[Establishment of a "central zone" in the scaphoid bone by computer analysis of three-dimensional reconstructions of computed tomography imaging and selection of central location of the scaphoid screw].

Objective: To establish an area by generating a surface model located a certain distance inside the scaphoid bone by computer analysis of three-dimensional reconstructions of computed tomography images, and define the central zone of the scaphoid.

Methods: Twenty cases of three-dimensional computed tomography reconstructions of normal scaphoids in a computerized operation planning and simulation system (Vxwork software) were obtained. The scaphoid surface model was shrunk by using the function "erode" in the software until the waist portion became the one third size of the original waist portion of the scaphoid, and then another 1.5 mm shrinkage was made to get the central zone. Geometry and size of the central zone were evaluated and measured.

Results: Geometry of all central zones was similar, as irregular as the scaphoid. The central zone could be divided into distal pole, waist portion and proximal pole. The narrowest part in the central zone was the waist portion, whose diameter ranged from 0.8-1.2 mm. Based on irregularity and size of the central zone, a screw axis could only be possibly contained completely either in the proximal, waist or distal central zone area, as it was very difficult to place the screw centrally in the whole scaphoid.

Conclusion: The establishment of the central zone of the scaphoid three-dimensional computed tomography images could provide a baseline for discussion of central placement for scaphoid screw.