[Morphology of the surgically treated dens fracture]

The peculiarities within the microarchitecture of the base of the dens have to be assumed as one of the underlying causes for type II and III fractures of the dens according to Anderson and D'Alonzo. As can be demonstrated in a section of the dens of a patient after primary osteosynthesis using two small fragment AO cancellous screws this leads to multiple local trabecular fractures and destruction of the cancellous microarchitecture. Further more compression by the screws results in a higher density of the bone mass in the region of fracture. Apart from the fact that two AO screws guarantee rotational stability, this type of osteosynthesis seems to favour intracorporal bony fusion by increased trabecular bone volume and induction of microcallus within the base of the dens. In a patient with a small intracortical transverse diameter of the dens the available space is completely filled by the screws threads. Partial penetration of the threads through the cortical bone seems to be of no clinical and biomechanical relevance and can be avoided using screws of smaller diameter.