Inflatable Spinal Implant Could Help Relieve Chronic Back Pain

An inflation innovation could provide an easy way for patients with chronic pain to access an effective therapy that bypasses painkilling opioid drugs.

Anyone who is sat reading this article at a computer has probably experienced some back pain. But while a brief stretch or walk can relieve minor pain, for many millions of people around the world, including up to 8% of the US population, simple solutions just don’t cut it. These people suffer from intractable back pain, where painkillers, such as non-steroidal anti-inflammatory drugs (NSAIDs), no longer work.

For these individuals, proposed therapeutic solutions involve potentially addictive opioid drugs, or electrical stimulation methods that disrupt pain signaling between the nerves of the spinal cord and the brain; but optimum stimulation methods come at a price. The most effective devices involve invasive surgery, where stimulator electrode “paddles” are implanted into the spinal cord. While the signals produced by these devices can offer pain relief, for many patients, such surgery is a step too far.

Now, a new electrical stimulation device could offer the benefits of a paddle stimulator via a more simple procedure that could open stimulation-based therapies to far more pain patients.

“Spinal cord stimulators have been used in the clinic for pain management for over 50 years,” says Dr. Christopher Proctor, a group leader of the Bionic Systems Group in the Engineering Department at the University of Cambridge and coauthor of a new study that shows off the prototype device.

Solutions for chronic pain

Currently available stimulators fall into one of two categories – the paddle-shaped stimulator mentioned above, or a thinner wire-shaped stimulator that use less invasive keyhole surgery. These wire electrodes release their electrical signals in a less-targeted way and suffer from displacement issues, where the devices move around after implantation, reducing their effectiveness.

While paddle-type stimulators can offer a more effective solution, they aren’t suitable for some of the most vulnerable patients –  elderly people who experience chronic pain alongside other comorbidities, like diabetes or Parkinson’s disease. “Many of these patients are simply too frail to undergo the invasive surgery to implant the paddle-like electrode,” says Proctor.

The device is inflated to a paddle shape after insertion into the epidural space. Credit: Woodington et al. 

As a result of these issues, only 100,000 people each year seek stimulation-based solutions, despite the global burden. This includes patients with other pain conditions that can be relieved by stimulation, including angina. “There are a probably about a billion people worldwide that suffer from pain conditions,” Proctor points out.

The new device, which remains at an experimental stage, would be implanted via an outpatient procedure. “The implant goes into a cavity [called the epidural space] between the dura, a skin-like sheath that protects the spinal cord, and the spinal column,” explains Proctor.

The device itself is minuscule, just 60 microns thick, and is made of a combination of thin-film electronics and a fluidics system. This latter feature allows the device to be “inflated” by infusing a combination of air and water into it. This makes it expand to a paddle shape within the epidural space, covering a much greater area of the spinal cord than wire stimulators. The air and water is then sucked back out of the device, allowing it to fit snugly in the tissue in the epidural space. “We are trying to combine the best of both worlds here,” says Proctor, “Minimally invasive surgery to get a paddle-like device that can provide the best treatment and is least likely to have issues with displacement.”

A clinical journey

As with other stimulators, the device would undergo a trial period, where the patient would work with a doctor to establish the best level of stimulation to relieve their pain. After the trial, a battery pack is implanted separately, often near the patient’s hip. This battery can be rechargeable, with some models providing 10 years’ worth of stimulation before needing replaced. One nifty feature of the inflatable device is that it can be removed in the same way it was implanted, says Proctor, meaning no serious surgery will be required, even if the patient prefers another treatment method after the trial period.

“We are aiming to be ready for first in-human clinical trials in three years,” – Dr. Christopher Proctor. 

In their paper, Proctor and his team examined the device’s engineering, showing that it could successfully inflate inside an in vitro model of the spinal cord, and that it could be successfully implanted into an actual spinal cord by using a human cadaver to validate the technique. This is the beginning of a journey that will task the researchers with proving its safety and efficacy in pre-clinical animal models and then in human patients. Proctor hopes that progress will be rapid, “We are aiming to be ready for first in-human clinical trials in three years,” he says.

Proctor is aware of the scale of the task – funding and expertise will be required to move from the team’s lab setting to a regulated space that is suitable for medical device production, and much more evidence will be required to prove the device’s worth, but the potential benefits to pain patients make it worthwhile.

“Spinal cord stimulation isn’t going to be the answer for a billion people, but it could be the answer for a lot more people than it is now, and it can dramatically improve a lot of patients’ lives. I think our innovations is going to allow a lot more patients to access this highly effective treatment,” Proctor concludes.

Reference: Woodington BJ, Curto VF, Yu, Y et al., Electronics with shape actuation for minimally invasive spinal cord stimulation. Sci. Adv. 2021: 7.