Could have tethered: predicting the proportion of scoliosis patients most appropriate for thoracic anterior spinal tethering.

BACKGROUND: Posterior spinal fusion (PSF) has proven to be a safe, reliable technique to treat spinal deformities in adolescents. In recent early reports, vertebral body tethering (VBT) is showing promise as a method to modulate growth, driving scoliosis correction, while offering the potential added benefit of maintaining some flexibility in the instrumented segment. With recent FDA humanitarian device exemption (HDE) approval, VBT is poised to become more widely available as a treatment for a subset of current PSF candidates. Our aim was to use approved criteria from a recent FDA IDE to determine who could have been tethered in the years preceding approval.

METHODS: A retrospective analysis was performed of patients with idiopathic scoliosis treated with PSF or VBT at a large pediatric spine center from 1/1/2016 to 6/25/2019. Tethering indications followed the criteria outlined by an ongoing FDA IDE: age 8-16, Sanders bone age ≤ 4, primary thoracic curve between 35° and 60°, and lumbar curve < 35°. Risser sign and triradiate cartilage status were also employed to ascertain skeletal maturity in the absence of Sanders score.

RESULTS: Of the 359 patients (78.6% female) who underwent PSF or VBT for idiopathic scoliosis, 75 (20.9%) met IDE criteria for VBT (57 had PSF and 18 had VBT). 284 were not appropriate for thoracic VBT: 77 (21.4%) had a non-thoracic primary curve, 80 (22.3%) were too mature at presentation, 36 (10.0%) had a lumbar curve > 34°, 9 (2.5%) had a main thoracic curve out of range, and 1 had a proximal thoracic curve > 40°. 81 patients (22.6%) had multiple exclusionary criteria.

CONCLUSIONS: After decades with a successful treatment for AIS (PSF), we are at an inflection point: VBT is conditionally approved by the FDA as an HDE device, unleashing more widespread use. Many pediatric spine surgeons will want to know what proportion of PSFs will someday be VBTs. If FDA IDE criteria are used to ensure that a VBT candidate has an appropriate maturity stage and scoliosis deformity pattern, 20.9% of our 359 surgical range patients would have qualified for thoracic VBT.

LEVEL OF EVIDENCE: Level III.