Fractures of the odontoid process in small children: biomechanical analysis and report of three cases.

Odontoid "fractures" in young children typically involve the cartilaginous plate (synchondrosis) that separates the odontoid process from the body of the axis; 58 cases have been described in the literature. We report two cases in which 2-year-old children were involved as backseat passengers in head-on motor vehicle accidents, both were restrained by four-point child's seat harnesses. A biomechanical investigation was carried out using simulation in a real car crash test with a child dummy. This revealed that head-on collisions with a speed absorption of at least 40 km/h are the typical mechanism of injury in children under the age of 3 years involved in motor vehicle accidents. Shearing force is all that is necessary to explain the dens fracture. Both children were immediately symptomatic, and the diagnosis was obvious on radiographs. Neither child had neurological deficit, which correlates well with the literature, where neurological injuries were found only in conjunction with head injuries. After closed reduction, both cases were initially treated conservatively with halo and plaster vest for 12 weeks. In one case, in which the anterior dislocation was less than the diameter of the odontoid shaft, eventless healing occurred. In our second case, despite an anatomic reduction, the odontoid fracture failed to unite. After a temporary posterior fixation of C1/C2 we reamed the synchondrosis from anterior and performed autogenous bone grafting. The posterior fixation wire was removed after 5 months. In contrast to the literature, we do not recommend a permanent posterior fusion of C1/C2. Our two young patients were both followed-up for more than 3 years. Clinical and radiological examination at final follow-up was normal with no signs of atypical growth of the odontoid. In cases of major dislocation with greater instability we recommend primary open reduction and osteosynthesis with appropriate implants. This was done in a third case: a 1 1/2-year-old boy who fell down the stairs and sustained a head injury and an unstable lesion of the odontoid with subtotal paraplegia. The odontoid was fixed with two screws.