Using TENS for knee pain

Background

About one-quarter of adults suffer from frequent knee pain, which limits their mobility, disrupts their sleep and decreases their quality of life.  Chronic knee pain is usually treated with anti-inflammatory drugs such as ibuprofen, and sometimes with prescription opioids.  However, these medications may not be effective and often have side effects.  Opioids are particularly worrisome because of their addiction potential.  Knee replacement surgery, called total knee arthroplasty, is an option for some patients, however it is expensive and has a long recovery time.  There is an urgent need for drug- free and non-surgical treatments for chronic knee pain.

Transcutaneous Electrical Nerve Stimulation

Transcutaneous electrical nerve stimulation (TENS) is a safe, non-invasive treatment for chronic pain.  TENS devices generate an electric current that is passed through two, and sometimes more, electrodes that are placed in the vicinity of the pain.  The strength of the electric current, called intensity, is increased until the user feels a strong, non-painful sensation around the electrodes.  The medical term for this sensation is paresthesia.  The user typically experiences a decrease in pain within 10-20 minutes.  It is recommended that each treatment session last 30-60 minutes.  Pain relief occurs during stimulation and for a short time afterwards, and so treatment should be repeated multiple times a day (and even overnight) to help manage pain.

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How does TENS work?

TENS has been used for 50 years to provide pain relief, however the reason it works remains something of a mystery.  The most common explanation is based on the pain regulation theory proposed by Drs. Ronald Melzack and Patrick Wall in 1965 called the “pain gate theory.”  This theory states that stimulation of nerves carrying non-painful sensations (called A-beta nerve fibers) closes a neurological “gate” in the spinal cord that reduces transmission from pain nerves (called A-delta and C nerve fibers) to the brain.  By preventing pain signals from reaching the brain, the perception of pain decreases.  An illustration of the Melzack and Wall theory is shown below.

 

Let’s say you have inflammation in the knee causing pain.  This signal will be carried from your knee to the spinal cord by C and A-delta nerve fibers.  Once in the spinal cord, the signal is passed to a projection neuron that sends it on to your brain (sensory cortex) which results in you feeling the pain.  However, if you simultaneously stimulate the A-beta nerve fibers with a TENS device, then that non-painful signal will be carried to the spinal cord where it activates an interneuron that inhibits the projection neuron from sending the pain signal from the C and A-delta nerve fibers to your brain, leading you to feel less pain.  If you think of the projection neuron as a “pain gate” then the stimulation of the A-beta nerve fibers “closes the gate.”  In reality the biological mechanisms are considerably more complicated than depicted here, nevertheless the pain gate theory remains a useful tool for understanding how TENS works.

How effective is TENS for chronic knee pain?

As for most pain relief approaches, the answer is complicated.  There have been many, in fact hundreds, of clinical studies of TENS for knee pain, both for acute pain following knee surgery and for chronic pain.   Many studies suggested that TENS was effective in reducing knee pain, however some were unable to show that TENS actually reduced knee pain.  This situation is not unexpected for studies evaluating pain treatments because of the complexity of pain.  Experts in the TENS field, such as Professors Mark Johnson of Leeds Beckett University in the UK and Kathleen Sluka of the University of Iowa, believe that the inconclusive results are primarily due to poorly designed studies that used TENS sub-optimally. A common error in many studies, and also one made by people using TENS at home, is an inadequate stimulation intensity. It is crucial that TENS feel strong, otherwise an insufficient number of nerve fibers have been activated. Stimulation that is barely felt will not produce pain relief.  The required intensity will vary from person to person.  Another common problem is using TENS sporadically, such as 20-30 minutes a few times a week, and yet expecting substantial improvement in pain that is nearly constant.  TENS provides transient pain relief and needs to be used regularly to improve pain.  One should be skeptical of claims that a single brief TENS treatment will provide prolonged pain relief.

On balance it appears that TENS is effective for knee pain.  As for any pain treatment, it will not work for everyone and the amount of pain relief will vary.  You can increase your chances of getting meaningful pain relief by using as strong an intensity as comfortable and using your TENS device regularly when you are experiencing pain.

Will it work for me?

Knee pain is complicated.  In some people it is primarily caused by irritation of pain fibers around the knee, such as by inflammation.  In others, it may be due to hypersensitivity resulting from changes in the way pain is processed in the spinal cord and brain, called central sensitization.  Moreover, people react differently to similar pain because of their genetic, physiological and psychological make-up.  So, while it is true that TENS can be effective in knee pain, it is not possible to predict who will benefit and how much.  This is really no different than any other pain treatment.  The good news is that TENS is completely safe and so you can explore whether it helps you manage your pain and improve your quality of life.

Quell® for Knee Pain

Quell is a wearable pain relief device designed specifically for knee pain.  It is prescription strength and the most advanced TENS device available, and best of all you can get it quickly without a prescription.

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