**5. Conclusions**

The majority of participants had the conus medullaris at the caudal level of the T12-L1 disk (92.2%), and the conus medullaris was located cranially to the T12 vertebral level in only 7.8% of the 629 healthy volunteers. Lower height and smaller PI were associated with the caudally placed conus medullaris; thus, skeletal differences were significantly associated with the conus medullaris level.

**Author Contributions:** H.N. designed the study and wrote the manuscript; K.I., Y.K. and M.T. performed the data collection; K.A., K.K., M.M., S.I. (Sadayuki Ito), H.K., N.S. and H.T. provided clinical experience; S.I. (Shiro Imagama) supervised the entire study. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by institutional funds and by gran<sup>t</sup> research funds, which are intended for promoting hospital functions, of the Japan Labor Health and Welfare Organization (Kawasaki, Japan).

**Institutional Review Board Statement:** The Japanese volunteers were recruited after the purpose of this study was officially announced and after obtaining institutional review board approval from the Chubu Rosai Hospital (IRB approval no., 2009-2). All participants provided written informed consent prior to participation. The research procedure was carried out in accordance with the principles of the Declaration of Helsinki.

**Informed Consent Statement:** All participants gave written informed consent prior to participation.

**Data Availability Statement:** The data of this study are available from the corresponding authors upon request.

**Acknowledgments:** We are grateful to Fumihiko Kato and Yasutsugu Yukawa at Chubu Rosai Hospital for their assistance throughout this study.

**Conflicts of Interest:** The authors declare that there is no conflict of interest regarding the publication of this paper.
