TENS (Transcutaneous Electrical Nerve Stimulation) is a non-invasive method using mild electrical current delivered through electrodes to manage pain. This portable therapy is often used for conditions like Carpal Tunnel Syndrome (CTS), which involves compression of the median nerve in the wrist. TENS machines disrupt the transmission of pain signals to the brain, providing temporary relief from associated numbness, tingling, and discomfort. Effective relief depends heavily on the proper placement of electrodes, ensuring electrical impulses target the affected nerve pathway.
The Strategy for TENS Placement in Carpal Tunnel
The effectiveness of TENS for Carpal Tunnel Syndrome relies on understanding the median nerve’s path through the wrist and forearm. Electrode placement must focus on the area around the compression site or along the nerve’s route. TENS therapy operates on two main theories of pain relief that influence placement strategy.
The Gate Control Theory suggests that high-frequency impulses can override pain signals traveling to the brain. Alternatively, low-frequency stimulation may trigger the release of the body’s natural painkillers, called endorphins. Applying electrodes near the painful site aims to engage these mechanisms. The strategy involves placing electrodes directly over the area of compression or positioning them more proximally along the forearm to target the nerve higher up.
Specific Electrode Placement Techniques
Selecting the right electrode size is important for effective application on the wrist and forearm. Common sizes include round electrodes around 3.2 cm or square ones up to 4×4 cm.
Longitudinal Placement (Wrist)
This common technique targets the direct source of pain at the wrist. One pad is placed on the palm side of the wrist, just above the crease. The second pad is placed slightly distal to the first, closer to the palm’s base. This longitudinal arrangement aims to send the current directly across the carpal tunnel.
Proximal Placement (Forearm)
This technique focuses on the nerve pathway in the forearm. One electrode is positioned on the inner side of the forearm, about two to three inches above the wrist joint. The second electrode is placed a few inches further up the forearm. This maintains a clear path for the current to stimulate the median nerve before it enters the carpal tunnel.
Cross-Sectional Placement (Hand/Wrist)
This option addresses radiating pain into the hand, particularly the thumb, index, and middle fingers. This involves placing the pads on the back and front of the wrist or hand. For example, one pad is placed on the dorsal (back) side and one on the palmar (palm) side. This cross-sectional approach ensures the median nerve is surrounded by the electrical field. Pads must be placed on clean, unbroken skin and should not touch each other.
Optimizing TENS Unit Settings
Once electrodes are positioned, the unit’s settings must be adjusted to optimize pain relief. The three main parameters are frequency (Hz), pulse width (µs), and intensity (mA).
Frequency (Hz)
Frequency refers to the number of electrical pulses per second. A high frequency between 80 to 120 Hz is used for immediate, sensory-level pain relief, working primarily through the Gate Control Theory. For longer-lasting relief, a low frequency of 2 to 10 Hz is recommended, as this stimulates the release of endorphins.
Pulse Width (µs)
The pulse width determines the duration of each electrical pulse. A common starting point for nerve-related pain is a range of 150 to 200 microseconds (µs).
Intensity (mA)
Intensity, measured in milliamperes (mA), must be set to achieve a strong but comfortable tingling sensation without causing muscle contraction. Users should slowly increase the intensity until a noticeable, non-painful stimulation is felt under the pads.
Safety and Duration of Use
For safe and effective use, TENS therapy sessions for Carpal Tunnel Syndrome are recommended to last between 20 to 30 minutes. This duration can be repeated two to three times daily as needed for pain relief. Do not wear the TENS unit while sleeping, as this can lead to overstimulation or skin irritation.
TENS use must be avoided in certain situations. Individuals with pacemakers or other implanted electronic devices should not use TENS therapy due to the risk of electrical interference. Electrodes should never be placed over areas of broken skin, open wounds, or areas with decreased sensation. Avoid placing electrodes over the front of the neck, the eyes, or directly over the heart. If symptoms worsen or do not improve, consult a physical therapist or doctor.