The FDA has approved the first spinal tether device intended to be used in children and adolescents, who have not responded to conservative treatment options, such as external bracing, to correct idiopathic scoliosis.
Idiopathic scoliosis is a sideways curvature of the spine. It is the most common spinal deformity in children and is most often diagnosed between ages 10 to 18. Its causes are unknown.
The Zimmer Biomet Spine device, called The Tether—Vertebral Body Tethering System, is intended, according to an August 16, 2019 FDA announcement, “to treat growing children and adolescents whose spinal curves are approaching or have reached the range where surgical treatment is an option.”
About 6,800 U.S. patients develop progressive curvatures every year that do not respond to bracing. For these patients, spinal fusion surgery can be used to permanently stabilize and correct spinal curvatures.
However, fusion permanently restricts the motion of the spine and may have long-term complications such as pain, arthritis and future spinal deformities. But the Zimmer Biomet system, according to the agency, is designed to continue to correct the curvature while maintaining a fuller range of motion.
The System
Here’s how the FDA says it works:
Anchors and vertebral body screws are placed into the same side of each vertebra in the curved section of the spine through an incision on the side of the chest. A flexible cord, the tether, is connected to the screws. Tension is applied to the tether during surgery to compress one side of the spine and to partially correct the curve.
“Over time, the tether slows growth on the curved side of the spine and promotes growth on the opposite side. This provides additional correction of the curve as the patient continues to grow.”
A company press release noted that unlike fusion metallic rods, the device is positioned utilizing an endoscopic minimally invasive approach through a few small openings between the ribs.
The system is not intended to be removed unless certain problems, such as overcorrections, develop.
Health care professionals monitor patients, conducting follow-up x-rays, to track the spinal curvature and identify any potential problems that might require additional surgery to revise or remove the device.
If the curves are not adequately corrected by the system, spinal fusion surgery is still possible.
Humanitarian Device Exemption
The FDA reviewed data for the system through the humanitarian device exemption (HDE) process. intended to benefit to patients by treating or diagnosing a disease or condition that affects not more than 8,000 individuals in the U.S. per year.
The FDA reviewed clinical data from 57 patients who received the device.
According to the FDA, at two years, 43 patients had sufficient improvement of the curvature of their spines and did not need spinal fusion.
The most common serious adverse events observed included “overcorrection of the curvature, tether breakage, and pneumothorax or air leakage into the space between the lung and chest wall. General complications consistent with any spinal surgical procedure were also noted including pain, respiratory problems, nerve injuries and bleeding.”
Surgeon Training
Baron Lonner, M.D., Chief of Minimally Invasive Scoliosis Surgery at The Mount Sinai Health System and one of the developers of the implant, told OTW that tethering is not something surgeons should be approaching without the proper practice and training. “It is an exacting and precise procedure which has an associated learning curve. Personally, my team and I progressed through the learning curve and optimized our techniques beginning 25 years ago with minimally invasive, thoracoscopic approaches for spinal fusion for thoracic and thoracolumbar scoliosis which are the same approaches used to perform tethering.
“FDA regulatory status through the HDE pathway may give more surgeons the impetus to learn the best indications, learn the how-to of the approaches for tethering, and then begin to progress through the learning curve utilizing cadaver courses, hands-on simulations, surgeon visitation and tackling simpler cases early on, such as ones in which fewer instrumented segments are required for smaller and more flexible curves as opposed to larger, more rigid deformities which are more challenging.”
The company statement from Zimmer Biomet said this approval “marks the culmination of more than five years of cooperation between the FDA and Zimmer Biomet to bring innovative pediatric solutions to market and represents the first approval order for a humanitarian use device in spinal pediatrics within the last 15 years. Considering the recent removal (per FDA final rule) of many semi-rigid stabilization systems that were historically used for anterior vertebral body tethering (AVBT), this solution arrives at a critical time for continuation of care.”
