Effect of magnetically controlled growing rods on three-dimensional changes in deformity correction

Abstract

Introduction: Magnetically controlled growing rods (MCGRs) have been shown to achieve similar coronal plane correction as traditional growing rods. Changes in sagittal and axial planes are factors indicating potential for proximal junctional kyphosis and rotational deformity, but they remain largely unknown. This study aimed to determine the three-dimensional changes in deformity correction with MCGR distractions. Methods: Patients with early-onset scoliosis who underwent dual MCGRs and minimum 2-year follow-up with images were recruited. Three-dimensional reconstructions of 6-monthly biplanar images were assessed for changes in coronal, sagittal, and axial planes. Changes in growth parameters were scaled to changes in coronal Cobb’s angles, rotational, and sagittal profile (T1-12, T4-12, L1-L5, L1-S1) at the proximal thoracic, main thoracic ,and lumbar curves. Pelvic parameters (sagittal and lateral pelvic tilt, pelvis rotation) were studied. Results: Ten patients with early-onset scoliosis were studied with mean age of 8.2 ± 3.0 years at index surgery. Six patients had rod exchange. Mean duration between index surgery and rod exchange was 29.5 ± 11.8 months. Despite consistent gains in body height and arm span, the main changes in coronal and rotational profiles only occurred at initial rod implantation surgery with only small changes at subsequent follow-up examinations. Flattening of sagittal plane occurred at initial surgery with rebound within first 2 years after surgery, without significant changes thereafter. No pelvic parameters changes were observed. Conclusion: The three-dimensional changes with MCGR are mainly observed with initial rod implantation and no significant changes are observed with distractions. The MCGR is able to prevent deformity progression in the transverse plane.