Shape analysis for safe placement of a screw in carpal scaphoid through 3D surface model

Abstract

In this paper, we analyze the inner space of carpal scaphoid bone to help scaphoid bone fracture surgery. Through the analysis with 3D surface model, we expect that surgeon make decision about surgical path more easily and more accurate. The analysis of carpal scaphoid shape is conducted with 3D surface model. To generate 3D surface model, CT images are obtained. Thirteen wrists computed tomograms of male which showed as normal and no arthritic change were included in this study. In the volume data of wrists, carpal scaphoid bones are segmented at all slices individually. To extract carpal scaphoid bones, region growing method is applied, which considers gradient map information to enhance the result of bone segmentation. Then, through the segmented scaphoid data, surface models are reconstructed with marching cube algorithm. Through collision experiment between the scaphoid and the headless screw models, the marginal space in the scaphoid model is computed with respect to the position and orientation of the screw in the bone. Over 90% case, the range of safe angle was 7 degrees-31 degrees in anteroposterior view and -1 degrees to 31 degrees in lateral view. In 100%, the range of safe angle was 8 degrees-27 degrees in anteroposterior view and 2 degrees-26 degrees in lateral view. This range can be used as a guide reference when surgeon insert the screw and want to confirm the screw to be in safe position in the scaphoid.