The presence of effusions between the volar plate of the proximal interphalangeal joint and the flexor digitorum tendon is a common phenomenon: a single-center, cross sectional study

Aim: In clinical practice, an anechoic signal was often exhibited between the volar plate (VP) of the proximal interphalan - geal joint (PIPJ) (PIPJVP) and the flexor digitorum tendon (FDT) on ultrasound, which suggests the presence of effusions (PIPJVP-FDT effusions). The purpose of this study was to investigate the prevalence of PIPJVP-FDT effusions and to explore the possible mechanism preliminarily. Material and methods: A single-center, cross sectional study in hand osteoarthritis (HOA) patients, rheumatoid arthritis (RA) patients and healthy controls was conducted. Ultrasound examination was per - formed by the same real-time scanner with 18-MHz linear array transducer. Bilateral interphalangeal joints (IPJs) of the thumb, 2 ed , 3 rd , 4 th and 5 th PIPJs were examined. The PIPJVP-FDT effusions was defined as an anechoic signal between the PIPJVP and FDT in two perpendicular ultrasound planes. Results: In total, 200 patients with HOA, 78 patients with RA and 101 healthy controls were eligible for the study. 37.6% of healthy controls and 35.0% of HOA patients showed PIPJVP-FDT effusions, while only 11.5% of RA patients had PIPJVP-FDT effusions (p<0.001). The 2 ed , 3 rd and 4 th PIPJs showed more PIPJVP-FDT effusions, while the IPJs of the thumbs and 5 th PIPJs showed less PIPJVP-FDT effusions (p<0.05). Furthermore, the prevalence of PIPJVP-FDT effusions in different age groups were similar in HOA patients and healthy controls. Conclu sion: To the best of our knowledge, this paper is the first to demonstrate that the presence of PIPJVP-FDT effusions is a very common phenomenon in HOA patients and healthy individuals, and may be unrelated to inflammation, degeneration and age.