✓ The authors describe a lumbar spine fracture that is characterized on anteroposterior x-ray views by separation of the pedicular shadows. It is almost invariably associated with posterior interlaminar herniation of the cauda equina through a dorsal dural split, and anterolateral entrapment or amputation of the nerve root. The fracture is unstable and requires internal fixation and fusion at the time of neurolysis. Fractures meeting these criteria should be explored as soon as the patient's condition permits. Myelography is usually unnecessary and may be contraindicated in some cases. The postulated mechanism of injury is hyperextension with vertical impaction and rupture of the ring made up of the lamina, pedicle, and vertebral body. The ring is fractured in several places in a manner similar to that seen in “Jefferson fracture” of C-1. The special anatomical relationships of the thoracolumbar junction and the plane of the lumbar facets are also discussed.