PURPOSE: To investigate in vivo 3-dimensional patterns of dorsal intercalated segment instability deformity resulting from scapholunate dissociation. METHODS: We studied 6 patients with stage IV scapholunate dissociation in which there were complete tears of the scapholunate interosseous ligament and dorsal intercalated segment instability deformity. Of these, 3 patients had a dorsally displaced distal radius malunion, a condition known to aggravate or produce a dorsal intercalated segment instability deformity. With the wrist in neutral, we created 3-dimensional bone models of the wrists from computed tomography. We calculated centroid locations of each carpal and the rotational angle of the scaphoid and lunate relative to the radius and compared them with those of 6 normal subjects. The joint contact area was visualized to evaluate congruity of the radiocarpal and midcarpal joints. RESULTS: In the scapholunate dissociated wrists, the scaphoid translated dorsally and radially with rotation in the direction of flexion and pronation. The lunate was extended and supinated. The capitate, trapezoid, and trapezium translated dorsally. Contact area of the radioscaphoid joint shifted dorsoradially owing to dorsoradial subluxation of the scaphoid proximal pole. Congruity was retained in the radiolunate, lunocapitate, and scaphotrapeziotrapezoid joints. In the malunion cases, the scaphoid and distal carpal rows translated more dorsally along dorsal angulation of the distal radius; therefore, incongruity of the radioscaphoid joint became more pronounced. CONCLUSIONS: Dorsoradial subluxation of the scaphoid proximal pole over the dorsal rim of the radius led to incongruity of the radioscaphoid joint. Dorsal translation of the distal carpal row occurred with maintaining congruency of the radiolunate, lunocapitate, and scaphotrapeziotrapezoid joints. These results suggest that for realignment of the carpal axis of an advanced scapholunate dissociated wrist, we should restore scapholunate rotational malalignment and reduce the dorsally translated distal carpal row back to the anatomical position.
PURPOSE: To investigate in vivo 3-dimensional patterns of dorsal intercalated segment instability deformity resulting from scapholunate dissociation. METHODS: We studied 6 patients with stage IV scapholunate dissociation in which there were complete tears of the scapholunate interosseous ligament and dorsal intercalated segment instability deformity. Of these, 3 patients had a dorsally displaced distal radius malunion, a condition known to aggravate or produce a dorsal intercalated segment instability deformity. With the wrist in neutral, we created 3-dimensional bone models of the wrists from computed tomography. We calculated centroid locations of each carpal and the rotational angle of the scaphoid and lunate relative to the radius and compared them with those of 6 normal subjects. The joint contact area was visualized to evaluate congruity of the radiocarpal and midcarpal joints. RESULTS: In the scapholunate dissociated wrists, the scaphoid translated dorsally and radially with rotation in the direction of flexion and pronation. The lunate was extended and supinated. The capitate, trapezoid, and trapezium translated dorsally. Contact area of the radioscaphoid joint shifted dorsoradially owing to dorsoradial subluxation of the scaphoid proximal pole. Congruity was retained in the radiolunate, lunocapitate, and scaphotrapeziotrapezoid joints. In the malunion cases, the scaphoid and distal carpal rows translated more dorsally along dorsal angulation of the distal radius; therefore, incongruity of the radioscaphoid joint became more pronounced. CONCLUSIONS: Dorsoradial subluxation of the scaphoid proximal pole over the dorsal rim of the radius led to incongruity of the radioscaphoid joint. Dorsal translation of the distal carpal row occurred with maintaining congruency of the radiolunate, lunocapitate, and scaphotrapeziotrapezoid joints. These results suggest that for realignment of the carpal axis of an advanced scapholunate dissociated wrist, we should restore scapholunaterotational malalignment and reduce the dorsally translated distal carpal row back to the anatomical position.