Advancements in sagittal alignment parameters and management of adult spine deformities.

Adult spinal deformity (ASD) is increasingly recognized as a condition in which sagittal alignment plays a role in pain, disability, and mechanical failure. Historically, sagittal correction strategies relied on global radiographic parameters such as sagittal vertical axis (SVA) and pelvic incidence-lumbar lordosis (PI-LL) mismatch. While these measures demonstrated important associations with health-related quality of life, they incompletely account for compensated deformities, segmental mechanics, and directionality of correction. Over the past decade, alignment planning has evolved toward more individualized frameworks that incorporate pelvic morphology, age, segmental lordosis distribution, and direction-sensitive metrics. Outcome-derived strategies, such as age-adjusted alignment targets, have contributed valuable insights but remain controversial and are not universally accepted as definitive sagittal goals. Radiographic parameters, including the L1 pelvic angle (L1PA) and T4-L1-hip axis, provide reproducible, intraoperatively modifiable feedback and improved prediction of mechanical failure risk when applied with appropriate clinical context. This review synthesizes the evolution of sagittal alignment strategies in ASD, highlighting the strengths and limitations of historical global metrics, age-adjusted frameworks, and emerging vector-based and segmental alignment concepts. Emphasis is placed on integrated, patient-specific approaches that balance global, segmental, and directional parameters to optimize outcomes.