Alignment Goals in Adult Spinal Deformity Surgery

Abstract

Study Design Narrative review. Objectives Adult spinal deformity (ASD) surgery has progressively transitioned from mean regional alignment targets to individualized segmental alignment goals, and from health-related quality of life (HRQL) alignment goals to the prevention of mechanical complications. Methods Narrative review discussing sagittal alignment concepts and goals in ASD surgery. Results Traditional metrics for measuring sagittal spinal alignment such as pelvic incidence - lumbar lordosis (PI-LL), thoracic kyphosis, and sagittal vertical axis (SVA) may lack the specificity necessary for individualized alignment planning. Compensatory pelvic retroversion and knee flexion are critical determinants of maintaining the upright position. Research has been conflicting as to whether postoperative sagittal alignment is associated with improvements in HRQOL’s. However, this may reflect a lack of sensitivity in the traditional alignment targets and PROM’s measures, rather than a true lack of relationship between sagittal alignment and functional outcomes. Recent studies show that sagittal parameters have a limited impact on HRQL scores in non-operated patients, but significantly impact post-operative HRQOL measures and mechanical complications in patients treated with spinal fusion. Latest evidence suggests that compensatory mechanisms need to be eliminated and the ideal shape needs to be restored with surgery, to reduce postoperative mechanical complications. Multiple alignment strategies are proposed for that purpose. Conclusions While best evidence shows an improvement in ASD alignment strategies over the last decade, mechanical failures and reoperations are still a cause for concern. This narrative review analyzes the strengths and weaknesses of the different alignment strategies and identifies the main areas of debate.