Separation of the odontoid process of the axis, occurring either as a congenital abnormality or as a result of trauma or rheumatoid arthritis may, by permitting abnormal movement of the atlas on the axis, lead in time, sometimes gradually after many years (less often more acutely), to a myelopathy from compression of the cord (Stevens et al. 1971).
The subluxation can be demonstrated using CT myelography. Whereas atlantoaxial subluxation is the most common lesion in rheumatoid cervical myelopathy, some patients have subaxial subluxation alone and others have subluxation in addition between other cervical vertebrae. The preferred treatment is occipitocervical fusion; operative decompression of the upper cervical cord in such cases is sometimes complicated by haematomyelia.