Impact of Cervical Sagittal Alignment Changes on Postoperative C5 Palsy: A Systematic Review and Meta-Analysis

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BACKGROUND AND OBJECTIVES: Postoperative C5 palsy (CP) is a recognized complication after cervical decompressive surgery for degenerative cervical myelopathy. Although cervical sagittal alignment has been implicated in its pathogenesis, the relative impact of static alignment parameters vs postoperative alignment changes remains unclear. This study aimed to evaluate the association between cervical sagittal alignment and postoperative CP, with emphasis on the magnitude of alignment correction. METHODS: A systematic review and meta-analysis was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines. PubMed, Web of Science, Scopus, and Embase were searched from inception to January 2025. Retrospective cohort studies comparing degenerative cervical myelopathy patients with and without postoperative CP and reporting cervical sagittal parameters were included. Outcomes included preoperative values, postoperative values, and magnitude of change (Δ) in C2-C7 lordosis, C2-C7 sagittal vertical axis (SVA), C4-C5 segmental lordosis, T1 slope, T1 slope-cervical lordosis mismatch, and Ishihara index. Standardized mean differences (SMDs) with 95% CIs were pooled. RESULTS: Thirty-seven studies comprising 4948 patients were included, with an overall CP incidence of 10.83%. Static preoperative parameters, including C2-C7 lordosis, C2-C7 SVA, T1 slope, and T1 slope-cervical lordosis mismatch, were not significantly associated with CP. By contrast, patients who developed CP demonstrated significantly greater postoperative increases in C2-C7 lordosis (SMD = 1.04), C2-C7 SVA (SMD = 1.38), C4-C5 segmental lordosis (SMD = 0.44), and Ishihara index (SMD = 1.79). Subgroup analyses showed significant associations in anterior procedures and laminectomy, but not in laminoplasty. CONCLUSION: Postoperative CP is primarily driven by the magnitude of sagittal alignment correction rather than baseline alignment. These findings support a stretch-mediated mechanism related to postoperative spinal cord and nerve root biomechanics and highlight the importance of balanced sagittal correction to reduce the risk of CP.

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