A 42 year old woman, with rheumatoid arthritis for 14 years, treated with leflunomide 20 mg/day and prednisolone 5 mg/day, had mechanical pain over the dorsum of the right foot for 3 weeks. She had increased her walking activities a couple of weeks before the pain started. On clinical examination, there was a marked swelling and painful area on the second metatarsal. Plain radiographs were normal.

Sonography of the foot was obtained with a Esaote MP system and a 7.5–13 MHz linear transducer. Only the dorsal aspect of the foot was required in a longitudinal and axial view. A hypoechoic haematoma with periosteal elevation …