Biomechanical Comparison of Hybrid Technique and Traditional Dual-Growing Rods Alone in the Treatment of Severe Early Onset Scoliosis

Background: Currently, there is a lack of biomechanical studies on traditional dual-growing rods (TDGR) combined with apical osteotomy and short-segment fusion (hybrid technique, HT). This study compared the differences in clinical outcomes and biomechanics between TDGR and HT in the treatment of severe early-onset scoliosis (sEOS) via finite element analysis (FEA) and in vitro biomechanical experiments. Methods: Two scoliotic FEA models and 12 in vitro scoliotic models were created. In the FEA, the initial surgeries for TDGR and HT, two subsequent lengthenings, and up to 12 months of physeal spinal growth were simulated. In the in vitro biomechanical experiments, the initial surgeries were simulated. Correction outcomes, spinal height, and stress were compared between the TDGR and HT groups. Results: (1) FEA: Compared with TDGR, HT achieved better correction (62.4% vs. 36.2%) and a greater increase in spinal height (26.43 mm vs. 12.58 mm) after the initial surgery. During follow-up, HT resulted in better correction maintenance and could better sustain spinal growth than TDGR. HT reduced the stress on the proximal and distal instrumented vertebral bodies, junctional intervertebral discs, and instrumentation compared with TDGR. (2) In vitro biomechanical experiment: After the initial surgery, the mean Cobb angle of the main curve (24.58 ± 2.80° vs. 38.97 ± 3.23°) and AVT (8.87 ± 1.64 mm vs. 13.15 ± 3.58 mm) in the HT group were significantly lower than those in the TDGR group (p < 0.05). The increase in spinal height in the HT group was significantly greater than that in the TDGR group (3.83 ± 0.45 cm vs. 1.85 ± 0.72 cm, p < 0.001). Compared with TDGR, HT significantly decreased rod strain (p < 0.05). Conclusions: Compared with TDGR, HT can significantly improve correction outcomes and maintain spinal growth. Apical anchors can effectively disperse stress on the spine and instrumentation, which may reduce the risk of complications and potentially delay intervertebral disc degeneration, although clinical validation is required.