A facet joint replacement device being tested in clinical trials could soon offer a motion-preserving treatment for two common spinal conditions that affect the low back.
The TOPS facet arthroplasty device was developed by Premia Spine
as a new treatment option for people with spinal stenosis and spondylolisthesis, two common conditions that affect the lower back, or lumbar spine.
Spinal stenosis is a narrowing of the canal through which the spinal cord runs. It can cause low back pain, as well as numbness, tingling, or weakness in a leg or foot.
is a type of spinal instability in which one of the bones of the spine (vertebra) slips out of place on the vertebra below. This can cause back stiffness or pain, and numbness, tingling, or weakness in a leg or foot.
Degenerative spondylolisthesis, which is due to age-related changes in the spine, is the most common type.
Both of these conditions can lead to compression of a spinal nerve, which can cause nerve-related symptoms such as numbness or tingling. Treatment for this may involve easing the pressure on the spinal nerves, also known as spinal decompression.
Decompression may need to be followed by spinal fusion
. In this procedure, two adjacent vertebrae are joined with metal hardware and a bone graft to increase the stability of the spine. Spinal fusion is effective, but it reduces the motion at that level of the spine.
The TOPS facet arthroplasty device offers an alternative to spinal fusion, one that provides stability after spinal decompression and maintains motion at that level.
How facet joint replacement works
Facet joints are synovial joints, which have a fluid-filled space where the bones of the joint meet. Between each adjacent vertebrae of the spine, there are two facet joints, one on each side.
The facet joints allow for motion of the spine, but also provide support and prevent certain movements of the spine. This helps to protect the spinal cord and nerves.
The TOPS device is constructed of two titanium plates that are connected by a soft disc made of polycarbonate urethane and a strong ribbon. This setup allow for the spine at that level to twist and bend in all directions, but without moving too far.
As with spinal fusion, the TOPS device is used after spinal decompression. During this procedure, a surgeon removes bone and tissue that is pressing on the spinal nerves to cause pain or other symptoms. The TOPS device is then implanted to stabilize the spine and allow for normal motion.
The surgeon implants the device from the back (posterior) using screws to attach it to the vertebrae. Accessing the spine this way avoids having to move the organs and blood vessels in the abdominal cavity out of the way.
Dr. Dom Coric
, a spine surgeon at Carolina Neurosurgery and Spine Associates in Charlotte, North Carolina, and lead investigator of Premia’s U.S. clinical trial of the device, says implanting the device is very straightforward.
“The elegance of the device comes from it's biomechanics and the way it's designed,” he says. “This does not necessarily translate into making it difficult to put in.”
From start to finish, the surgery takes about an hour and fifteen minutes, says Coric.
Early clinical trials show positive results
Early clinical studies
of the TOPS device found that the procedure reduced pain in the lower back and the leg, and also improved patients’ quality of life.
The device is now being tested in a larger clinical trial
in the United States comparing it to spinal fusion in patients with spinal stenosis and spondylolisthesis in the lower back. Patients will be followed for five years after their surgery.
Success of the device will be based on how well it improves patients’ symptoms, whether there is a need for additional treatment or surgery, and if there are any safety concerns.
Dr. Grant D. Shifflett
, an orthopedic spine surgeon at DISC Sports & Spine Center in Newport Beach, California, says it is important to see how well the device improves patient outcomes, as well as how the device functions over the long run.
“I think durability will be absolutely critical to [the device’s] success,” he says. “If this procedure fails after a few years, I think the clinical advantage would be lost.”
Coric says the company expects to enroll enough patients for the first part of its study by this year. Once the company has enough data, it will submit an application to the FDA for approval.
While this device is being tested as a treatment for people with spinal stenosis and spondylolisthesis, Shifflett says the device might also work for people with facetogenic low back pain.
This condition is caused by repetitive stress or low-level trauma to the facet joint, leading to stretching and inflammation of the joint capsule.
“There are millions of patients who suffer from this disease and who receive fusions which may or may not improve their symptoms,” he says. “The TOPS procedure could potentially be a great option for them.”
Before the device could be used for facetogenic pain, though, it would need to be tested in a clinical trial as a treatment for this condition.
Facet joint replacement offers several advantages
Although spinal fusion is effective at stabilizing the spine, it limits the motion at the level that is fused. This loss of motion itself may not affect a patient immediately.
“There are six discs that are motion segments in the low back,” says Coric. “When you’re doing a one-level fusion, you’re only losing one-sixth of the motion. That’s not a horrific loss of motion.”
Because the TOPS device allows for more natural motion, there is less stress on the adjacent levels of the spine. By maintaining the motion, there is less stress on those other spinal levels.
“This procedure would allow adequate decompression and stabilization of a segment,” says Shifflett, “with the theoretical advantages of avoiding progressive instability [in the spine].”
This might reduce the risk of the neighboring vertebrae being negatively affected, also known as adjacent segment disease.
However, “it’s not proven that by maintaining the motion and decreasing the stresses that you decrease the adjacent level operations,” says Coric. The ongoing clinical trial may provide some answers to this question.
Facet joint replacement has another advantage over spinal fusion. With fusion, patients not only have to recover from surgery, they also have to wait for the fusion to occur.
“The spinal fusion operation really isn’t done until the bone has grown [around the implanted rods and screws],” says Coric. “That typically takes six to 12 months to occur.”
With facet joint surgery, the device is implanted with screws, so no fusion has to happen. The device is stable right away. So patients typically recover within four to eight weeks after this procedure.
“With [the TOPS] device, you’re not waiting for fusion to occur,” says Coric. “In fact, as soon as the device is put in, it should function the same as it does in a year or five years.”
Updated: July 26, 2021