Os radiostyloideum

Os radiostyloideum (or persistent radial styloid) is an accessory ossicle of the wrist located adjacent to the radial styloid process and lateral to the mid-portion of the scaphoid.

This should not be confused with another bony ossicle in the wrist, os styloideum (part of a carpal boss), which is located between the bases of the 2 and 3 metacarpals.