Relationship between the fracture location and the kinematic pattern in scaphoid nonunion.

PURPOSE: The purpose of this study was to obtain 3-dimensional and quantitative information regarding the pathological kinematics of the wrist with scaphoid nonunion using an in vivo and 3-dimensional motion analysis. We specifically tested the hypothesis that the fracture location is related to the kinematic pattern.

METHODS

We studied wrist kinematics during wrist flexion-extension motion and radioulnar deviation in 13 patients with scaphoid nonunion, using a markerless bone registration technique. Magnetic resonance images or computed tomography (CT) images of the wrist were acquired with the wrist in the neutral and 4 extreme positions of flexion, extension, radial deviation, and ulnar deviation. Three-dimensional animations were created of the carpal motions and interfragmentary motions between the distal and proximal fragments of the scaphoid. Based on the fracture location, accurate estimates of the relative positions and orientations of the carpal bones were analyzed.

RESULTS

There were 2 clear patterns of the interfragmentary motions of the scaphoid based on the fracture location. In the mobile type scaphoid nonunion (7 cases), the fracture was located distal to the apex of the scaphoid dorsal ridge (scaphoid apex), and the distal scaphoid was unstable relative to the proximal scaphoid. The distal fragment showed a "book-opening" motion from wrist flexion to extension. In the stable type scaphoid nonunion (6 cases), the fracture was located proximal to the scaphoid apex, and the interfragmentary motion was considerably less than with the distal type.

CONCLUSIONS

Carpal instability following scaphoid nonunion appears to be related to whether the fracture line passes distal or proximal to the scaphoid apex, where the dorsal scapholunate interosseous ligament and the dorsal intercarpal ligament attach. Three-dimensional imaging should be considered when assessing scaphoid nonunions to identify the exact location of the fracture. This may allow the clinician to choose the best treatment option.