Morphological and Volumetric Analysis of the Development of Atlantoaxial Vertical Subluxation in Rheumatoid Arthritis

[ABSTRACT] [Background] Cervical disorders in rheumatoid arthritis (RA) patients have been an important problem for a long time. Although the recent progression of the treatment strategies for RA might change the progression of atlantoaxial vertical subluxation (VS) in RA patients, to reveal the risk factors for VS progression should be important at present. Osteoporosis (OP) and RA share the same risk factors. The purposes of this study were to identify the progression of VS in RA, and to evaluate the relationship between the VS development and OP. [Methods] Eighty female patients with RA and 18 female patients with OP were retrospectively analyzed. The RA patients were divided into VS (10 patients) and non-VS groups (70 patients). Morphological parameters on coronal reconstructed computed tomography images were evaluated. Three-dimensional analysis was used to measure volumes and volumetric bone mineral densities (vBMDs) at the upper cervical spine (UCS). [Results] The VS group had higher age, longer RA symptom duration, and lower BMD at the lumbar spine compared to the non-VS group. Volumes and vBMDs at the UCS in RA group were greater than those in the OP group. In accordance with VS development, the lateral masses at the UCS became shorter, the Cl facet angle became sharper, and the volumes at the UCS decreased. However, there was no statistically significant relationship between vBMDs at the UCS and the VS development. [Conclusion] The Cl facet angle became sharper with VS progression. Although 3-dimensional analysis revealed that decreases in the volumes at the UCS were associated with VS development, no significant relation-ship between OP and the VS development was observed.