There are several different types of scoliosis, a condition that causes a sideways spinal curve, that affect children and adolescents. According to the American Academy of Orthopaedic Surgeons (AAOS), the most common type is idiopathic, meaning the exact cause is unknown. Most idiopathic scoliosis cases happen between the age of 10 and the time the child is fully grown, although it can occur at a younger age. The disease is rarely painful—children and their parents may not notice smaller curves. It may be first spotted during a school screening or regular pediatric checkup. Idiopathic scoliosis is also not related to specific behaviors or activities, according to AAOS—carrying a heavy backpack or having poor posture aren’t responsible for abnormal curvature.

Idiopathic scoliosis curves vary in size, and mild curves are more common. If a child is still growing, however, the scoliosis curve can worsen rapidly during a growth spurt. In these cases, the scoliosis is called “progressive.” Treatments for progressive idiopathic scoliosis in children and adolescents involve conservative, non-surgical therapies like external bracing to correct the spinal curvature. Unfortunately, according to the U.S. Food and Drug Administration (FDA), about 6,800 U.S. patients will develop progressive curvatures that don’t respond to bracing.

The next option in these cases is spinal fusion surgery to permanently stabilize and correct spinal curvatures. Though often successful, spinal fusion surgery restricts the spine’s motion and can present long-term complications like pain, arthritis, and future spinal deformities—all of which require additional surgical treatment.

The pediatric orthopedic and spinal markets have historically been underserved because it is typically not the demographic experiencing musculoskeletal conditions. However, as alternatives to spinal fusion, the FDA recently approved two first-of-their-kind devices to treat idiopathic scoliosis: Zimmer Biomet’s The Tether – Vertebral Body Tethering System and ApiFix’s Minimally Invasive Deformity Correction (MID-C) system. Both were approved through the FDA’s humanitarian device exemption (HDE) process. A Humanitarian Use Device (HUD) is intended to treat or diagnose a disease affecting not more than 8,000 people in the U.S. per year. According to Zimmer Biomet, The Tether is the first approval order for an HUD in spinal pediatrics within the last 15 years.

The Tether – Vertebral Body Tethering System—an anterior vertebral body tethering (AVBT) solution—works by placing anchors and vertebral body screws into the same side of each vertebra in the curved spinal section through an incision on the side of the chest. A flexible cord (tether) is connected to the screws. The surgeon applies tension to the tether to compress one side of the spine, partially correcting the curve. Over time, the tether slows growth on the curved spinal side and promotes growth on the opposite side. It isn’t intended to be removed unless overcorrections or other problems develop. (Those whose curves aren’t adequately corrected by the device are still able to undergo spinal fusion surgery.)

“Often growth in children with scoliosis results in curve progression. With AVBT, that growth can be harnessed to gradually further correct the tethered portion of the spine,” Dr. Amer Samdani, board-certified neurosurgeon and chief of Surgery for Shriners Hospitals for Children in Philadelphia, noted to the press. “The Tether provides clinicians who take care of children with spinal curves another option for treatment. When utilized in the appropriately selected patient, the results are dramatic with respect to curve control and maintenance of a mobile spine.”

ApiFix’s MID-C system was approved for progressive adolescent idiopathic scoliosis (AIS) via an HDE a week later. According to the FDA, it’s the first posterior non-fusion device to treat adolescents with the condition. MID-C is specifically a posterior dynamic deformity correction system that lets surgeons perform a unique treatment providing permanent curve correction while retaining spine flexibility, all via a much less invasive procedure than spinal fusion. The MID-C system functions as an “internal brace” with a unidirectional, self-adjusting rod mechanism and motion-preserving polyaxial joints, facilitating additional post-operative correction over time.

“This FDA approval will enable surgeons to offer the first posterior dynamic deformity correction technology for treating Lenke Type 1 and Type 5 curves in patients with progressive AIS,” commented Baron Lonner, M.D., chief of Minimally Invasive Scoliosis Surgery at Mount Sinai Hospital in New York, N.Y., and professor of Orthopaedic Surgery at the Icahn School of Medicine. “MID-C is an alternative that fills the significant treatment gap for patients between non-operative therapies and irreversible spinal fusion.”

Further, Zimmer Biomet will be partnering with the Harms Study Group—a cohort of surgeons dedicated to advancing treatment for children and adolescents with spinal deformities—to build a patient data registry to help assess the long-term performance of The Tether System.

“The FDA continues to collaborate with stakeholders to encourage the development of registries, including the one being developed for this device, as an additional tool to gather and track real-world evidence,” FDA Principal Deputy Commissioner Amy Abernethy, M.D., Ph.D., stated to the press. “This type of post-market data generation can provide ongoing device safety surveillance and additional evidence for effectiveness. More broadly, real-world evidence can help support innovative developments while ensuring that patient health and safety remains the top priority.”