What is Spinal Cord Stimulation?

As the use of spinal cord stimulation has grown, so have the indications. A common indication for spinal cord stimulation is failed back surgery syndrome, (or FBSS). In FBSS patients have undergone a prior form of surgery to treat spinal pain. Unfortunately, their pain did not resolve with surgery. Some of these patients may be given the option to have an alternative surgical procedure. In others, the cause of persistent or recurrent pain is not apparent. spinal cord stimulation provides an opportunity for long lasting relief in both groups. However, one must note that there are two types of FBSS patients; those with nerve symptoms and those with back pain symptoms. Back pain patients have traditionally been less successful at managing their symptoms with spinal cord stimulation. However, newer technologies are now resulting in better outcomes for FBSS whose symptoms are primarily back pain.

Arachnoiditis is another indication for spinal cord stimulation. Arachnoiditis is a term describing chronic inflammation of the nerve roots traveling up and down the spine. A layer of tissue enveloping the nerves, called the arachnoid layer, becomes inflamed. This inflammation in turn causes pain emanating from the nerve roots themselves. Primary Arachnoiditis is rare. Most cases are seen after spinal surgery and probably are best classified as a form of FBSS.

Complex regional pain syndrome (CRPS) is another indication for spinal cord stimulation.

CRPS is a condition where an injury to a nerve in or out of the spine results in a complex and painful syndrome, usually affecting a limb. Patients with CRPS suffer from a heightened and uncomfortable skin sensitivity, alterations in limb temperature, swelling, weakness, changes in skin and other uncomfortable signs and symptoms. It is common for CRPS patients to have a delayed diagnosis and to have tried many multiple injection procedures before being recommended for spinal cord stimulation. When a spinal cord stimulator is implanted, it is successful in most cases that have been properly selected.

Chronic neck pain and low back pain is a condition where pain has been persistent for at least 12 weeks. In the majority of cases, a careful analysis will determine the cause of chronic pain, called the “pain generator.” Injections, procedures or surgery can then be tailored to target the pain generator. Nonetheless, a portion of these patients are being offered spinal cord stimulation as a treatment option. It is important to note that there is little evidence to support the use of spinal cord stimulation as a final treatment option in chronic neck and back pain patients who have not tried another form of potentially definitive treatment. As a result, spinal cord stimulation is only indicated when there is no identifiable pain cause that can be addressed by surgery. If there is a surgically addressable cause, spinal cord stimulation is indicated only when the patient cannot tolerate the needed surgery.

spinal cord stimulation is only indicated when certain psychological conditions have been ruled out. These include severe cognitive impairment, poorly controlled or untreated addiction, social dysfunction or other disorders.

There are several other less common, but still important indications for spinal cord stimulation. Patients with vascular disease suffer from blockages to the arteries of the heart and limbs. Angina is a condition where heart blockages result in chest pain. When the blockages cannot be repaired, spinal cord stimulation is a treatment option for angina patients. Similarly, blockages in the leg can cause leg pain. This is called claudication. spinal cord stimulation may also be used as a means of treating claudication related pain.

Every spinal cord stimulator has certain key components. The lead is the portion that is placed against the back of the spinal cord. Each lead consists of multiple electrodes. Each electrode has an anode and a cathode. Electrical current travels from the anode to the cathode. As many as 16 electrodes are present in needle placed leads (called cylindrical leads) and 32 in surgically placed leads (called paddle leads). The current amplitude flowing to each electrode can be switched on, off or adjusted. As a result, a greater number of electrodes in a lead allows physicians to alter the shape of the electrical stimulation field over the spinal cord in order to obtain the desired effect from stimulation.

The lead is connected to a generator. The generator is a power source that provides current and voltage to the electrodes in a lead via a connection. During a trial, or test of effectiveness, generators are connected to the implanted leads outside the body. After a successful trial, a new generator is implanted into the body and the connection with the leads is inside the body. For power, generators now come in rechargeable forms. This is advantageous because modern spinal cord stimulation systems require more power than before. Older systems would require an incision for removal and re-implantation of a freshly charged generator. Today, there is one generator system that can generate a current inside of an implanted lead without a physical connection. The generator is rechargabe and can be worn outside the body, like a pager. Unfortunately, this system is limited in the type of stimulation that it can provide.

The generator contains a program, telling the generator exactly how to administer the stimulation current. The program can govern voltage, current, the frequency of stimulation pulses, the amplitude and width of the stimulation pulses and whether the stimulation pulses are given in bursts or are constant.

Before being considered for spinal cord stimulation as a long-term treatment, a spinal cord stimulator trial is performed. The spinal cord stimulator trial is placed in a procedure room or operating room. In a trial, a physician places a lead delivery needle in the back. Through this needle a cylindrical lead, often referred to as a percutaneous lead, is placed. Using X-ray guidance, the physician advances the lead to the target location in the spinal cord. For low back pain the target is usually T8 or T9. For neck pain the target is usually C4 or C5. The needle is placed in the spine several segments below the target location.

After placing the lead and removing the needle the patient is left with a lead emanating from the skin of the back. The lead is then connected to a generator. At this point the physician, along with a technical expert, begin stimulation of the awake patient and adjust various stimulation parameters to see if there is adequate pain relief. As noted above, many different parameters can be altered while seeking optimal pain relief. This includes the number of electrodes activated and the current flow through those electrodes, the frequency of the stimulation pulse and width (in microseconds) of each pulse and the type of stimulation pulse. Multiple parameters will be adjusted in the operating room until adequate stimulation can be achieved. Sterile dressings are then applied and the patient returns to their normal activity to determine if pain relief is adequate. The trial phase typically lasts 3-10 days.

A spinal cord stimulation trial is considered successful if the patient has >50% drop in pain and improvement in functional abilities. At this point the patient is offered a permanent spinal cord stimulator implant. Like the trial, a spinal cord stimulator implant is performed in the operating room. The old trial lead is disconnected from the external generator. The old lead is then carefully removed. A small incision is then made in the back. If placing a cylindrical lead, a needle is then inserted into the spine and a new electrode is advanced to the target location. Leads with a greater number of electrodes are available but are too large to place through a needle. To place these leads a surgeon performs an opening in the back of the spine and manually inserts the leads.

The lead, placed through a skin incision, is then inserted and tunneled through the skin by puncturing the side of the incision. Meanwhile, an incision has been made over the back of the pelvis or lower abdomen and a small pocket has been surgically created for the implantable generator. The lead tunnels from the back wound, under the skin, and emerges inside the surgical pocket. The lead is connected to the generator. The incisions are then closed. Finally, the generator is programed, (this occurs externally, or outside the body), and spinal cord stimulation is begun.