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

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: T4, T5. Lower instrumented levels: L3, L4) 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 T3 vertebrae decreased by 6.2%, stress on T3/4 disc decreased by 6.7%, stress on T3/4 ligament decreased by 27.7%, stress on T6 vertebrae decreased by 16.9%, stress on T5/6 disc decreased by 1.2%, stress on T5/6 ligament decreased by 40.4%, stress on L2 vertebrae decreased by 32.6%, stress on L2/3 disc decreased by 30%, stress on L2/3 ligament decreased by 15.6%, stress on L5 vertebrae decreased by 1.2%, stress on L4/5 disc decreased by 15.7%, stress on L4/5 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 T3 vertebrae decreased by 2.8% and 2.2%, stress on T3/4 disc decreased by 2.4% and 1.5%, stress on T3/4 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. Key words: Scoliosis; Internal fixators; Biomechanics; Finite element analysis