Joint of accessory carpal bone

The joint of accessory carpal bone is the joint between the accessory carpal bone and the ulnar carpal bone.

The accessory carpal bone also has a second articular surface for the styloid process of the ulna. This articular surface is more or less developed depending on the species: it is small in carnivores and clearly marked in horses. As the styloid process of the ulna usually fuses entirely with the radius in this species, some authors consider that the accessory carpal bone articulates with the radius. It would be logical to consider this second joint as belonging to the antebrachiocarpal joint and more specifically to the ulnocarpal joint. The joint of accessory carpal bone would therefore be equivalent to the pisiform joint in humans (pisopyramidal joint).