Upper cervical involvement in rheumatoid arthritis.

Atlanto-axial dislocation and upward migration of the odontoid were studied in patients with rheumatoid arthritis treated conservatively and those treated by atlanto-axial posterior fusion. Upward migration of the odontoid was evaluated by Ranawat's and Redlund-Johnell's methods after determining the normal range in healthy Japanese adults. Of the 100 patients treated conservatively, atlanto-axial dislocation was found in 49% and upward migration of the odontoid in 26% by the former method, and in 8% by the latter method. The detection rate of these lesions increased with the increase in the duration of the disease and progression of rheumatoid lesions. Abnormal Ranawat values are associated with lesions in the C1-C2 segment and abnormal Redlund-Johnell values with 0-C2 lesions. The latter suggests severe conditions and seems to be a useful indicator for the diagnosis of upward migration of the odontoid in our study. Though rheumatoid lesions in the upper cervical spine mainly involved the C1-C2 level, marked deterioration of the atlanto-occipital joints was also occasionally observed. Therefore, in surgical treatment, attention should be paid also to this region. Patients with abnormal Redlund-Johnell values require spinal fixation including the occipital bone.