New approach to wrist imaging and its use in diagnosing carpal instabilities

An approach has been developed which accurately determines the boundaries of bones from CT images and uses a tile surfacing technique to display the 3-D geometries. The 3-D data offer a tremendous amount of previously unknown basic data as well as clinically applicable information. This method will allow the study of normal wrist parameters as well as a variety of traumatic and disease states. Cadaver wrists were imaged using a GE Model 9800 CT scanner. The contours of each bone are assembled from all sections in which that bone appears. A triangular tiling program is used to generate 3-D surfaces of the bones. The volume and surface area of each bone are computed as well as the major, minor, and antipodal axes. The orientation of the carpal bones is described with respect to a coordinate system based on landmarks derived from the centroids of the capitate, the hamate, and the trapezoid bones. Within this coordinate system, several parameters for each carpal bone can be measured including the rotational and antipodal axes for all carpal bones. 3-D angles were then measured, based on the antipodal axes, which were found to be the most reliable representation of the bones, for ten cadaver wrists assumed to be normal and one wrist with a soft tissue instability. The method resulting from this research, provides means of describing bones in a more automated and visual way. It also indicates that the antipodal axes gives a more accurate representation of carpal bone spatial orientation than the rotational axis. Thus, comparisons of normal vs. pathologic configurations can be presented in graphical form for any of the carpal bones or alternatively as a numerical x, y, z measure compared to the normal range and/or the patient's contralateral wrist.