Prevalence of Elbow Joint Arthritis and Enthesitis in Rheumatoid Arthritis.

Objectives: The prevalence of elbow joint arthritis in rheumatoid arthritis (RA) assessed by ultrasound has not yet been investigated.

Methods: We investigated 102 patients with RA and 50 patients without rheumatological disease. Both elbow joints were examined by ultrasound for effusion, hypervascularization, and enthesitis. A clinical examination was performed, and Disease Activity Score in 28 joints (DAS28), and visual analog scale for pain (VASp) were recorded. Arthritis was defined as joint effusion (≥grade II) and synovial hyperperfusion.

Results: The RA cohort versus the control group displayed a joint effusion in 54.9% vs. 6.9%, a hypervascularization in 6.8% vs. 0%. Arthritis was detected in 36 RA patients (35.29%) and no one in the control group. Four (3.8%) RA patients and one (1%) control displayed enthesitis. The RA cohort showed a significant correlation between movement restriction and joint effusion (-value = 0.001) as well as DAS28 (-value = 0.02) and between DAS28 and ultrasound detected arthritis (-value = 0.022). In an overall analysis, a highly significant correlation of VASp with movement restriction (MR) (-value ≤ 0.001), the presence of joint effusion (-value ≤ 0.001), and the diagnosis of RA (-value ≤ 0.001) were observed. Interrater analysis of ultrasound imaging showed good agreement with Cohen's kappa of 0.896.

Conclusion: The prevalence of elbow arthritis in RA seems to be high, with 35.29%. Movement restriction is a good indicator, but not in all RA patients (32 vs. 70 patients without MR) compared to the control group (5 vs. 45 patients without MR). Reported pain correlates with joint effusion and MR (-value ≤ 0.001).