Did ossification of the posterior longitudinal ligament of the spine evolve in the modern period? A paleopathologic study of ancient human skeletons in Japan

Objective. To investigate the historical origins of ligamentous ossifications of the spine in Japan. Methods. We studied skeletons of Jomonese of the period 5000-2300 years BP, of Japanese of the 17th-19th century Edo Period, and of Ainu of the 18th-20th century in Japan with special emphasis on spinal ligament ossifications as in the posterior longitudinal ligament. A comparison to our previous study on ancient Chinese skeletons was done. Results. Cervical ossification of the posterior longitudinal ligament (OPLL) was the only ossification that increased significantly in prevalence in people of the near-modem period in comparison to the Neolithic gathering-hunting people. Conclusion. Socioeconomic changes from a subsistence gathering-hunting economy to the near-modern livelihood depending on rice-eating and a diet high in vegetable protein are speculated to be responsible for the prevalence increase of cervical OPLL.