Janet B. Van Dyke, DVM, DACVSMR
Therapeutic plans in veterinary rehabilitation generally involve a combination of manual therapies (joint mobilizations and soft tissue mobilizations), physical modalities (laser, therapeutic ultrasound, e-stim, shockwave), and therapeutic exercises. The modalities are generally used to prepare the tissues for the manual therapies and therapeutic exercises. Physical modalities should never be the sole therapeutic method applied to any patient. Therapeutic parameters for each modality are chosen based upon the acuity of the injury, so the therapist must be well versed on the definitions of the acute, subacute, and chronic phases of healing. The mechanism of action for neuromuscular electrical stimulation (NMES) is electrical stimulation causing muscle contraction. The mechanism of action for transcutaneous electrical nerve stimulation is electrical stimulation at a frequency that does not cause muscle contraction but that blocks afferent input leading to pain relief.
NMES has many applications in veterinary rehabilitation including reduction of edema, muscle reeducation, reversal of atrophy, and wound healing. At the cellular level, NMES causes excitation of nerve cells leading to changes in cell membrane permeability, stimulation of protein synthesis and stimulation of fibroblast and osteoblast activity. Wound healing is enhanced through increased blood flow to the area and stimulated cell turnover. TENS is used for pain control. In very simplistic terms, TENS works along the lines of the Gate Theory introduced by Wall and Melczak in the 1960s: the severity of pain sensation is a result of the balance between the excitatory and inhibitory inputs to the T cells in the spinal cord. By stimulating peripheral nerves at proper frequencies, the excitatory nociceptive inputs can be blocked from traveling to the brain where pain is recognized. TENS has a short-lived effect, lasting perhaps up to an hour after the application is stopped. It is used in veterinary rehabilitation as immediate post-operative pain control and during therapy sessions to allow pain free movement during exercises.
Electrotherapy variables include intensity, mode, ramp duration, on:off time, pulse width, frequency, treatment duration, and treatment frequency. Intensity is measured in milliamps (mA), and is generally between 50 and 400 mA. Intensity determines how many nerve fibers are stimulated. Mode can be set to constant, synchronous, or alternate. In constant, there is a constant flow of current through both channels. In synchronous, both channels turn on and off simultaneously. In alternate, the one channel turns on as the other turns off. Ramp durations is the time that the stimulus takes to reach peak intensity and is measured in seconds, on:off time is the ratio of time during which the intermittent current is on and is measured in seconds. Pulse width is the length of time that pulses of electricity are on and is measured in microseconds. Pulse width determines which nerve fibers are stimulated, and widths of greater than 150 microseconds are more comfortable for the patient. Frequency, measured in Hertz (Hz) or pulses per second, is the speed at which pulses enter the body, and determines the amount of muscle tension that is developed. Higher frequency is more comfortable. Frequencies of 1 to 10 Hz are used for pain management, while frequencies of 25–50 Hz generate strong tetanic muscle contractions. Treatment duration is generally between 15 and 20 minutes, and treatment frequency is generally at least two to three times per week. Depth of penetration is determined by the distance between the electrodes. Electrodes must be flexible to conform to the patient’s muscles, low resistance (less than 100 ohms), highly conductive, reusable, inexpensive, and appropriately sized for the patient. A medium, usually gel, is necessary to transmit the current between the electrode and the patient’s skin.