Os hamuli proprium
The hook of the hamate has its own ossification center, which may fail to fuse with the body of the hamate, creating an ossicle. This ossicle is referred to as an os hamuli proprium or unfused hamulus
In some instances, this can be difficult to distinguish from a fracture of the hook, but is suggested when the finding is bilateral, being observed in the asymptomatic side as well. If visible, smooth corticated margins at this site also support this finding.