Biomechanical effects on adjacent segments of different growing-rod fixation in early onset scoliosis

Abstract

Objective: To analyse the biomechanical effects on adjacent segments of different growing-rod (GR) fixation in early onset scoliosis through a finite element analysis method. Methods: A severe early-onset scoliosis patient was selected and the pre-operation and post-GR-operation (Upper instrumented levels: T(4), T(5). Lower instrumented levels: L(3), L(4)) whole spine 3-dimentional CT scan data were collected to build the finite models. Based on the different models, biomechanical differences on adjacent segments were analysed. Results: The stress on the adjacent structures decreased after the GR surgery compared with the pre-operation. Compared with the single GR, stress on T(3) vertebrae decreased by 6.2%, stress on T(3/4) disc decreased by 6.7%, stress on T(3/4) ligament decreased by 27.7%, stress on T(6) vertebrae decreased by 16.9%, stress on T(5/6) disc decreased by 1.2%, stress on T(5/6) ligament decreased by 40.4%, stress on L(2) vertebrae decreased by 32.6%, stress on L(2/3) disc decreased by 30%, stress on L(2/3) ligament decreased by 15.6%, stress on L(5) vertebrae decreased by 1.2%, stress on L(4/5) disc decreased by 15.7%, stress on L(4/5) ligament decreased by 100.0% in dual GR structure. The application of hook (s) on the upper instrumented vertebrae (s) decreased the stress on the cranial adjacent segment. Stress on T(3) vertebrae decreased by 2.8% and 2.2%, stress on T(3/4) disc decreased by 2.4% and 1.5%, stress on T(3/4) ligament decreased by 3.6% and 5.7% in single GR and dual GR models separately when the hook (s) were utilized. In the meanwhile, the stress on the adjacent segment was more concentrated in the single GR model. Conclusion: Dual-rod growing-rod and the application of hook (s) on the upper instrumented vertebrae could reduce the stress on the adjacent segments more effectively in patients with early onset scoliosis.