Avulsion of the cervical spinal ring apophyses: acute and chronic appearance.

Avulsion of the superior or inferior ring apophyses of the cervical spine was found in 12 of 1922 patients aged 10-20 years. Clinical and radiological follow-up of 9 of these patients was undertaken 3-25 years after trauma. Avulsion of the superior apophysis occurs after flexion, while extension trauma causes avulsion of the inferior ring apophysis. The follow-up appearance is characteristic in both instances. In superior ring apophysis avulsion, there is a bow shape of the superior aspect of the involved vertebral body. In inferior avulsion, the avulsed apophysis fuses with the vertebral body and forms an "osteophyte", whose shape and size depend on the degree of displacement.