Trans-scaphoid perilunate fracture dislocation: 'notjust a scaphoid fracture'.

Rowan CH, Downing ND. BMJ Case Rep 2017. doi:10.1136/bcr-2017-221041 Description Perilunate dislocations are uncommon high-energy injuries which are missed in approximately 25% of cases on initial presentation. We present the X-rays of a 25-year-old man who fell from a height of approximately 2 metres onto an extended wrist. Plain radiographs (figure 1) show classical signs of a trans-scaphoid perilunate fracture dislocation. Pre-reduction, he had median nerve symptoms which settled with reduction and elevation. Reduction was performed in the emergency department with analgesia/sedation. The sequence of events in this injury is well described: (1) the force begins radially and passes through the scaphoid causing it to fracture; (2) the force is transmitted ulnarly through the lunocapitate interval, and the lunate projects through the space of Poirier (between the intercarpal ligaments volar to the bones); (3) the distal portion of the scaphoid and remaining carpal bones dislocate around the lunate and (4) the lunotriquetral joint is disrupted. Key radiological signs demonstrated (figure 2) include: 1. Disruption of the normal carpal arcs (Gilula’s arcs) on the posteroanterior (PA) radiograph 2. Loss of colinearity between the radius, lunate and capitate on the lateral radiograph 3. ‘Crowding’ of the carpal bones on the PA radiograph 4. ‘Piece of pie’ sign on the PA radiograph representing the lunate 5. Displaced waist of scaphoid fracture 6. An abnormal scapholunate angle (normal range 30°–60°). Knowledge and understanding of the pattern of injury and the radiological signs (figure 2) will reduce the risk of focusing on the scaphoid fracture and overlooking the significant and disabling perilunate dislocation.