Anterior vertebral body tethering for thoracic idiopathic scoliosis leads to asymmetric growth of the periapical vertebrae

Purpose: To evaluate 3D growth of the periapical vertebrae and discs in the 2 years after anterior vertebral body tether (AVBT) placement in patients with idiopathic scoliosis (IS). Methods: Patients with IS treated with AVBT, ≥ 2 years of follow-up, and 3D spine reconstructions created from simultaneous, biplanar radiographs were studied. Patients were divided into two groups: progressive scoliosis correction (PC) or no/limited correction (NPC). The average of the 3 apical vertebral and disc heights and angular measures were made. The rate of change for each measure (mm/mo, °/mo) from first erect to 2-year follow-up was compared between groups. Results: Fourteen (Risser 0, Sanders 2–3) patients aged 11.4 ± 1.4 years with right thoracic scoliosis of 52 ± 9° were included. There were 7 patients per group (6F, 1M). Mean follow-up was 3.6 ± 1.1 (range 2–5) years. PC left-sided vertebral height increased 0.13 mm/months compared to 0.05 mm/mo in the NPC group (p = 0.001). Right (tethered side) vertebral growth was not different (PC: 0.07 mm/mo, NPC: 0.05 mm/mo, p = 0.2). Coronal vertebral wedging occurred at − 0.11°/mo compared to − 0.02°/mo for the PC and NPC groups, respectively (p = 0.004). Coronal disc angulation change was − 0.12°/mo in the PC group and − 0.04°/mo in the NPC group (p = 0.03), and was associated with loss of right disc height (PC: − 0.06 mm/mo) with little effect on the left disc height (PC: −0.01 mm/mo). Conclusions: AVBT in immature patients with thoracic scoliosis can asymmetrically modulate growth of the periapical vertebrae and discs. Progressive reduction in scoliosis after AVBT was associated with greater concave growth rates in the vertebrae and loss of disc height on the convex side.