A case of isolated bursting atlantal fracture associated with rupture of the transverse ligament is reported and discussed. This associated ligamentous rupture is seldom recognized. The amounts of displacement of the lateral masses possible in bursting fractures of the atlas were studied experimentally and indicated that if the lateral mass displacement is greater than 6.9 millimeters, the transverse ligament probably is torn.

Roentgenograms can show whether the transverse ligament is intact and whether arthrodesis is indicated to prevent delayed subluxation.