**5. Conclusions**

This study is the first to compare conventional ACCF and the hybrid fusion technique focusing exclusively on patients with severe OPLL involving three or more levels. Although both procedures can achieve satisfactory neurologic outcomes in patients with multilevel OPLL, hybrid fusion was superior to the conventional ACCF technique in terms of fusion rate and perioperative graft stability.

**Author Contributions:** Conceptualization, T.H., T.Y. (Toshitaka Yoshii), K.S. (Kenichiro Sakai) and A.O.; Data collection, H.I., M.Y., T.Y. (Tsuyoshi Yamada), Y.M., S.U., S.M., S.E., H.O., Y.K., K.U., J.H., A.K., T.T. (Tomoyuki Tanaka), T.M., T.T. (Takuya Takahashi), and M.H.; Formal Analysis, T.H., M.Y. and T.K.; Writing—Original Draft Preparation, T.H., H.I., Y.A. and A.O.; Software, Validation, T.H., T.Y. (Toshitaka Yoshii) T.H., T.Y. (Tsuyoshi Yamada), K.S. (Kentaro Sakaeda) and S.K., A.O.; T.Y (Toshitaka Yoshii) and Y.A.; Funding Acquisition, T.H., T.Y. (Tsuyoshi Yamada), T.K., K.S. (Kenichiro Sakai) and

A.O.; Writing—Review and Editing, T.H. and Y.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by a Health and Labor Science Research gran<sup>t</sup> (201610008B).

**Institutional Review Board Statement:** The study was conducted in accordance with the Declaration of Helsinki, and the study was approved by our institutional ethics committee (M2017-118).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Detailed data are available on request from corresponding author.

**Acknowledgments:** We thank Nobuko Nakajima, Yukiko Oya, Mika Morikawa and Namiko Katayama for data collection.

**Conflicts of Interest:** The authors declare no conflict of interest. The sponsors had no role in the design, execution, interpretation, or writing of the study.
