Besides making frequent appearances on emergency medicine standardized exams, carpal dislocations, most commonly lunate and perilunate dislocations, present frequently to Emergency Departments. They are orthopedic emergencies and can be associated with significant complications.
Lunate dislocation (top image) occurs when the lunate is displaced and subluxed anteriorly. This often subluxes into the carpal tunnel causing an acute median neuropathy. It is seen as a “moon-“ or “saucer-shaped” bone flipped volarly, with the more distal capitate sliding proximally against the distal radius.
In a perilunate dislocation, the lunate-radius articulation is preserved and the capitate (as well as the entire distal carpal row with attached metacarpals) “jumps” dorsally “out of the saucer”.
Both of these carpal dissociations are often associated with scaphoid fracture and always portend significant ligamentous damage usually requiring operative repair.
Another classic complication is Kienbock’s disease, or avascular necrosis of the lunate bone, which occurs with interruption of the bone’s tenuous blood supply, as in the scaphoid. Notice loss of bone density and height.