What Is Epidural Electrical Stimulation?

Epidural electrical stimulation (EES) is a medical technology using a continuous electrical current on the spinal cord to address functional loss after neurological injuries. The goal is to improve motor, sensory, and autonomic functions by delivering electrical impulses through an implanted device. This process enhances communication between the brain and body, offering a new avenue for rehabilitation for those with certain spinal cord damage.

The Mechanism of Action

The principle of EES is not to directly force muscle contraction, but to modulate the excitability of neural networks below the injury level. After a spinal cord injury, many circuits controlling movement become dormant from a lack of brain input. EES delivers a low-voltage electrical current to the dura, the spinal cord’s protective membrane, to “reawaken” these dormant circuits.

This process is like turning up the volume on a radio with a weak signal. The electrical current raises the excitability of neurons in the targeted spinal region, making them more responsive to faint, residual signals from the brain. This allows for voluntary muscle control to be re-established by amplifying disrupted brain signals and directing them to motor function areas.

The stimulation is highly targeted. By placing the electrode array over specific segments of the lumbosacral spinal cord, clinicians can selectively activate different neural circuits. For instance, stimulating certain dorsal roots can facilitate standing and stepping, while different patterns can influence autonomic functions. This specificity allows for a tailored approach to support various movements.

The Implantable System and Procedure

The EES technology is a surgically implanted system with two primary components. The first is an implantable pulse generator (IPG), a small, battery-powered device similar to a cardiac pacemaker that generates electrical pulses. The second is a thin, paddle-shaped electrode array that delivers these pulses to the spinal cord.

The system is installed during a minimally invasive surgery under general anesthesia. A surgeon performs a laminotomy, removing a small piece of bone to access the epidural space. The electrode paddle is then positioned over the dura mater at a location chosen to best influence the desired motor functions.

An insulated wire is then tunneled under the skin from the spine to the abdomen or buttock, where the IPG is placed in a pocket and connected. After implantation, patients and therapists use a handheld remote to communicate with the IPG. This remote controls the stimulation and allows for adjustments to parameters like frequency and intensity for specific activities.

Applications in Spinal Cord Injury

EES is applied to restore a range of functions in patients with spinal cord injuries. A primary goal is recovering voluntary motor control in the lower limbs. With the stimulator active, individuals have regained the ability to perform voluntary movements, such as flexing their hips, knees, and ankles. This progress enables actions like pedaling a stationary bicycle or taking assisted steps.

EES has also shown benefits for trunk stability and core control. This improvement helps patients sit upright without support and stand for longer periods, contributing to greater independence and allowing for more complex movements.

The technology also addresses the recovery of autonomic functions, which are often impacted by spinal cord injuries. EES has led to improvements in:

• Regulation of blood pressure
• Bladder and bowel control
• Sexual function
• Sensory perception in areas that were previously numb

Rehabilitation and Functional Recovery

Functional gains with EES require a rigorous and personalized rehabilitation program. The implanted device does not passively create movement but instead creates a state of readiness in the spinal cord. This readiness allows patients to engage in intensive physical therapy that would otherwise be impossible.

Rehabilitation begins shortly after surgery with a specialized team of physical therapists. They work with the patient to “map” the stimulator’s settings by testing electrode combinations and stimulation parameters. This process identifies the configurations that produce the most effective motor patterns for tasks like standing or stepping and is unique to each individual.

Once optimal settings are identified, the patient undergoes extensive task-specific training with the stimulator turned on. They practice activities like standing, shifting weight, and attempting to walk, often with a body-weight support system. This repetitive training helps the brain and spinal cord re-learn how to work together, strengthening neural connections and improving motor control.

Patient Candidacy and Considerations

Determining a suitable candidate for EES involves evaluation by a multidisciplinary team. The specifics of the spinal cord injury are considered, as the technology has shown promise for both motor complete and incomplete injuries. The injury’s location is also a factor, with procedures often targeting injuries between the C4 and T10 vertebrae. Candidates should be several months post-injury to ensure their condition is stable.

A patient’s overall health is another consideration, as they must have sufficient skeletal and cardiovascular health for intensive rehabilitation. A high level of motivation and psychological readiness is also required. The patient must be able to commit to the demanding, long-term physical therapy regimen to achieve functional gains.

As with any surgery, there are risks, such as infection or issues with the implanted hardware like lead migration. Prospective patients must also consider the significant commitment of time and resources for post-operative rehabilitation. A thorough screening process helps ensure that selected individuals are likely to benefit and are fully aware of the challenges involved.