Pelvic Obliquity Deterioration after Floating Fusion for Spastic Neuromuscular Scoliosis: Identifying Thresholds to Guide Fusion Level Selection

Abstract

Introduction: Floating fusion without pelvic fixation reduces surgical invasiveness in neuromuscular scoliosis (NMS). Concerns regarding pelvic obliquity (PO) deterioration remain, particularly in spastic cases. The risk factors for postoperative PO deterioration remain unclear. This study aimed to determine incidence of postoperative PO deterioration and identify preoperative and postoperative risk factors in patients with spastic NMS undergoing floating fusion ending at L5.

Methods: This two-center study retrospectively reviewed 41 consecutive non-ambulatory patients with spastic NMS who underwent spinal fusion ending at L5 and were followed for ≥2 years. Radiographs were obtained preoperatively, immediately after surgery, and 2 years postoperatively. PO was measured using Maloney' s method. PO deterioration was defined as an increase in PO ≥10°. Receiver operating characteristic curve analysis was used to identify the optimal postoperative and preoperative thresholds predictive of deterioration.

Results: PO deterioration occurred in five patients (12.2%). Postoperative PO demonstrated the strongest predictive accuracy (area under the curve [AUC] = 0.90), with an optimal cutoff of 22°. Patients with postoperative PO ≥22° showed significantly greater progression during follow-up. Preoperative PO also demonstrated predictive value (AUC = 0.78; cutoff = 35°), although with lower accuracy. Patients with preoperative PO ≥35° were substantially less likely to achieve postoperative PO <22°.

Conclusions: In spastic NMS, postoperative PO ≥22° was identified as a strong predictor of PO deterioration after floating fusion. Preoperative PO ≥35° identified patients at risk of residual postoperative PO ≥22°. Achieving postoperative PO <22° may serve as a surgical target, and awareness of this risk may contribute to better surgical planning for patients with notable preoperative PO.