Posterior cord or spinal cord neurostimulation is a minimally invasive technique for chronic pain control that was introduced by Shealy in 1967. Currently about 50,000 neurostimulators are implanted each year around the world for the treatment of different pathologies.
Technique
Spinal neurostimulation consists of the following components: 1 or 2 electrodes, an extension cable, a pulse generator and an external programmer. The electrodes can have from 4 to 8 poles and are placed in the epidural space in a number of one or two. They are usually inserted through the skin under local anesthesia and sedation as this is the least invasive procedure. The electrodes advance through the epidural space until they are located in a region of the spinal cord that picks up the sensitivity of the patient’s painful area. Electrical impulses are sent, the patient then notices a tingling stimulus, not painful, which covers the area affected by the pain and seeks to “cover” or block the painful impulses.
This procedure is called first time since the electrodes are left in that area and a temporary cable connected to an external generator comes out through the skin. The parameters of frequency, amplitude and intensity of the electrical impulses are programmed and the patient is instructed on how to use, turn on and turn off the system. It is a provisional period of one or two weeks after which, if the patient has noticed a decrease in pain of 50% or more, together with an improvement in his quality of life, he is considered to have responded to the treatment and a definitive generator is placed under the skin.
Mechanism of action
There are different theories to explain the analgesia produced by spinal cord neurostimulation. One of them is the gateway theory of pain, proposed by Melzack and Wall in 1965. Painful impulses from an area of the body are transmitted by nerve pathways to the spinal cord and from there to the brain, which makes us aware of the pain. By means of electrical impulses that travel faster than the pain, it is possible to block their entry into the spinal cord and mitigate the painful sensation. Also, spinal neurostimulation produces dilation of the capillaries (very small blood vessels), causing more blood to reach the stimulated areas.
Indications
Medullary neurostimulation has been applied most frequently in the so-called “failed back surgery syndrome”, that is, in those patients who have undergone one or more spinal operations for herniated discs and who have not achieved relief of their lumbar or leg pain. It is also applied in pain secondary to nerve injury, as in cases of postherpetic neuralgia, peripheral neuropathies, occipital neuralgia, reflex sympathetic dystrophy. In cases of obstruction of the arteries that produce ischemia of the extremities in those patients who are not subsidiaries of more surgical interventions and in special cases of myocardial angina.
Complications
It is a relatively safe procedure. The most frequent complication is that the electrodes move from the right place and have to be repositioned. Another complication is infection of the surgical wound, but this is very infrequent with the correct aseptic measures.
Cost and effectiveness
In observations in patients with previous spinal surgery, it has been noted that the initial cost is significant, but if adequate pain relief is achieved it is an alternative to reoperation. In addition, in the long run, the use of analgesics, visits to specialists or the use of medical resources such as rehabilitation are reduced.
Conclusion
Spinal cord stimulation has demonstrated satisfactory clinical efficacy in methodologically correct research. It is postulated as an alternative to be considered in cases of patients with chronic pain that is difficult to alleviate and does not respond to pharmacological or rehabilitation treatments.