Prevention of Postoperative Coronal Imbalance in Patients with Adolescent Idiopathic Scoliosis with a Major Lumbar Curve

Background: Patients who have undergone corrective surgery for adolescent idiopathic scoliosis (AIS), especially those with a major lumbar curve, may have persistent postoperative coronal imbalance (PCI) due to an insufficient ability to compensate for lumbar curve overcorrection. However, the optimal amount of curve correction required to prevent PCI remains uncertain. Therefore, this study aimed to evaluate the use of the intraoperative crossbar coronal-balancing technique as a strategy to minimize the risk of PCI in patients with AIS with a major lumbar curve (Lenke type-5 and 6 curves), and to confirm that the tilt angle of the lowest instrumented vertebra (LIV), intraoperatively and at the final follow-up, could be predicted from the preoperative supine right-side-bending (RSB) radiograph that was used to guide the correction. Methods: This study involved 39 patients with Lenke 5 or 6 AIS who underwent posterior spinal fusion and had a minimum 2-year follow-up. The median age was 14 years, 15% were male, and all were of Malaysian ethnicity: 84.6% Chinese, 12.8% Malay, and 2.6% Indian. The LIV tilt angle measured on the preoperative supine RSB radiograph, adjusted according to the pelvic obliquity (PO) measured on the erect radiograph (α angle), was used as a guide for the intraoperative LIV tilt angle (β angle). Following curve correction, the crossbar was centered over the sacrum intraoperatively. The position of the C7 vertebra was then assessed relative to the crossbar, and the amount of correction was adjusted to ensure that the proximal portion of the crossbar bisected the C7 vertebra under fluoroscopy. Outcomes included the coronal balance distance (CBD) and the LIV tilt angle at the final follow-up (δ angle). Results: Only 2 (5.1%) of the patients in the cohort had PCI at the final follow-up. At that time, the mean CBD was −6.6 ± 9.2 mm and the mean δ angle was −12.4° ± 4.8°. There were no significant differences between the α and β angles (p = 0.799) or between the α and δ angles (p = 0.705). The α angle correlated strongly with the β angle (ρ = 0.707) and the δ angle (ρ = 0.730, p < 0.001). Conclusions: The intraoperative crossbar coronal-balancing technique was shown to be an effective method to minimize the risk of PCI in patients with AIS with a major lumbar curve. Guided by the α angle measured preoperatively, this approach may help facilitate the determination of the optimal intraoperative LIV tilt angle (β), which corresponds to the LIV tilt angle at the final folow-up ( δ ). Level of Evidence: Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.