Osteoarthritis (OA), a disease that mainly targets cartilage, also affects ligaments, the subchondral bone and synovium, and, according to recent definitions, it is a disease of the joint as an organ.1 Its most characteristic radiographic features are joint space narrowing, bone sclerosis and osteophytes;2 bone erosions, and in particular subchondral bone erosions, have also been found in some patients.3 Bone erosions that classically affect the interphalangeal (IP) joints identify a disease subset called erosive osteoarthritis (OA).4 The particular localisation of erosive OA is considered so characteristic of the disease that the term has been used, since it was first described by Peter et al,5 almost interchangeably with erosive hand OA. A growing body of evidence, however, suggests that it is time to re-evaluate the definition, since the term erosive OA can be appropriately applied to other OA localisations including at the thumb base (TB)6 and facet joints.7 These different disease subsets share not only the same classic radiographic features, such as subchondral bone erosions, but also the severity …