Presentation
A known case of rheumatoid arthritis.
Patient Data

In addition to the erosive changes and periarticular osteoporosis routinely seen in rheumatoid arthritis, there is an erosion of the radial side of the distal radioulnar joint; known as the "scallop sign".

Erosion of the radial side of the DRUJ; the scallop sign.
Case Discussion
The scallop sign is the term used to describe the scooped-out appearance of the sigmoid notch of the distal radius that results from synovial proliferation and bone erosion of the distal radioulnar joint. It is characterised by a sclerotic border indicating slow development.
According to Freiberg et al, the scallop sign correlates with a high risk for extensor tendon rupture 1.