Os styloideum

An accessory bone or supernumerary bone is a bone that is not normally present in the body, but can be found as a variant in a significant number of people. They pose a risk of being misdiagnosed as bone fractures on radiography. An accessory bone or supernumerary bone is a bone that is not normally present in the body, but can be found as a variant in a significant number of people. They pose a risk of being misdiagnosed as bone fractures on radiography. The os ulnostyloideum is an ulnar styloid process that is not fused to the rest of the ulna bone. On X-rays, an os ulnostyloideum is sometimes mistaken for an avulsion fracture of the styloid process. However, the distinction between these is extremely difficult. It is alleged that the os ulnostyloideum has a close relationship with or is synonymous with the os triquetrum secundarium. The os carpi centrale (also briefly os centrale) is, where present, located on the dorsal side of the wrist between the scaphoid, the trapezoid and capitate, radially to the deep fossa of the capitate. The bone is present in almost every human embryo of 17–49 mm length, but then usually fuses with the ulnar side of the scaphoid. Sometimes it fuses with the capitate or the trapezoid. The literature also refers to an os centrale at the palm of the carpus, but this existence is questioned. The os carpi centrale appears in many other primates as an independent bone. In chimpanzees, the bone fuses with the scaphoid first after birth, while in gibbons and orangutans this occurs first at older age.