Accessory ossicles of the wrist

The full list 2 can be broadly split into three groups: those around the carpometacarpal joints, those around the scaphoid and those around the lunate.

The distal row, from ulnar margin to radial margin are:

·        os vesalianum (hand)

·        os ulnare externum

·        os hamuli proprium:

o   The hook of the hamate has its own ossification center, which may fail to fuse with body of the hamate, creating an ossicle. This ossicle is reffered to as an os hamuli proprium or unfused hamulus 

o   DDx: hook fracture

·        secondary capitate

·        gruber ossicle

·        os styloideum:  

o   between the 2nd and 3rd metacarpal bases, dorsal aspect

o   DDx: carpal boss

·        secondary trapezoid

·        trapezium secondarium: between the 1st and 2nd metacarpal bases

·        os paratrapezium:

o    between distal and radial aspect of the radius and the base of the 1st metacarpal. 

o   DDx: loose bodies secondary to trapreziometacarpal joint osteoarthritis, or secondary to trauma (e.g. Bennett's fracture)

The ossicles that surround the scaphoid (starting at the radioscaphoid joint and working anti-clockwise):

·        paranavicular

·        os radiostyloideum (persistent radial styloid)

o   adjacent to the radial styloid process and lateral to the mid-portion of the scaphoid. 

·        os radiale externum

·        epitrapezium

·        os centrale carpi:

o   positioned dorsally between the scaphoid, the trapezoid and the capitate bones

o   DDx: soft tissue calcification, bipartite scaphoid, nonunion of scaphoid fracture

The ossicles that surround the lunate (starting at the scapholunate joint and working anti-clockwise):

·        os hypolunatum:

o   between the scaphoid and lunate carpal bones, lying at the most proximal border of the capitate bone 

o   DDx: a fracture of an adjacent carpal bone

·        os epilunatum:

o   at the dorsal surface of the lunocapitate articulation.

o   DDx: a loose body, carpal bone fracture

·        epipyramis

·        accessory bone between lunate and triquetrum

·        lunula:

o   lies in the TFCC, between the tip of the ulna styloid process and the triquetrum.

o   It may be fused to the ulna styloid, giving it an elongated appearance. 

o   DDx: os triangulare, ulna styloid fracture, persistent ulna styloid ossicle

·        os triangulare:

o   AKA:  os intermedium antebrachii or os triquetrum secundarium

o   between the ulnar styloid, lunate and triquetrum

o   DDx: lunula , ulna styloid fracture, persistent ulna styloid ossicle

·        persistent ulnar styloid:

o   ulna styloid ossification centre fails to unite with the ulna.

o   DDx: lunula , os triangulare, ulna styloid fracture.

·        small bony element at the radioulnar joint

REFERENCE:

·        Radiopedia:

o   https://bit.ly/2QfPRhf

o   https://bit.ly/2R5z01R

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·       bit.ly/wristossicles