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Os Odontoideum as a Consequence of a Posttraumatic Displaced Ossiculum TerminaleA Case Report
Eiji Wada, MD1; Takashi Matsuoka, MD2; Hideo Kawai, MD2
1 Department of Orthopaedic Surgery, Ehime Prefectural Central Hospital, 83-banchi, Kasugamachi, Matsuyama, Ehime 790-0024, Japan. E-mail address: weijiw1961@kjc.biglobe.ne.jp
2 Department of Orthopaedic Surgery, Hoshigaoka Koseinenkin Hospital, 4-8-1 Hoshigaoka, Hirakata, Osaka 573-8511, Japan
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.
Investigation performed at the Department of Orthopaedic Surgery, Hoshigaoka Koseinenkin Hospital, Hirakata, Osaka, Japan

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2009 Jul 01;91(7):1750-1754. doi: 10.2106/JBJS.H.01182
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The os odontoideum is a separate bone with smooth, rounded cortical margins, usually about half the size of the odontoid process. The gap between the os odontoideum and the second cervical vertebra (the axis) is wide and lies above the level of its superior facet1.Whether the origin of an os odontoideum is developmental or posttraumatic remains a matter of debate2-10. In 1980, Fielding et al. reported on nine patients who subsequently had development of an os odontoideum despite radiographic documentation of a normal odontoid process immediately after trauma1. The evidence suggests that an unrecognized fracture and possible subsequent osteonecrosis might be the cause of os odontoideum.
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