For a study, researchers sought to understand how traditional growth rod (TGR) and spring distraction system (SDS) treatment for early-onset scoliosis differed biomechanically. They created the SDS to overcome these restrictions using continuous, dynamic forces. TGR and SDS implantation were compared in this FEA, followed by an 18-month growth phase. For this investigation, 2 ligamentous scoliotic FEA models were built, 1 representing TGR and the other representing SDS. Physical spinal development was reproduced for up to 18 months after initial implantation. The SDS model was constantly distracted during this time, while the TGR model included 2 more distractions after index surgery. Differences in rod stress, spinal morphology, and iVD stress-shielding were among the findings. SDS had a maximum postoperative von Mises stress of 249 MPa, while TGR had a maximum of 205 MPa. TGR rod stress increased twofold over the 6-month TGR distraction, reaching a maximum of 417 MPa, compared to a maximum of 262 MPa in the SDS model at the 6-month follow-up. TGR rod stress remained consistently higher than stresses in the SDS model over subsequent follow-up periods.
In comparison to the SDS model, additional lengthenings in the TGR model resulted in a lower residual curve (16.08) and higher T1-S1 growth (359 mm) at 18 months (26.98, 348 mm). When compared to the TGR model, the SDS model showed reduced stress-shielding of the IVDs throughout follow-up. The SDS model’s upper and lower IVD surfaces were loaded in compression more than their TGR counterparts at the 18-month follow-up (mean upper: +112 ±19N; mean lower: +100 ±17N). In this FEA, TGR treatment resulted in a slightly higher curve correction than SDS, but at the cost of increased IVD stress-shielding and a higher risk of rod fractures.