Retro-lunar dislocation of carpal bones with trans-capitate, trans-lunate fractures and intact scaphoid. What if Bain was right?

Abstract

We report the case of retro-lunar dislocation of carpal bones detaching the proximal pole of the capitate with intact scaphoid, associated with lunate fracture. A rare case where the pathomechanics of the lesion has not yet been precisely identified. We present our conservative approach in the treatment of the capitate fracture and propose a theory-based explanatory pattern that combines the ligaments injuries sequences described by Mayfield from lateral to medial (corresponding to Johnson's lesser arc injuries), and the displacement of the transmitted force along Wagner's dislocation line from medial to lateral, causing bones injuries, following Johnson's greater arc injuries and Bain's translunate arc. Our management after closed reduction of the dislocation was surgical through dorsal approach and fixation of the proximal pole of the capitate. 25 months after surgery, despite the installation of early osteoarthritis, the functional outcome is satisfactory. Keywords: Retro-lunar dislocation, Capitate fracture, Lunate fracture, Greater arc, Lesser arc, Translunate arc