A clinical study was performed to evaluate a new classification for
odontoid process fractures. The external and internal anatomy of the
axis has been studied. The files of 97 patients with a fracture of the
odontoid process admitted to our institution were reviewed and
classified according to the proposed new classification. The method was
tested for reliability and validity. The patients were followed for a
mean period of 14 years, in order to evaluate the outcome of these
fractures and to correlate it to the fracture type. Intraobserver and
interobserver agreement was excellent with intraclass correlation
coefficients at levels of 0.98 and 0.85, respectively. Four types of
odontoid process fractures are distinguished. Type B fractures are
associated with high risk of pseudarthrosis. Existing classifications
are inadequate and misleading since they do not include all types of
odontoid process fractures, nor they consider the internal anatomy of
the odontoid process. Classification of the odontoid process fractures
has to be reconsidered as novel-imaging technology has shown new
patterns of fractures. The analysis of the imaging data in the present
study justifies the new classification
