How can the various carpal dislocations be classified?
Typically into 4 stages of increasing severity: stage I = scapholunate dissociation; stage II = perilunate dislocation; stage III = midcarpal dislocation; stage IV = lunate dislocation.
How does this differ from a perilunate dislocation?
In perilunate dislocations which are often associated with scaphoid fractures, the radiolunate articulation is preserved and the rest of the carpus is displaced dorsally with respect to the lunate.
There is fracture of the ulnar styloid. On the AP projection there is disruption of the normal alignment of the proximal carpal row with the lunate appearing triangular in shape and superimposed over the capitate. Lunate dislocation is confirmed on the lateral film.