Diagnosis and Management of Os Odontoideum

Kim, Seong Min; Yoon, Do Heum; Cho, Yong Eun; Kim, Young Soo

Abstract

The authors analyzed 17 cases of os odontoideum. a very rare condition and one of the causes of atlantoaxial instability. We investigated the radiographic findings of os odontoideum and classified the patients according to clinical grade, radiographic findings and direction of atlantoaxial instability. Their mean age was 33.4 years, and the male to female ratio was. 7: 10. Thirteen patients(76.5%) were classified as clinical grade 3, indicating fixed or progressive myelopathy. They were classified as one of two types, according to the location of the os, five were dystopic and ten were orthotopic. In remaining two patients, it was difficult to classify. We measured SAC(space available for cord) laterally, using plain film, and sagittally, using MR imaging, and compared the results with clinical symptoms. SAC as seen on cervical MRI, correlated more closely with severity of cord compression than did SAC seen on plain film. The 15 patients underwent various operative methods including C1/2 fixation, occipito-cervical fusion, and transoral decompression; because of postoperative hardware failure, two required further surgery. Postoperatively, twelve patients showed excellent or good neurologic improvement. In this retrospective study, SAC seen on cervical MRI was a very good indicator of the need for surgery, and surgery should be considered in patients whose clinical grade is higher than 2.