The role of radiology in the quantification of digital ulnar deviation in rheumatoid arthritis patients

Rheumatoid arthritis (RA) is a common inflammatory polyarthritis, which causes functional digital ulnar deviation (UD). Radiographic and magnetic resonance imaging (MRI) assessment of the hands is essential in RA, but its role in the quantification of UD remains unclear.

To compare UD measurements in RA patients between clinical goniometric assessments versus standardized radiographs and MRI.

Fifteen RA patients with clinically apparent UD and 11 RA patients without UD underwent a rheumatological examination prior to recruitment to this study. Goniometric measurements for UD at the metacarpophalangeal (MCP) joints were performed by an occupational therapist (OT). Standardized hand radiographs, and MRI studies of the dominant hand using 3T MRI scanner with 16 channel hand/wrist coil were evaluated. Angulation measurements for radiographs and MRI were performed independently by two experienced musculoskeletal radiologists who were blinded to the rheumatologist's, occupational therapist's and each other's assessments.

Inter-observer correlation between radiologists was >0.97 for both radiographic and MRI measurements. Correlation between OT goniometric measurements and the imaging-based measurements was limited at 0.496 for radiographs and 0.317 for MRI. Correlation between imaging modalities was 0.513. Compared to OT measurements, radiographic and MRI study measurements significantly underestimate the angulation in RA patients with UD (P < 0.001).

The results of this study demonstrated discordance between radiological and goniometric measurements of digital ulnar angulation at the MCP joints in RA patients. Although imaging plays a key role in understanding structural damage and disease activity in RA, it should be emphasized that radiological measurements underrate joint malalignment.