When conservative methods like physical therapy and medication fail to provide sustained relief for chronic pain, advanced interventions become necessary. The Spinal Cord Stimulator (SCS) is an implantable neurostimulation device designed to manage persistent discomfort. The SCS system works by sending mild electrical impulses to the spinal cord, modulating pain signals before they reach the brain.
How Spinal Cord Stimulators Interrupt Pain Signals
The SCS system operates through three primary components: a pulse generator, insulated wires called leads, and a patient remote controller. The leads are carefully positioned within the epidural space, the area surrounding the spinal cord’s protective membrane. This placement allows the electrical current to interact with the dorsal columns, which are bundles of nerve fibers carrying sensory information, including pain signals, toward the brain.
The earliest SCS devices were theorized to work based on the Gate Control Theory of pain. This theory proposed that electrical stimulation of large, non-pain-carrying nerve fibers could “close the gate” on the smaller pain-carrying fibers. This conventional stimulation often resulted in a tingling sensation, known as paresthesia, which masked the feeling of pain.
Modern technology has evolved beyond this, introducing stimulation types that are often “sub-perception,” meaning they provide pain relief without the tingling sensation. Newer modalities, such as high-frequency stimulation and burst stimulation, operate at different electrical parameters and engage more complex mechanisms. These advanced programs may alter the local neurochemistry within the spinal cord, influencing the release of inhibitory neurotransmitters like Gamma-aminobutyric acid (GABA) and serotonin.
Clinical Evidence of Efficacy
Clinical trials provide objective evidence that SCS is an effective treatment for specific chronic pain conditions. Success is often defined as a 50% or greater reduction in a patient’s pain score. One of the most common indications is Failed Back Surgery Syndrome (FBSS), which describes persistent pain following one or more back surgeries. Randomized controlled trials have demonstrated that SCS is superior to conventional medical management and even repeat surgery for improving pain scores and functional outcomes in this patient population.
Another condition with strong supporting evidence is Complex Regional Pain Syndrome (CRPS), a debilitating chronic pain condition that usually affects a limb. Studies have shown that SCS can lead to sustained pain relief and improved quality of life for patients with CRPS Type I.
The development of advanced stimulation waveforms has further improved efficacy, particularly for difficult-to-treat pain, such as axial back pain. For example, high-frequency systems, which deliver impulses at 10,000 Hz, have shown superior results compared to traditional low-frequency stimulation in some trials for chronic back and leg pain.
The Essential Trial Period
Before a permanent SCS system is implanted, every patient must undergo a temporary trial period, which is considered a mandatory diagnostic phase. This measure is designed to eliminate the risk of implanting an expensive, ineffective device. The trial typically lasts between three and seven days, though some protocols may extend this to ten days. This allows for a comprehensive assessment of pain relief during normal daily activities.
During the trial, the physician percutaneously inserts temporary leads into the epidural space using a needle and real-time X-ray guidance. These leads are then connected to an external pulse generator worn on a belt or waistband outside the body. This external setup allows the patient to test the stimulation at home and control the programming within preset safety limits.
The trial is considered a success if the patient achieves a meaningful improvement in their pain, usually measured as a 50% or greater reduction in their typical pain level. Patients are instructed to keep a detailed pain diary, noting their pain levels, activity, and any side effects. If the relief criteria are met, the patient and physician can confidently proceed with the permanent implantation. If the trial is unsuccessful, the temporary leads are simply removed, and the treatment plan is re-evaluated.
Living with the Implanted Device
Following a successful trial, the permanent SCS system, including the generator, is implanted under the skin, often in the lower back, flank, or abdomen. The pulse generator contains the battery, which is a primary consideration for long-term management. These generators come in two main types: non-rechargeable and rechargeable.
Non-rechargeable batteries have a finite lifespan, often lasting up to eleven years depending on the energy demands of the programmed settings. They require a minor surgical procedure to replace the generator when depleted. Rechargeable systems require the patient to periodically charge the battery, sometimes for about an hour daily or weekly, but they can last for nine to fifteen years. Higher stimulation settings require more frequent charging, directly linking the chosen therapy to battery longevity.
A significant aspect of living with an SCS is compatibility with Magnetic Resonance Imaging (MRI). Many modern systems are designed with technology that allows for full-body MRI access under specific conditions. This is important since a large percentage of patients may need an MRI for an unrelated condition within a few years of implantation.
Before any MRI, patients must inform their providers and may need to activate a special “MRI mode” on their device using the remote programmer. Patients must follow all manufacturer guidelines, as certain older models may restrict the type or location of the scan.