Endo T, Imagama S, Kato S, Kaito T, Sakai H, Ikegawa S, Kawaguchi Y, Kanayama M, Hisada Y, Koike Y, Ando K, Kobayashi K, Oda I, Okada K, Takagi R, Iwasaki N, Takahata M. Association Between Vitamin A Intake and Disease Severity in Early-Onset Heterotopic Ossification of the Posterior Longitudinal Ligament of the Spine. Global Spine J. [Epub ahead of print]