Transcutaneous electrical nerve stimulation (TENS) is a non-pharmacological technique that delivers low-voltage electrical impulses through the skin to manage pain. This modality is commonly integrated into the recovery protocol following Total Knee Arthroplasty (TKA), or knee replacement surgery. The device works by stimulating sensory nerves, effectively interfering with or blocking the transmission of pain signals to the brain, which is often described as the “gate control theory” of pain modulation. Using a TENS unit can significantly reduce the intense, acute pain experienced after surgery, potentially decreasing the reliance on prescribed pain medications. Proper application of the electrode pads and correct operational settings are necessary to achieve maximum therapeutic benefit during rehabilitation.
Safety First: Pre-Application Guidelines
Before incorporating a TENS unit into a post-surgical recovery plan, consult with the orthopedic surgeon or a physical therapist. They can confirm that TENS is appropriate for the individual’s specific condition and recovery timeline. There are certain medical contraindications where TENS should not be used, most notably if a patient has an implanted electronic device, such as a cardiac pacemaker or defibrillator, as the electrical current could potentially interfere with its function.
The electrode pads must never be placed directly over the surgical incision, or on skin that is swollen, irritated, or broken. Prior to application, the skin in the intended placement area should be cleaned and dried to ensure optimal adhesion and electrical conduction. The TENS unit must be turned off before the pads are connected or applied to the skin. This prevents a sudden, uncomfortable electrical jolt when the pads make contact.
The use of a TENS unit is intended to be a supplementary tool that works alongside other pain management strategies and physical therapy exercises. It is not a replacement for prescribed pain medication, but rather a method to help control discomfort during periods of activity or rest. Patients should be mindful of skin sensation in the area, as TENS should be used with caution on areas of reduced feeling.
Primary Placement for Incisional and Joint Pain
The most common and effective method for targeting acute post-surgical pain immediately around the joint is known as “bracketing” the area of discomfort. This involves using electrode pads to create a therapeutic electrical field that surrounds the painful knee. For a standard four-pad unit, a common approach is to place two pads above the knee and two pads below the knee, positioning them on the fleshy parts of the thigh and calf. An alternative bracketing method involves placing one pair of pads on the medial (inner) side of the knee and the second pair on the lateral (outer) side. Regardless of the pattern chosen, the pads should be positioned so that the electrical current crosses through the painful joint area.
The pads must be kept at least one inch (five centimeters) away from the surgical incision to prevent irritation and ensure proper healing. It is important to avoid placing the pads directly on the kneecap or on any bony prominences, as the sensation can be less comfortable and less effective. The goal is to place the pads over muscle tissue or nerve pathways surrounding the area where the pain originates. Finding the exact placement that provides the most relief may require slight adjustments during the first few sessions.
Alternative Placement for Referred or Muscular Pain
While joint-specific placement targets the surgical site, pain following TKA often radiates or presents as muscle spasms in the surrounding musculature. When the primary placement does not provide sufficient relief, pads can be moved to target the large muscle groups of the thigh, such as the quadriceps. The quadriceps muscle group, specifically the vastus medialis obliquus (VMO), is often weakened and contributes to knee instability and discomfort following surgery.
To address muscular discomfort in the quadriceps, pads can be placed over the muscle belly, such as positioning one pad over the distal vastus medialis and the other over the proximal vastus lateralis. This placement targets the muscle tissue and motor points to help alleviate tension and cramping. For pain that seems to radiate down the back of the leg, pads can be placed over the hamstring muscle group, with one pad near the gluteal fold and the other just above the back of the knee.
It is important to understand that TENS, which is used for pain relief, is distinct from Neuromuscular Electrical Stimulation (NMES), which is used to induce a muscle contraction for strengthening. When using TENS for pain, the intensity should remain at a level that causes a strong but comfortable tingling, without causing the muscle to visibly contract. This distinction is necessary to ensure the device is used for pain control rather than a therapeutic exercise that might be too strenuous for the early post-operative phase.
Understanding TENS Settings and Duration
Effective pain relief depends not only on correct pad placement but also on selecting the appropriate operational settings. For acute post-operative pain, the conventional TENS mode is typically recommended. This mode often uses a high frequency, usually set between 80 and 120 Hertz (Hz), combined with a narrow pulse width ranging from 50 to 200 microseconds (µs). The intensity, or amplitude, should be slowly increased until the patient feels a strong, buzzing, or tingling sensation that is comfortable and not painful.
This sensory level stimulation is necessary to activate the pain-blocking mechanisms in the nervous system. If the sensation begins to fade during a session, the intensity may need to be adjusted higher to maintain the therapeutic effect.
A single TENS session for post-operative pain typically lasts for 20 to 30 minutes, though some protocols recommend up to 60 minutes. TENS can be applied multiple times a day, often before or during physical therapy exercises to help minimize movement-related discomfort. Regular, consistent use is generally more effective than intermittent use, but breaks are recommended between sessions to reduce the risk of skin irritation.