Thoracolumbar curve behavior after selective thoracic anterior vertebral body tethering in Lenke 1A vs Lenke 1C curve patterns

STUDY DESIGN: Retrospective review of a prospective database. OBJECTIVES: The purpose of this study is to evaluate changes in the thoracic and thoracolumbar/lumbar curves and truncal balance in patients treated with selective thoracic anterior vertebral body tethering (AVBT) with Lenke 1A vs 1C curves at a minimum of 2 years follow-up. SUMMARY: Lenke 1C curves treated with selective thoracic AVBT demonstrate equivalent thoracic curve correction and reduced thoracolumbar/lumbar curve correction compared to Lenke 1A curves. Additionally, at the most recent follow-up, both curve types demonstrate comparable coronal alignment at C7 and the lumbar curve apex, though 1C curves have better alignment at the lowest instrumented vertebra (LIV). Rates of revision surgery are equivalent between the two groups. METHODS: A matched cohort of 43 Risser 0-1, Sanders Maturity Scale (SMS) 2-5 AIS pts with Lenke 1A (1A group)and 19 pts with Lenke 1C curves (1C group) treated with selective thoracic AVBT and a minimum of 2-year follow-up were included. Digital radiographic software was used to assess Cobb angle and coronal alignment on preoperative, postoperative and subsequent follow-up radiographs. Coronal alignment was assessed by measuring the distance from the center sacral vertical line (CSVL) to the midpoint of the LIV, apical vertebra for thoracic and lumbar curves and C7. RESULTS: There was no difference in the thoracic curve measured preoperatively, at first erect, pre-rupture or at the most recent follow-up, nor was there a significant difference in C7 alignment (p = 0.057) or apical thoracic alignment (p = 0.272) between the 1A and 1C groups. Thoracolumbar/lumbar curves were smaller in the 1A group at all-time points. However, there was no significant difference between the percent correction between the two groups thoracic (p = 0.453) and thoracolumbar/lumbar (p = 0.105). The Lenke 1C curves had improved coronal translational alignment of the LIV at the most recent follow-up p = 0.0355. At the most recent follow-up the number of patients considered to have successful curve correction (Cobb angle correction of both the thoracic and thoracolumbar//lumbar curves to ≤ 35 degrees), was equivalent between Lenke 1A and Lenke 1C curves (p = 0.80). There was also no difference in the rate of revision surgery between the two groups (p = 0.546). CONCLUSION: This is the first study to compare the impact of lumbar curve modifier type on outcomes in thoracic AVBT. We found that Lenke 1C curves treated with selective thoracic AVBT demonstrate less absolute correction of the thoracolumbar/lumbar curve at all time points but have equivalent percent correction of the thoracic and thoracolumbar/lumbar curves. The two groups have equivalent alignment at C7 and the thoracic curve apex, and Lenke 1C curves have better alignment at the LIV at the most recent follow-up. Furthermore, they have an equivalent rate of revision surgery compared to Lenke 1A curves. Selective thoracic AVBT is a viable option for selective Lenke 1C curves, but despite equivalent correction of the thoracic curve, there is less correction of the thoracolumbar/lumbar curve at all-time points.