Backward luxation of the atlas. Two cases of an uncommon condition.

Neck involvement in cases of rheumatoid arthritis is extremely common, and the radiological features have been investigated by several authors, particularly Martel (1961, 1964), Bland, Davis, London, Van Buskirk, and Duarte(1963), Serre, Simon, Janicot, and Levy (1964) and Conlon, Isdale, and Rose (1966). The features most characteristic are atlanto-axial subluxation, serial subluxation, and disc narrowing without osteophytosis. Atlanto-axial subluxation may be of any degree, and surprisingly is not usually associated with neurological abnormalities. Such subluxation is characterized by a forward movement of the atlas on the axis. Backward luxation is so rarely seen that the two following cases are thought worthy of report. CASE 1