Spinal Cord Stimulation

What is spinal cord stimulation?

Spinal cord stimulation (also known as dorsal column stimulation) uses a device that is surgically placed under your skin to send mild electric shocks to your spinal cord. A small wire called a lead carries the shocks from a generator/battery implanted in your abdomen to the nerve fibers of the spinal cord causing pain. When turned on, the stimulation feels like a mild tingling. Your pain is reduced because the mild electrical shocks interrupt the pain signal to your brain.

Stimulation does not eliminate the source of pain, it simply interferes with the signal, and so the amount of pain relief varies for each person. Also, some patients find the tingling sensation unpleasant. For these reasons a trial stimulation is performed before the device is permanently implanted. The goal for spinal cord stimulation is a 50-70% reduction in pain. Stimulation does not work for everyone; the implant is removable and does not damage the spinal cord or nerves.

Spinal Cord Stimulation (SCS)

Spinal cord stimulation uses low voltage stimulation of the spinal nerves to block the feeling of pain. Used since the 1970’s, it may be an option if a patient experiences intractable long-term (chronic) back pain, particularly leg pain, which have not found relief through traditional methods. A small implantable pulse generator (IPG), implanted in the patient's back or abdomen, transmits an electrical current to your spinal cord. The result is a tingling sensation called paresthesia instead of pain. By interrupting the pain signal, the procedure has demonstrated success in returning some patients to an active lifestyle. This surgical procedure can help treat chronic pain caused by:

• Failed back surgery syndrome: failure of one or more surgeries to control persistent leg pain (sciatica), but not technical failure of the original procedure.

• Reflex sympathetic dystrophy: a progressive disease of the nervous system in which patients feel constant chronic burning pain

• Causalgia: a burning pain caused by peripherial nerve injury.

• Arachnoiditis: painful inflammation and scarring of the meninges (protective layers) of the spinal nerves.

The technique is believed to inhibit chronic pain by stimulating large diameter afferent nerve fibres in the spinal cord. According to the pain gate theory proposed by Melzack and Wall in 1965, ascending impulses in these fibres may inhibit the conduction of pain signals to the brain. The implantation procedure involves placing electrodes in the epidural space, along with an IPG that allows alteration of parameters such as pulse width, duration and intensity of stimulation. Repetitive electrical impulses are then delivered to the spinal cord.

Mechanism of Action of Spinal Cord Stimulation

Spinal cord stimulation has been demonstrated to promote local blood flow and ischaemic ulcer healing in patients with peripheral vascular disease. Positron emission tomography (PET) shows a more homogenous pattern of coronary flow following spinal cord stimulation in patients with myocardial ischaemia but no increase in total flow. This redistribution of blood flow to areas that were previously ischaemic, may explain why there is an increase in exercise capacity prior to the inevitable onset of angina. To date there has been no proof of an increase in coronary flow velocity when patients undergo spinal cord stimulation.
It has been suggested that spinal cord stimulation might alter the sympathetic/parasympathetic balance, but no change in heart rate variability has been shown in a group of patients post spinal cord stimulation.

Spinal Cord Stimulator Implantation

Spinal cord stimulator implantation is a surgical procedure requiring complete aseptic technique and prophylactic antibiotics. The system has three components: an epidural lead with a number of electrodes over a variable length, an extension lead and an implanted pulse generator. The patient lies prone on the x-ray screening table and a Tuohy needle is placed epidurally (using loss of resistance to confirm that it is correctly sited) from a paramedian approach under local anaesthetic at the level of T3-4 or T4-5. The electrode is then fed through the needle and is positioned in the midline at the appropriate level under fluoroscopy. (For patients with angina this is usually with the tip at C6/7 and the electrode at T1/3.) Then the electrode is attached to an external stimulator which produces paraesthesia. The final position of the electrode is determined when the area of paraesthesia produced matches that where pain is usually experienced. The distance between the insertion point and electrode tip should be as long as possible to minimise the risk of dislocation.
The patient is then turned over and anaesthetised as the remainder of the implantation can be painful. The IPG (very similar to a pacemaker) is placed subcutaneously in the left side of the abdomen (in a comfortable position that has been determined prior to the procedure with the patient standing) and it is then connected to the electrode by an extension lead that is also tunnelled under the skin.