[Mobility of unstable fractures of the odontoid during helmet removal. A biomechanical study]

In severe motorcyclist accidents unstable injuries of the cervical spine can usually not be excluded before an X-ray has been taken in the hospital. Despite this the helmet has to be taken off at the place of the accident in order to provide adequate treatment and airway management of the injured driver. There are no data in the current literature showing what happens to unstable lesions of the cervical spine during helmet removal. An experimental unstable lesion of the cervical spine was created by an osteotomy of the odontoid in 10 fresh frozen cadavers with intact soft tissues. All motions occurring in the segments C1-2 and C2-3 during helmet removal were recorded by fluoroscopy. The average motion in the unstable segment C1-2 was 23.7 degrees during a full range of extension-flexion movement of the cervical spine without any signs of dislocation of the segment. After application of the helmet there was one case of dislocation of C1-2 in neutral supine position already, and two further cases of dislocations during helmet removal. The average motion of C1-2 recorded during helmet removal was 19.0 degrees (2-25 degrees ), median 18.0 degrees. In order to avoid fracture dislocations and motion in the unstable upper cervical spine the helmet should better be cut in pieces at the place of the accident. There is a need for discussions with helmet producers to develop a new generation of helmets that can be removed easily without manipulating the head.