[Operative versus non operative treatment of odontoid non unions. How dangerous is it not to stabilize a non union of the dens?].

INTRODUCTION: Injuries precede the vast majority of all odontoid pseudarthroses. Because of specific anatomic conditions type II injuries lead more often than other types to non unions. For its development insufficient internal or external fixation and a persisting fracture gap are crucial. METHODS AND
RESULTS: In 71 patients after operative stabilization of odontoid fractures with two anterior lag-screws we detected 8 non unions. In 3 patients the interval between accident and operation amounted to more than 5 weeks, seven times we did not succeed in closing the fracture gap. Technical mistakes like insufficient reduction (n = 1) or screw misplacement (n = 3) were additional reasons. According to the literature and own observations an os odontoideum must be considered in most instances as a pseudarthrosis after a lesion of the subdental synchondrosis in childhood. The most important diagnostic tool in odontoid non unions is a dynamic examination of the upper cervical spine under fluoroscopic control in maximum flexion and extension. We propose a classification of posttraumatic dens non unions into 4 types. Type I corresponds to a stable "non union" in approximate anatomical position of the dens and without signs of instability in the former fracture zone. Type II describes a relatively stable grossly displaced non union that is not to be reduced by simple, closed means. Type III means an unstable non union and Type IV a posttraumatic os odontoideum.
CONCLUSIONS: Therapeutical recommendations need to be differentiated. Unstable non unions are most often responsible for persistent pain, may result in acute or chronic myelopathy++ and therefore - as well as ossa odontoidea - need operative fixation. In considerably displaced non unions a closed reduction manoeuver with long term traction should be tried. The operative treatment of choice is the posterior transarticular screw fixation C1/C2 desirably in a percutaneous technique. Tight, "stable" pseudarthroses in the sense of a persisting fracture gap in painfree patients should first be controlled radiologically. If the odontoid position remains unchanged, non operative treatment may be continued.