Preoperative Sacral Slope Change (ΔSS) as a Risk Factor for Mechanical Complications after Adult Spinal Deformity Surgery

Study Design: Retrospective observational study. Objective: To investigate whether the preoperative change in sacral slope (ΔSS) from sitting to standing is associated with mechanical complications, including proximal junctional kyphosis (PJK) and rod fracture (Rod Fx), after adult spinal deformity (ASD) surgery. Summary of Background Data: Despite efforts to optimize alignment and construct stability, mechanical complications remain prevalent after ASD surgery. Dynamic spinopelvic parameters such as ΔSS have recently gained attention as potential markers of spinal flexibility and postoperative risk. Methods: We analyzed 181 women who underwent ASD surgery. ΔSS was calculated from preoperative standing and seated lateral radiographs. Multivariate logistic regression was conducted to assess ΔSS as an independent risk factor for PJK and Rod Fx. Receiver operating characteristic (ROC) analysis was also performed. Results: Mechanical complications were observed in 47.0% (PJK) and 49.7% (Rod Fx). A higher ΔSS was independently associated with increased risk of both PJK and Rod Fx. Specifically, each 1° increase in ΔSS was associated with a 10% increase in the risk of symptomatic Rod Fx (adjusted OR: 1.10, 95% CI: 1.05–1.15, p < 0.001). ROC analysis showed optimal ΔSS cutoffs of 20° for PJK and 16° for Rod Fx, with AUCs of 0.80 and 0.79, respectively. Conclusions: ΔSS is an independent risk factor for mechanical complications following ASD surgery. Preoperative dynamic spinopelvic assessment may improve surgical planning and outcomes. Multivariate logistic regression analysis demonstrated that ΔSS was independently associated with symptomatic Rod Fx (adjusted OR: 1.10, 95% CI: 1.05–1.15, p < 0.001), as shown in Table 6.