Stabilizing the spine without fusion

 In February 2021, Dawn Lissy went to see an orthopaedic surgeon about pain radiating from her back down her leg. When the surgeon pulled up her X-rays, Lissy — a biomedical engineer who has spent decades testing spinal implants — immediately saw the problem. Her spine was degenerating in a way that caused a vertebra to shift out of alignment, a condition known as lumbar degenerative spondylolisthesis.

“We’re going to get you a fusion,” the doctor told Lissy, referring to the standard treatment for spondylolisthesis.

“I said, ‘No, no you’re not,’” Lissy recalled.

Fusion involves permanently locking two vertebrae together using screws, rods and bone grafts. It means days in the hospital, months in a brace, restricted movement for life and an increased likelihood of needing future surgeries when other vertebrae begin to degenerate. Lissy was 50, active, and already angry that back and leg pain had forced her to give up skiing, paddleboarding and biking.

Instead, Lissy pursued more conservative, temporary treatments and waited. She knew what she eventually wanted: a device called the LimiFlex Dynamic Sagittal Tether, which restores anatomic stability to the vertebral segment while still allowing the spine to bend. Developed at Stanford Medicine for patients with the degenerative spondylolisthesis, it was still in clinical trials, but Lissy held on. In April 2026, Lissy flew from her home in Colorado Springs to Stanford Hospital and became one of the first two American patients to receive the device once commercially available.

“When I woke up from the surgery, I had immediate relief,” Lissy said. “To not have that constant nerve pain was incredible. You don’t know what it’s like until you’re dealing with it.”

The spinal implant is more than 20 years in the making. In the spring of 2004, mechanical engineer Louie Fielding was finishing a master’s degree and participating in a program offered by Stanford Biodesign (now named the Stanford Mussallem Center for Biodesign) that brings together students, faculty and industry mentors to tackle biomedical innovation challenges. Fielding’s team landed on the goal of developing a flexible device that could stabilize the spine’s vertebrae.

“At that point, our ideas were conceptual sketches,” Fielding recalled.

But Stanford Medicine spine surgeon Todd Alamin, MD, immediately saw the promise of one of their sketches. For years, he had been hoping for a way to stabilize the spine in place for this condition without completely immobilizing it.

“The biggest question for treating so many spinal issues has literally been: Can we do something other than a fusion for stability, which often seems like overkill?” said Alamin, a professor of orthopaedic surgery. “To control stability, do you need to really get rid of all the motion? There’s got to be a better way.”

Degenerative spondylolisthesis, the primary condition Alamin thought the device could be used for, is often confused with a herniated or “slipped” disc, in which the soft tissue between vertebrae bulges or ruptures. In spondylolisthesis, the vertebral bone slips out of alignment. As it does, it can pinch the nerves that run through the spine, a condition called spinal stenosis, producing the kind of radiating leg pain that sent Lissy to her surgeon.

A fusion treats the condition by eliminating movement in the affected area of the spine, preventing not only the slippage of the vertebra but also the bending and twisting of everyday life. Alamin, Fielding and Biodesign partners Colin Cahill and Ian Benett wanted something that could stabilize the slippage but allow motion. They envisioned a device that could be tethered the vertebral segment to restore stability but still allow anatomic spinal motion.

“We first tried materials that were essentially like a rubber band,” Fielding said. “But they all tend to stretch out over time.”

Their solution: a pair of small titanium springs with textile bands that loop around the protrusions on the back of vertebra called the spinous processes. The design allows bending of the spine but ensures that the vertebrae don’t move out of alignment with each other. The new materials also turned out to be much more resilient than the first iterations of the device.

“It’s like your car suspension; it’s going to be the same at a hundred thousand miles as it was at the first,” Fielding said.

The implant is used in combination with a decompression procedure, in which the surgeon removes tissue that is pressing on the spinal nerves. It is then secured to the vertebrae, preventing future slippage. The device works for patients with degenerative spondylolisthesis whose X-ray shows their vertebrae are slipped 25% or less out of alignment and don’t need the spine completely realigned.

In 2011, LimiFlex was launched commercially in Europe, where more than 2,000 patients were treated with the implant over a few years. In 2014, changes to the German markets made focusing on that market no longer viable. Fielding and Alamin started over in the United States, founding Empirical Spine Inc. and launching the pivotal U.S. clinical trial.

The trial, which included nearly 300 patients, showed that, compared to a fusion surgery, LimiFlex procedures were no less effective, shorter, could be carried out without an overnight hospital stay in appropriately selected patients, and enabled patients to return more quickly to work and daily life.

The U.S. Food and Drug Administration gave Empirical Spine approval to market the device in the U.S. in February 2026. On April 30, more than 20 years after the first sketches in a Stanford Biodesign classroom, the concept came to fruition with Alamin performing Lissy’s surgery in a Stanford Hospital operating room.

It’s great to see these patients four or five days out from surgery feeling fine, knowing that if they’d had a fusion operation, they’d be in an entirely different place,” Alamin said.