The effect of flexion-extension movement on vertical atlantoaxial subluxation measurements.

Flexion-extension movement and atlantoaxial subluxation (AAS) serve to alter the relations between the anatomical landmarks used in the diagnosis of vertical subluxations. The effects of such alterations are examined here. Lateral view radiographs of the cervical spine taken during flexion and extension were studied in 86 female patients with rheumatoid arthritis, 56 of whom also had AAS. All the methods used (McRae, McGregor, Redlund and Sakaguchi-Kauppi) showed a shift of the mean values in a pathological direction during flexion (p less than 0.001, Sakaguchi-Kauppi: p less than 0.003). The difference between the flexion and extension values (McRae, Redlund, Sakaguchi-Kauppi) correlated with the severity of AAS in flexion (correlation coefficients and p values: 0.403, 0.303 and 0.441, p less than 0.001, p = 0.005, p less than 0.001 respectively). Thus, some vertical movement is connected with AAS during flexion and this should be taken into consideration when weighing treatment options.