Atlantoaxial instability in a 7-year-old boy associated with traumatic disrupture of the ossiculum terminale (apical odontoid epiphysis).

A case of atlantoaxial instability with a rare etiology in a boy of 7 years and 3 months is presented. Computerized tomography with three-dimensional reconstruction revealed avulsion of the ossiculum terminale (apical odontoid epiphysis). Developmental peculiarities and relevant disorders of the infantile upper cervical spine are discussed. Temporary posterior C1/C2 fusion and transdental screw fixation of the ossiculum terminale were attempted in order to stabilize C1/C2 and avoid permanent fusion. After removal of the dorsal implants, the transdental screw broke, the instability recurred and a permanent atlantoaxial fusion had to be performed.