Long-Term Clinical Benefits of Age-Adjusted Sagittal Correction in Adult Spinal Deformity Surgery: Results From Patient Grouping Using a Hierarchical Cluster Analysis.

Age-adjusted sagittal alignment correction has emerged as a critical consideration for adult spinal deformity (ASD) surgery. This study aimed to explore the long-term clinical benefits of age-adjusted sagittal alignment by integrating multiple sagittal parameters (pelvic incidence minus lumbar lordosis, pelvic tilt, T1 pelvic angle, and sagittal vertical axis) using hierarchical cluster analysis. A retrospective analysis was conducted on 386 patients with ASD who underwent surgical correction with at least 5-level fusion, including sacrum/pelvis, with a minimum follow-up of 2 years. Hierarchical cluster analysis was used to stratify patients based on postoperative offsets between age-adjusted alignment targets and actual pelvic incidence minus lumbar lordosis, pelvic tilt, T1 pelvic angle, and sagittal vertical axis values. Radiographic outcomes, proximal junctional kyphosis/failure, and clinical outcomes (Oswestry Disability Index, Scoliosis Research Society-22 revised) were compared across clusters. Hierarchical cluster analysis grouped patients into 3 clusters: 72 in cluster A, 211 in cluster B, and 103 in cluster C. The mean offset values were significantly greater in cluster C, followed by clusters B and A, for all sagittal parameters with an overcorrected tendency in cluster C and an undercorrected tendency for cluster A. The mean follow-up duration was 36.6 months. Proximal junctional kyphosis/failure rates were significantly higher in cluster C (37.9%) compared with cluster B (27.5%) and cluster A (20.9%) (P = .046). At final follow-up, clinical outcomes were significantly better in cluster B than in clusters A and C regarding Oswestry Disability Index (P = .034) and Scoliosis Research Society-22 revised scores (P < .001). Hierarchical cluster analysis effectively stratified ASD patients based on postoperative sagittal parameter offsets and identified a balanced alignment (cluster B) that optimizes clinical outcomes and minimizes mechanical complications. These results suggest a practical and nuanced approach to sagittal alignment correction in ASD surgery, emphasizing the integration of multiple parameters for improved outcomes.