Which Global Sagittal Parameter Could Most Effectively Predict the Surgical Outcome for Patients With Adult Degenerative Scoliosis?

STUDY DESIGN: Retrospective study. OBJECTIVE: To evaluate the predictive effect of the 3 global sagittal parameters (Sagittal Vertical Axis [SVA], T1 Pelvic Angle [TPA], and relative TPA [rTPA]) in the surgical outcome of patients with adult degenerative scoliosis (ADS), then to define the optimum corrective goal based on the best of them. METHODS: 117 ADS patients were included in this study and followed-up for an average of 3 years. Functional evaluation and radiographs were assessed preoperatively and postoperatively. The predictive accuracy of SVA, TPA, and relative TPA was analyzed through receiver operating characteristic (ROC) curve. The cutoff value of TPA was obtained at the maximal Youden index from ROC curve. RESULTS: TPA most highly correlated with postoperative oswestry disability index (ODI). The best cutoff value of TPA was set at 19.3° (area under curve =0.701). TPA >19.3° was the highest risk factor in multivariate logistic regression analysis (OR = 7.124, P = 0.022). Patients with TPA <19.3° at 3 months after operation showed a better ODI than those with TPA >19.3°. Correcting TPA less than 19.3° for patients with preoperative TPA >19.3° attributed to a better health related quality of life (HRQOL) and sagittal balance at last follow-up. The formula “Postoperative TPA = 0.923 × PI - 0.241 × postoperative LL - 0.593 × postoperative SS - 2.471 (r = 0.914, r(2) = 0.836, P < .001)” described the relation between SS, LL, PI, and TPA. CONCLUSION: TPA was a useful global parameter for the prediction of postoperative HRQOL for patients with ADS. Keeping TPA <19.3° could improve the postoperative HRQOL for ADS patients with preoperative TPA >19.3°, and TPA <19.3° could be an optimum correction target for patients with ADS.