Triquetral fractures are the 2nd most common carpal fractures (scaphoid).

Dorsal surface most commonly.

Usually occur from impingement from the ulnar styloid, shear injury or from ligamentous avulsion.

XR: best seen on the lateral projection

http://images.radiopaedia.org/images/902179/42b3487baf4fb66183c51cd982477d_big_gallery.jpg

Remember this injury/radiographic appearance the next time you see an avulsion fracture dorsal to the proximal row of carpal bones on the lateral film but are unsure of the donor site.