IntroductionThe stability of the atlantoaxial motion segment is unique. The lack of typical vertebral bodies and the arrangement of articular facets without protection against horizontal gliding make the articular system dependent mostly on the ligaments. Anterior C1-C2 dislocation is a rare and severe lesion in distraction caused by a predominantly ligamentous lesion, leading to displacement of the atlas on the axis [13].Vertebral displacements require reduction for neural decompression and stabilization. The most frequently used reduction mode is traction. This creates an unusual kind of stress in the craniocervical transition, called vertical distraction. Without ligamentous integrity, even a simple cranial traction can not be counterbalanced and may cause overdistraction among the vertebrae, with its consequences. Recently, traumatic vertical (longitudinal) dissociation between C1 and C2 has been described [8,15,19]. It is extremely difficult to predict which patient will develop this lesion after being subjected to the traction. Here, we describe the case of a patient with traumatic anterior atlantoaxial dislocation who developed a vertical dissociation after skull traction, studying its complications and how they are related to the skull traction. Case reportA 16-year-old female patient, E.C.S., who was run over by a vehicle on 5 May 1997, was immediately taken to the first aid clinic of Conjunto Hospitalar do Mandaqui, São Paulo, Brazil.Cardiorespiratory arrest was detected upon examination. She was submitted to resuscitation attempts. The patient was hemodynamically stabilized, and remained in a coma without opening her eyes and with no motor response, with a score of 3 on the Glasgow coma scale. She was submitted to computed axial tomography (CAT) of the skull, which permitted visualization of the high cervical column and identification of an anterior C1-C2 dislocation (scout view) (Fig. 1). The CAT scan showed a wide separation between the odontoid and the anterior C1 arch and a minimal bilateral displaced fracture of the anterior C1 arch (Fig. 2).Abstract Traumatic overdistraction between C1 and C2 may occur when all the ligaments connecting C2 to the skull are ruptured, and may be manifested when an attempt to reduce C1-C2 subluxation is made by means of traction. We describe here the case of a patient with traumatic anterior atlantoaxial dislocation, who developed atlantoaxial vertical dissociation after skull traction using a Gardner-Halo with lb 4.02 (1.5 kg) of weight. The identification of patients who are susceptible to this complication is difficult. In this case, it might have been prevented by avoiding spinal traction. The aim of this report was to show that vertical dissociation may occur in C1-C2 anterior dislocation submitted to spinal traction, and that other forms of reduction must be considered to treat these pathologies and avoid this potentially fatal complication.