Simulated scaphoid proximal pole fracture

Five fresh cadaver upper extremities were studied with use of a static positioning frame, pressure-sensitive film, a microcomputer-based videodigitizing system, and a Sun station image analysis system to assess the load bearing characteristics of the scaphoid in the proximal carpal joint. Specimens were studied in their normal condition, after a proximal pole osteotomy of the scaphoid, and after resection of the proximal pole of the scaphoid. The amount of contact area born through the scaphoid fossa was essentially the same whether the scaphoid was intact, or after a simulated scaphoid fracture of its proximal pole, or after resection of the proximal pole. The scaphoid contact area and pressure, although overall relatively constant, was redistributed after osteotomy, resulting in increased contact area under the distal fragment and no change or a slight decrease in the contact area under the proximal fragment of the scaphoid. After resection of the proximal fragment, all scaphoid contact area and pressure was born by the distal scaphoid fragment. The contact area and pressure characteristics of the lunate remained unchanged in all conditions compared with the normal condition. There were no significant changes in the locations of the centroids of the scaphoid segments and the lunate in any of the conditions tested.