct sites of application depend on the variety of clinical and individual conditions. The electrodes can be positioned on trigger points (Fig. 10.8a, b), tender points, peripheral nerve, dermatomes, spinal nerve roots, motor points, and acupuncture points. Depending on the location of the painful area, the electrodes can be placed transversely, longitudinally (Fig. 10.8c), in a crossed manner (Fig. 10.8d), contralaterally, in a transarticular, or in a “Y”
piggyback position [44, 45].
a b c
+ - Fig. 10.7 (a) Spike wave, (b) symmetric rectangular wave, (c) asymmetric rectangular wave
a b
d c
Fig. 10.8 (a) Trigger points for ankle pain, (b) trigger points for cervico-brachial pain syndrome, (c) longitudinal disposition, (d) crossed disposition
10 Physical Therapy Modalities for Older Persons
88
TENS can be effective in management of acute post-operative pain. Many high- quality studies have demonstrated the analgesic effect of TENS in acute post- operative pain and the advantage of simple positioning of the electrodes sidelong the surgical wound. The reported placebo effect of TENS is between 20% and 40%
and the analgesic effect between 70% and 85%.
Nowadays, the main indications of TENS include: sports injuries, acute neck pain, low back pain, dysmenorrhea, etc. In adulthood, TENS is used in pain related to TMJ disorders and during the dental treatment of root canal and dental extraction.
Several studies evaluated the role of TENS in the treatment of chronic pain, in par- ticular in rheumatoid arthritis, myofascial pain, neuropathic pain, and low back pain [46–48]. TENS can also improve obstetric, oncologic, and cardiac pain. Treatment modes of TENS for pain relief are resumed in Table 10.3 (Fig. 10.9).
TENS is contraindicated in patients with cardiovascular problems (cardiac pace- maker), venous or arterial thrombosis, cancer, various dermatological conditions, bleeding disorders and in pregnant women. In patients with epilepsy, TENS should be used carefully; the electrodes should not be positioned over the neck or head [49]. Recently, a new type of transcutaneous electrical stimulator has gained popu- larity that uses current intensities too small to excite peripheral nerves. The most common term used to describe these generators is microcurrent electrical nerve
Table 10.3 Common treatment modes of TENS for pain relief Mode
TENS
characteristics Advantages Disadvantages
Duration of treatment Conventional Frequency:
10–100 Hz Intensity: low to medium
Comfortable Fast action (10–15 min) Acute or chronic pain
Accommodation 30 min to hours
Strong low rate or acupuncture like
Frequency:
10 Hz Intensity: high
Medium lasting pain relief
Muscle spasms Fatigue
30–60 min
Brief intense Frequency:
60–150 Hz Intensity: high
Fast action Long lasting (6 h) Accommodation: rare
May not be effective for chronic pain Muscle spasms
15–30 min
Burst Frequency:
60–100 Hz Intensity: low to high
Long lasting analgesia More comfortable than low-frequency TENS
Small adaptation
Pain Fatigue
30–60 min
Modulated Frequency:
Pulse duration and amplitude are modulated Intensity: low to high
Comfortable Fast action Small adaptation Acute or chronic pain
May have shorter lasting effects May be uncomfortable
20–40 min
Hyperstimulation Frequency:
1–100 Hz Intensity: high
Comfortable Accommodation: rare
Slow acting 20–60 min A. Musumeci et al.
89
stimulators (MENS). Most recently the term MENS has been replaced by the new term low-intensity stimulation (LIS) [50].
Electroacupuncture uses low-frequency, high intensity electrical stimulation, applied on the traditional acupuncture points, to determine muscle contraction and pain relief. This technique is commonly used for acute musculoskeletal disorders [51].