In vivo segmental motion of the cervical spine in rheumatoid arthritis patients with atlantoaxial subluxation

Objective The dynamic mechanism underlying cervical spine involvement in rheumatoid arthritis (RA) remains unidentified. The purpose of the current study was to determine the in vivo cervical segmental motion in RA patients with atlantoaxial subluxation (AAS) using a patient-based three-dimensional magnetic resonance imaging (MRI) computer model. Methods Healthy volunteers and RA patients with AAS (all females, n=10) underwent MRI examination of the cervical spine. Each vertebral body from the occipital bone (Oc) to the first thoracic vertebra (T1) was reconstructed from slices of T2-weighted sagittal MR images in the neutral, flexion, and extension positions. Using volume merge methods, each reconstructed vertebral body was virtually rotated and translated. Rotational segmental and translational segmental motions were obtained in three major planes. Results Overall, the axial translational motions in the RA group were lower than those in the healthy volunteers; however the axial translational motion at only C1-C2 during flexion was at the same level as that in the healthy volunteers and was greater on the bottom side than that at other intervertebral levels. The frontal rotational motions at C1-C2 during extension were greater in the RA patients than those in the healthy volunteers (p<0.05). Conclusion The atlantoaxial joints in the RA patients with AAS showed great frontal rotational motion during extension and great axial translation on the bottom side during flexion. The current noninvasive MRI-based method could be useful in evaluating the 3-D dynamic mechanism underlying cervical involvement in RA in vivo.