5.5-mm Cobalt-Chrome vs 6-mm Titanium Alloy Rods in Surgical Treatment of Lenke 1 Adolescent Idiopathic Scoliosis With High-Density Pedicle Screws and Direct Vertebral Rotation on Differently Shaped Rods: A Retrospective Comparative Cohort Study

Background The gold standard of surgical treatment of adolescent idiopathic scoliosis (AIS) consists of a posterior approach requiring complex 3-dimensional correction with multisegmental pedicle screws and 2 contoured rods. The substantial corrective forces and the ability of the rod to withstand these forces rely on its biomechanical properties. The aim of this study is to compare outcomes of 5.5-mm cobalt-chrome (CoCr) and 6-mm titanium alloy (TiAl) rods in surgical correction in Lenke 1 AIS patients. TiAl has greater elasticity, which may facilitate the correction maneuver, whereas the stiffness of CoCr may result in stronger correction forces. The literature provides no clear indications about which rod may allow better correction and safety.

Methods A total of 64 consecutive patients (30 CoCr vs 34 TiAl) with Lenke 1 AIS <100°, with 2 years minimum follow-up, requiring correction and posterior fusion at our institution were included. The primary outcome measure was coronal and sagittal correction and loss of correction at 2-year follow-up. Secondary outcome measures compared peri- and postoperative complications.

Results The mean coronal correction was higher in the CoCr group: −73.6% ± 7.4 vs −65.5% ± 11 (P = 0.001). Mean T5-T12 kyphosis did not change significantly after surgery. In patients with hypokyphosis (<10°), an improvement in thoracic kyphosis was observed in both groups, but the improvement was significantly higher in the TiAl group (P = 0.038). In patients with hyperkyphosis (>40°), a similar reduction in thoracic kyphosis was observed in both groups. At follow-up, no coronal correction loss occurred. The sagittal correction loss was slight (0.5° ± 1.5 for the CoCr group, 1.5° ± 3 for the TiAl group) but statistically higher in the TiAl group (P = 0.032). There were no mechanical complications. One revision was required for infection in the CoCr group.

Conclusion In this series of Lenke 1 AIS, with the limitations of the study, 5.5-mm CoCr rods have provided better correction in the coronal plane than 6-mm TiAl rods. However, TiAl rods have been found to be associated with higher increase of thoracic kyphosis in hypokyphotic curves, although the clinical relevance of this finding could be questionable.

Clinical Relevance This article provides surgeons with more information regarding rod material options when correcting Lenke 1 AIS.

Level of Evidence 3.