Serum Periostin Level Reflects Progression of Ossification of the Posterior Longitudinal Ligament oleh Yoshiharu Kawaguchi, MD, PhD, Isao Kitajima, MD, PhD, Taketoshi Yasuda, MD, PhD, Shoji Seki, MD, PhD, Kayo Suzuki, MD, PhD, Hiroto Makino, MD, Yasuhiro Ujihara, MT, Tomohiro Ueno, MT, PhD, Nguyen Tran Canh Tung, MD, Yasuhito Yahara, MD, PhD