Aims: To examine whether functional radiography and functional magnetic resonance imaging (MRI) are equal to detect the extent of unstabile anterior atlantoaxial subluxation (aAAS) in rheumatic patients. Methods: The series consisted of 23 patients with unstable aAAS (diagnosed by functional radiography) examined by functional MRI because of a neck symptom. Twenty-two patients had rheumatoid arthritis and one had juvenile idiopathic arthritis. aAAS was diagnosed if the anterior atlanto-axial diameter (AAD) was > 3 mm and was considered unstable if the AAD differed > 2 mm between flexion and extension radiographs. The AAD was measured from radiographs (flexion and extension) and MRI images (flexion and neutral). Results: The extent of aAAS during flexion measured by radiography was greater than that found by MRI in all our 23 cases [the mean difference was 3 mm (95% CI: 2 to 4)]. In 4 patients (17%) MRI could not find aAAS. The difference between the AAD measurements during flexion by these two methods was substantial (i.e. , ≥ 4 mm) in 9 cases (39%). Severe aAAS (≥ 9 mm) was seen in 15 patients (65%) by functional radiography and in 4 (17%) by functional MRI. Conclusions: The magnitude of aAAS was often substantially smaller in functional MRI than in functional radiography. Thus one cannot rely on functional MRI alone; functional radiographs are needed to show the size of unstable aAAS.

Aims: To evaluate whether the atlantoaxial disorders (anterior atlantoaxial subluxation and atlantoaxial impaction) associate with destruction of shoulder or peripheral joints, and bone mineral density (BMD) in patients with long-term rheumatoid arthritis (RA). Methods: An inception cohort 67 patients with seropositive and erosive RA were followed up for 20 years. Cervical spine, shoulder, hand and foot radiographs, and the BMD of the lumbar spine and femoral neck were evaluated. Results: A positive relationship was detected between the occurrence of atlantoaxial disorders and the destruction of both shoulder (p < 0.001) and peripheral (p = 0.001) joints. In addition, the severity of atlantoaxial disorders positively correlated with the grade of destruction in the evaluated joints. Furthermore, a positive relationship was found between the occurrence of the atlantoaxial disorders and a decrease in BMD of the femoral neck (p = 0.019). Conclusions: Patients with severe RA and osteoporosis have an increased risk for atlantoaxial disorders, therefore the cervical spine radiographs of these patients should be analysed before major surgery and also at regular intervals. The co-existence of shoulder and cervical spine disorders makes the differential diagnosis of shoulder and neck pain challenging.