Reverse Perilunate Injuries-The "Extended Scaphoid" Sign.

Reverse perilunate injuries (REPLI) are rare variants of the classic radial-sided perilunate injuries (PLI) whose mechanism was described by Mayfield in 1980. Classic radial-sided nontranscaphoid dorsal PLI invariably display a flexed, foreshortened position of the scaphoid on their initial posteroanterior (PA) and lateral radiographs. We observed that some dorsal perilunate dislocations displayed an position of the scaphoid on their initial radiographs. Our hypothesis is that this extended position of the scaphoid was associated with a REPLI pattern.  The PA and lateral initial emergency radiographs of our specialized wrist surgery series of 114 dorsal pure ligamentous PLI (within a 186 cases series of PLI treated between 2004 and 2020) were reviewed as well as the available figures of the current REPLI literature.  A total of seven cases of cases within our dorsal PLI series displayed an extended position of the scaphoid on their initial PA and lateral radiographs, while 107 cases displayed a flexed, foreshortened position. The PA and lateral radiographs available in the REPLI literature displayed an extended position of the scaphoid, a lunotriquetral dissociation, and a dorsal dislocation of the capitate with respect to the lunate.  This study confirms our hypothesis. By contrast to the dorsal classic radial-sided pure ligamentous PLI pattern of scaphoid displacement (scaphoid flexed and foreshortened with scapholunate gap), the dorsal REPLI pattern displays an extended position of the scaphoid with scapholunate step-off and overlap rather than a gap. The combination of a lunotriquetral dissociation with a dorsal dislocation of the capitate from the lunate yet an extended position of the scaphoid with almost normal radioscaphoid relationships should raise a high suspicion for REPLI.