What is spinal cord stimulation?
Spinal cord stimulation (SCS) is a surgical treatment option for patients with chronic pain. Since the inception of SCS in 1971, research and advances in technology have established spinal cord stimulation as an effective method of treating various manifestations of pain.
How many patients use spinal cord stimulation?
A majority of the 50,000 neuromodulation devices implanted every year are spinal cord stimulators. SCS has proven to effectively treat chronic pain in the majority of cases (50% to 70%).
What kinds of pain does spinal cord stimulation treat?
SCS is used for treatment of chronic pain that has failed multimodal therapy. Neuropathic pain tends to be more responsive than other forms of pain, and radicular symptoms tend to respond better than axial symptoms. Conditions most commonly treated by SCS include complex regional pain syndrome type 1, failed back surgery syndrome, and neuropathic pain.
Who is a candidate for spinal cord stimulation therapy?
Patients who undergo SCS therapy typically (a) have been afflicted with chronic pain that has persisted for more than 6 months, (b) have exhausted conventional pain therapy, and (c) have undergone a trial period of stimulation lasting 5 to 7 days, which has demonstrated efficacy in relieving pain. Patients who undergo SCS therapy complete a psychological evaluation and magnetic resonance imaging, where the lead will be placed prior to SCS implantation.
What does trial stimulation involve?
A trial stimulator is implanted prior to implantation of a permanent stimulator to ensure that SCS adequately covers the patient’s area of pain. The trial SCS pulse generator is carried outside of the body. A permanent SCS device is implanted only if pain relief efficacy of trial stimulation is greater than 50%.
How are spinal cord stimulation devices implanted?
The three components of SCS devices are the implantable pulse generator (IPG), connecting wires, and electrodes.
The IPG is a battery-powered generator responsible for creating the electrical impulses that stimulate the spinal cord. The IPG can be controlled through a remote control and may be rechargeable or nonrechargeable. SCS may be percutaneous or paddle leads.
Percutaneous electrodes are rod-shaped leads, and thus exhibit a cylindrical energy distribution vector. As a result, percutaneous electrodes exhibit multidirectional energy distribution, meaning that energy delivery of percutaneous electrodes is less effective than paddle electrodes. The size and shape of percutaneous leads allow placement through a needle. Paddle electrodes exhibit a unidirectional energy distribution vector, epidurally only, and are implanted through a laminotomy. Which type of lead is placed is variable depending on patient and implanter.
What is the mechanism of spinal cord stimulation action?
Although the mechanism of SCS action has not been fully understood, the Melzack-Wall gate control theory of pain provides a partial explanation of how SCS stimulation can decrease pain perception. Electrical stimulation of Aβ afferent fibers works to downregulate the anterolateral pain perception tract, resulting in the analgesic effects characteristic of SCS. A consequence of electrical stimulation of Aβ afferent fibers is the sensation of paresthesia, a tingling sensation in stimulated dermatomes.
Although the Melzack-Wall gate control theory of pain partially explains the analgesic mechanisms of SCS, this theory does not fully explain SCS mechanism of action. Specifically, high-frequency stimulation (HFS), a stimulation pattern characterized by frequency of stimulation of 1000–10,000 Hz, does not induce paresthesia characteristic of traditional SCS. Loss of paresthesia sensation in HFS indicates that the Melzack-Wall gate control theory of pain does not fully account for SCS mechanism of action.
Spinal cord stimulation electrical impulses have qualities such as amplitude, frequency, and pulse width. What do these mean?
Amplitude, frequency, and pulse width are characteristics of any form of electric current. These parameters can be adjusted to best optimize pain relief.
Amplitude refers to the magnitude of electrical stimulation, and is measured in volts. Frequency refers to number of impulses per second, and is measured in hertz. Pulse width refers to duration of the electrical impulse, and is measured in microseconds. Amplitude, frequency, and pulse width can be increased to increase intensity of stimulation.