When a patient is deemed a potential candidate for an SCS device, the first step is to schedule a trial. A trial consists of sterilely and percutaneously inserting electrodes into the posterior epidural space under fluoroscopic guidance. These wires are externally attached to a programmable internal pulse generator (IPG) and secured in place for 5–7 days, often with a combination of sutures and dressings. During the trial period, there is daily communication with the patient to evaluate for improvements in function (able to walk further, stand longer) and quality of life (improved sleep, better pain control with reduction in pain medications). At the end of the trial, the SCS leads are removed. If the trial is successful, the patient will be scheduled for permanent insertion of the SCS device.

Permanent implantation of the device is a same day surgical procedure. It involves a small thoracic incision to insert percutaneous electrodes or paddle electrodes placed via a laminotomy. The wire leads are then subcutaneously tunneled to the IPG which is typically buried 1–2 cm below the skin, just inferior to the beltline dorsally on the patient’s dominant side (Figs. 11.2 and 11.3).

SCS devices and their respective IPGs vary in size and function (e.g., rechargeable vs. nonrechargeable). These devices are approximately the size of a pacemaker, but are cosmetically more appealing due to the abundance of soft tissue in the buttocks.

As of January 2016, companies that have Food and Drug Administration (FDA) approval for SCS include Medtronic, Boston Scientific, St. Jude Medical, Nevro, and Greatbatch. Each company boasts a unique device for a specific niche. For example, St. Jude Medical has developed the longest lasting nonrechargeable IPG that is still relatively small in size, the EonC™ Primary Cell IPG. The battery life will vary depending on specific settings, but has an average lifespan of 7 years. This may be an ideal product for patients who are unable or would prefer not to regularly charge their device [4]. Patients who may have difficulty charging their device may be those who are morbidly obese, elderly, or who have poor upper extremity mobility and or dexterity. The rechargeable IPGs are generally a more popular choice for patients as they are typically smaller in size and therefore more cosmetically appealing. Rechargeable IPGs also boast a longer lifespan that average 9–10 years. That being said, St. Jude has recently unveiled their newest nonrechargeable IPG, the Proclaim™, which is substantially smaller in size in comparison to its antecedent. Below is a visual demonstration of the size of the Proclaim™ as well as its rechargeable counterpart, the Protégé™ [5] (Figs. 11.4 and 11.5).

Some patients with chronic pelvic pain may have a history of gynecologic cancer. If obtaining a pelvic or chest magnetic resonance imaging (MRI) in the future will be clinically important, then one must consider implanting an MRI-compatible SCS. With a traditional SCS device, there is risk for thermal injury at the site of the leads and generator. A recent case series at a tertiary care center identified four patients between 2001 and 2011 (n = 199) who had their SCS device explanted due to the primary need for an MRI scan [6].

Medtronic has developed an insulation that allows heat to be dissipated and is the only company that currently offers an SCS that is FDA approved for total body MRI scan. It is important to note that not all Medtronic SCS devices are MRI compatible. Performing an MRI scan with a device or a lead that is not “MR Conditional” is unsafe and may cause damage to the implanted leads and/or device. Serious injury may occur to the patient, including death. Prior to any imaging studies, it is necessary to find out the specific make and model of the device and refer to www.​medtronic.​com/​mri to review the most up-to-date guidelines including what Tesla of the MRI machine is deemed safe (1.5 T vs. 3 T).

Historically, patients have struggled with SCS devices that vary in their performance as the body changes position (supine, standing, seated). This may be related to the effects of posture on intracranial pressure that is directly related to changes in cerebrospinal fluid (CSF) volume, as measured by MRI flow studies [7]. Medtronic has also recently introduced AdaptiveStim technology. Using a sensor with a triple-axis accelerometer, the device is able to perceive changes in body position and automatically adjust amplitude, pulse width, and electrode configurations to maintain optimal therapy.

Traditional SCS devices work by a phenomenon known as pain/paresthesia overlap. Patients experience a buzzing or a tingling sensation in the areas in the body that were previously afflicted by neuropathic pain. This sensation is typically described as pleasant. However, it is unsafe to operate heavy machinery while using the device and patients often have difficulty sleeping with the device turned on. As of May 2015, Nevro has entered the SCS market with a device that offers high-frequency stimulation. This technology involves stimulation at a frequency of 10,000 Hz at the dorsal column. Patients with a Nevro SCS achieve similar, if not superior, pain relief without experiencing paresthesias. The pros to this system include the absence of limitation in use of the device as it may be kept on during sleep and while driving. Since the device is always at high frequency, it is recommended that patients must charge this device on a daily basis. It is safe for use with MRI of the head and extremities, but not for abdominal or thoracic MRIs (Fig. 11.6).

A patient is considered a candidate for an SCS device if they have had chronic pain for greater than 6 months, other treatment modalities have failed or are unsuitable, and the patient has undergone careful screening and assessment from a multidisciplinary team including a psychological evaluation [8]. The FDA has specific indications for the use of each of these devices [9–12]. These indications are not universal, but are similar and are listed in Table 11.1.

Although rare, there is risk for nerve damage, infection, and/or bleeding into the epidural space. If any of these occur, they may be a medical or a neurosurgical emergency. The most common adverse event to happen following permanent implantation of an SCS is electrode “lead migration,” which has been reported to occur in a recent study in up to 12 % of patients [13]. Lead migration may result in an inability of the device to function properly. This may take place following high-impact trauma such as a motor vehicle collision. A surgical revision would be necessary to reposition the electrodes.