Background Rheumatoid arthritis (RA) can cause various types of foot and ankle deformities. However, the foot and ankle are not always taken into account in indices of RA severity such as the Disease Activity Score in 28 Joints (DAS28). Although joint ultrasonography is frequently used for the evaluation of disease activity in RA, few studies have used it for the joints of the foot and ankle.

Objectives We aimed to assess the prevalence of foot and ankle synovitis in RA patients using joint ultrasonography.

Methods Sixty patients (18 men and 42 women) with 82 arthritic feet and a mean age of 65 years (range 27 to 88) took part in the study. Thirty-seven were Steinbrocker class I, 14 were class II, and 9 were class III. Fifteen were in disease stage I, 18 in stage II, 7 in stage III, and 20 in stage IV. Power Doppler ultrasonography was performed by a single examiner. The scanned area included the distal part of the lateral malleolus (peroneal tendon), the subtalar joint (sinus tarsi, tibiocalcaneal part of the medial ligament of the ankle joint), the anterior ankle, the calcaneocuboid joint, the talonavicular and cuneonavicular joints, the posterior tibial tendon, and the first through fifth metatarsophalangeal joints. Synovitis was defined as the presence of a blood flow signal on ultrasonography.

Results Synovitis of the foot or ankle was detected in 49 of 82 feet (59.8%). It was observed in 78.3% of the patients with moderate to high disease activity scores on the DAS28 as assessed based on erythrocyte sedimentation rate, as well as 44.7% of those with low disease activity. Even among patients without foot complaints, synovitis was present in 22 of 49 feet (44.9%).

Conclusions According to some recent reports, the number of foot surgeries performed for RA has been increasing in spite of advances in pharmacotherapy. This study found a high prevalence of synovitis of the foot or ankle in RA patients irrespective of the presence or absence of symptoms or the degree of disease activity, although some cases may have been related to other diseases, as the scanned area included the peroneal and posterior tibial tendons. We propose that RA patients with persistent synovitis may be candidates for further treatment, and clinicians should consider additional pharmacotherapy to prevent joint destruction. For selected patients with foot and ankle synovitis, excision of the synovial membranes of small joints may be beneficial. Regarding the technical aspects of ultrasonography, it was difficult to differentiate joint synovitis from tendon sheath synovitis in the subtalar joint; the reason for this requires further investigation.

Acknowledgements The authors thank Miss Sasaki, for her assistance with this project.

Disclosure of Interest None declared