Effect of Vertebral Body Tether Tensioning on Vertebral Body Growth Modulation.

Abstract

The relationship between tether tension and spinal growth modulation following vertebral body tethering (VBT) has not been studied in growing children. This study aims to explore the relationship between vertebral body growth modulation under varying tether tension. A retrospective, multicenter pediatric registry was queried for idiopathic scoliosis patients treated with right-sided VBT, with recorded intraoperative tension (using an ordinal scale of 0-3), and 3D reconstructions from biplanar radiographs at the first erect (FE) and 2-year post-operative visits. Custom MATLAB code was used to calculate vertebral height (mm) on the untethered and tethered sides from T5-T12. Generalized linear mixed models were used to analyze the effect of tension on vertebral body growth. Fifty-two subjects (47 female) were included with a mean age of 12.5 ± 1 years. Patients were skeletally immature (triradiate cartilage open in 23 patients) with Proximal Femoral Maturity Index scores of 2 (nine patients), 3 (21 patients), 4 (20 patients), and 5 (two patients). A total of 330 vertebral bodies were analyzed. Mean height change of the vertebral bodies from FE to 2 years was 1.6 + 1.9 mm (untethered) and 1.2 + 1.8 mm (tethered). On the tethered side, greater tension resulted in less height change, with the greatest differential growth observed between maximal tension and no tension (0.8 mm vs. 0.2 mm, <i>p</i> = 0.02). Greater tension resulted in less vertebral body growth and greater differential growth. Future studies should quantify forces applied during VBT surgery, as well as the forces maintained in the post-operative period with spinal motion. Intraoperative intervertebral tensioning significantly affects vertebral body growth over 2 years.