Transcutaneous Electrical Nerve Stimulation (TENS) is a non-invasive, medication-free method for managing chronic or acute pain. This small, battery-operated device delivers mild, low-voltage electrical currents through pads placed on the skin. TENS aims to reduce the perception of pain by targeting specific nerve pathways, making it popular for localized issues like knee pain. Proper electrode placement is the single most important factor for effective relief, ensuring the impulses reach the correct nerves surrounding the joint.
Understanding TENS Therapy Basics
TENS works by activating two biological mechanisms to achieve its analgesic effect. The first is the Gate Control Theory of pain, which provides immediate, short-term relief. Gentle electrical stimulation activates large, non-pain-carrying nerve fibers, effectively “closing a gate” in the spinal cord. This prevents smaller nerve fibers from transmitting pain signals to the brain, masking the sensation of pain.
The second mechanism involves the body’s natural pain regulation system, providing longer-lasting relief. When the TENS unit is set to specific parameters, it stimulates the release of endogenous opioids, such as endorphins. These chemicals act as natural painkillers, binding to receptors in the nervous system to reduce pain intensity.
Essential Rules for Proper Pad Placement
Before applying electrodes, preparing the skin is necessary to ensure consistent electrical conduction. The skin must be clean, dry, and free of lotions or oils, which can degrade the adhesive and block the current. If the area is excessively hairy, trimming the hair is recommended for better adhesion and to prevent discomfort upon removal.
Selecting the correct electrode size is important; pads that are too small may not cover the target area, and pads that are too large may cause current overlap. Pads must never touch each other and should be positioned at least one inch apart. They should always bracket or surround the area of pain, avoiding placement directly over a bony prominence or the joint itself, such as the kneecap.
Targeted Pad Placements for Knee Pain
The most effective placement strategy for the knee depends directly on the location and nature of the pain.
Front of the Knee Pain
For pain primarily around the front of the knee, a vertical alignment is often used. This involves placing one pad slightly above the kneecap on the lower quadriceps muscle and the second pad directly below the kneecap on the upper shin. This setup targets the nerve branches feeding the front of the joint while safely avoiding direct placement on the patella bone.
Deep Joint Pain
When discomfort is felt deep within the joint or along the joint line, such as with meniscal issues or localized arthritis, a side-to-side placement is more beneficial. This “sandwich” technique places one pad on the inner (medial) side of the knee and the corresponding pad on the outer (lateral) side. The current travels horizontally through the joint space, effectively targeting the deep nerves responsible for the localized pain.
Generalized or Diffuse Pain
For generalized, diffuse, or deep aching pain covering a larger area, a wider bracketing or cross-hatch technique is recommended. One pair of pads can be placed high on the thigh and high on the calf to capture the main nerve pathways supplying the entire knee joint. Alternatively, a four-pad cross-hatch pattern can be used, placing pads diagonally above and below the joint on the front and back of the leg.
Optimal TENS Settings and Usage Duration
Once the pads are secured, adjusting the TENS unit settings is necessary to customize the treatment for the type of pain experienced.
Settings for Acute Pain
For immediate, acute pain relief, use a high frequency (typically 80 to 120 Hertz or Hz) and a low intensity. This setting maximizes the Gate Control Theory effect, providing a strong, continuous tingling sensation that overrides pain signals.
Settings for Chronic Pain
For chronic or persistent pain, a low-frequency setting (usually 2 to 10 Hz) coupled with a higher intensity is more appropriate. This promotes the release of the body’s natural opioid chemicals, leading to longer-lasting pain relief that persists after the session ends.
Users should always start with a low intensity and gradually increase it until a strong but tolerable tingling or buzzing sensation is felt. Avoid any setting that causes muscle contraction or discomfort.
Usage Duration and Safety
The recommended duration for a TENS session typically ranges from 20 to 40 minutes, which can be repeated two to three times per day as needed. Avoid using the TENS unit over broken skin, near the eyes or throat, or if the user has an implanted electronic device like a pacemaker.