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Spinal Cord Stimulation: Fundamentals

Interventional pain specialists offer an overview of spinal cord stimulation (dorsal column neuromodulation) fundamentals that referring physicians can use in clinical practice.
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The process of the trial percutaneous spinal cord stimulator approach should involve an alert and communicative patient who can provide the practitioner with correct lead positioning. The patient should be made comfortable with local anesthesia infiltration at the insertion sites. The interventional pain specialist can use the trial screening lead(s) during the screening trial. Once the screening lead is positioned at the exact locations (determined from communication between the patient and the interventional spine specialist), then the temporary external power source (screener) is connected. When both the patient and physician are satisfied that the stimulation coverage is satisfactory, then the spinal cord stimulator leads are sutured tightly with anchors to the skin. Subsequently, the completed circuits are taped securely to the skin and covered to prevent them from accidently being pulled out but still allow them to be attached to the programmer. Then, to verify the final electrode position, anteroposterior and lateral radiographs should be obtained with the fluoroscopy films.

Postprocedure Care
The patient routinely recovers after 30 to 60 minutes in a postoperative recovery setting.7,9-11 Once the patient is awake and alert in the recovery area, the patient's spinal cord stimulator settings should be optimized. The adjustable parameters of electrical stimulation in spinal cord stimulators are frequency (Hz), pulse width (stimulus duration), and amplitude (volts). A typical frequency is 50 to 80 Hz, although a higher frequency may be used as a stronger counterstimulus. Increasing the pulse width increases the density of the stimulus, which provides for deeper penetration into the spinal cord. Clinically, this usually means a broader disbursement of paresthesia. This may be beneficial when, for example, the stimulation pattern needs to cover the back but is only covering the hip. The pulse width can be increased and the paresthesia pattern may then incorporate the lower back. The amplitude represents the electrical force of the stimulus. Clinically, this usually means that the patient experiences a more dense stimulation pattern, thus, making it harder for the pain to "break through" the stimulation pattern. When the amplitude is adjusted too high, the patient may have a noxious experience.

As long as the recovery period is uneventful, the patient can be discharged home with postoperative instructions. During the recovery period, the spinal cord stimulator programming is fine-tuned, the patient and/or patient's family is educated on how to use the device, and any questions are answered. The patient is told to keep the spinal cord stimulator area clean and dry and specifically told not to bathe or shower but to take sponge baths during the trial period. Prophylactic oral antibiotics are provided and the patient is instructed to avoid excessive bending or twisting as this may dislodge the spinal cord stimulator lead. In addition, they are told not to alter medication consumption and to maintain their routine activity level. The patient also is instructed to alert the physician in case of any alteration in stimulation pattern, signs of infection, or any other unusual occurrences. Follow up is usually within 3 to 7 days following implantation, at which point the lead is removed, the efficacy of the SCS is assessed, and the physician should then determine whether to proceed with placement of a permanent spinal cord stimulator.

Permanent Surgical Implantation

The patient undergoing a permanent spinal cord stimulator implantation is brought into the ambulatory surgical center or hospital the morning of the procedure. A urinalysis, complete blood count with differential and sedimentation rate, should be obtained within 72 hours prior to the implantation. A chest x-ray and electrocardiogram should be obtained in all patients who are more than 45 years old, have a history of cardiac or pulmonary disease, or show ongoing signs or symptoms of cardiac or pulmonary difficulty.

Permanent spinal cord stimulator systems can be placed with percutaneously inserted round wire leads, or via open placement of flat plate or paddle leads (Figure 1). In either case, the sublaminar epidural leads are connected by wires to a subcutaneously installed generator at a separate operative site.

Percutaneous placement of wire leads is minimally invasive and is typically done without general anesthesia. The same general technique used in trial lead placement is used for permanent lead placement. After lead placement is complete, lead wires are tunneled with a trochar to a subcutaneously placed generator and the generator incision is closed. The minimally invasive nature of percutaneous lead placement may be preferable in patients who are unwilling to undergo or unsuitable for general anesthesia (Figure 2).

Although more invasive, openpaddle lead placement offers several advantages over percutaneous placement of wire leads. Placement of paddle leads is done under direct visualization, potentially mitigating the risk of dural breach. Paddle leads are less subject to migration and can provide broader stimulation coverage, with better overall clinical outcomes.41,42

A versatile technique for placement of sublaminar paddle leads for low back pathology is via approximately T8-T10 laminectomy, with the precise level being adapted to results of previous trial stimulation. This can be done either under general anesthesia or conscious sedation. In either case, this is easily accomplished in an outpatient setting. The patient is placed in the prone position on a surgical saddle frame. Using fluoroscopic guidance, a midline incision is made over the spinous process and is taken through the dorsal fascia. Paraspinous muscles are elevated off of the lamina, and a complete facet-sparing laminectomy is performed. The epidural space is developed using a dural dissector. If lower extremity peripheral nerve stimulation is desired, a lead may be placed caudally to cover the posterior spinal cord, conus medullaris, and anterior cauda equina. Otherwise, the lead is placed anteriorly over the appropriate thoracic level.

Appropriate lead position is confirmed with anteroposterior and lateral fluoroscopy. If the procedure is done in an awake patient, test stimulation can be performed. Neurophysiological mapping may be used if desired for confirmation of localization with general anesthesia.43 Once a satisfactory position is confirmed, the wire leading into the lead is anchored to the remnant of the interspinous ligament or directly to the adjacent spinous process utilizing a sleeve and a non-absorbable suture. Wires are then passed through a trochar to the generator, which is implanted in a subcutaneous pouch commonly just below the iliac crest. Incisions are closed in a layered fashion and the patient is transported to the post-anesthesia recovery unit, where appropriate stimulation coverage is confirmed once the patient is fully awake.

Last updated on: June 1, 2015
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