A Novel Dynamic Growth Rod Inducing Spinal Growth Modulation for the Correction of Spinal Deformities

Background: Growth rods are the gold standard for treating early-onset scoliosis (EOS). However, current treatments with growth rods do not optimize spinal growth in EOS patients, and frequent distraction surgeries significantly increase complications, imposing considerable economic and psychological burdens on patients. An improved growth rod is urgently required to address the need for dynamic growth and external regulation. Methods: This study designed a novel growth rod (NGR) with unidirectional sliding and external regulation capabilities. By establishing a three-dimensional model of the EOS spine, we simulated the implantation of traditional growth rods (TGR) and NGR. We applied a compressive load of 400 N to test axial stiffness and a moment of 1 NM to assess bending stiffness under six different conditions. Additionally, we evaluated the range of motion (ROM) of the spinal joints, and the distribution of Von Mises stress in vertebrae, intervertebral discs, and the growth rods, and calculated the axial force, moment, fatigue life, and strain energy of the device. Results: NGR exhibits higher axial compression and torsional stiffness than TGR and the Intact group. Additionally, Von Mises stress values for NGR are higher than those for TGR across all operating conditions, albeit with slightly lower total strain energy than TGR. Although Von Mises stress in NGR concentrates near the screw fixation, the fatigue life remains adequate for basic living requirements. Conclusion: Overall, NGR demonstrates superior stiffness and stress distribution. NGR's distraction-based implant features a unidirectional sliding component with a spring-driven mechanism for dynamic correction and a novel non-invasive extension mechanism to reduce infections. Compared to leading EOS implants, NGR offers improved stability, showing promise for enhancing EOS surgical interventions.