**5. Conclusions**

The main finding of this work was that preoperative ODI showed the strongest association with the postoperative clinical outcomes after spine fusion for adult deformity correction. Other parameters such as age, health status, or LIV presented only a weak association with the long-term ODI or VAS values. Thus, surgery should be performed in a timely manner to avoid patients reaching high preoperative ODI values.

**Author Contributions:** A.B., conception, data interpretation, draft and revision, final approval of the work; F.M., statistical analysis, draft and revision, final approval of the work; P.B. (Paolo Barletta), data acquisition, draft and revision, final approval of the work; F.L., C.L., P.B. (Pedro Berjano), P.T., E.Q., R.C. and M.D., data interpretation, draft and revision, final approval of the work, logistic support. All authors have read and agreed to the published version of the manuscript.

**Funding:** Funding for this study was provided by the Italian Ministry of Health (CO-2016-02364645).

**Institutional Review Board Statement:** Ethical approval for this study was asked for and waived by the local Medical Research Ethics Committee (Fourth Amendment to the SPINEREG Protocol, Issued on 10 October 2019). The study fell outside the remit of the law for Medical Research Involving Human Subjects Act and was approved by the local ethical committee.

**Informed Consent Statement:** Waived as not required by local law for retrospective studies.

**Data Availability Statement:** The dataset used and/or analyzed in the present study is available from the corresponding author upon reasonable request.

**Conflicts of Interest:** Berjano, P. and Lamartina, C. disclose grants and personal fees from Nuvasive, personal fees from Depuy Sinthes, personal fees from Medacta, personal fees from Zimmer, personal fees from K2M, personal fees from Medtronic, grants from Stoeckli Medical, outside the submitted work. Trobisch, P. is a consultant for Globus Medical and Zimmer Biomet. Cecchinato, R. and Damilano, M. disclose personal fees from Nuvasive and Medacta. Baroncini, A., Migliorini, F., Langella, F., Barletta, P., and Quarto, E. have no conflict of interest to disclose.
