Biomechanical simulations of costo-vertebral and anterior vertebral body tethers for the fusionless treatment of pediatric scoliosis

Compression-based fusionless tethers are an alternative to conventional surgical treatments of pediatric scoliosis. Anterior approaches place an anterior (ANT) tether on the anterolateral convexity of the deformed spine to modify growth. Posterior, or costo-vertebral (CV), approaches have not been assessed for biomechanical and corrective effectiveness. The objective was to biomechanically assess CV and ANT tethers using six patient-specific, finite element models of adolescent scoliotic patients (11.9 +/- 0.7 years, Cobb 34 degrees +/- 10 degrees). A validated algorithm simulated the growth and Hueter-Volkmann growth modulation over a period of 2 years with the CV and ANT tethers at two initial tensions (100, 200N). The models without tethering also simulated deformity progression with Cobb angle increasing from 34 degrees to 56 degrees, axial rotation 11 degrees to 13 degrees, and kyphosis 28 degrees to 32 degrees (mean values). With the CV tether, the Cobb angle was reduced to 27 degrees and 20 degrees for tensions of 100 and 200N, respectively, kyphosis to 21 degrees and 19 degrees, and no change in axial rotation. With the ANT tether, Cobb was reduced to 32 degrees and 9 degrees for 100 and 200N, respectively, kyphosis unchanged, and axial rotation to 3 degrees and 0 degrees. While the CV tether mildly corrected the coronal curve over a 2-year growth period, it had sagittal lordosing effect, particularly with increasing initial axial rotation (>15 degrees). The ANT tether achieved coronal correction, maintained kyphosis, and reduced the axial rotation, but over-correction was simulated at higher initial tensions. This biomechanical study captured the differences between a CV and ANT tether and indicated the variability arising from the patient-specific characteristics. (c) 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:254-264, 2018.