Mayfield, Johnson and Kilcoyne described a pattern of carpal injury caused by wrist hyperextension, ulnar deviation and intercarpal supination in 1980. In their original research on cadavers, progressive hyperextension force was applied and resulted in a consistent injury pattern to the carpal bones and ligaments.
The result of their pattern is known as the four stages of carpal instability:
1. Scapholunate dissociation
2. Perilunate dislocation
3. Perilunate and triquetral dislocation
4. Lunate dislocation
Each stage represents a sequential intercarpal injury that creates progressive carpal instability and progressive ligamentous injury. There may also be associated bony fractures such as fractures of the radial styloid, scaphoid, capitate and triquetrum.
This particular stage, the perilunate dislocation, may be better thought of as a capitate dislocation as there is no perilunate bone, but the perilunate description accurately illustrates the stepwise process of the ligamentous instability of the wrist as first laid out by Mayfield.
L= Lunate; C= Capitate