Does joint position affect US findings in inflammatory arthritis?

Objective: Musculoskeletal US is being increasingly used for the assessment of synovitis, although questions remain about its reliability. One potential factor affecting reliability is the lack of consensus of image acquisition methods such as using different joint positions. This may have an implication on the reproducibility of studies that use US as an outcome measure. The aim of this study was to determine whether a change in joint position might significantly alter the quantification of US-detected synovitis in patients with inflammatory arthritis (IA).

Methods: IA patients with clinically swollen wrists, MCP and/or knee joints were recruited. These joints were assessed quantitatively for the presence of synovitis when they were placed in different positions.

Results: Seventy-five patients with IA were assessed. The greatest grey scale (GS) and power Doppler (PD) scores for the MCP joints were found in the flat (0°) position (91 and 100% of cases, respectively) compared with other positions (P < 0.001). Similar results were found in the wrist joints. The greatest GS and PD scores for the knee joint were found in 30° flexion [100 and 95.6% of cases, respectively, compared with other positions (P < 0.001)]. The inter- and intra-reader reliability was good to excellent.

Conclusion: The position in which a joint is scanned for synovitis appears to significantly influence the US assessment of synovitis. Our study suggests that the standardized scanning of the hand joints in a flat position and the knees in a 30° position are associated with the highest GS and PD scores.