Limitations of posterior spinal fusion to L5 for flaccid neuromuscular scoliosis focusing on pelvic obliquity

STUDY DESIGN Retrospective comparison based on the degree of pelvic obliquity (PO). PURPOSE To assess the controversial indications for and limitations of ending the instrumentation for posterior spinal fusion (PSF) at L5 in patients with flaccid neuromuscular scoliosis (fNMS). METHODS We reviewed the cases of 45 patients with progressive spinal deformity as a result of fNMS treated by PSF to L5 and followed for an average of 4 years postoperatively with adequate clinical and radiological data. Anterior-posterior and lateral whole spine radiographs were evaluated. We divided patients into two groups based on the degree of pelvic obliquity (PO) at the final follow-up. Radiographic data from the two groups were analyzed to identify the indications and limitations of this surgical method focusing on PO. RESULTS Preoperatively, there were significant differences between the two groups in Cobb angle, PO, thoracolumbar kyphosis, and lumbar lordosis (LL) while sitting; Cobb angle and LL while supine (Supine Cobb, and Supine LL); and major curve flexibility. Multivariate logistic regression analysis identified Supine Cobb and Supine LL as independent risk factors for residual PO at the final follow-up (Supine Cobb: odds ratio, 1.1; 95% confidence interval 1.0-1.2, Supine LL: odds ratio, 0.9; 95% confidence interval 0.8-1.0). CONCLUSION Patients with larger preoperative Cobb angle and smaller LL while supine may not achieve adequate spine and pelvic correction and this may lead to deterioration in the PO over time, even after spinal fusion ending at L5.